xnu-4570.71.2.tar.gz

[apple/xnu.git] / bsd / kern / kern_prot.c

/*
 * Copyright (c) 2000-2008 Apple Inc. All rights reserved.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
 * 
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. The rights granted to you under the License
 * may not be used to create, or enable the creation or redistribution of,
 * unlawful or unlicensed copies of an Apple operating system, or to
 * circumvent, violate, or enable the circumvention or violation of, any
 * terms of an Apple operating system software license agreement.
 * 
 * Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this file.
 * 
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 * Please see the License for the specific language governing rights and
 * limitations under the License.
 * 
 * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
 *
 *
 * Copyright (c) 1995 NeXT Computer, Inc. All Rights Reserved
 * 
 *
 * Copyright (c) 1982, 1986, 1989, 1990, 1991, 1993
 *      The Regents of the University of California.  All rights reserved.
 * (c) UNIX System Laboratories, Inc.
 * All or some portions of this file are derived from material licensed
 * to the University of California by American Telephone and Telegraph
 * Co. or Unix System Laboratories, Inc. and are reproduced herein with
 * the permission of UNIX System Laboratories, Inc.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *      @(#)kern_prot.c 8.9 (Berkeley) 2/14/95
 * 
 *
 * NOTICE: This file was modified by McAfee Research in 2004 to introduce
 * support for mandatory and extensible security protections.  This notice
 * is included in support of clause 2.2 (b) of the Apple Public License,
 * Version 2.0.
 *
 *
 * NOTICE: This file was modified by SPARTA, Inc. in 2005 to introduce
 * support for mandatory and extensible security protections.  This notice
 * is included in support of clause 2.2 (b) of the Apple Public License,
 * Version 2.0.
 *
 */

/*
 * System calls related to processes and protection
 */

#include <sys/param.h>
#include <sys/acct.h>
#include <sys/systm.h>
#include <sys/ucred.h>
#include <sys/proc_internal.h>
#include <sys/user.h>
#include <sys/kauth.h>
#include <sys/timeb.h>
#include <sys/times.h>
#include <sys/malloc.h>
#include <sys/persona.h>

#include <security/audit/audit.h>

#if CONFIG_MACF
#include <security/mac_framework.h>
#endif

#include <sys/mount_internal.h>
#include <sys/sysproto.h>
#include <mach/message.h>
#include <mach/host_security.h>

#include <kern/host.h>
#include <kern/task.h>          /* for current_task() */
#include <kern/assert.h>


/*
 * Credential debugging; we can track entry into a function that might
 * change a credential, and we can track actual credential changes that
 * result.
 *
 * Note:        Does *NOT* currently include per-thread credential changes
 *
 *              We don't use kauth_cred_print() in current debugging, but it
 *              can be used if needed when debugging is active.
 */
#if DEBUG_CRED
#define DEBUG_CRED_ENTER                printf
#define DEBUG_CRED_CHANGE               printf
extern void kauth_cred_print(kauth_cred_t cred);
#else   /* !DEBUG_CRED */
#define DEBUG_CRED_ENTER(fmt, ...)      do {} while (0)
#define DEBUG_CRED_CHANGE(fmt, ...)     do {} while (0)
#endif  /* !DEBUG_CRED */

#if DEVELOPMENT || DEBUG
extern void task_importance_update_owner_info(task_t);
#endif


/*
 * setprivexec
 *
 * Description: (dis)allow this process to hold task, thread, or execption
 *              ports of processes about to exec.
 *
 * Parameters:  uap->flag                       New value for flag
 *
 * Returns:     int                             Previous value of flag
 *
 * XXX:         Belongs in kern_proc.c
 */
int
setprivexec(proc_t p, struct setprivexec_args *uap, int32_t *retval)
{
        AUDIT_ARG(value32, uap->flag);
        *retval = p->p_debugger;
        p->p_debugger = (uap->flag != 0);
        return(0);
}


/*
 * getpid
 *
 * Description: get the process ID
 *
 * Parameters:  (void)
 *
 * Returns:     pid_t                           Current process ID
 *
 * XXX:         Belongs in kern_proc.c
 */
int
getpid(proc_t p, __unused struct getpid_args *uap, int32_t *retval)
{

        *retval = p->p_pid;
        return (0);
}


/*
 * getppid
 *
 * Description: get the parent process ID
 *
 * Parameters:  (void)
 *
 * Returns:     pid_t                           Parent process ID
 *
 * XXX:         Belongs in kern_proc.c
 */
int
getppid(proc_t p, __unused struct getppid_args *uap, int32_t *retval)
{

        *retval = p->p_ppid;
        return (0);
}


/*
 * getpgrp
 *
 * Description: get the process group ID of the calling process
 *
 * Parameters:  (void)
 *
 * Returns:     pid_t                           Process group ID
 *
 * XXX:         Belongs in kern_proc.c
 */
int
getpgrp(proc_t p, __unused struct getpgrp_args *uap, int32_t *retval)
{

        *retval = p->p_pgrpid;
        return (0);
}


/*
 * getpgid
 *
 * Description: Get an arbitary pid's process group id
 *
 * Parameters:  uap->pid                        The target pid
 *
 * Returns:     0                               Success
 *              ESRCH                           No such process
 *
 * Notes:       We are permitted to return EPERM in the case that the target
 *              process is not in the same session as the calling process,
 *              which could be a security consideration
 *
 * XXX:         Belongs in kern_proc.c
 */
int
getpgid(proc_t p, struct getpgid_args *uap, int32_t *retval)
{
        proc_t pt;
        int refheld = 0;

        pt = p;
        if (uap->pid == 0)
                goto found;

        if ((pt = proc_find(uap->pid)) == 0)
                return (ESRCH);
        refheld = 1;
found:
        *retval = pt->p_pgrpid;
        if (refheld != 0)
                proc_rele(pt);
        return (0);
}


/*
 * getsid
 *
 * Description: Get an arbitary pid's session leaders process group ID
 *
 * Parameters:  uap->pid                        The target pid
 *
 * Returns:     0                               Success
 *              ESRCH                           No such process
 *
 * Notes:       We are permitted to return EPERM in the case that the target
 *              process is not in the same session as the calling process,
 *              which could be a security consideration
 *
 * XXX:         Belongs in kern_proc.c
 */
int
getsid(proc_t p, struct getsid_args *uap, int32_t *retval)
{
        proc_t pt;
        int refheld = 0;
        struct session * sessp;

        pt = p;
        if (uap->pid == 0)
                goto found;

        if ((pt = proc_find(uap->pid)) == 0)
                return (ESRCH);
        refheld = 1;
found:
        sessp = proc_session(pt);
        *retval = sessp->s_sid;
        session_rele(sessp);

        if (refheld != 0)
                proc_rele(pt);
        return (0);
}


/*
 * getuid
 *
 * Description: get real user ID for caller
 *
 * Parameters:  (void)
 *
 * Returns:     uid_t                           The real uid of the caller
 */
int
getuid(__unused proc_t p, __unused struct getuid_args *uap, int32_t *retval)
{

        *retval = kauth_getruid();
        return (0);
}


/*
 * geteuid
 *
 * Description: get effective user ID for caller
 *
 * Parameters:  (void)
 *
 * Returns:     uid_t                           The effective uid of the caller
 */
int
geteuid(__unused proc_t p, __unused struct geteuid_args *uap, int32_t *retval)
{

        *retval = kauth_getuid();
        return (0);
}


/*
 * gettid
 *
 * Description: Return the per-thread override identity.
 *
 * Parameters:  uap->uidp                       Address of uid_t to get uid
 *              uap->gidp                       Address of gid_t to get gid
 *
 * Returns:     0                               Success
 *              ESRCH                           No per thread identity active
 */
int
gettid(__unused proc_t p, struct gettid_args *uap, int32_t *retval)
{
        struct uthread *uthread = get_bsdthread_info(current_thread());
        int     error;

        /*
         * If this thread is not running with an override identity, we can't
         * return one to the caller, so return an error instead.
         */
        if (!(uthread->uu_flag & UT_SETUID))
                return (ESRCH);

        if ((error = suword(uap->uidp, kauth_cred_getruid(uthread->uu_ucred))))
                return (error);
        if ((error = suword(uap->gidp, kauth_cred_getrgid(uthread->uu_ucred))))
                return (error);

