xnu-7195.101.1.tar.gz

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

/*
 * Copyright (c) 2000-2020 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, 1997 Apple Computer, Inc. All Rights Reserved */
/*
 * Copyright (c) 1982, 1986, 1989, 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_fork.c 8.8 (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.
 */

#include <kern/assert.h>
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/filedesc.h>
#include <sys/kernel.h>
#include <sys/malloc.h>
#include <sys/proc_internal.h>
#include <sys/kauth.h>
#include <sys/user.h>
#include <sys/reason.h>
#include <sys/resourcevar.h>
#include <sys/vnode_internal.h>
#include <sys/file_internal.h>
#include <sys/acct.h>
#include <sys/codesign.h>
#include <sys/sysproto.h>
#if CONFIG_PERSONAS
#include <sys/persona.h>
#endif
#include <sys/doc_tombstone.h>
#if CONFIG_DTRACE
/* Do not include dtrace.h, it redefines kmem_[alloc/free] */
extern void (*dtrace_proc_waitfor_exec_ptr)(proc_t);
extern void dtrace_proc_fork(proc_t, proc_t, int);

/*
 * Since dtrace_proc_waitfor_exec_ptr can be added/removed in dtrace_subr.c,
 * we will store its value before actually calling it.
 */
static void (*dtrace_proc_waitfor_hook)(proc_t) = NULL;

#include <sys/dtrace_ptss.h>
#endif

#include <security/audit/audit.h>

#include <mach/mach_types.h>
#include <kern/coalition.h>
#include <kern/kern_types.h>
#include <kern/kalloc.h>
#include <kern/mach_param.h>
#include <kern/task.h>
#include <kern/thread.h>
#include <kern/thread_call.h>
#include <kern/zalloc.h>

#include <os/log.h>

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

#include <vm/vm_map.h>
#include <vm/vm_protos.h>
#include <vm/vm_shared_region.h>

#include <sys/shm_internal.h>   /* for shmfork() */
#include <mach/task.h>          /* for thread_create() */
#include <mach/thread_act.h>    /* for thread_resume() */

#include <sys/sdt.h>

#if CONFIG_MEMORYSTATUS
#include <sys/kern_memorystatus.h>
#endif

/* XXX routines which should have Mach prototypes, but don't */
void thread_set_parent(thread_t parent, int pid);
extern void act_thread_catt(void *ctx);
void thread_set_child(thread_t child, int pid);
void *act_thread_csave(void);
extern boolean_t task_is_exec_copy(task_t);
int nextpidversion = 0;


thread_t cloneproc(task_t, coalition_t *, proc_t, int, int);
proc_t forkproc(proc_t);
void forkproc_free(proc_t);
thread_t fork_create_child(task_t parent_task,
    coalition_t *parent_coalitions,
    proc_t child,
    int inherit_memory,
    int is_64bit_addr,
    int is_64bit_data,
    int in_exec);
void proc_vfork_begin(proc_t parent_proc);
void proc_vfork_end(proc_t parent_proc);

static LCK_GRP_DECLARE(rethrottle_lock_grp, "rethrottle");
static ZONE_DECLARE(uthread_zone, "uthreads",
    sizeof(struct uthread), ZC_ZFREE_CLEARMEM);

SECURITY_READ_ONLY_LATE(zone_t) proc_zone;
ZONE_INIT(&proc_zone, "proc", sizeof(struct proc), ZC_ZFREE_CLEARMEM,
    ZONE_ID_PROC, NULL);

ZONE_DECLARE(proc_stats_zone, "pstats",
    sizeof(struct pstats), ZC_NOENCRYPT | ZC_ZFREE_CLEARMEM);

ZONE_DECLARE(proc_sigacts_zone, "sigacts",
    sizeof(struct sigacts), ZC_NOENCRYPT);

#define DOFORK  0x1     /* fork() system call */
#define DOVFORK 0x2     /* vfork() system call */

/*
 * proc_vfork_begin
 *
 * Description: start a vfork on a process
 *
 * Parameters:  parent_proc             process (re)entering vfork state
 *
 * Returns:     (void)
 *
 * Notes:       Although this function increments a count, a count in
 *              excess of 1 is not currently supported.  According to the
 *              POSIX standard, calling anything other than execve() or
 *              _exit() following a vfork(), including calling vfork()
 *              itself again, will result in undefined behaviour
 */
void
proc_vfork_begin(proc_t parent_proc)
{
        proc_lock(parent_proc);
        parent_proc->p_lflag  |= P_LVFORK;
        parent_proc->p_vforkcnt++;
        proc_unlock(parent_proc);
}

/*
 * proc_vfork_end
 *
 * Description: stop a vfork on a process
 *
 * Parameters:  parent_proc             process leaving vfork state
 *
 * Returns:     (void)
 *
 * Notes:       Decrements the count; currently, reentrancy of vfork()
 *              is unsupported on the current process
 */
void
proc_vfork_end(proc_t parent_proc)
{
        proc_lock(parent_proc);
        parent_proc->p_vforkcnt--;
        if (parent_proc->p_vforkcnt < 0) {
                panic("vfork cnt is -ve");
        }
        if (parent_proc->p_vforkcnt == 0) {
                parent_proc->p_lflag  &= ~P_LVFORK;
        }
        proc_unlock(parent_proc);
}


/*
 * vfork
 *
 * Description: vfork system call
 *
 * Parameters:  void                    [no arguments]
 *
 * Retval:      0                       (to child process)
 *              !0                      pid of child (to parent process)
 *              -1                      error (see "Returns:")
 *
 * Returns:     EAGAIN                  Administrative limit reached
 *              EINVAL                  vfork() called during vfork()
 *              ENOMEM                  Failed to allocate new process
 *
 * Note:        After a successful call to this function, the parent process
 *              has its task, thread, and uthread lent to the child process,
 *              and control is returned to the caller; if this function is
 *              invoked as a system call, the return is to user space, and
 *              is effectively running on the child process.
 *
 *              Subsequent calls that operate on process state are permitted,
 *              though discouraged, and will operate on the child process; any
 *              operations on the task, thread, or uthread will result in
 *              changes in the parent state, and, if inheritable, the child
 *              state, when a task, thread, and uthread are realized for the
 *              child process at execve() time, will also be effected.  Given
 *              this, it's recemmended that people use the posix_spawn() call
 *              instead.
 *
 * BLOCK DIAGRAM OF VFORK
 *
 * Before:
 *
 *     ,----------------.         ,-------------.
 *     |                |   task  |             |
 *     | parent_thread  | ------> | parent_task |
 *     |                | <.list. |             |
 *     `----------------'         `-------------'
 *    uthread |  ^             bsd_info |  ^
 *            v  | vc_thread            v  | task
 *     ,----------------.         ,-------------.
 *     |                |         |             |
 *     | parent_uthread | <.list. | parent_proc | <-- current_proc()
 *     |                |         |             |
 *     `----------------'         `-------------'
 *    uu_proc |
 *            v
 *           NULL
 *
 * After:
 *
 *                 ,----------------.         ,-------------.
 *                 |                |   task  |             |
 *          ,----> | parent_thread  | ------> | parent_task |
 *          |      |                | <.list. |             |
 *          |      `----------------'         `-------------'
 *          |     uthread |  ^             bsd_info |  ^
 *          |             v  | vc_thread            v  | task
 *          |      ,----------------.         ,-------------.
 *          |      |                |         |             |
 *          |      | parent_uthread | <.list. | parent_proc |
 *          |      |                |         |             |
 *          |      `----------------'         `-------------'
 *          |     uu_proc |  . list
 *          |             v  v
 *          |      ,----------------.
 *          `----- |                |
 *      p_vforkact | child_proc     | <-- current_proc()
 *                 |                |
 *                 `----------------'
 */
int
vfork(proc_t parent_proc, __unused struct vfork_args *uap, int32_t *retval)
{
        thread_t child_thread;
        int err;

