[apple/xnu.git] / bsd / security / audit / audit_worker.c

/*-
 * Copyright (c) 1999-2016 Apple Inc.
 * Copyright (c) 2006-2008 Robert N. M. Watson
 * All rights reserved.
 *
 * 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.  Neither the name of Apple Inc. ("Apple") 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 APPLE AND ITS 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 APPLE OR ITS 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.
 */

#include <sys/param.h>
#include <sys/fcntl.h>
#include <sys/kernel.h>
#include <sys/lock.h>
#include <sys/namei.h>
#include <sys/proc_internal.h>
#include <sys/kauth.h>
#include <sys/queue.h>
#include <sys/systm.h>
#include <sys/time.h>
#include <sys/ucred.h>
#include <sys/uio.h>
#include <sys/unistd.h>
#include <sys/file_internal.h>
#include <sys/vnode_internal.h>
#include <sys/user.h>
#include <sys/syscall.h>
#include <sys/malloc.h>
#include <sys/un.h>
#include <sys/sysent.h>
#include <sys/sysproto.h>
#include <sys/vfs_context.h>
#include <sys/domain.h>
#include <sys/protosw.h>
#include <sys/socketvar.h>

#include <bsm/audit.h>
#include <bsm/audit_internal.h>
#include <bsm/audit_kevents.h>

#include <security/audit/audit.h>
#include <security/audit/audit_bsd.h>
#include <security/audit/audit_private.h>

#include <mach/host_priv.h>
#include <mach/host_special_ports.h>
#include <mach/audit_triggers_server.h>

#include <kern/host.h>
#include <kern/zalloc.h>
#include <kern/sched_prim.h>
#include <kern/task.h>

#include <net/route.h>

#include <netinet/in.h>
#include <netinet/in_pcb.h>

/*
 * Worker thread that will schedule disk I/O, etc.
 */
static thread_t audit_thread;

/*
 * audit_ctx and audit_vp are the stored credential and vnode to use for
 * active audit trail.  They are protected by audit_worker_sl, which will be
 * held across all I/O and all rotation to prevent them from being replaced
 * (rotated) while in use.  The audit_file_rotate_wait flag is set when the
 * kernel has delivered a trigger to auditd to rotate the trail, and is
 * cleared when the next rotation takes place.  It is also protected by
 * audit_worker_sl.
 */
static int                      audit_file_rotate_wait;
static struct slck              audit_worker_sl;
static struct vfs_context       audit_ctx;
static struct vnode             *audit_vp;

#define AUDIT_WORKER_SX_INIT()          slck_init(&audit_worker_sl,     \
                                            "audit_worker_sl")
#define AUDIT_WORKER_SX_XLOCK()         slck_lock(&audit_worker_sl)
#define AUDIT_WORKER_SX_XUNLOCK()       slck_unlock(&audit_worker_sl)
#define AUDIT_WORKER_SX_ASSERT()        slck_assert(&audit_worker_sl, SL_OWNED)
#define AUDIT_WORKER_SX_DESTROY()       slck_destroy(&audit_worker_sl)

/*
 * The audit_q_draining flag is set when audit is disabled and the audit
 * worker queue is being drained.
 */
static int                      audit_q_draining;

/*
 * The special kernel audit record, audit_drain_kar, is used to mark the end of
 * the queue when draining it.
 */
static struct kaudit_record     audit_drain_kar = {
        .k_ar = {
                .ar_event = AUE_NULL,
        },
        .k_ar_commit = AR_DRAIN_QUEUE,
};

/*
 * Write an audit record to a file, performed as the last stage after both
 * preselection and BSM conversion.  Both space management and write failures
 * are handled in this function.
 *
 * No attempt is made to deal with possible failure to deliver a trigger to
 * the audit daemon, since the message is asynchronous anyway.
 */
static void
audit_record_write(struct vnode *vp, struct vfs_context *ctx, void *data,
    size_t len)
{
        static struct timeval last_lowspace_trigger;
        static struct timeval last_fail;
        static int cur_lowspace_trigger;
        struct vfsstatfs *mnt_stat;
        int error;
        static int cur_fail;
        uint64_t temp;
        off_t file_size;