        *retval = 0;
        return (0);
}


/*
 * getgid
 *
 * Description: get the real group ID for the calling process
 *
 * Parameters:  (void)
 *
 * Returns:     gid_t                           The real gid of the caller
 */
int
getgid(__unused proc_t p, __unused struct getgid_args *uap, int32_t *retval)
{

        *retval = kauth_getrgid();
        return (0);
}


/*
 * getegid
 *
 * Description: get the effective group ID for the calling process
 *
 * Parameters:  (void)
 *
 * Returns:     gid_t                           The effective gid of the caller
 *
 * Notes:       As an implementation detail, the effective gid is stored as
 *              the first element of the supplementary group list.
 *
 *              This could be implemented in Libc instead because of the above
 *              detail.
 */
int
getegid(__unused proc_t p, __unused struct getegid_args *uap, int32_t *retval)
{

        *retval = kauth_getgid();
        return (0);
}


/*
 * getgroups
 *
 * Description: get the list of supplementary groups for the calling process
 *
 * Parameters:  uap->gidsetsize                 # of gid_t's in user buffer
 *              uap->gidset                     Pointer to user buffer
 *
 * Returns:     0                               Success
 *              EINVAL                          User buffer too small
 *      copyout:EFAULT                          User buffer invalid
 *
 * Retval:      -1                              Error
 *              !0                              # of groups
 *
 * Notes:       The caller may specify a 0 value for gidsetsize, and we will
 *              then return how large a buffer is required (in gid_t's) to
 *              contain the answer at the time of the call.  Otherwise, we
 *              return the number of gid_t's catually copied to user space.
 *
 *              When called with a 0 gidsetsize from a multithreaded program,
 *              there is no guarantee that another thread may not change the
 *              number of supplementary groups, and therefore a subsequent
 *              call could still fail, unless the maximum possible buffer
 *              size is supplied by the user.
 *
 *              As an implementation detail, the effective gid is stored as
 *              the first element of the supplementary group list, and will
 *              be returned by this call.
 */
int
getgroups(__unused proc_t p, struct getgroups_args *uap, int32_t *retval)
{
        int ngrp;
        int error;
        kauth_cred_t cred;
        posix_cred_t pcred;

        /* grab reference while we muck around with the credential */
        cred = kauth_cred_get_with_ref();
        pcred = posix_cred_get(cred);

        if ((ngrp = uap->gidsetsize) == 0) {
                *retval = pcred->cr_ngroups;
                kauth_cred_unref(&cred);
                return (0);
        }
        if (ngrp < pcred->cr_ngroups) {
                kauth_cred_unref(&cred);
                return (EINVAL);
        }
        ngrp = pcred->cr_ngroups;
        if ((error = copyout((caddr_t)pcred->cr_groups,
                                        uap->gidset, 
                                        ngrp * sizeof(gid_t)))) {
                kauth_cred_unref(&cred);
                return (error);
        }
        kauth_cred_unref(&cred);
        *retval = ngrp;
        return (0);
}


/*
 * Return the per-thread/per-process supplementary groups list.
 *
 * XXX implement getsgroups
 *
 */

int
getsgroups(__unused proc_t p, __unused struct getsgroups_args *uap, __unused int32_t *retval)
{
        return(ENOTSUP);
}

/*
 * Return the per-thread/per-process whiteout groups list.
 * 
 * XXX implement getwgroups
 *
 */

int
getwgroups(__unused proc_t p, __unused struct getwgroups_args *uap, __unused int32_t *retval)
{
        return(ENOTSUP);
}


/*
 * setsid
 *
 * Description: Create a new session and set the process group ID to the
 *              session ID
 *
 * Parameters:  (void)
 *
 * Returns:     0                               Success
 *              EPERM                           Permission denied
 *
 * Notes:       If the calling process is not the process group leader; there
 *              is no existing process group with its ID, and we are not
 *              currently in vfork, then this function will create a new
 *              session, a new process group, and put the caller in the
 *              process group (as the sole member) and make it the session
 *              leader (as the sole process in the session).
 *
 *              The existing controlling tty (if any) will be dissociated
 *              from the process, and the next non-O_NOCTTY open of a tty
 *              will establish a new controlling tty.
 *
 * XXX:         Belongs in kern_proc.c
 */
int
setsid(proc_t p, __unused struct setsid_args *uap, int32_t *retval)
{
        struct pgrp * pg = PGRP_NULL;

        if (p->p_pgrpid == p->p_pid || (pg = pgfind(p->p_pid)) || p->p_lflag & P_LINVFORK) {
                if (pg != PGRP_NULL)
                        pg_rele(pg);
                return (EPERM);
        } else {
                /* enter pgrp works with its own pgrp refcount */
                (void)enterpgrp(p, p->p_pid, 1);
                *retval = p->p_pid;
                return (0);
        }
}


/*
 * setpgid
 *
 * Description: set process group ID for job control
 *
 * Parameters:  uap->pid                        Process to change
 *              uap->pgid                       Process group to join or create
 *
 * Returns:     0                       Success
 *              ESRCH                   pid is not the caller or a child of
 *                                      the caller
 *      enterpgrp:ESRCH                 No such process
 *              EACCES                  Permission denied due to exec
 *              EINVAL                  Invalid argument
 *              EPERM                   The target process is not in the same
 *                                      session as the calling process
 *              EPERM                   The target process is a session leader
 *              EPERM                   pid and pgid are not the same, and
 *                                      there is no process in the calling
 *                                      process whose process group ID matches
 *                                      pgid
 *
 * Notes:       This function will cause the target process to either join
 *              an existing process process group, or create a new process
 *              group in the session of the calling process.  It cannot be
 *              used to change the process group ID of a process which is
 *              already a session leader.
 *
 *              If the target pid is 0, the pid of the calling process is
 *              substituted as the new target; if pgid is 0, the target pid
 *              is used as the target process group ID.
 *
 * Legacy:      This system call entry point is also used to implement the
 *              legacy library routine setpgrp(), which under POSIX 
 *
 * XXX:         Belongs in kern_proc.c
 */
int
setpgid(proc_t curp, struct setpgid_args *uap, __unused int32_t *retval)
{
        proc_t targp = PROC_NULL;       /* target process */
        struct pgrp *pg = PGRP_NULL;    /* target pgrp */
        int error = 0;
        int refheld = 0;
        int samesess = 0;
        struct session * curp_sessp = SESSION_NULL;
        struct session * targp_sessp = SESSION_NULL;

        curp_sessp = proc_session(curp);

        if (uap->pid != 0 && uap->pid != curp->p_pid) {
                if ((targp = proc_find(uap->pid)) == 0 || !inferior(targp)) {
                        if (targp != PROC_NULL)
                                refheld = 1;
                        error = ESRCH;
                        goto out;
                }
                refheld = 1;
                targp_sessp = proc_session(targp);
                if (targp_sessp != curp_sessp) {
                        error = EPERM;
                        goto out;
                }
                if (targp->p_flag & P_EXEC) {
                        error = EACCES;
                        goto out;
                }
        } else {
                targp = curp;
                targp_sessp = proc_session(targp);
        }

        if (SESS_LEADER(targp, targp_sessp)) {
                error = EPERM;
                goto out;
        }
        if (targp_sessp != SESSION_NULL) {
                session_rele(targp_sessp);
                targp_sessp = SESSION_NULL;
        }

        if (uap->pgid < 0) {
                error = EINVAL;
                goto out;
        }
        if (uap->pgid == 0)
                uap->pgid = targp->p_pid;
        else if (uap->pgid != targp->p_pid) {
                if ((pg = pgfind(uap->pgid)) == 0){
                        error = EPERM;
                        goto out;
                }
                samesess = (pg->pg_session != curp_sessp); 
                pg_rele(pg);
                if (samesess != 0) {
                        error = EPERM;
                        goto out;
                }
        }
        error = enterpgrp(targp, uap->pgid, 0);
out:
        if (targp_sessp != SESSION_NULL)
                session_rele(targp_sessp);
        if (curp_sessp != SESSION_NULL)
                session_rele(curp_sessp);
        if (refheld != 0)
                proc_rele(targp);
        return(error);
}