        if ((err = fork1(parent_proc, &child_thread, PROC_CREATE_VFORK, NULL)) != 0) {
                retval[1] = 0;
        } else {
                uthread_t ut = get_bsdthread_info(current_thread());
                proc_t child_proc = ut->uu_proc;

                retval[0] = child_proc->p_pid;
                retval[1] = 1;          /* flag child return for user space */

                /*
                 * Drop the signal lock on the child which was taken on our
                 * behalf by forkproc()/cloneproc() to prevent signals being
                 * received by the child in a partially constructed state.
                 */
                proc_signalend(child_proc, 0);
                proc_transend(child_proc, 0);

                proc_knote(parent_proc, NOTE_FORK | child_proc->p_pid);
                DTRACE_PROC1(create, proc_t, child_proc);
                ut->uu_flag &= ~UT_VFORKING;
        }

        return err;
}


/*
 * fork1
 *
 * Description: common code used by all new process creation other than the
 *              bootstrap of the initial process on the system
 *
 * Parameters: parent_proc              parent process of the process being
 *              child_threadp           pointer to location to receive the
 *                                      Mach thread_t of the child process
 *                                      created
 *              kind                    kind of creation being requested
 *              coalitions              if spawn, the set of coalitions the
 *                                      child process should join, or NULL to
 *                                      inherit the parent's. On non-spawns,
 *                                      this param is ignored and the child
 *                                      always inherits the parent's
 *                                      coalitions.
 *
 * Notes:       Permissable values for 'kind':
 *
 *              PROC_CREATE_FORK        Create a complete process which will
 *                                      return actively running in both the
 *                                      parent and the child; the child copies
 *                                      the parent address space.
 *              PROC_CREATE_SPAWN       Create a complete process which will
 *                                      return actively running in the parent
 *                                      only after returning actively running
 *                                      in the child; the child address space
 *                                      is newly created by an image activator,
 *                                      after which the child is run.
 *              PROC_CREATE_VFORK       Creates a partial process which will
 *                                      borrow the parent task, thread, and
 *                                      uthread to return running in the child;
 *                                      the child address space and other parts
 *                                      are lazily created at execve() time, or
 *                                      the child is terminated, and the parent
 *                                      does not actively run until that
 *                                      happens.
 *
 *              At first it may seem strange that we return the child thread
 *              address rather than process structure, since the process is
 *              the only part guaranteed to be "new"; however, since we do
 *              not actualy adjust other references between Mach and BSD (see
 *              the block diagram above the implementation of vfork()), this
 *              is the only method which guarantees us the ability to get
 *              back to the other information.
 */
int
fork1(proc_t parent_proc, thread_t *child_threadp, int kind, coalition_t *coalitions)
{
        thread_t parent_thread = (thread_t)current_thread();
        uthread_t parent_uthread = (uthread_t)get_bsdthread_info(parent_thread);
        proc_t child_proc = NULL;       /* set in switch, but compiler... */
        thread_t child_thread = NULL;
        uid_t uid;
        size_t count;
        int err = 0;
        int spawn = 0;
        rlim_t rlimit_nproc_cur;

        /*
         * Although process entries are dynamically created, we still keep
         * a global limit on the maximum number we will create.  Don't allow
         * a nonprivileged user to use the last process; don't let root
         * exceed the limit. The variable nprocs is the current number of
         * processes, maxproc is the limit.
         */
        uid = kauth_getruid();
        proc_list_lock();
        if ((nprocs >= maxproc - 1 && uid != 0) || nprocs >= maxproc) {
#if (DEVELOPMENT || DEBUG) && !defined(XNU_TARGET_OS_OSX)
                /*
                 * On the development kernel, panic so that the fact that we hit
                 * the process limit is obvious, as this may very well wedge the
                 * system.
                 */
                panic("The process table is full; parent pid=%d", parent_proc->p_pid);
#endif
                proc_list_unlock();
                tablefull("proc");
                return EAGAIN;
        }
        proc_list_unlock();

        /*
         * Increment the count of procs running with this uid. Don't allow
         * a nonprivileged user to exceed their current limit, which is
         * always less than what an rlim_t can hold.
         * (locking protection is provided by list lock held in chgproccnt)
         */
        count = chgproccnt(uid, 1);
        rlimit_nproc_cur = proc_limitgetcur(parent_proc, RLIMIT_NPROC, TRUE);
        if (uid != 0 &&
            (rlim_t)count > rlimit_nproc_cur) {
#if (DEVELOPMENT || DEBUG) && !defined(XNU_TARGET_OS_OSX)
                /*
                 * On the development kernel, panic so that the fact that we hit
                 * the per user process limit is obvious.  This may be less dire
                 * than hitting the global process limit, but we cannot rely on
                 * that.
                 */
                panic("The per-user process limit has been hit; parent pid=%d, uid=%d", parent_proc->p_pid, uid);
#endif
                err = EAGAIN;
                goto bad;
        }

#if CONFIG_MACF
        /*
         * Determine if MAC policies applied to the process will allow
         * it to fork.  This is an advisory-only check.
         */
        err = mac_proc_check_fork(parent_proc);
        if (err != 0) {
                goto bad;
        }
#endif

        switch (kind) {
        case PROC_CREATE_VFORK:
                /*
                 * Prevent a vfork while we are in vfork(); we should
                 * also likely preventing a fork here as well, and this
                 * check should then be outside the switch statement,
                 * since the proc struct contents will copy from the
                 * child and the tash/thread/uthread from the parent in
                 * that case.  We do not support vfork() in vfork()
                 * because we don't have to; the same non-requirement
                 * is true of both fork() and posix_spawn() and any
                 * call  other than execve() amd _exit(), but we've
                 * been historically lenient, so we continue to be so
                 * (for now).
                 *
                 * <rdar://6640521> Probably a source of random panics
                 */
                if (parent_uthread->uu_flag & UT_VFORK) {
                        printf("fork1 called within vfork by %s\n", parent_proc->p_comm);
                        err = EINVAL;
                        goto bad;
                }

                /*
                 * Flag us in progress; if we chose to support vfork() in
                 * vfork(), we would chain our parent at this point (in
                 * effect, a stack push).  We don't, since we actually want
                 * to disallow everything not specified in the standard
                 */
                proc_vfork_begin(parent_proc);

                /* The newly created process comes with signal lock held */
                if ((child_proc = forkproc(parent_proc)) == NULL) {
                        /* Failed to allocate new process */
                        proc_vfork_end(parent_proc);
                        err = ENOMEM;
                        goto bad;
                }