        AUDIT_WORKER_SX_ASSERT();       /* audit_file_rotate_wait. */

        if (vp == NULL) {
                return;
        }

        if (vnode_getwithref(vp)) {
                return /*(ENOENT)*/;
        }

        mnt_stat = &vp->v_mount->mnt_vfsstat;

        /*
         * First, gather statistics on the audit log file and file system so
         * that we know how we're doing on space.  Consider failure of these
         * operations to indicate a future inability to write to the file.
         */
        error = vfs_update_vfsstat(vp->v_mount, ctx, VFS_KERNEL_EVENT);
        if (error) {
                goto fail;
        }
        error = vnode_size(vp, &file_size, ctx);
        if (error) {
                goto fail;
        }
        audit_fstat.af_currsz = (u_quad_t)file_size;

        /*
         * We handle four different space-related limits:
         *
         * - A fixed (hard) limit on the minimum free blocks we require on
         *   the file system, and results in record loss, a trigger, and
         *   possible fail stop due to violating invariants.
         *
         * - An administrative (soft) limit, which when fallen below, results
         *   in the kernel notifying the audit daemon of low space.
         *
         * - An audit trail size limit, which when gone above, results in the
         *   kernel notifying the audit daemon that rotation is desired.
         *
         * - The total depth of the kernel audit record exceeding free space,
         *   which can lead to possible fail stop (with drain), in order to
         *   prevent violating invariants.  Failure here doesn't halt
         *   immediately, but prevents new records from being generated.
         *
         * Possibly, the last of these should be handled differently, always
         * allowing a full queue to be lost, rather than trying to prevent
         * loss.
         *
         * First, handle the hard limit, which generates a trigger and may
         * fail stop.  This is handled in the same manner as ENOSPC from
         * VOP_WRITE, and results in record loss.
         */
        if (mnt_stat->f_bfree < AUDIT_HARD_LIMIT_FREE_BLOCKS) {
                error = ENOSPC;
                goto fail_enospc;
        }

        /*
         * Second, handle falling below the soft limit, if defined; we send
         * the daemon a trigger and continue processing the record.  Triggers
         * are limited to 1/sec.
         */
        if (audit_qctrl.aq_minfree != 0) {
                temp = mnt_stat->f_blocks / (100 / audit_qctrl.aq_minfree);
                if (mnt_stat->f_bfree < temp &&
                    ppsratecheck(&last_lowspace_trigger,
                    &cur_lowspace_trigger, 1)) {
                        (void)audit_send_trigger(
                                AUDIT_TRIGGER_LOW_SPACE);
                }
        }

        /*
         * If the current file is getting full, generate a rotation trigger
         * to the daemon.  This is only approximate, which is fine as more
         * records may be generated before the daemon rotates the file.
         */
        if ((audit_fstat.af_filesz != 0) && (audit_file_rotate_wait == 0) &&
            ((u_quad_t)file_size >= audit_fstat.af_filesz)) {
                AUDIT_WORKER_SX_ASSERT();

                audit_file_rotate_wait = 1;
                (void)audit_send_trigger(AUDIT_TRIGGER_ROTATE_KERNEL);
        }