/*
 * issetugid
 *
 * Description: Is current process tainted by uid or gid changes system call
 *
 * Parameters:  (void)
 *
 * Returns:     0                               Not tainted
 *              1                               Tainted
 *
 * Notes:       A process is considered tainted if it was created as a retult
 *              of an execve call from an imnage that had either the SUID or
 *              SGID bit set on the executable, or if it has changed any of its
 *              real, effective, or saved user or group IDs since beginning
 *              execution.
 */
int
issetugid(proc_t p, __unused struct issetugid_args *uap, int32_t *retval)
{
        /*
         * Note: OpenBSD sets a P_SUGIDEXEC flag set at execve() time,
         * we use P_SUGID because we consider changing the owners as
         * "tainting" as well.
         * This is significant for procs that start as root and "become"
         * a user without an exec - programs cannot know *everything*
         * that libc *might* have put in their data segment.
         */

        *retval = (p->p_flag & P_SUGID) ? 1 : 0;
        return (0);
}


/*
 * setuid
 *
 * Description: Set user ID system call
 *
 * Parameters:  uap->uid                        uid to set
 *
 * Returns:     0                               Success
 *      suser:EPERM                             Permission denied
 *
 * Notes:       If called by a privileged process, this function will set the
 *              real, effective, and saved uid to the requested value.
 *
 *              If called from an unprivileged process, but uid is equal to the
 *              real or saved uid, then the effective uid will be set to the
 *              requested value, but the real and saved uid will not change.
 *
 *              If the credential is changed as a result of this call, then we
 *              flag the process as having set privilege since the last exec.
 */
int
setuid(proc_t p, struct setuid_args *uap, __unused int32_t *retval)
{
        uid_t uid;
        uid_t svuid = KAUTH_UID_NONE;
        uid_t ruid = KAUTH_UID_NONE;
        uid_t gmuid = KAUTH_UID_NONE;
        int error;
        kauth_cred_t my_cred, my_new_cred;
        posix_cred_t my_pcred;

        uid = uap->uid;

        /* get current credential and take a reference while we muck with it */
        my_cred = kauth_cred_proc_ref(p);
        my_pcred = posix_cred_get(my_cred);

        DEBUG_CRED_ENTER("setuid (%d/%d): %p %d\n", p->p_pid, (p->p_pptr ? p->p_pptr->p_pid : 0), my_cred, uap->uid);
        AUDIT_ARG(uid, uid);

        for (;;) {
                if (uid != my_pcred->cr_ruid &&         /* allow setuid(getuid()) */
                    uid != my_pcred->cr_svuid &&        /* allow setuid(saved uid) */
                    (error = suser(my_cred, &p->p_acflag))) {
                        kauth_cred_unref(&my_cred);
                        return (error);
                }

                /*
                 * If we are privileged, then set the saved and real UID too;
                 * otherwise, just set the effective UID
                 */
                if (suser(my_cred, &p->p_acflag) == 0) {
                        svuid = uid;
                        ruid = uid;
                } else {
                        svuid = KAUTH_UID_NONE;
                        ruid = KAUTH_UID_NONE;
                }
                /*
                 * Only set the gmuid if the current cred has not opt'ed out;
                 * this normally only happens when calling setgroups() instead
                 * of initgroups() to set an explicit group list, or one of the
                 * other group manipulation functions is invoked and results in
                 * a dislocation (i.e. the credential group membership changes
                 * to something other than the default list for the user, as
                 * in entering a group or leaving an exclusion group).
                 */
                if (!(my_pcred->cr_flags & CRF_NOMEMBERD))
                        gmuid = uid;

                /* 
                 * Set the credential with new info.  If there is no change,
                 * we get back the same credential we passed in; if there is
                 * a change, we drop the reference on the credential we
                 * passed in.  The subsequent compare is safe, because it is
                 * a pointer compare rather than a contents compare.
                 */
                my_new_cred = kauth_cred_setresuid(my_cred, ruid, uid, svuid, gmuid);
                if (my_cred != my_new_cred) {

                        DEBUG_CRED_CHANGE("setuid CH(%d): %p/0x%08x -> %p/0x%08x\n", p->p_pid, my_cred, my_pcred->cr_flags, my_new_cred, posix_cred_get(my_new_cred)->cr_flags);

                        /*
                         * If we're changing the ruid from A to B, we might race with another thread that's setting ruid from B to A.
                         * The current locking mechanisms don't allow us to make the entire credential switch operation atomic,
                         * thus we may be able to change the process credentials from ruid A to B, but get preempted before incrementing the proc
                         * count of B. If a second thread sees the new process credentials and switches back to ruid A, that other thread
                         * may be able to decrement the proc count of B before we can increment it. This results in a panic.
                         * Incrementing the proc count of the target ruid, B, before setting the process credentials prevents this race.
                         */
                        if (ruid != KAUTH_UID_NONE && !proc_has_persona(p)) {
                                (void)chgproccnt(ruid, 1);
                        }

                        proc_ucred_lock(p);
                        /*
                         * We need to protect for a race where another thread
                         * also changed the credential after we took our
                         * reference.  If p_ucred has changed then we should
                         * restart this again with the new cred.
                         *
                         * Note: the kauth_cred_setresuid has consumed a reference to my_cred, it p_ucred != my_cred, then my_cred must not be dereferenced!
                         */
                        if (p->p_ucred != my_cred) {
                                proc_ucred_unlock(p);
                                /*
                                 * We didn't successfully switch to the new ruid, so decrement
                                 * the procs/uid count that we incremented above.
                                 */
                                if (ruid != KAUTH_UID_NONE && !proc_has_persona(p)) {
                                        (void)chgproccnt(ruid, -1);
                                }
                                kauth_cred_unref(&my_new_cred);
                                my_cred = kauth_cred_proc_ref(p);
                                my_pcred = posix_cred_get(my_cred);
                                /* try again */
                                continue;
                        }
                        p->p_ucred = my_new_cred;
                        /* update cred on proc */
                        PROC_UPDATE_CREDS_ONPROC(p);

                        OSBitOrAtomic(P_SUGID, &p->p_flag);
                        proc_ucred_unlock(p);
                        /*
                         * If we've updated the ruid, decrement the count of procs running
                         * under the previous ruid
                         */
                        if (ruid != KAUTH_UID_NONE && !proc_has_persona(p)) {
                                (void)chgproccnt(my_pcred->cr_ruid, -1);
                        }
                }
                break;
        }
        /* Drop old proc reference or our extra reference */
        kauth_cred_unref(&my_cred);
        
        set_security_token(p);
        return (0);
}


/*
 * seteuid
 *
 * Description: Set effective user ID system call
 *
 * Parameters:  uap->euid                       effective uid to set
 *
 * Returns:     0                               Success
 *      suser:EPERM                             Permission denied
 *
 * Notes:       If called by a privileged process, or called from an
 *              unprivileged process but euid is equal to the real or saved
 *              uid, then the effective uid will be set to the requested
 *              value, but the real and saved uid will not change.
 *
 *              If the credential is changed as a result of this call, then we
 *              flag the process as having set privilege since the last exec.
 */
int
seteuid(proc_t p, struct seteuid_args *uap, __unused int32_t *retval)
{
        uid_t euid;
        int error;
        kauth_cred_t my_cred, my_new_cred;
        posix_cred_t my_pcred;

        DEBUG_CRED_ENTER("seteuid: %d\n", uap->euid);

        euid = uap->euid;
        AUDIT_ARG(euid, euid);

        my_cred = kauth_cred_proc_ref(p);
        my_pcred = posix_cred_get(my_cred);

        for (;;) {

                if (euid != my_pcred->cr_ruid && euid != my_pcred->cr_svuid &&
                        (error = suser(my_cred, &p->p_acflag))) {
                        kauth_cred_unref(&my_cred);
                        return (error);
                }

                /* 
                 * Set the credential with new info.  If there is no change,
                 * we get back the same credential we passed in; if there is
                 * a change, we drop the reference on the credential we
                 * passed in.  The subsequent compare is safe, because it is
                 * a pointer compare rather than a contents compare.
                 */
                my_new_cred = kauth_cred_setresuid(my_cred, KAUTH_UID_NONE, euid, KAUTH_UID_NONE, my_pcred->cr_gmuid);
        
                if (my_cred != my_new_cred) {

                        DEBUG_CRED_CHANGE("seteuid CH(%d): %p/0x%08x -> %p/0x%08x\n", p->p_pid, my_cred, my_pcred->cr_flags, my_new_cred, posix_cred_get(my_new_cred)->cr_flags);

