FreeBSD/Linux Kernel Cross Reference
sys/security/audit/audit_worker.c

     /*-
      * SPDX-License-Identifier: BSD-3-Clause
      *
      * Copyright (c) 1999-2008 Apple Inc.
      * Copyright (c) 2006-2008, 2016, 2018 Robert N. M. Watson
      * All rights reserved.
      *
      * Portions of this software were developed by BAE Systems, the University of
      * Cambridge Computer Laboratory, and Memorial University under DARPA/AFRL
     * contract FA8650-15-C-7558 ("CADETS"), as part of the DARPA Transparent
     * Computing (TC) research program.
     *
     * 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/cdefs.h>
    __FBSDID("$FreeBSD$");
    
    #include <sys/param.h>
    #include <sys/condvar.h>
    #include <sys/conf.h>
    #include <sys/file.h>
    #include <sys/filedesc.h>
    #include <sys/fcntl.h>
    #include <sys/ipc.h>
    #include <sys/kernel.h>
    #include <sys/kthread.h>
    #include <sys/malloc.h>
    #include <sys/mount.h>
    #include <sys/namei.h>
    #include <sys/proc.h>
    #include <sys/queue.h>
    #include <sys/socket.h>
    #include <sys/socketvar.h>
    #include <sys/protosw.h>
    #include <sys/domain.h>
    #include <sys/sx.h>
    #include <sys/sysproto.h>
    #include <sys/sysent.h>
    #include <sys/systm.h>
    #include <sys/ucred.h>
    #include <sys/uio.h>
    #include <sys/un.h>
    #include <sys/unistd.h>
    #include <sys/vnode.h>
    
    #include <bsm/audit.h>
    #include <bsm/audit_internal.h>
    #include <bsm/audit_kevents.h>
    
    #include <netinet/in.h>
    #include <netinet/in_pcb.h>
    
    #include <security/audit/audit.h>
    #include <security/audit/audit_private.h>
    
    #include <vm/uma.h>
    
    #include <machine/stdarg.h>
    
    /*
     * Worker thread that will schedule disk I/O, etc.
     */
    static struct proc              *audit_thread;
    
    /*
     * audit_cred and audit_vp are the stored credential and vnode to use for
     * active audit trail.  They are protected by the audit worker lock, 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
     * the audit worker lock.
     */
    static int               audit_file_rotate_wait;
    static struct ucred     *audit_cred;
    static struct vnode     *audit_vp;
   static off_t             audit_size;
   static struct sx         audit_worker_lock;
   
   #define AUDIT_WORKER_LOCK_INIT()        sx_init(&audit_worker_lock, \
                                               "audit_worker_lock");
   #define AUDIT_WORKER_LOCK_ASSERT()      sx_assert(&audit_worker_lock, \
                                               SA_XLOCKED)
   #define AUDIT_WORKER_LOCK()             sx_xlock(&audit_worker_lock)
   #define AUDIT_WORKER_UNLOCK()           sx_xunlock(&audit_worker_lock)
   
   static void
   audit_worker_sync_vp(struct vnode *vp, struct mount *mp, const char *fmt, ...)
   {
           struct mount *mp1;
           int error;
           va_list va;
   
           va_start(va, fmt);
           error = vn_start_write(vp, &mp1, 0);
           if (error == 0) {
                   VOP_LOCK(vp, LK_EXCLUSIVE | LK_RETRY);
                   (void)VOP_FSYNC(vp, MNT_WAIT, curthread);
                   VOP_UNLOCK(vp);
                   vn_finished_write(mp1);
           }
           vfs_unbusy(mp);
           vpanic(fmt, va);
           va_end(va);
   }
   
   /*
    * 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 ucred *cred, void *data,
       size_t len)
   {
           static struct timeval last_lowspace_trigger;
           static struct timeval last_fail;
           static int cur_lowspace_trigger;
           struct statfs *mnt_stat;
           struct mount *mp;
           int error;
           static int cur_fail;
           long temp;
   
           AUDIT_WORKER_LOCK_ASSERT();
   
           if (vp == NULL)
                   return;
   
           mp = vp->v_mount;
           if (mp == NULL) {
                   error = EINVAL;
                   goto fail;
           }
           error = vfs_busy(mp, 0);
           if (error != 0) {
                   mp = NULL;
                   goto fail;
           }
           mnt_stat = &mp->mnt_stat;
   
           /*
            * 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_STATFS(mp, mnt_stat);
           if (error != 0)
                   goto fail;
   