// XXX BEGIN: wants to move to be common code (and safe)
#if CONFIG_MACF
                /*
                 * allow policies to associate the credential/label that
                 * we referenced from the parent ... with the child
                 * JMM - this really isn't safe, as we can drop that
                 *       association without informing the policy in other
                 *       situations (keep long enough to get policies changed)
                 */
                mac_cred_label_associate_fork(child_proc->p_ucred, child_proc);
#endif

                /*
                 * Propogate change of PID - may get new cred if auditing.
                 *
                 * NOTE: This has no effect in the vfork case, since
                 *      child_proc->task != current_task(), but we duplicate it
                 *      because this is probably, ultimately, wrong, since we
                 *      will be running in the "child" which is the parent task
                 *      with the wrong token until we get to the execve() or
                 *      _exit() call; a lot of "undefined" can happen before
                 *      that.
                 *
                 * <rdar://6640530> disallow everything but exeve()/_exit()?
                 */
                set_security_token(child_proc);

                AUDIT_ARG(pid, child_proc->p_pid);

// XXX END: wants to move to be common code (and safe)

                /*
                 * BORROW PARENT TASK, THREAD, UTHREAD FOR CHILD
                 *
                 * Note: this is where we would "push" state instead of setting
                 * it for nested vfork() support (see proc_vfork_end() for
                 * description if issues here).
                 */
                child_proc->task = parent_proc->task;

                child_proc->p_lflag  |= P_LINVFORK;
                child_proc->p_vforkact = parent_thread;
                child_proc->p_stat = SRUN;

                /*
                 * Until UT_VFORKING is cleared at the end of the vfork
                 * syscall, the process identity of this thread is slightly
                 * murky.
                 *
                 * As long as UT_VFORK and it's associated field (uu_proc)
                 * is set, current_proc() will always return the child process.
                 *
                 * However dtrace_proc_selfpid() returns the parent pid to
                 * ensure that e.g. the proc:::create probe actions accrue
                 * to the parent.  (Otherwise the child magically seems to
                 * have created itself!)
                 */
                parent_uthread->uu_flag |= UT_VFORK | UT_VFORKING;
                parent_uthread->uu_proc = child_proc;
                parent_uthread->uu_userstate = (void *)act_thread_csave();
                parent_uthread->uu_vforkmask = parent_uthread->uu_sigmask;

                /* temporarily drop thread-set-id state */
                if (parent_uthread->uu_flag & UT_SETUID) {
                        parent_uthread->uu_flag |= UT_WASSETUID;
                        parent_uthread->uu_flag &= ~UT_SETUID;
                }

                /* blow thread state information */
                /* XXX is this actually necessary, given syscall return? */
                thread_set_child(parent_thread, child_proc->p_pid);

                child_proc->p_acflag = AFORK;   /* forked but not exec'ed */

                /*
                 * Preserve synchronization semantics of vfork.  If
                 * waiting for child to exec or exit, set P_PPWAIT
                 * on child, and sleep on our proc (in case of exit).
                 */
                child_proc->p_lflag |= P_LPPWAIT;
                pinsertchild(parent_proc, child_proc);  /* set visible */

                break;

        case PROC_CREATE_SPAWN:
                /*
                 * A spawned process differs from a forked process in that
                 * the spawned process does not carry around the parents
                 * baggage with regard to address space copying, dtrace,
                 * and so on.
                 */
                spawn = 1;

                OS_FALLTHROUGH;

        case PROC_CREATE_FORK:
                /*
                 * When we clone the parent process, we are going to inherit
                 * its task attributes and memory, since when we fork, we
                 * will, in effect, create a duplicate of it, with only minor
                 * differences.  Contrarily, spawned processes do not inherit.
                 */
                if ((child_thread = cloneproc(parent_proc->task,
                    spawn ? coalitions : NULL,
                    parent_proc,
                    spawn ? FALSE : TRUE,
                    FALSE)) == NULL) {
                        /* Failed to create thread */
                        err = EAGAIN;
                        goto bad;
                }

                /* copy current thread state into the child thread (only for fork) */
                if (!spawn) {
                        thread_dup(child_thread);
                }

                /* child_proc = child_thread->task->proc; */
                child_proc = (proc_t)(get_bsdtask_info(get_threadtask(child_thread)));

// XXX BEGIN: wants to move to be common code (and safe)
#if CONFIG_MACF
                /*
                 * allow policies to associate the credential/label that
                 * we referenced from the parent ... with the child
                 * JMM - this really isn't safe, as we can drop that
                 *       association without informing the policy in other
                 *       situations (keep long enough to get policies changed)
                 */
                mac_cred_label_associate_fork(child_proc->p_ucred, child_proc);
#endif

                /*
                 * Propogate change of PID - may get new cred if auditing.
                 *
                 * NOTE: This has no effect in the vfork case, since
                 *      child_proc->task != current_task(), but we duplicate it
                 *      because this is probably, ultimately, wrong, since we
                 *      will be running in the "child" which is the parent task
                 *      with the wrong token until we get to the execve() or
                 *      _exit() call; a lot of "undefined" can happen before
                 *      that.
                 *
                 * <rdar://6640530> disallow everything but exeve()/_exit()?
                 */
                set_security_token(child_proc);

                AUDIT_ARG(pid, child_proc->p_pid);

// XXX END: wants to move to be common code (and safe)

                /*
                 * Blow thread state information; this is what gives the child
                 * process its "return" value from a fork() call.
                 *
                 * Note: this should probably move to fork() proper, since it
                 * is not relevent to spawn, and the value won't matter
                 * until we resume the child there.  If you are in here
                 * refactoring code, consider doing this at the same time.
                 */
                thread_set_child(child_thread, child_proc->p_pid);

                child_proc->p_acflag = AFORK;   /* forked but not exec'ed */

#if CONFIG_DTRACE
                dtrace_proc_fork(parent_proc, child_proc, spawn);
#endif  /* CONFIG_DTRACE */
                if (!spawn) {
                        /*
                         * Of note, we need to initialize the bank context behind
                         * the protection of the proc_trans lock to prevent a race with exit.
                         */
                        task_bank_init(get_threadtask(child_thread));
                }

                break;

        default:
                panic("fork1 called with unknown kind %d", kind);
                break;
        }


        /* return the thread pointer to the caller */
        *child_threadp = child_thread;

bad:
        /*
         * In the error case, we return a 0 value for the returned pid (but
         * it is ignored in the trampoline due to the error return); this
         * is probably not necessary.
         */
        if (err) {
                (void)chgproccnt(uid, -1);
        }

        return err;
}


/*
 * vfork_return
 *
 * Description: "Return" to parent vfork thread() following execve/_exit;
 *              this is done by reassociating the parent process structure
 *              with the task, thread, and uthread.
 *
 *              Refer to the ASCII art above vfork() to figure out the
 *              state we're undoing.
 *
 * Parameters:  child_proc              Child process
 *              retval                  System call return value array
 *              rval                    Return value to present to parent
 *
 * Returns:     void
 *
 * Notes:       The caller resumes or exits the parent, as appropriate, after
 *              calling this function.
 */
void
vfork_return(proc_t child_proc, int32_t *retval, int rval)
{
        task_t parent_task = get_threadtask(child_proc->p_vforkact);
        proc_t parent_proc = get_bsdtask_info(parent_task);
        thread_t th = current_thread();
        uthread_t uth = get_bsdthread_info(th);

        act_thread_catt(uth->uu_userstate);