                        proc_ucred_lock(p);
                        /*
                         * We need to protect for a race where another thread
                         * also changed the credential after we took our
                         * reference.  If p_ucred has changed then we
                         * should restart this again with the new cred.
                         */
                        if (p->p_ucred != my_cred) {
                                proc_ucred_unlock(p);
                                kauth_cred_unref(&my_new_cred);
                                my_cred = kauth_cred_proc_ref(p);
                                my_pcred = posix_cred_get(my_cred);
                                /* try again */
                                continue;
                        }
                        p->p_ucred = my_new_cred;
                        /* update cred on proc */
                        PROC_UPDATE_CREDS_ONPROC(p);
                        OSBitOrAtomic(P_SUGID, &p->p_flag);
                        proc_ucred_unlock(p);
                }
                break;
        }
        /* drop old proc reference or our extra reference */
        kauth_cred_unref(&my_cred);

        set_security_token(p);
        return (0);
}


/*
 * setreuid
 *
 * Description: Set real and effective user ID system call
 *
 * Parameters:  uap->ruid                       real uid to set
 *              uap->euid                       effective uid to set
 *
 * Returns:     0                               Success
 *      suser:EPERM                             Permission denied
 *
 * Notes:       A value of -1 is a special case indicating that the uid for
 *              which that value is specified not be changed.  If both values
 *              are specified as -1, no action is taken.
 *
 *              If called by a privileged process, the real and effective uid
 *              will be set to the new value(s) specified.
 *
 *              If called from an unprivileged process, the real uid may be
 *              set to the current value of the real uid, or to the current
 *              value of the saved uid.  The effective uid may be set to the
 *              current value of any of the effective, real, or saved uid.
 *
 *              If the newly requested real uid or effective uid does not
 *              match the saved uid, then set the saved uid to the new
 *              effective uid (potentially unrecoverably dropping saved
 *              privilege).
 *
 *              If the credential is changed as a result of this call, then we
 *              flag the process as having set privilege since the last exec.
 */
int
setreuid(proc_t p, struct setreuid_args *uap, __unused int32_t *retval)
{
        uid_t ruid, euid;
        int error;
        kauth_cred_t my_cred, my_new_cred;
        posix_cred_t my_pcred;

        DEBUG_CRED_ENTER("setreuid %d %d\n", uap->ruid, uap->euid);

        ruid = uap->ruid;
        euid = uap->euid;
        if (ruid == (uid_t)-1)
                ruid = KAUTH_UID_NONE;
        if (euid == (uid_t)-1)
                euid = KAUTH_UID_NONE;
        AUDIT_ARG(euid, euid);
        AUDIT_ARG(ruid, ruid);

        my_cred = kauth_cred_proc_ref(p);
        my_pcred = posix_cred_get(my_cred);

        for (;;) {

                if (((ruid != KAUTH_UID_NONE &&         /* allow no change of ruid */
                      ruid != my_pcred->cr_ruid &&      /* allow ruid = ruid */
                      ruid != my_pcred->cr_uid &&       /* allow ruid = euid */
                      ruid != my_pcred->cr_svuid) ||    /* allow ruid = svuid */
                     (euid != KAUTH_UID_NONE &&         /* allow no change of euid */
                      euid != my_pcred->cr_uid &&       /* allow euid = euid */
                      euid != my_pcred->cr_ruid &&      /* allow euid = ruid */
                      euid != my_pcred->cr_svuid)) &&   /* allow euid = svuid */
                    (error = suser(my_cred, &p->p_acflag))) { /* allow root user any */
                        kauth_cred_unref(&my_cred);
                        return (error);
                }

                uid_t new_euid;
                uid_t svuid = KAUTH_UID_NONE;

                new_euid = my_pcred->cr_uid;
                /* 
                 * Set the credential with new info.  If there is no change,
                 * we get back the same credential we passed in; if there is
                 * a change, we drop the reference on the credential we
                 * passed in.  The subsequent compare is safe, because it is
                 * a pointer compare rather than a contents compare.
                 */
                if (euid != KAUTH_UID_NONE && my_pcred->cr_uid != euid) {
                        /* changing the effective UID */
                        new_euid = euid;
                        OSBitOrAtomic(P_SUGID, &p->p_flag);
                }
                /*
                 * If the newly requested real uid or effective uid does
                 * not match the saved uid, then set the saved uid to the
                 * new effective uid.  We are protected from escalation
                 * by the prechecking.
                 */
                if (my_pcred->cr_svuid != uap->ruid &&
                    my_pcred->cr_svuid != uap->euid) {
                        svuid = new_euid;
                        OSBitOrAtomic(P_SUGID, &p->p_flag);
                }

                my_new_cred = kauth_cred_setresuid(my_cred, ruid, euid, svuid, my_pcred->cr_gmuid);
        
                if (my_cred != my_new_cred) {

                        DEBUG_CRED_CHANGE("setreuid CH(%d): %p/0x%08x -> %p/0x%08x\n", p->p_pid, my_cred, my_pcred->cr_flags, my_new_cred, posix_cred_get(my_new_cred)->cr_flags);

                        /*
                         * If we're changing the ruid from A to B, we might race with another thread that's setting ruid from B to A.
                         * The current locking mechanisms don't allow us to make the entire credential switch operation atomic,
                         * thus we may be able to change the process credentials from ruid A to B, but get preempted before incrementing the proc
                         * count of B. If a second thread sees the new process credentials and switches back to ruid A, that other thread
                         * may be able to decrement the proc count of B before we can increment it. This results in a panic.
                         * Incrementing the proc count of the target ruid, B, before setting the process credentials prevents this race.
                         */
                        if (ruid != KAUTH_UID_NONE && !proc_has_persona(p)) {
                                (void)chgproccnt(ruid, 1);
                        }

                        proc_ucred_lock(p);
                        /*
                         * We need to protect for a race where another thread
                         * also changed the credential after we took our
                         * reference.  If p_ucred has changed then we should
                         * restart this again with the new cred.
                         *
                         * Note: the kauth_cred_setresuid has consumed a reference to my_cred, it p_ucred != my_cred, then my_cred must not be dereferenced!
                         */
                        if (p->p_ucred != my_cred) {
                                proc_ucred_unlock(p);
                                if (ruid != KAUTH_UID_NONE && !proc_has_persona(p)) {
                                        /*
                                         * We didn't successfully switch to the new ruid, so decrement
                                         * the procs/uid count that we incremented above.
                                         */
                                        (void)chgproccnt(ruid, -1);
                                }
                                kauth_cred_unref(&my_new_cred);
                                my_cred = kauth_cred_proc_ref(p);
                                my_pcred = posix_cred_get(my_cred);
                                /* try again */
                                continue;
                        }

                        p->p_ucred = my_new_cred;
                        /* update cred on proc */
                        PROC_UPDATE_CREDS_ONPROC(p);
                        OSBitOrAtomic(P_SUGID, &p->p_flag);
                        proc_ucred_unlock(p);

                        if (ruid != KAUTH_UID_NONE && !proc_has_persona(p)) {
                                /*
                                 * We switched to a new ruid, so decrement the count of procs running
                                 * under the previous ruid
                                 */
                                (void)chgproccnt(my_pcred->cr_ruid, -1);
                        }
                }
                break;
        }
        /* drop old proc reference or our extra reference */
        kauth_cred_unref(&my_cred);

        set_security_token(p);
        return (0);
}


/*
 * setgid
 *
 * Description: Set group ID system call
 *
 * Parameters:  uap->gid                        gid to set
 *
 * Returns:     0                               Success
 *      suser:EPERM                             Permission denied
 *
 * Notes:       If called by a privileged process, this function will set the
 *              real, effective, and saved gid to the requested value.
 *
 *              If called from an unprivileged process, but gid is equal to the
 *              real or saved gid, then the effective gid will be set to the
 *              requested value, but the real and saved gid will not change.
 *
 *              If the credential is changed as a result of this call, then we
 *              flag the process as having set privilege since the last exec.
 *
 *              As an implementation detail, the effective gid is stored as
 *              the first element of the supplementary group list, and
 *              therefore the effective group list may be reordered to keep
 *              the supplementary group list unchanged.
 */
int
setgid(proc_t p, struct setgid_args *uap, __unused int32_t *retval)
{
        gid_t gid;
        gid_t rgid = KAUTH_GID_NONE;
        gid_t svgid = KAUTH_GID_NONE;
        int error;
        kauth_cred_t my_cred, my_new_cred;
        posix_cred_t my_pcred;