        /*
         * If the estimated amount of audit data in the audit event queue
         * (plus records allocated but not yet queued) has reached the amount
         * of free space on the disk, then we need to go into an audit fail
         * stop state, in which we do not permit the allocation/committing of
         * any new audit records.  We continue to process records but don't
         * allow any activities that might generate new records.  In the
         * future, we might want to detect when space is available again and
         * allow operation to continue, but this behavior is sufficient to
         * meet fail stop requirements in CAPP.
         */
        if (audit_fail_stop) {
                if ((unsigned long)((audit_q_len + audit_pre_q_len + 1) *
                    MAX_AUDIT_RECORD_SIZE) / mnt_stat->f_bsize >=
                    (unsigned long)(mnt_stat->f_bfree)) {
                        if (ppsratecheck(&last_fail, &cur_fail, 1)) {
                                printf("audit_record_write: free space "
                                    "below size of audit queue, failing "
                                    "stop\n");
                        }
                        audit_in_failure = 1;
                } else if (audit_in_failure) {
                        /*
                         * Note: if we want to handle recovery, this is the
                         * spot to do it: unset audit_in_failure, and issue a
                         * wakeup on the cv.
                         */
                }
        }

        error = vn_rdwr(UIO_WRITE, vp, data, len, (off_t)0, UIO_SYSSPACE,
            IO_APPEND | IO_UNIT, vfs_context_ucred(ctx), NULL,
            vfs_context_proc(ctx));
        if (error == ENOSPC) {
                goto fail_enospc;
        } else if (error) {
                goto fail;
        }

        /*
         * Catch completion of a queue drain here; if we're draining and the
         * queue is now empty, fail stop.  That audit_fail_stop is implicitly
         * true, since audit_in_failure can only be set of audit_fail_stop is
         * set.
         *
         * Note: if we handle recovery from audit_in_failure, then we need to
         * make panic here conditional.
         */
        if (audit_in_failure) {
                if (audit_q_len == 0 && audit_pre_q_len == 0) {
                        (void)VNOP_FSYNC(vp, MNT_WAIT, ctx);
                        panic("Audit store overflow; record queue drained.");
                }
        }

        vnode_put(vp);
        return;

fail_enospc:
        /*
         * ENOSPC is considered a special case with respect to failures, as
         * this can reflect either our preemptive detection of insufficient
         * space, or ENOSPC returned by the vnode write call.
         */
        if (audit_fail_stop) {
                (void)VNOP_FSYNC(vp, MNT_WAIT, ctx);
                panic("Audit log space exhausted and fail-stop set.");
        }
        (void)audit_send_trigger(AUDIT_TRIGGER_NO_SPACE);
        audit_suspended = 1;

        /* FALLTHROUGH */
fail:
        /*
         * We have failed to write to the file, so the current record is
         * lost, which may require an immediate system halt.
         */
        if (audit_panic_on_write_fail) {
                (void)VNOP_FSYNC(vp, MNT_WAIT, ctx);
                panic("audit_worker: write error %d\n", error);
        } else if (ppsratecheck(&last_fail, &cur_fail, 1)) {
                printf("audit_worker: write error %d\n", error);
        }
        vnode_put(vp);
}

/*
 * Given a kernel audit record, process as required.  Kernel audit records
 * are converted to one, or possibly two, BSM records, depending on whether
 * there is a user audit record present also.  Kernel records need be
 * converted to BSM before they can be written out.  Both types will be
 * written to disk, and audit pipes.
 */
static void
audit_worker_process_record(struct kaudit_record *ar)
{
        struct au_record *bsm;
        au_class_t class;
        au_event_t event;
        au_id_t auid;
        int error, sorf;
        int trail_locked;

        /*
         * We hold the audit_worker_sl lock over both writes, if there are
         * two, so that the two records won't be split across a rotation and
         * end up in two different trail files.
         */
        if (((ar->k_ar_commit & AR_COMMIT_USER) &&
            (ar->k_ar_commit & AR_PRESELECT_USER_TRAIL)) ||
            (ar->k_ar_commit & AR_PRESELECT_TRAIL)) {
                AUDIT_WORKER_SX_XLOCK();
                trail_locked = 1;
        } else {
                trail_locked = 0;
        }