        /* clear vfork state in parent proc structure */
        proc_vfork_end(parent_proc);

        /* REPATRIATE PARENT TASK, THREAD, UTHREAD */
        uth->uu_userstate = 0;
        uth->uu_flag &= ~UT_VFORK;
        /* restore thread-set-id state */
        if (uth->uu_flag & UT_WASSETUID) {
                uth->uu_flag |= UT_SETUID;
                uth->uu_flag &= ~UT_WASSETUID;
        }
        uth->uu_proc = 0;
        uth->uu_sigmask = uth->uu_vforkmask;

        proc_lock(child_proc);
        child_proc->p_lflag &= ~P_LINVFORK;
        child_proc->p_vforkact = 0;
        proc_unlock(child_proc);

        thread_set_parent(th, rval);

        if (retval) {
                retval[0] = rval;
                retval[1] = 0;                  /* mark parent */
        }
}


/*
 * fork_create_child
 *
 * Description: Common operations associated with the creation of a child
 *              process
 *
 * Parameters:  parent_task             parent task
 *              parent_coalitions       parent's set of coalitions
 *              child_proc                      child process
 *              inherit_memory          TRUE, if the parents address space is
 *                                                      to be inherited by the child
 *              is_64bit_addr           TRUE, if the child being created will
 *                                                      be associated with a 64 bit address space
 *              is_64bit_data           TRUE if the child being created will use a
 *                                                       64-bit register state
 *              in_exec                         TRUE, if called from execve or posix spawn set exec
 *                                                      FALSE, if called from fork or vfexec
 *
 * Note:        This code is called in the fork() case, from the execve() call
 *              graph, if implementing an execve() following a vfork(), from
 *              the posix_spawn() call graph (which implicitly includes a
 *              vfork() equivalent call, and in the system bootstrap case.
 *
 *              It creates a new task and thread (and as a side effect of the
 *              thread creation, a uthread) in the parent coalition set, which is
 *              then associated with the process 'child'.  If the parent
 *              process address space is to be inherited, then a flag
 *              indicates that the newly created task should inherit this from
 *              the child task.
 *
 *              As a special concession to bootstrapping the initial process
 *              in the system, it's possible for 'parent_task' to be TASK_NULL;
 *              in this case, 'inherit_memory' MUST be FALSE.
 */
thread_t
fork_create_child(task_t parent_task,
    coalition_t *parent_coalitions,
    proc_t child_proc,
    int inherit_memory,
    int is_64bit_addr,
    int is_64bit_data,
    int in_exec)
{
        thread_t        child_thread = NULL;
        task_t          child_task;
        kern_return_t   result;

        /* Create a new task for the child process */
        result = task_create_internal(parent_task,
            parent_coalitions,
            inherit_memory,
            is_64bit_addr,
            is_64bit_data,
            TF_NONE,
            in_exec ? TPF_EXEC_COPY : TPF_NONE,                        /* Mark the task exec copy if in execve */
            (TRW_LRETURNWAIT | TRW_LRETURNWAITER),                     /* All created threads will wait in task_wait_to_return */
            &child_task);
        if (result != KERN_SUCCESS) {
                printf("%s: task_create_internal failed.  Code: %d\n",
                    __func__, result);
                goto bad;
        }

        if (!in_exec) {
                /*
                 * Set the child process task to the new task if not in exec,
                 * will set the task for exec case in proc_exec_switch_task after image activation.
                 */
                child_proc->task = child_task;
        }

        /* Set child task process to child proc */
        set_bsdtask_info(child_task, child_proc);

        /* Propagate CPU limit timer from parent */
        if (timerisset(&child_proc->p_rlim_cpu)) {
                task_vtimer_set(child_task, TASK_VTIMER_RLIM);
        }

        /*
         * Set child process BSD visible scheduler priority if nice value
         * inherited from parent
         */
        if (child_proc->p_nice != 0) {
                resetpriority(child_proc);
        }

        /*
         * Create a new thread for the child process. Pin it and make it immovable.
         * The new thread is waiting on the event triggered by 'task_clear_return_wait'
         */
        result = thread_create_waiting(child_task,
            (thread_continue_t)task_wait_to_return,
            task_get_return_wait_event(child_task),
            TH_CREATE_WAITING_OPTION_PINNED | TH_CREATE_WAITING_OPTION_IMMOVABLE,
            &child_thread);

        if (result != KERN_SUCCESS) {
                printf("%s: thread_create failed. Code: %d\n",
                    __func__, result);
                task_deallocate(child_task);
                child_task = NULL;
        }

        /*
         * Tag thread as being the first thread in its task.
         */
        thread_set_tag(child_thread, THREAD_TAG_MAINTHREAD);

bad:
        thread_yield_internal(1);

        return child_thread;
}


/*
 * fork
 *
 * Description: fork system call.
 *
 * Parameters:  parent                  Parent process to fork
 *              uap (void)              [unused]
 *              retval                  Return value
 *
 * Returns:     0                       Success
 *              EAGAIN                  Resource unavailable, try again
 *
 * Notes:       Attempts to create a new child process which inherits state
 *              from the parent process.  If successful, the call returns
 *              having created an initially suspended child process with an
 *              extra Mach task and thread reference, for which the thread
 *              is initially suspended.  Until we resume the child process,
 *              it is not yet running.
 *
 *              The return information to the child is contained in the
 *              thread state structure of the new child, and does not
 *              become visible to the child through a normal return process,
 *              since it never made the call into the kernel itself in the
 *              first place.
 *
 *              After resuming the thread, this function returns directly to
 *              the parent process which invoked the fork() system call.
 *
 * Important:   The child thread_resume occurs before the parent returns;
 *              depending on scheduling latency, this means that it is not
 *              deterministic as to whether the parent or child is scheduled
 *              to run first.  It is entirely possible that the child could
 *              run to completion prior to the parent running.
 */
int
fork(proc_t parent_proc, __unused struct fork_args *uap, int32_t *retval)
{
        thread_t child_thread;
        int err;

        retval[1] = 0;          /* flag parent return for user space */

        if ((err = fork1(parent_proc, &child_thread, PROC_CREATE_FORK, NULL)) == 0) {
                task_t child_task;
                proc_t child_proc;

                /* Return to the parent */
                child_proc = (proc_t)get_bsdthreadtask_info(child_thread);
                retval[0] = child_proc->p_pid;

                /*
                 * Drop the signal lock on the child which was taken on our
                 * behalf by forkproc()/cloneproc() to prevent signals being
                 * received by the child in a partially constructed state.
                 */
                proc_signalend(child_proc, 0);
                proc_transend(child_proc, 0);

                /* flag the fork has occurred */
                proc_knote(parent_proc, NOTE_FORK | child_proc->p_pid);
                DTRACE_PROC1(create, proc_t, child_proc);

#if CONFIG_DTRACE
                if ((dtrace_proc_waitfor_hook = dtrace_proc_waitfor_exec_ptr) != NULL) {
                        (*dtrace_proc_waitfor_hook)(child_proc);
                }
#endif