        DEBUG_CRED_ENTER("setgid(%d/%d): %d\n", p->p_pid, (p->p_pptr ? p->p_pptr->p_pid : 0), uap->gid);

        gid = uap->gid;
        AUDIT_ARG(gid, gid);

        /* get current credential and take a reference while we muck with it */
        my_cred = kauth_cred_proc_ref(p);
        my_pcred = posix_cred_get(my_cred);

        for (;;) {
                if (gid != my_pcred->cr_rgid &&         /* allow setgid(getgid()) */
                    gid != my_pcred->cr_svgid &&        /* allow setgid(saved gid) */
                    (error = suser(my_cred, &p->p_acflag))) {
                        kauth_cred_unref(&my_cred);
                        return (error);
                }

                /*
                 * If we are privileged, then set the saved and real GID too;
                 * otherwise, just set the effective GID
                 */
                if (suser(my_cred,  &p->p_acflag) == 0) {
                        svgid = gid;
                        rgid = gid;
                } else {
                        svgid = KAUTH_GID_NONE;
                        rgid = KAUTH_GID_NONE;
                }

                /* 
                 * Set the credential with new info.  If there is no change,
                 * we get back the same credential we passed in; if there is
                 * a change, we drop the reference on the credential we
                 * passed in.  The subsequent compare is safe, because it is
                 * a pointer compare rather than a contents compare.
                 */
                my_new_cred = kauth_cred_setresgid(my_cred, rgid, gid, svgid);
                if (my_cred != my_new_cred) {

                        DEBUG_CRED_CHANGE("setgid(CH)%d: %p/0x%08x->%p/0x%08x\n", p->p_pid, my_cred, my_cred->cr_flags, my_new_cred, my_new_cred->cr_flags);

                        proc_ucred_lock(p);
                        /*
                         * We need to protect for a race where another thread
                         * also changed the credential after we took our
                         * reference.  If p_ucred has changed then we
                         * should restart this again with the new cred.
                         */
                        if (p->p_ucred != my_cred) {
                                proc_ucred_unlock(p);
                                kauth_cred_unref(&my_new_cred);
                                /* try again */
                                my_cred = kauth_cred_proc_ref(p);
                                my_pcred = posix_cred_get(my_cred);
                                continue;
                        }
                        p->p_ucred = my_new_cred;
                        /* update cred on proc */
                        PROC_UPDATE_CREDS_ONPROC(p);
                        OSBitOrAtomic(P_SUGID, &p->p_flag);
                        proc_ucred_unlock(p);
                }
                break;
        }
        /* Drop old proc reference or our extra reference */
        kauth_cred_unref(&my_cred);
        
        set_security_token(p);
        return (0);
}


/*
 * setegid
 *
 * Description: Set effective group ID system call
 *
 * Parameters:  uap->egid                       effective gid to set
 *
 * Returns:     0                               Success
 *      suser:EPERM
 *
 * Notes:       If called by a privileged process, or called from an
 *              unprivileged process but egid is equal to the real or saved
 *              gid, then the effective gid will be set to the requested
 *              value, but the real and saved gid will not change.
 *
 *              If the credential is changed as a result of this call, then we
 *              flag the process as having set privilege since the last exec.
 *
 *              As an implementation detail, the effective gid is stored as
 *              the first element of the supplementary group list, and
 *              therefore the effective group list may be reordered to keep
 *              the supplementary group list unchanged.
 */
int
setegid(proc_t p, struct setegid_args *uap, __unused int32_t *retval)
{
        gid_t egid;
        int error;
        kauth_cred_t my_cred, my_new_cred;
        posix_cred_t my_pcred;

        DEBUG_CRED_ENTER("setegid %d\n", uap->egid);

        egid = uap->egid;
        AUDIT_ARG(egid, egid);

        /* get current credential and take a reference while we muck with it */
        my_cred = kauth_cred_proc_ref(p);
        my_pcred = posix_cred_get(my_cred);


        for (;;) {
                if (egid != my_pcred->cr_rgid &&
                    egid != my_pcred->cr_svgid &&
                    (error = suser(my_cred, &p->p_acflag))) {
                        kauth_cred_unref(&my_cred);
                        return (error);
                }
                /* 
                 * Set the credential with new info.  If there is no change,
                 * we get back the same credential we passed in; if there is
                 * a change, we drop the reference on the credential we
                 * passed in.  The subsequent compare is safe, because it is
                 * a pointer compare rather than a contents compare.
                 */
                my_new_cred = kauth_cred_setresgid(my_cred, KAUTH_GID_NONE, egid, KAUTH_GID_NONE);
                if (my_cred != my_new_cred) {

                        DEBUG_CRED_CHANGE("setegid(CH)%d: %p/0x%08x->%p/0x%08x\n", p->p_pid, my_cred, my_pcred->cr_flags, my_new_cred, posix_cred_get(my_new_cred)->cr_flags);

                        proc_ucred_lock(p);
                        /*
                         * We need to protect for a race where another thread
                         * also changed the credential after we took our
                         * reference.  If p_ucred has changed then we
                         * should restart this again with the new cred.
                         */
                        if (p->p_ucred != my_cred) {
                                proc_ucred_unlock(p);
                                kauth_cred_unref(&my_new_cred);
                                /* try again */
                                my_cred = kauth_cred_proc_ref(p);
                                my_pcred = posix_cred_get(my_cred);
                                continue;
                        }
                        p->p_ucred = my_new_cred;
                        /* update cred on proc */
                        PROC_UPDATE_CREDS_ONPROC(p);
                        OSBitOrAtomic(P_SUGID, &p->p_flag);
                        proc_ucred_unlock(p);
                }
                break;
        }

        /* Drop old proc reference or our extra reference */
        kauth_cred_unref(&my_cred);

        set_security_token(p);
        return (0);
}

/*
 * setregid
 *
 * Description: Set real and effective group ID system call
 *
 * Parameters:  uap->rgid                       real gid to set
 *              uap->egid                       effective gid to set
 *
 * Returns:     0                               Success
 *      suser:EPERM                             Permission denied
 *
 * Notes:       A value of -1 is a special case indicating that the gid for
 *              which that value is specified not be changed.  If both values
 *              are specified as -1, no action is taken.
 *
 *              If called by a privileged process, the real and effective gid
 *              will be set to the new value(s) specified.
 *
 *              If called from an unprivileged process, the real gid may be
 *              set to the current value of the real gid, or to the current
 *              value of the saved gid.  The effective gid may be set to the
 *              current value of any of the effective, real, or saved gid.
 *
 *              If the new real and effective gid will not be equal, or the
 *              new real or effective gid is not the same as the saved gid,
 *              then the saved gid will be updated to reflect the new
 *              effective gid (potentially unrecoverably dropping saved
 *              privilege).
 *
 *              If the credential is changed as a result of this call, then we
 *              flag the process as having set privilege since the last exec.
 *
 *              As an implementation detail, the effective gid is stored as
 *              the first element of the supplementary group list, and
 *              therefore the effective group list may be reordered to keep
 *              the supplementary group list unchanged.
 */
int
setregid(proc_t p, struct setregid_args *uap, __unused int32_t *retval)
{
        gid_t rgid, egid;
        int error;
        kauth_cred_t my_cred, my_new_cred;
        posix_cred_t my_pcred;

        DEBUG_CRED_ENTER("setregid %d %d\n", uap->rgid, uap->egid);

        rgid = uap->rgid;
        egid = uap->egid;

        if (rgid == (uid_t)-1)
                rgid = KAUTH_GID_NONE;
        if (egid == (uid_t)-1)
                egid = KAUTH_GID_NONE;
        AUDIT_ARG(egid, egid);
        AUDIT_ARG(rgid, rgid);