           /*
            * 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) {
                           if (ppsratecheck(&last_lowspace_trigger,
                               &cur_lowspace_trigger, 1)) {
                                   (void)audit_send_trigger(
                                       AUDIT_TRIGGER_LOW_SPACE);
                                   printf("Warning: disk space low (< %d%% free) "
                                       "on audit log file-system\n",
                                       audit_qctrl.aq_minfree);
                           }
                   }
           }
   
           /*
            * 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_size >= audit_fstat.af_filesz * (audit_file_rotate_wait + 1)) {
                   AUDIT_WORKER_LOCK_ASSERT();
   
                   audit_file_rotate_wait++;
                   (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, cred, NULL, NULL, curthread);
           if (error == ENOSPC)
                   goto fail_enospc;
           else if (error)
                   goto fail;
           AUDIT_WORKER_LOCK_ASSERT();
           audit_size += len;
   
           /*
            * 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) {
                           audit_worker_sync_vp(vp, mp,
                               "Audit store overflow; record queue drained.");
                   }
           }
   
           vfs_unbusy(mp);
           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) {
                   audit_worker_sync_vp(vp, mp,
                       "Audit log space exhausted and fail-stop set.");
           }
           (void)audit_send_trigger(AUDIT_TRIGGER_NO_SPACE);
           audit_trail_suspended = 1;
           audit_syscalls_enabled_update();
   
           /* 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) {
                   audit_worker_sync_vp(vp, mp,
                       "audit_worker: write error %d\n", error);
           } else if (ppsratecheck(&last_fail, &cur_fail, 1))
                   printf("audit_worker: write error %d\n", error);
           if (mp != NULL)
                   vfs_unbusy(mp);
   }
   
   /*
    * 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 locked;
   
           /*
            * We hold the audit worker 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_LOCK();
                   locked = 1;
           } else
                   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_LOCK_ASSERT();
                   audit_record_write(audit_vp, audit_cred, 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_DTRACE) == 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_LOCK_ASSERT();
                   audit_record_write(audit_vp, audit_cred, 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);
   
   #ifdef KDTRACE_HOOKS
           /*
            * Version of the dtaudit commit hook that accepts BSM.
            */
           if (ar->k_ar_commit & AR_PRESELECT_DTRACE) {
                   if (dtaudit_hook_bsm != NULL)
                           dtaudit_hook_bsm(ar, auid, event, class, sorf,
                               bsm->data, bsm->len);
           }
   #endif
   
           kau_free(bsm);
   out:
           if (locked)
                   AUDIT_WORKER_UNLOCK();
   }
   
   /*
    * 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.
    */
   static void
   audit_worker(void *arg)
   {
           struct kaudit_queue ar_worklist;
           struct kaudit_record *ar;
           int lowater_signal;
   
           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(&audit_worker_cv, &audit_mtx);
   
                   /*
                    * 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);
                           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(struct ucred *cred, struct vnode *vp)
   {
           struct ucred *old_audit_cred;
           struct vnode *old_audit_vp;
           struct vattr vattr;
   
           KASSERT((cred != NULL && vp != NULL) || (cred == NULL && vp == NULL),
               ("audit_rotate_vnode: cred %p vp %p", cred, vp));
   
           if (vp != NULL) {
                   vn_lock(vp, LK_SHARED | LK_RETRY);
                   if (VOP_GETATTR(vp, &vattr, cred) != 0)
                           vattr.va_size = 0;
                   VOP_UNLOCK(vp);
           } else {
                   vattr.va_size = 0;
           }
   
           /*
            * Rotate the vnode/cred, and clear the rotate flag so that we will
            * send a rotate trigger if the new file fills.
            */
           AUDIT_WORKER_LOCK();
           old_audit_cred = audit_cred;
           old_audit_vp = audit_vp;
           audit_cred = cred;
           audit_vp = vp;
           audit_size = vattr.va_size;
           audit_file_rotate_wait = 0;
           audit_trail_enabled = (audit_vp != NULL);
           audit_syscalls_enabled_update();
           AUDIT_WORKER_UNLOCK();
   
           /*
            * If there was an old vnode/credential, close and free.
            */
           if (old_audit_vp != NULL) {
                   vn_close(old_audit_vp, AUDIT_CLOSE_FLAGS, old_audit_cred,
                       curthread);
                   crfree(old_audit_cred);
           }
   }
   
   void
   audit_worker_init(void)
   {
           int error;
   
           AUDIT_WORKER_LOCK_INIT();
           error = kproc_create(audit_worker, NULL, &audit_thread, RFHIGHPID,
               0, "audit");
           if (error)
                   panic("audit_worker_init: kproc_create returned %d", error);
   }

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