                /* "Return" to the child */
                task_clear_return_wait(get_threadtask(child_thread), TCRW_CLEAR_ALL_WAIT);

                /* drop the extra references we got during the creation */
                if ((child_task = (task_t)get_threadtask(child_thread)) != NULL) {
                        task_deallocate(child_task);
                }
                thread_deallocate(child_thread);
        }

        return err;
}


/*
 * cloneproc
 *
 * Description: Create a new process from a specified process.
 *
 * Parameters:  parent_task             The parent task to be cloned, or
 *                                      TASK_NULL is task characteristics
 *                                      are not to be inherited
 *                                      be cloned, or TASK_NULL if the new
 *                                      task is not to inherit the VM
 *                                      characteristics of the parent
 *              parent_proc             The parent process to be cloned
 *              inherit_memory          True if the child is to inherit
 *                                      memory from the parent; if this is
 *                                      non-NULL, then the parent_task must
 *                                      also be non-NULL
 *              memstat_internal        Whether to track the process in the
 *                                      jetsam priority list (if configured)
 *
 * Returns:     !NULL                   pointer to new child thread
 *              NULL                    Failure (unspecified)
 *
 * Note:        On return newly created child process has signal lock held
 *              to block delivery of signal to it if called with lock set.
 *              fork() code needs to explicity remove this lock before
 *              signals can be delivered
 *
 *              In the case of bootstrap, this function can be called from
 *              bsd_utaskbootstrap() in order to bootstrap the first process;
 *              the net effect is to provide a uthread structure for the
 *              kernel process associated with the kernel task.
 *
 * XXX:         Tristating using the value parent_task as the major key
 *              and inherit_memory as the minor key is something we should
 *              refactor later; we owe the current semantics, ultimately,
 *              to the semantics of task_create_internal.  For now, we will
 *              live with this being somewhat awkward.
 */
thread_t
cloneproc(task_t parent_task, coalition_t *parent_coalitions, proc_t parent_proc, int inherit_memory, int memstat_internal)
{
#if !CONFIG_MEMORYSTATUS
#pragma unused(memstat_internal)
#endif
        task_t child_task;
        proc_t child_proc;
        thread_t child_thread = NULL;

        if ((child_proc = forkproc(parent_proc)) == NULL) {
                /* Failed to allocate new process */
                goto bad;
        }

        /*
         * In the case where the parent_task is TASK_NULL (during the init path)
         * we make the assumption that the register size will be the same as the
         * address space size since there's no way to determine the possible
         * register size until an image is exec'd.
         *
         * The only architecture that has different address space and register sizes
         * (arm64_32) isn't being used within kernel-space, so the above assumption
         * always holds true for the init path.
         */
        const int parent_64bit_addr = parent_proc->p_flag & P_LP64;
        const int parent_64bit_data = (parent_task == TASK_NULL) ? parent_64bit_addr : task_get_64bit_data(parent_task);

        child_thread = fork_create_child(parent_task,
            parent_coalitions,
            child_proc,
            inherit_memory,
            parent_64bit_addr,
            parent_64bit_data,
            FALSE);

        if (child_thread == NULL) {
                /*
                 * Failed to create thread; now we must deconstruct the new
                 * process previously obtained from forkproc().
                 */
                forkproc_free(child_proc);
                goto bad;
        }

        child_task = get_threadtask(child_thread);
        if (parent_64bit_addr) {
                OSBitOrAtomic(P_LP64, (UInt32 *)&child_proc->p_flag);
        } else {
                OSBitAndAtomic(~((uint32_t)P_LP64), (UInt32 *)&child_proc->p_flag);
        }

#if CONFIG_MEMORYSTATUS
        if (memstat_internal) {
                proc_list_lock();
                child_proc->p_memstat_state |= P_MEMSTAT_INTERNAL;
                proc_list_unlock();
        }
#endif

        /* make child visible */
        pinsertchild(parent_proc, child_proc);

        /*
         * Make child runnable, set start time.
         */
        child_proc->p_stat = SRUN;
bad:
        return child_thread;
}


/*
 * Destroy a process structure that resulted from a call to forkproc(), but
 * which must be returned to the system because of a subsequent failure
 * preventing it from becoming active.
 *
 * Parameters:  p                       The incomplete process from forkproc()
 *
 * Returns:     (void)
 *
 * Note:        This function should only be used in an error handler following
 *              a call to forkproc().
 *
 *              Operations occur in reverse order of those in forkproc().
 */
void
forkproc_free(proc_t p)
{
#if CONFIG_PERSONAS
        persona_proc_drop(p);
#endif /* CONFIG_PERSONAS */

#if PSYNCH
        pth_proc_hashdelete(p);
#endif /* PSYNCH */

        /* We held signal and a transition locks; drop them */
        proc_signalend(p, 0);
        proc_transend(p, 0);

        /*
         * If we have our own copy of the resource limits structure, we
         * need to free it.  If it's a shared copy, we need to drop our
         * reference on it.
         */
        proc_limitdrop(p);

#if SYSV_SHM
        /* Need to drop references to the shared memory segment(s), if any */
        if (p->vm_shm) {
                /*
                 * Use shmexec(): we have no address space, so no mappings
                 *
                 * XXX Yes, the routine is badly named.
                 */
                shmexec(p);
        }
#endif

        /* Need to undo the effects of the fdcopy(), if any */
        fdfree(p);

        /*
         * Drop the reference on a text vnode pointer, if any
         * XXX This code is broken in forkproc(); see <rdar://4256419>;
         * XXX if anyone ever uses this field, we will be extremely unhappy.
         */
        if (p->p_textvp) {
                vnode_rele(p->p_textvp);
                p->p_textvp = NULL;
        }

        /* Update the audit session proc count */
        AUDIT_SESSION_PROCEXIT(p);

        lck_mtx_destroy(&p->p_mlock, &proc_mlock_grp);
        lck_mtx_destroy(&p->p_fdmlock, &proc_fdmlock_grp);
        lck_mtx_destroy(&p->p_ucred_mlock, &proc_ucred_mlock_grp);
#if CONFIG_DTRACE
        lck_mtx_destroy(&p->p_dtrace_sprlock, &proc_lck_grp);
#endif
        lck_spin_destroy(&p->p_slock, &proc_slock_grp);
        lck_rw_destroy(&p->p_dirs_lock, &proc_dirslock_grp);

        /* Release the credential reference */
        kauth_cred_t tmp_ucred = p->p_ucred;
        kauth_cred_unref(&tmp_ucred);
        p->p_ucred = tmp_ucred;

        proc_list_lock();
        /* Decrement the count of processes in the system */
        nprocs--;

        /* Take it out of process hash */
        LIST_REMOVE(p, p_hash);

        proc_list_unlock();

        thread_call_free(p->p_rcall);