        /* get current credential and take a reference while we muck with it */
        my_cred = kauth_cred_proc_ref(p);
        my_pcred = posix_cred_get(my_cred);

        for (;;) {

                if (((rgid != KAUTH_UID_NONE &&         /* allow no change of rgid */
                      rgid != my_pcred->cr_rgid &&      /* allow rgid = rgid */
                      rgid != my_pcred->cr_gid &&       /* allow rgid = egid */
                      rgid != my_pcred->cr_svgid) ||    /* allow rgid = svgid */
                     (egid != KAUTH_UID_NONE &&         /* allow no change of egid */
                      egid != my_pcred->cr_groups[0] && /* allow no change of egid */
                      egid != my_pcred->cr_gid &&       /* allow egid = egid */
                      egid != my_pcred->cr_rgid &&      /* allow egid = rgid */
                      egid != my_pcred->cr_svgid)) &&   /* allow egid = svgid */
                    (error = suser(my_cred, &p->p_acflag))) { /* allow root user any */
                        kauth_cred_unref(&my_cred);
                        return (error);
                }

                uid_t new_egid = my_pcred->cr_gid;
                uid_t new_rgid = my_pcred->cr_rgid;
                uid_t svgid = KAUTH_UID_NONE;

                
                /* 
                 * Set the credential with new info.  If there is no change,
                 * we get back the same credential we passed in; if there is
                 * a change, we drop the reference on the credential we
                 * passed in.  The subsequent compare is safe, because it is
                 * a pointer compare rather than a contents compare.
                 */
                if (egid != KAUTH_UID_NONE && my_pcred->cr_gid != egid) {
                        /* changing the effective GID */
                        new_egid = egid;
                        OSBitOrAtomic(P_SUGID, &p->p_flag);
                }
                if (rgid != KAUTH_UID_NONE && my_pcred->cr_rgid != rgid) {
                        /* changing the real GID */
                        new_rgid = rgid;
                        OSBitOrAtomic(P_SUGID, &p->p_flag);
                }
                /*
                 * If the newly requested real gid or effective gid does
                 * not match the saved gid, then set the saved gid to the
                 * new effective gid.  We are protected from escalation
                 * by the prechecking.
                 */
                if (my_pcred->cr_svgid != uap->rgid &&
                    my_pcred->cr_svgid != uap->egid) {
                        svgid = new_egid;
                        OSBitOrAtomic(P_SUGID, &p->p_flag);
                }

                my_new_cred = kauth_cred_setresgid(my_cred, rgid, egid, svgid);
                if (my_cred != my_new_cred) {

                        DEBUG_CRED_CHANGE("setregid(CH)%d: %p/0x%08x->%p/0x%08x\n", p->p_pid, my_cred, my_pcred->cr_flags, my_new_cred, posix_cred_get(my_new_cred)->cr_flags);

                        proc_ucred_lock(p);
                        /* need to protect for a race where another thread
                         * also changed the credential after we took our
                         * reference.  If p_ucred has changed then we
                         * should restart this again with the new cred.
                         */
                        if (p->p_ucred != my_cred) {
                                proc_ucred_unlock(p);
                                kauth_cred_unref(&my_new_cred);
                                /* try again */
                                my_cred = kauth_cred_proc_ref(p);
                                my_pcred = posix_cred_get(my_cred);
                                continue;
                        }
                        p->p_ucred = my_new_cred;
                        /* update cred on proc */
                        PROC_UPDATE_CREDS_ONPROC(p);
                        OSBitOrAtomic(P_SUGID, &p->p_flag); /* XXX redundant? */
                        proc_ucred_unlock(p);
                }
                break;
        }
        /* Drop old proc reference or our extra reference */
        kauth_cred_unref(&my_cred);

        set_security_token(p);
        return (0);
}


/*
 * Set the per-thread override identity.  The first parameter can be the
 * current real UID, KAUTH_UID_NONE, or, if the caller is privileged, it
 * can be any UID.  If it is KAUTH_UID_NONE, then as a special case, this
 * means "revert to the per process credential"; otherwise, if permitted,
 * it changes the effective, real, and saved UIDs and GIDs for the current
 * thread to the requested UID and single GID, and clears all other GIDs.
 */
int
settid(proc_t p, struct settid_args *uap, __unused int32_t *retval)
{
        kauth_cred_t uc;
        struct uthread *uthread = get_bsdthread_info(current_thread());
        uid_t uid;
        gid_t gid;

        uid = uap->uid;
        gid = uap->gid;
        AUDIT_ARG(uid, uid);
        AUDIT_ARG(gid, gid);

        if (proc_suser(p) != 0) 
                return (EPERM);
        
        if (uid == KAUTH_UID_NONE) {

                /* must already be assuming another identity in order to revert back */
                if ((uthread->uu_flag & UT_SETUID) == 0)
                        return (EPERM);

                /* revert to delayed binding of process credential */
                uc = kauth_cred_proc_ref(p);
                kauth_cred_unref(&uthread->uu_ucred);
                uthread->uu_ucred = uc;
                uthread->uu_flag &= ~UT_SETUID;
        } else {
                kauth_cred_t my_cred, my_new_cred;

                /* cannot already be assuming another identity */
                if ((uthread->uu_flag & UT_SETUID) != 0) {
                        return (EPERM);
                }

                /*
                 * Get a new credential instance from the old if this one
                 * changes; otherwise kauth_cred_setuidgid() returns the
                 * same credential.  We take an extra reference on the
                 * current credential while we muck with it, so we can do
                 * the post-compare for changes by pointer.
                 */
                kauth_cred_ref(uthread->uu_ucred); 
                my_cred = uthread->uu_ucred;
                my_new_cred = kauth_cred_setuidgid(my_cred, uid, gid);
                if (my_cred != my_new_cred)
                        uthread->uu_ucred = my_new_cred;
                uthread->uu_flag |= UT_SETUID;

                /* Drop old uthread reference or our extra reference */
                kauth_cred_unref(&my_cred);
        }
        /*
         * XXX should potentially set per thread security token (there is
         * XXX none).
         * XXX it is unclear whether P_SUGID should be st at this point;
         * XXX in theory, it is being deprecated.
         */
        return (0);
}


/*
 * Set the per-thread override identity.  Use this system call for a thread to
 * assume the identity of another process or to revert back to normal identity
 * of the current process.
 *
 * When the "assume" argument is non zero the current thread will assume the
 * identity of the process represented by the pid argument.
 *
 * When the assume argument is zero we revert back to our normal identity.
 */
int
settid_with_pid(proc_t p, struct settid_with_pid_args *uap, __unused int32_t *retval)
{
        proc_t target_proc;
        struct uthread *uthread = get_bsdthread_info(current_thread());
        kauth_cred_t my_cred, my_target_cred, my_new_cred;
        posix_cred_t my_target_pcred;

        AUDIT_ARG(pid, uap->pid);
        AUDIT_ARG(value32, uap->assume);

        if (proc_suser(p) != 0) {
                return (EPERM);
        }

        /*
         * XXX should potentially set per thread security token (there is
         * XXX none).
         * XXX it is unclear whether P_SUGID should be st at this point;
         * XXX in theory, it is being deprecated.
         */

        /*
         * assume argument tells us to assume the identity of the process with the
         * id passed in the pid argument.
         */
        if (uap->assume != 0) {
                /* can't do this if we have already assumed an identity */
                if ((uthread->uu_flag & UT_SETUID) != 0)
                        return (EPERM);
        
                target_proc = proc_find(uap->pid);
                /* can't assume the identity of the kernel process */
                if (target_proc == NULL || target_proc == kernproc) {
                        if (target_proc!= NULL)
                                proc_rele(target_proc);
                        return (ESRCH);
                }
        
                /*
                 * Take a reference on the credential used in our target
                 * process then use it as the identity for our current
                 * thread.  We take an extra reference on the current
                 * credential while we muck with it, so we can do the
                 * post-compare for changes by pointer.
                 *
                 * The post-compare is needed for the case that our process
                 * credential has been changed to be identical to our thread
                 * credential following our assumption of a per-thread one,
                 * since the credential cache will maintain a unique instance.
                 */
                kauth_cred_ref(uthread->uu_ucred); 
                my_cred = uthread->uu_ucred;
                my_target_cred = kauth_cred_proc_ref(target_proc);
                my_target_pcred = posix_cred_get(my_target_cred);
                my_new_cred = kauth_cred_setuidgid(my_cred, my_target_pcred->cr_uid, my_target_pcred->cr_gid);
                if (my_cred != my_new_cred)
                        uthread->uu_ucred = my_new_cred;
        
                uthread->uu_flag |= UT_SETUID;
                