        /*
         * First, handle the user record, if any: commit to the system trail
         * and audit pipes as selected.
         */
        if ((ar->k_ar_commit & AR_COMMIT_USER) &&
            (ar->k_ar_commit & AR_PRESELECT_USER_TRAIL)) {
                AUDIT_WORKER_SX_ASSERT();
                audit_record_write(audit_vp, &audit_ctx, ar->k_udata,
                    ar->k_ulen);
        }

        if ((ar->k_ar_commit & AR_COMMIT_USER) &&
            (ar->k_ar_commit & AR_PRESELECT_USER_PIPE)) {
                audit_pipe_submit_user(ar->k_udata, ar->k_ulen);
        }

        if (!(ar->k_ar_commit & AR_COMMIT_KERNEL) ||
            ((ar->k_ar_commit & AR_PRESELECT_PIPE) == 0 &&
            (ar->k_ar_commit & AR_PRESELECT_TRAIL) == 0 &&
            (ar->k_ar_commit & AR_PRESELECT_FILTER) == 0)) {
                goto out;
        }

        auid = ar->k_ar.ar_subj_auid;
        event = ar->k_ar.ar_event;
        class = au_event_class(event);
        if (ar->k_ar.ar_errno == 0) {
                sorf = AU_PRS_SUCCESS;
        } else {
                sorf = AU_PRS_FAILURE;
        }

        error = kaudit_to_bsm(ar, &bsm);
        switch (error) {
        case BSM_NOAUDIT:
                goto out;

        case BSM_FAILURE:
                printf("audit_worker_process_record: BSM_FAILURE\n");
                goto out;

        case BSM_SUCCESS:
                break;

        default:
                panic("kaudit_to_bsm returned %d", error);
        }

        if (ar->k_ar_commit & AR_PRESELECT_TRAIL) {
                AUDIT_WORKER_SX_ASSERT();
                audit_record_write(audit_vp, &audit_ctx, bsm->data, bsm->len);
        }

        if (ar->k_ar_commit & AR_PRESELECT_PIPE) {
                audit_pipe_submit(auid, event, class, sorf,
                    ar->k_ar_commit & AR_PRESELECT_TRAIL, bsm->data,
                    bsm->len);
        }

        if (ar->k_ar_commit & AR_PRESELECT_FILTER) {
                /*
                 *  XXXss - This needs to be generalized so new filters can
                 *  be easily plugged in.
                 */
                audit_sdev_submit(auid, ar->k_ar.ar_subj_asid, bsm->data,
                    bsm->len);
        }

        kau_free(bsm);
out:
        if (trail_locked) {
                AUDIT_WORKER_SX_XUNLOCK();
        }
}

/*
 * The audit_worker thread is responsible for watching the event queue,
 * dequeueing records, converting them to BSM format, and committing them to
 * disk.  In order to minimize lock thrashing, records are dequeued in sets
 * to a thread-local work queue.
 *
 * Note: this means that the effect bound on the size of the pending record
 * queue is 2x the length of the global queue.
 */
__attribute__((noreturn))
static void
audit_worker(void)
{
        struct kaudit_queue ar_worklist;
        struct kaudit_record *ar;
        int lowater_signal;

        if (audit_ctx.vc_thread == NULL) {
                audit_ctx.vc_thread = current_thread();
        }

        TAILQ_INIT(&ar_worklist);
        mtx_lock(&audit_mtx);
        while (1) {
                mtx_assert(&audit_mtx, MA_OWNED);

                /*
                 * Wait for a record.
                 */
                while (TAILQ_EMPTY(&audit_q)) {
                        cv_wait_continuation(&audit_worker_cv, &audit_mtx,
                            (thread_continue_t)audit_worker);
                }