        /* Free allocated memory */
        zfree(proc_sigacts_zone, p->p_sigacts);
        p->p_sigacts = NULL;
        zfree(proc_stats_zone, p->p_stats);
        p->p_stats = NULL;
        if (p->p_subsystem_root_path) {
                zfree(ZV_NAMEI, p->p_subsystem_root_path);
        }

        proc_checkdeadrefs(p);
        zfree(proc_zone, p);
}


/*
 * forkproc
 *
 * Description: Create a new process structure, given a parent process
 *              structure.
 *
 * Parameters:  parent_proc             The parent process
 *
 * Returns:     !NULL                   The new process structure
 *              NULL                    Error (insufficient free memory)
 *
 * Note:        When successful, the newly created process structure is
 *              partially initialized; if a caller needs to deconstruct the
 *              returned structure, they must call forkproc_free() to do so.
 */
proc_t
forkproc(proc_t parent_proc)
{
        proc_t child_proc;      /* Our new process */
        static int nextpid = 0, pidwrap = 0;
        static uint64_t nextuniqueid = 0;
        int error = 0;
        struct session *sessp;
        uthread_t parent_uthread = (uthread_t)get_bsdthread_info(current_thread());
        rlim_t rlimit_cpu_cur;

        child_proc = zalloc_flags(proc_zone, Z_WAITOK | Z_ZERO);
        child_proc->p_stats = zalloc_flags(proc_stats_zone, Z_WAITOK | Z_ZERO);
        child_proc->p_sigacts = zalloc_flags(proc_sigacts_zone, Z_WAITOK);

        /* allocate a callout for use by interval timers */
        child_proc->p_rcall = thread_call_allocate((thread_call_func_t)realitexpire, child_proc);
        if (child_proc->p_rcall == NULL) {
                zfree(proc_sigacts_zone, child_proc->p_sigacts);
                zfree(proc_stats_zone, child_proc->p_stats);
                zfree(proc_zone, child_proc);
                child_proc = NULL;
                goto bad;
        }


        /*
         * Find an unused PID.
         */

        proc_list_lock();

        nextpid++;
retry:
        /*
         * If the process ID prototype has wrapped around,
         * restart somewhat above 0, as the low-numbered procs
         * tend to include daemons that don't exit.
         */
        if (nextpid >= PID_MAX) {
                nextpid = 100;
                pidwrap = 1;
        }
        if (pidwrap != 0) {
                /* if the pid stays in hash both for zombie and runniing state */
                if (pfind_locked(nextpid) != PROC_NULL) {
                        nextpid++;
                        goto retry;
                }

                if (pgfind_internal(nextpid) != PGRP_NULL) {
                        nextpid++;
                        goto retry;
                }
                if (session_find_internal(nextpid) != SESSION_NULL) {
                        nextpid++;
                        goto retry;
                }
        }
        nprocs++;
        child_proc->p_pid = nextpid;
        child_proc->p_idversion = OSIncrementAtomic(&nextpidversion);
        /* kernel process is handcrafted and not from fork, so start from 1 */
        child_proc->p_uniqueid = ++nextuniqueid;
#if 1
        if (child_proc->p_pid != 0) {
                if (pfind_locked(child_proc->p_pid) != PROC_NULL) {
                        panic("proc in the list already\n");
                }
        }
#endif
        /* Insert in the hash */
        child_proc->p_listflag |= (P_LIST_INHASH | P_LIST_INCREATE);
        LIST_INSERT_HEAD(PIDHASH(child_proc->p_pid), child_proc, p_hash);
        proc_list_unlock();

        if (child_proc->p_uniqueid == startup_serial_num_procs) {
                /*
                 * Turn off startup serial logging now that we have reached
                 * the defined number of startup processes.
                 */
                startup_serial_logging_active = false;
        }

        /*
         * We've identified the PID we are going to use; initialize the new
         * process structure.
         */
        child_proc->p_stat = SIDL;
        child_proc->p_pgrpid = PGRPID_DEAD;

        /*
         * The zero'ing of the proc was at the allocation time due to need
         * for insertion to hash.  Copy the section that is to be copied
         * directly from the parent.
         */
        __nochk_bcopy(&parent_proc->p_startcopy, &child_proc->p_startcopy,
            (unsigned) ((caddr_t)&child_proc->p_endcopy - (caddr_t)&child_proc->p_startcopy));

#if defined(HAS_APPLE_PAC)
        /*
         * The p_textvp and p_pgrp pointers are address-diversified by PAC, so we must
         * resign them here for the new proc
         */
        if (parent_proc->p_textvp) {
                child_proc->p_textvp = parent_proc->p_textvp;
        }

        if (parent_proc->p_pgrp) {
                child_proc->p_pgrp = parent_proc->p_pgrp;
        }
#endif /* defined(HAS_APPLE_PAC) */

        child_proc->p_sessionid = parent_proc->p_sessionid;

        /*
         * Some flags are inherited from the parent.
         * Duplicate sub-structures as needed.
         * Increase reference counts on shared objects.
         * The p_stats and p_sigacts substructs are set in vm_fork.
         */
#if CONFIG_DELAY_IDLE_SLEEP
        child_proc->p_flag = (parent_proc->p_flag & (P_LP64 | P_TRANSLATED | P_DISABLE_ASLR | P_DELAYIDLESLEEP | P_SUGID | P_AFFINITY));
#else /* CONFIG_DELAY_IDLE_SLEEP */
        child_proc->p_flag = (parent_proc->p_flag & (P_LP64 | P_TRANSLATED | P_DISABLE_ASLR | P_SUGID));
#endif /* CONFIG_DELAY_IDLE_SLEEP */

        child_proc->p_vfs_iopolicy = (parent_proc->p_vfs_iopolicy & (P_VFS_IOPOLICY_VALID_MASK));

        child_proc->p_responsible_pid = parent_proc->p_responsible_pid;

        /*
         * Note that if the current thread has an assumed identity, this
         * credential will be granted to the new process.
         */
        child_proc->p_ucred = kauth_cred_get_with_ref();
        /* update cred on proc */
        PROC_UPDATE_CREDS_ONPROC(child_proc);
        /* update audit session proc count */
        AUDIT_SESSION_PROCNEW(child_proc);

        lck_mtx_init(&child_proc->p_mlock, &proc_mlock_grp, &proc_lck_attr);
        lck_mtx_init(&child_proc->p_fdmlock, &proc_fdmlock_grp, &proc_lck_attr);
        lck_mtx_init(&child_proc->p_ucred_mlock, &proc_ucred_mlock_grp, &proc_lck_attr);
#if CONFIG_DTRACE
        lck_mtx_init(&child_proc->p_dtrace_sprlock, &proc_lck_grp, &proc_lck_attr);
#endif
        lck_spin_init(&child_proc->p_slock, &proc_slock_grp, &proc_lck_attr);
        lck_rw_init(&child_proc->p_dirs_lock, &proc_dirslock_grp, &proc_lck_attr);

        klist_init(&child_proc->p_klist);

        if (child_proc->p_textvp != NULLVP) {
                /* bump references to the text vnode */
                /* Need to hold iocount across the ref call */
                if ((error = vnode_getwithref(child_proc->p_textvp)) == 0) {
                        error = vnode_ref(child_proc->p_textvp);
                        vnode_put(child_proc->p_textvp);
                }

                if (error != 0) {
                        child_proc->p_textvp = NULLVP;
                }
        }