                /* Drop old uthread reference or our extra reference */
                proc_rele(target_proc);
                kauth_cred_unref(&my_cred);
                kauth_cred_unref(&my_target_cred);

                return (0);
        }
        
        /*
         * Otherwise, we are reverting back to normal mode of operation where
         * delayed binding of the process credential sets the credential in
         * the thread (uu_ucred)
         */
        if ((uthread->uu_flag & UT_SETUID) == 0)
                return (EPERM);

        /* revert to delayed binding of process credential */
        my_new_cred = kauth_cred_proc_ref(p);
        kauth_cred_unref(&uthread->uu_ucred);
        uthread->uu_ucred = my_new_cred;
        uthread->uu_flag &= ~UT_SETUID;
        
        return (0);
}


/*
 * setgroups1
 *
 * Description: Internal implementation for both the setgroups and initgroups
 *              system calls
 *
 * Parameters:  gidsetsize                      Number of groups in set
 *              gidset                          Pointer to group list
 *              gmuid                           Base gid (initgroups only!)
 *
 * Returns:     0                               Success
 *      suser:EPERM                             Permision denied
 *              EINVAL                          Invalid gidsetsize value
 *      copyin:EFAULT                           Bad gidset or gidsetsize is
 *                                              too large
 *
 * Notes:       When called from a thread running under an assumed per-thread
 *              identity, this function will operate against the per-thread
 *              credential, rather than against the process credential.  In
 *              this specific case, the process credential is verified to
 *              still be privileged at the time of the call, rather than the
 *              per-thread credential for this operation to be permitted.
 *
 *              This effectively means that setgroups/initigroups calls in
 *              a thread running a per-thread credential should occur *after*
 *              the settid call that created it, not before (unlike setuid,
 *              which must be called after, since it will result in privilege
 *              being dropped).
 *
 *              When called normally (i.e. no per-thread assumed identity),
 *              the per process credential is updated per POSIX.
 *
 *              If the credential is changed as a result of this call, then we
 *              flag the process as having set privilege since the last exec.
 */
static int
setgroups1(proc_t p, u_int gidsetsize, user_addr_t gidset, uid_t gmuid, __unused int32_t *retval)
{
        u_int ngrp;
        gid_t   newgroups[NGROUPS] = { 0 };
        int     error;
        kauth_cred_t my_cred, my_new_cred;
        struct uthread *uthread = get_bsdthread_info(current_thread());

        DEBUG_CRED_ENTER("setgroups1 (%d/%d): %d 0x%016x %d\n", p->p_pid, (p->p_pptr ? p->p_pptr->p_pid : 0), gidsetsize, gidset, gmuid);

        ngrp = gidsetsize;
        if (ngrp > NGROUPS)
                return (EINVAL);

        if ( ngrp < 1 ) {
                ngrp = 1;
        } else {
                error = copyin(gidset,
                        (caddr_t)newgroups, ngrp * sizeof(gid_t));
                if (error) {
                        return (error);
                }
        }

        my_cred = kauth_cred_proc_ref(p);
        if ((error = suser(my_cred, &p->p_acflag))) {
                kauth_cred_unref(&my_cred);
                return (error);
        }

        if ((uthread->uu_flag & UT_SETUID) != 0) {
#if DEBUG_CRED
                int my_cred_flags = uthread->uu_ucred->cr_flags;
#endif  /* DEBUG_CRED */
                kauth_cred_unref(&my_cred);

                /*
                 * If this thread is under an assumed identity, set the
                 * supplementary grouplist on the thread credential instead
                 * of the process one.  If we were the only reference holder,
                 * the credential is updated in place, otherwise, our reference
                 * is dropped and we get back a different cred with a reference
                 * already held on it.  Because this is per-thread, we don't
                 * need the referencing/locking/retry required for per-process.
                 */
                my_cred = uthread->uu_ucred;
                uthread->uu_ucred = kauth_cred_setgroups(my_cred, &newgroups[0], ngrp, gmuid);
#if DEBUG_CRED
                if (my_cred != uthread->uu_ucred) {
                        DEBUG_CRED_CHANGE("setgroups1(CH)%d: %p/0x%08x->%p/0x%08x\n", p->p_pid, my_cred, my_cred_flags, uthread->uu_ucred , uthread->uu_ucred ->cr_flags);
                }
#endif  /* DEBUG_CRED */
        } else {

                /*
                 * get current credential and take a reference while we muck
                 * with it
                 */
                for (;;) {
                        /* 
                         * Set the credential with new info.  If there is no
                         * change, we get back the same credential we passed
                         * in; if there is a change, we drop the reference on
                         * the credential we passed in.  The subsequent
                         * compare is safe, because it is a pointer compare
                         * rather than a contents compare.
                         */
                        my_new_cred = kauth_cred_setgroups(my_cred, &newgroups[0], ngrp, gmuid);
                        if (my_cred != my_new_cred) {

                                DEBUG_CRED_CHANGE("setgroups1(CH)%d: %p/0x%08x->%p/0x%08x\n", p->p_pid, my_cred, my_cred->cr_flags, my_new_cred, my_new_cred->cr_flags);

                                proc_ucred_lock(p);
                                /*
                                 * We need to protect for a race where another
                                 * thread also changed the credential after we
                                 * took our reference.  If p_ucred has 
                                 * changed then we should restart this again
                                 * with the new cred.
                                 */
                                if (p->p_ucred != my_cred) {
                                        proc_ucred_unlock(p);
                                        kauth_cred_unref(&my_new_cred);
                                        my_cred = kauth_cred_proc_ref(p);
                                        /* try again */
                                        continue;
                                }
                                p->p_ucred = my_new_cred;
                                /* update cred on proc */
                                PROC_UPDATE_CREDS_ONPROC(p);
                                OSBitOrAtomic(P_SUGID, &p->p_flag);
                                proc_ucred_unlock(p);
                        }
                        break;
                }
                /* Drop old proc reference or our extra reference */
                AUDIT_ARG(groupset, posix_cred_get(my_cred)->cr_groups, ngrp);
                kauth_cred_unref(&my_cred);


                set_security_token(p);
        }

        return (0);
}


/*
 * initgroups
 *
 * Description: Initialize the default supplementary groups list and set the
 *              gmuid for use by the external group resolver (if any)
 *
 * Parameters:  uap->gidsetsize                 Number of groups in set
 *              uap->gidset                     Pointer to group list
 *              uap->gmuid                      Base gid
 *
 * Returns:     0                               Success
 *      setgroups1:EPERM                        Permision denied
 *      setgroups1:EINVAL                       Invalid gidsetsize value
 *      setgroups1:EFAULT                       Bad gidset or gidsetsize is
 *
 * Notes:       This function opts *IN* to memberd participation
 *
 *              The normal purpose of this function is for a privileged
 *              process to indicate supplementary groups and identity for
 *              participation in extended group membership resolution prior
 *              to dropping privilege by assuming a specific user identity.
 *
 *              It is the first half of the primary mechanism whereby user
 *              identity is established to the system by programs such as
 *              /usr/bin/login.  The second half is the drop of uid privilege
 *              for a specific uid corresponding to the user.
 *
 * See also:    setgroups1()
 */
int
initgroups(proc_t p, struct initgroups_args *uap, __unused int32_t *retval)
{
        DEBUG_CRED_ENTER("initgroups\n");

        return(setgroups1(p, uap->gidsetsize, uap->gidset, uap->gmuid, retval));
}


/*
 * setgroups
 *
 * Description: Initialize the default supplementary groups list
 *
 * Parameters:  gidsetsize                      Number of groups in set
 *              gidset                          Pointer to group list
 *
 * Returns:     0                               Success
 *      setgroups1:EPERM                        Permision denied
 *      setgroups1:EINVAL                       Invalid gidsetsize value
 *      setgroups1:EFAULT                       Bad gidset or gidsetsize is
 *
 * Notes:       This functions opts *OUT* of memberd participation.
 *
 *              This function exists for compatibility with POSIX.  Most user
 *              programs should use initgroups() instead to ensure correct
 *              participation in group membership resolution when utilizing
 *              a directory service for authentication.
 *
 *              It is identical to an initgroups() call with a gmuid argument
 *              of KAUTH_UID_NONE.
 *
 * See also:    setgroups1()
 */
int
setgroups(proc_t p, struct setgroups_args *uap, __unused int32_t *retval)
{
        DEBUG_CRED_ENTER("setgroups\n");

        return(setgroups1(p, uap->gidsetsize, uap->gidset, KAUTH_UID_NONE, retval));
}


/*
 * Set the per-thread/per-process supplementary groups list.
 * 
 * XXX implement setsgroups
 *
 */

int
setsgroups(__unused proc_t p, __unused struct setsgroups_args *uap, __unused int32_t *retval)
{
        return(ENOTSUP);
}