                /*
                 * If there are records in the global audit record queue,
                 * transfer them to a thread-local queue and process them
                 * one by one.  If we cross the low watermark threshold,
                 * signal any waiting processes that they may wake up and
                 * continue generating records.
                 */
                lowater_signal = 0;
                while ((ar = TAILQ_FIRST(&audit_q))) {
                        TAILQ_REMOVE(&audit_q, ar, k_q);
                        audit_q_len--;
                        if (audit_q_len == audit_qctrl.aq_lowater) {
                                lowater_signal++;
                        }
                        TAILQ_INSERT_TAIL(&ar_worklist, ar, k_q);
                }
                if (lowater_signal) {
                        cv_broadcast(&audit_watermark_cv);
                }

                mtx_unlock(&audit_mtx);
                while ((ar = TAILQ_FIRST(&ar_worklist))) {
                        TAILQ_REMOVE(&ar_worklist, ar, k_q);
                        if (ar->k_ar_commit & AR_DRAIN_QUEUE) {
                                audit_q_draining = 0;
                                cv_broadcast(&audit_drain_cv);
                        } else {
                                audit_worker_process_record(ar);
                                audit_free(ar);
                        }
                }
                mtx_lock(&audit_mtx);
        }
}

/*
 * audit_rotate_vnode() is called by a user or kernel thread to configure or
 * de-configure auditing on a vnode.  The arguments are the replacement
 * credential (referenced) and vnode (referenced and opened) to substitute
 * for the current credential and vnode, if any.  If either is set to NULL,
 * both should be NULL, and this is used to indicate that audit is being
 * disabled.  Any previous cred/vnode will be closed and freed.  We re-enable
 * generating rotation requests to auditd.
 */
void
audit_rotate_vnode(kauth_cred_t cred, struct vnode *vp)
{
        kauth_cred_t old_audit_cred;
        struct vnode *old_audit_vp;

        KASSERT((cred != NULL && vp != NULL) || (cred == NULL && vp == NULL),
            ("audit_rotate_vnode: cred %p vp %p", cred, vp));


        mtx_lock(&audit_mtx);
        if (audit_enabled && (NULL == vp)) {
                /* Auditing is currently enabled but will be disabled. */

                /*
                 * Disable auditing now so nothing more is added while the
                 * audit worker thread is draining the audit record queue.
                 */
                audit_enabled = 0;

                /*
                 * Drain the auditing queue by inserting a drain record at the
                 * end of the queue and waiting for the audit worker thread
                 * to find this record and signal that it is done before
                 * we close the audit trail.
                 */
                audit_q_draining = 1;
                while (audit_q_len >= audit_qctrl.aq_hiwater) {
                        cv_wait(&audit_watermark_cv, &audit_mtx);
                }
                TAILQ_INSERT_TAIL(&audit_q, &audit_drain_kar, k_q);
                audit_q_len++;
                cv_signal(&audit_worker_cv);
        }

        /* If the audit queue is draining then wait here until it's done. */
        while (audit_q_draining) {
                cv_wait(&audit_drain_cv, &audit_mtx);
        }
        mtx_unlock(&audit_mtx);


        /*
         * Rotate the vnode/cred, and clear the rotate flag so that we will
         * send a rotate trigger if the new file fills.
         */
        AUDIT_WORKER_SX_XLOCK();
        old_audit_cred = audit_ctx.vc_ucred;
        old_audit_vp = audit_vp;
        audit_ctx.vc_ucred = cred;
        audit_vp = vp;
        audit_file_rotate_wait = 0;
        audit_enabled = (audit_vp != NULL);
        AUDIT_WORKER_SX_XUNLOCK();

        /*
         * If there was an old vnode/credential, close and free.
         */
        if (old_audit_vp != NULL) {
                if (vnode_get(old_audit_vp) == 0) {
                        vn_close(old_audit_vp, AUDIT_CLOSE_FLAGS,
                            vfs_context_kernel());
                        vnode_put(old_audit_vp);
                } else {
                        printf("audit_rotate_vnode: Couldn't close "
                            "audit file.\n");
                }
                kauth_cred_unref(&old_audit_cred);
        }
}

void
audit_worker_init(void)
{
        AUDIT_WORKER_SX_INIT();
        kernel_thread_start((thread_continue_t)audit_worker, NULL,
            &audit_thread);
        if (audit_thread == THREAD_NULL) {
                panic("audit_worker_init: Couldn't create audit_worker thread");
        }
}