        /*
         * Copy the parents per process open file table to the child; if
         * there is a per-thread current working directory, set the childs
         * per-process current working directory to that instead of the
         * parents.
         *
         * XXX may fail to copy descriptors to child
         */
        child_proc->p_fd = fdcopy(parent_proc, parent_uthread->uu_cdir);

#if SYSV_SHM
        if (parent_proc->vm_shm) {
                /* XXX may fail to attach shm to child */
                (void)shmfork(parent_proc, child_proc);
        }
#endif

        /*
         * Child inherits the parent's plimit
         */
        proc_limitfork(parent_proc, child_proc);

        rlimit_cpu_cur = proc_limitgetcur(child_proc, RLIMIT_CPU, TRUE);
        if (rlimit_cpu_cur != RLIM_INFINITY) {
                child_proc->p_rlim_cpu.tv_sec = (rlimit_cpu_cur > __INT_MAX__) ? __INT_MAX__ : rlimit_cpu_cur;
        }

        /* Intialize new process stats, including start time */
        /* <rdar://6640543> non-zeroed portion contains garbage AFAICT */
        microtime_with_abstime(&child_proc->p_start, &child_proc->p_stats->ps_start);

        if (parent_proc->p_sigacts != NULL) {
                (void)memcpy(child_proc->p_sigacts,
                    parent_proc->p_sigacts, sizeof *child_proc->p_sigacts);
        } else {
                (void)memset(child_proc->p_sigacts, 0, sizeof *child_proc->p_sigacts);
        }

        sessp = proc_session(parent_proc);
        if (sessp->s_ttyvp != NULL && parent_proc->p_flag & P_CONTROLT) {
                OSBitOrAtomic(P_CONTROLT, &child_proc->p_flag);
        }
        session_rele(sessp);

        /*
         * block all signals to reach the process.
         * no transition race should be occuring with the child yet,
         * but indicate that the process is in (the creation) transition.
         */
        proc_signalstart(child_proc, 0);
        proc_transstart(child_proc, 0, 0);

        child_proc->p_pcaction = 0;

        TAILQ_INIT(&child_proc->p_uthlist);
        TAILQ_INIT(&child_proc->p_aio_activeq);
        TAILQ_INIT(&child_proc->p_aio_doneq);

        /* Inherit the parent flags for code sign */
        child_proc->p_csflags = (parent_proc->p_csflags & ~CS_KILLED);

        /*
         * Copy work queue information
         *
         * Note: This should probably only happen in the case where we are
         *      creating a child that is a copy of the parent; since this
         *      routine is called in the non-duplication case of vfork()
         *      or posix_spawn(), then this information should likely not
         *      be duplicated.
         *
         * <rdar://6640553> Work queue pointers that no longer point to code
         */
        child_proc->p_wqthread = parent_proc->p_wqthread;
        child_proc->p_threadstart = parent_proc->p_threadstart;
        child_proc->p_pthsize = parent_proc->p_pthsize;
        if ((parent_proc->p_lflag & P_LREGISTER) != 0) {
                child_proc->p_lflag |= P_LREGISTER;
        }
        child_proc->p_dispatchqueue_offset = parent_proc->p_dispatchqueue_offset;
        child_proc->p_dispatchqueue_serialno_offset = parent_proc->p_dispatchqueue_serialno_offset;
        child_proc->p_dispatchqueue_label_offset = parent_proc->p_dispatchqueue_label_offset;
        child_proc->p_return_to_kernel_offset = parent_proc->p_return_to_kernel_offset;
        child_proc->p_mach_thread_self_offset = parent_proc->p_mach_thread_self_offset;
        child_proc->p_pth_tsd_offset = parent_proc->p_pth_tsd_offset;
#if PSYNCH
        pth_proc_hashinit(child_proc);
#endif /* PSYNCH */

#if CONFIG_PERSONAS
        child_proc->p_persona = NULL;
        error = persona_proc_inherit(child_proc, parent_proc);
        if (error != 0) {
                printf("forkproc: persona_proc_inherit failed (persona %d being destroyed?)\n", persona_get_uid(parent_proc->p_persona));
                forkproc_free(child_proc);
                child_proc = NULL;
                goto bad;
        }
#endif

#if CONFIG_MEMORYSTATUS
        /* Memorystatus init */
        child_proc->p_memstat_state = 0;
        child_proc->p_memstat_effectivepriority = JETSAM_PRIORITY_DEFAULT;
        child_proc->p_memstat_requestedpriority = JETSAM_PRIORITY_DEFAULT;
        child_proc->p_memstat_assertionpriority = 0;
        child_proc->p_memstat_userdata          = 0;
        child_proc->p_memstat_idle_start        = 0;
        child_proc->p_memstat_idle_delta        = 0;
        child_proc->p_memstat_memlimit          = 0;
        child_proc->p_memstat_memlimit_active   = 0;
        child_proc->p_memstat_memlimit_inactive = 0;
        child_proc->p_memstat_relaunch_flags    = P_MEMSTAT_RELAUNCH_UNKNOWN;
#if CONFIG_FREEZE
        child_proc->p_memstat_freeze_sharedanon_pages = 0;
#endif
        child_proc->p_memstat_dirty = 0;
        child_proc->p_memstat_idledeadline = 0;
#endif /* CONFIG_MEMORYSTATUS */

        if (parent_proc->p_subsystem_root_path) {
                size_t parent_length = strlen(parent_proc->p_subsystem_root_path) + 1;
                assert(parent_length <= MAXPATHLEN);
                child_proc->p_subsystem_root_path = zalloc_flags(ZV_NAMEI,
                    Z_WAITOK | Z_ZERO);
                memcpy(child_proc->p_subsystem_root_path, parent_proc->p_subsystem_root_path, parent_length);
        }

bad:
        return child_proc;
}

void
proc_lock(proc_t p)
{
        LCK_MTX_ASSERT(&proc_list_mlock, LCK_MTX_ASSERT_NOTOWNED);
        lck_mtx_lock(&p->p_mlock);
}

void
proc_unlock(proc_t p)
{
        lck_mtx_unlock(&p->p_mlock);
}

void
proc_spinlock(proc_t p)
{
        lck_spin_lock_grp(&p->p_slock, &proc_slock_grp);
}

void
proc_spinunlock(proc_t p)
{
        lck_spin_unlock(&p->p_slock);
}

void
proc_list_lock(void)
{
        lck_mtx_lock(&proc_list_mlock);
}

void
proc_list_unlock(void)
{
        lck_mtx_unlock(&proc_list_mlock);
}

void
proc_ucred_lock(proc_t p)
{
        lck_mtx_lock(&p->p_ucred_mlock);
}

void
proc_ucred_unlock(proc_t p)
{
        lck_mtx_unlock(&p->p_ucred_mlock);
}

void *
uthread_alloc(task_t task, thread_t thread, int noinherit)
{
        proc_t p;
        uthread_t uth;
        uthread_t uth_parent;
        void *ut;

        ut = zalloc_flags(uthread_zone, Z_WAITOK | Z_ZERO);

        p = (proc_t) get_bsdtask_info(task);
        uth = (uthread_t)ut;
        uth->uu_thread = thread;

        lck_spin_init(&uth->uu_rethrottle_lock, &rethrottle_lock_grp,
            LCK_ATTR_NULL);