/*
 * Set the per-thread/per-process whiteout groups list.
 * 
 * XXX implement setwgroups
 *
 */

int
setwgroups(__unused proc_t p, __unused struct setwgroups_args *uap, __unused int32_t *retval)
{
        return(ENOTSUP);
}


/*
 * Check if gid is a member of the group set.
 *
 * XXX This interface is going away; use kauth_cred_ismember_gid() directly
 * XXX instead.
 */
int
groupmember(gid_t gid, kauth_cred_t cred)
{
        int is_member;

        if (kauth_cred_ismember_gid(cred, gid, &is_member) == 0 && is_member)
                return (1);
        return (0);
}


/*
 * Test whether the specified credentials imply "super-user"
 * privilege; if so, and we have accounting info, set the flag
 * indicating use of super-powers.
 * Returns 0 or error.
 *
 * XXX This interface is going away; use kauth_cred_issuser() directly
 * XXX instead.
 *
 * Note:        This interface exists to implement the "has used privilege"
 *              bit (ASU) in the p_acflags field of the process, which is
 *              only externalized via private sysctl and in process accounting
 *              records.  The flag is technically not required in either case.
 */
int
suser(kauth_cred_t cred, u_short *acflag)
{
#if DIAGNOSTIC
        if (!IS_VALID_CRED(cred))
                panic("suser");
#endif
        if (kauth_cred_getuid(cred) == 0) {
                if (acflag)
                        *acflag |= ASU;
                return (0);
        }
        return (EPERM);
}


/*
 * getlogin
 *
 * Description: Get login name, if available.
 *
 * Parameters:  uap->namebuf                    User buffer for return
 *              uap->namelen                    User buffer length
 *
 * Returns:     0                               Success
 *      copyout:EFAULT
 *
 * Notes:       Intended to obtain a string containing the user name of the
 *              user associated with the controlling terminal for the calling
 *              process.
 *
 *              Not very useful on modern systems, due to inherent length
 *              limitations for the static array in the session structure
 *              which is used to store the login name.
 *
 *              Permitted to return NULL
 *
 * XXX:         Belongs in kern_proc.c
 */
int
getlogin(proc_t p, struct getlogin_args *uap, __unused int32_t *retval)
{
        char buffer[MAXLOGNAME+1];
        struct session * sessp;

        bzero(buffer, MAXLOGNAME+1);

        sessp = proc_session(p);

        if (uap->namelen > MAXLOGNAME)
                uap->namelen = MAXLOGNAME;

        if(sessp != SESSION_NULL) {
                session_lock(sessp);
                bcopy( sessp->s_login, buffer, uap->namelen);
                session_unlock(sessp);
        }
        session_rele(sessp);

        return (copyout((caddr_t)buffer, uap->namebuf, uap->namelen));
}


/*
 * setlogin
 *
 * Description: Set login name.
 *
 * Parameters:  uap->namebuf                    User buffer containing name
 *
 * Returns:     0                               Success
 *      suser:EPERM                             Permission denied
 *      copyinstr:EFAULT                        User buffer invalid
 *      copyinstr:EINVAL                        Supplied name was too long
 *
 * Notes:       This is a utility system call to support getlogin().
 *
 * XXX:         Belongs in kern_proc.c
 */
int
setlogin(proc_t p, struct setlogin_args *uap, __unused int32_t *retval)
{
        int error;
        size_t dummy=0;
        char buffer[MAXLOGNAME+1];
        struct session * sessp;

        if ((error = proc_suser(p)))
                return (error);

        bzero(&buffer[0], MAXLOGNAME+1);


        error = copyinstr(uap->namebuf,
            (caddr_t) &buffer[0],
            MAXLOGNAME - 1, (size_t *)&dummy);

        sessp = proc_session(p);

        if (sessp != SESSION_NULL) {
                session_lock(sessp);
                bcopy(buffer, sessp->s_login, MAXLOGNAME);
                session_unlock(sessp);
                session_rele(sessp);
        }


        if (!error) {
                AUDIT_ARG(text, buffer);
         } else if (error == ENAMETOOLONG)
                error = EINVAL;
        return (error);
}


/* Set the secrity token of the task with current euid and eguid */
/*
 * XXX This needs to change to give the task a reference and/or an opaque
 * XXX identifier.
 */
int
set_security_token(proc_t p)
{
        return set_security_token_task_internal(p, p->task);
}

/*
 * Set the secrity token of the task with current euid and eguid
 * The function takes a proc and a task, where proc->task might point to a
 * different task if called from exec.
 */

int
set_security_token_task_internal(proc_t p, void *t)
{
        security_token_t sec_token;
        audit_token_t    audit_token;
        kauth_cred_t my_cred;
        posix_cred_t my_pcred;
        host_priv_t host_priv;
        task_t task = t;

        /*
         * Don't allow a vfork child to override the parent's token settings
         * (since they share a task).  Instead, the child will just have to
         * suffer along using the parent's token until the exec().  It's all
         * undefined behavior anyway, right?
         */
        if (task == current_task()) {
                uthread_t        uthread;
                uthread = (uthread_t)get_bsdthread_info(current_thread());
                if (uthread->uu_flag & UT_VFORK)
                        return (1);
        }
                
        my_cred = kauth_cred_proc_ref(p);
        my_pcred = posix_cred_get(my_cred);

        /* XXX mach_init doesn't have a p_ucred when it calls this function */
        if (IS_VALID_CRED(my_cred)) {
                sec_token.val[0] = kauth_cred_getuid(my_cred);
                sec_token.val[1] = kauth_cred_getgid(my_cred);
        } else {
                sec_token.val[0] = 0;
                sec_token.val[1] = 0;
        }

        /*
         * The current layout of the Mach audit token explicitly
         * adds these fields.  But nobody should rely on such
         * a literal representation.  Instead, the BSM library
         * provides a function to convert an audit token into
         * a BSM subject.  Use of that mechanism will isolate
         * the user of the trailer from future representation
         * changes.
         */
        audit_token.val[0] = my_cred->cr_audit.as_aia_p->ai_auid;
        audit_token.val[1] = my_pcred->cr_uid;
        audit_token.val[2] = my_pcred->cr_gid;
        audit_token.val[3] = my_pcred->cr_ruid;
        audit_token.val[4] = my_pcred->cr_rgid;
        audit_token.val[5] = p->p_pid;
        audit_token.val[6] = my_cred->cr_audit.as_aia_p->ai_asid;
        audit_token.val[7] = p->p_idversion;

        host_priv = (sec_token.val[0]) ? HOST_PRIV_NULL : host_priv_self();
#if CONFIG_MACF
        if (host_priv != HOST_PRIV_NULL && mac_system_check_host_priv(my_cred))
                host_priv = HOST_PRIV_NULL;
#endif
        kauth_cred_unref(&my_cred);

#if DEVELOPMENT || DEBUG
        /* 
         * Update the pid an proc name for importance base if any
         */
        task_importance_update_owner_info(task);
#endif

        return (host_security_set_task_token(host_security_self(),
                                           task,
                                           sec_token,
                                           audit_token,
                                           host_priv) != KERN_SUCCESS);
}


int get_audit_token_pid(audit_token_t *audit_token);

int
get_audit_token_pid(audit_token_t *audit_token)
{
        /* keep in-sync with set_security_token (above) */
        if (audit_token)
                return (int)audit_token->val[5];
        return -1;
}


/*
 * Fill in a struct xucred based on a kauth_cred_t.
 */
__private_extern__
void
cru2x(kauth_cred_t cr, struct xucred *xcr)
{
        posix_cred_t pcr = posix_cred_get(cr);

        bzero(xcr, sizeof(*xcr));
        xcr->cr_version = XUCRED_VERSION;
        xcr->cr_uid = kauth_cred_getuid(cr);
        xcr->cr_ngroups = pcr->cr_ngroups;
        bcopy(pcr->cr_groups, xcr->cr_groups, sizeof(xcr->cr_groups));
}