        /*
         * Thread inherits credential from the creating thread, if both
         * are in the same task.
         *
         * If the creating thread has no credential or is from another
         * task we can leave the new thread credential NULL.  If it needs
         * one later, it will be lazily assigned from the task's process.
         */
        uth_parent = (uthread_t)get_bsdthread_info(current_thread());
        if ((noinherit == 0) && task == current_task() &&
            uth_parent != NULL &&
            IS_VALID_CRED(uth_parent->uu_ucred)) {
                /*
                 * XXX The new thread is, in theory, being created in context
                 * XXX of parent thread, so a direct reference to the parent
                 * XXX is OK.
                 */
                kauth_cred_ref(uth_parent->uu_ucred);
                uth->uu_ucred = uth_parent->uu_ucred;
                /* the credential we just inherited is an assumed credential */
                if (uth_parent->uu_flag & UT_SETUID) {
                        uth->uu_flag |= UT_SETUID;
                }
        } else {
                /* sometimes workqueue threads are created out task context */
                if ((task != kernel_task) && (p != PROC_NULL)) {
                        uth->uu_ucred = kauth_cred_proc_ref(p);
                } else {
                        uth->uu_ucred = NOCRED;
                }
        }


        if ((task != kernel_task) && p) {
                proc_lock(p);
                if (noinherit != 0) {
                        /* workq threads will not inherit masks */
                        uth->uu_sigmask = ~workq_threadmask;
                } else if (uth_parent) {
                        if (uth_parent->uu_flag & UT_SAS_OLDMASK) {
                                uth->uu_sigmask = uth_parent->uu_oldmask;
                        } else {
                                uth->uu_sigmask = uth_parent->uu_sigmask;
                        }
                }
                uth->uu_context.vc_thread = thread;
                /*
                 * Do not add the uthread to proc uthlist for exec copy task,
                 * since they do not hold a ref on proc.
                 */
                if (!task_is_exec_copy(task)) {
                        TAILQ_INSERT_TAIL(&p->p_uthlist, uth, uu_list);
                }
                proc_unlock(p);

#if CONFIG_DTRACE
                if (p->p_dtrace_ptss_pages != NULL && !task_is_exec_copy(task)) {
                        uth->t_dtrace_scratch = dtrace_ptss_claim_entry(p);
                }
#endif
        }

        return ut;
}

/*
 * This routine frees the thread name field of the uthread_t structure. Split out of
 * uthread_cleanup() so thread name does not get deallocated while generating a corpse fork.
 */
void
uthread_cleanup_name(void *uthread)
{
        uthread_t uth = (uthread_t)uthread;

        /*
         * <rdar://17834538>
         * Set pth_name to NULL before calling free().
         * Previously there was a race condition in the
         * case this code was executing during a stackshot
         * where the stackshot could try and copy pth_name
         * after it had been freed and before if was marked
         * as null.
         */
        if (uth->pth_name != NULL) {
                void *pth_name = uth->pth_name;
                uth->pth_name = NULL;
                kfree(pth_name, MAXTHREADNAMESIZE);
        }
        return;
}

/*
 * This routine frees all the BSD context in uthread except the credential.
 * It does not free the uthread structure as well
 */
void
uthread_cleanup(task_t task, void *uthread, void * bsd_info)
{
        uthread_t uth = (uthread_t)uthread;
        proc_t p = (proc_t)bsd_info;

#if PROC_REF_DEBUG
        if (__improbable(uthread_get_proc_refcount(uthread) != 0)) {
                panic("uthread_cleanup called for uthread %p with uu_proc_refcount != 0", uthread);
        }
#endif

        if (uth->uu_lowpri_window || uth->uu_throttle_info) {
                /*
                 * task is marked as a low priority I/O type
                 * and we've somehow managed to not dismiss the throttle
                 * through the normal exit paths back to user space...
                 * no need to throttle this thread since its going away
                 * but we do need to update our bookeeping w/r to throttled threads
                 *
                 * Calling this routine will clean up any throttle info reference
                 * still inuse by the thread.
                 */
                throttle_lowpri_io(0);
        }
        /*
         * Per-thread audit state should never last beyond system
         * call return.  Since we don't audit the thread creation/
         * removal, the thread state pointer should never be
         * non-NULL when we get here.
         */
        assert(uth->uu_ar == NULL);

        if (uth->uu_kqr_bound) {
                kqueue_threadreq_unbind(p, uth->uu_kqr_bound);
        }

        if (uth->uu_select.nbytes) {
                select_cleanup_uthread(&uth->uu_select);
        }

        if (uth->uu_cdir) {
                vnode_rele(uth->uu_cdir);
                uth->uu_cdir = NULLVP;
        }

        if (uth->uu_wqset) {
                if (waitq_set_is_valid(uth->uu_wqset)) {
                        waitq_set_deinit(uth->uu_wqset);
                }
                kheap_free(KHEAP_DEFAULT, uth->uu_wqset, uth->uu_wqstate_sz);
                uth->uu_wqset = NULL;
                uth->uu_wqstate_sz = 0;
        }

        os_reason_free(uth->uu_exit_reason);

        if ((task != kernel_task) && p) {
                if (((uth->uu_flag & UT_VFORK) == UT_VFORK) && (uth->uu_proc != PROC_NULL)) {
                        vfork_exit_internal(uth->uu_proc, 0, 1);
                }
                /*
                 * Remove the thread from the process list and
                 * transfer [appropriate] pending signals to the process.
                 * Do not remove the uthread from proc uthlist for exec
                 * copy task, since they does not have a ref on proc and
                 * would not have been added to the list.
                 */
                if (get_bsdtask_info(task) == p && !task_is_exec_copy(task)) {
                        proc_lock(p);

                        TAILQ_REMOVE(&p->p_uthlist, uth, uu_list);
                        p->p_siglist |= (uth->uu_siglist & execmask & (~p->p_sigignore | sigcantmask));
                        proc_unlock(p);
                }
#if CONFIG_DTRACE
                struct dtrace_ptss_page_entry *tmpptr = uth->t_dtrace_scratch;
                uth->t_dtrace_scratch = NULL;
                if (tmpptr != NULL && !task_is_exec_copy(task)) {
                        dtrace_ptss_release_entry(p, tmpptr);
                }
#endif
        }
}

/* This routine releases the credential stored in uthread */
void
uthread_cred_free(void *uthread)
{
        uthread_t uth = (uthread_t)uthread;

        /* and free the uthread itself */
        if (IS_VALID_CRED(uth->uu_ucred)) {
                kauth_cred_t oldcred = uth->uu_ucred;
                uth->uu_ucred = NOCRED;
                kauth_cred_unref(&oldcred);
        }
}

/* This routine frees the uthread structure held in thread structure */
void
uthread_zone_free(void *uthread)
{
        uthread_t uth = (uthread_t)uthread;

        if (uth->t_tombstone) {
                kfree(uth->t_tombstone, sizeof(struct doc_tombstone));
                uth->t_tombstone = NULL;
        }

        lck_spin_destroy(&uth->uu_rethrottle_lock, &rethrottle_lock_grp);

        uthread_cleanup_name(uthread);
        /* and free the uthread itself */
        zfree(uthread_zone, uthread);
}