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

     /*
      * Copyright (c) 1999-2005 Apple Computer, Inc.
      * Copyright (c) 2006 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 Computer, 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.
     *
     * $FreeBSD$
     */
    
    #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/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>
    
    /*
     * Worker thread that will schedule disk I/O, etc.
     */
    static struct proc              *audit_thread;
    
    /*
     * When an audit log is rotated, the actual rotation must be performed by the
     * audit worker thread, as it may have outstanding writes on the current
     * audit log.  audit_replacement_vp holds the vnode replacing the current
     * vnode.  We can't let more than one replacement occur at a time, so if more
     * than one thread requests a replacement, only one can have the replacement
     * "in progress" at any given moment.  If a thread tries to replace the audit
     * vnode and discovers a replacement is already in progress (i.e.,
     * audit_replacement_flag != 0), then it will sleep on audit_replacement_cv
     * waiting its turn to perform a replacement.  When a replacement is
     * completed, this cv is signalled by the worker thread so a waiting thread
     * can start another replacement.  We also store a credential to perform
     * audit log write operations with.
     *
     * The current credential and vnode are thread-local to audit_worker.
     */
    static struct cv                audit_replacement_cv;
    
    static int                      audit_replacement_flag;
    static struct vnode             *audit_replacement_vp;
    static struct ucred             *audit_replacement_cred;
    
    /*
    * Flags related to Kernel->user-space communication.
    */
   static int                      audit_file_rotate_wait;
   
   /*
    * 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, struct thread *td,
       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;
           int error, vfslocked;
           static int cur_fail;
           struct vattr vattr;
           long temp;
   
           if (vp == NULL)
                   return;
   
           mnt_stat = &vp->v_mount->mnt_stat;
           vfslocked = VFS_LOCK_GIANT(vp->v_mount);
   
           /*
            * 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(vp->v_mount, mnt_stat, td);
           if (error)
                   goto fail;
           vn_lock(vp, LK_EXCLUSIVE | LK_RETRY, td);
           error = VOP_GETATTR(vp, &vattr, cred, td);
           VOP_UNLOCK(vp, 0, td);
           if (error)
                   goto fail;
           audit_fstat.af_currsz = vattr.va_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) {
                   /*
                    * XXXAUDIT: Check math and block size calculations here.
                    */
                   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)send_trigger(AUDIT_TRIGGER_LOW_SPACE);
                                   printf("Warning: audit space low\n");
                           }
                   }
           }
   
           /*
            * 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) &&
               (vattr.va_size >= audit_fstat.af_filesz)) {
                   audit_file_rotate_wait = 1;
                   (void)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, td);
           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) {
                           VOP_LOCK(vp, LK_DRAIN | LK_INTERLOCK, td);
                           (void)VOP_FSYNC(vp, MNT_WAIT, td);
                           VOP_UNLOCK(vp, 0, td);
                           panic("Audit store overflow; record queue drained.");
                   }
           }
   
           VFS_UNLOCK_GIANT(vfslocked);
           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) {
                   VOP_LOCK(vp, LK_DRAIN | LK_INTERLOCK, td);
                   (void)VOP_FSYNC(vp, MNT_WAIT, td);
                   VOP_UNLOCK(vp, 0, td);
                   panic("Audit log space exhausted and fail-stop set.");
           }
           (void)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) {
                   VOP_LOCK(vp, LK_DRAIN | LK_INTERLOCK, td);
                   (void)VOP_FSYNC(vp, MNT_WAIT, td);
                   VOP_UNLOCK(vp, 0, td);
                   panic("audit_worker: write error %d\n", error);
           } else if (ppsratecheck(&last_fail, &cur_fail, 1))
                   printf("audit_worker: write error %d\n", error);
           VFS_UNLOCK_GIANT(vfslocked);
   }
   
   /*
    * If an appropriate signal has been received rotate the audit log based on
    * the global replacement variables.  Signal consumers as needed that the
    * rotation has taken place.
    *
    * The global variables and CVs used to signal the audit_worker to perform a
    * rotation are essentially a message queue of depth 1.  It would be much
    * nicer to actually use a message queue.
    */
   static void
   audit_worker_rotate(struct ucred **audit_credp, struct vnode **audit_vpp,
       struct thread *audit_td)
   {
           int do_replacement_signal, vfslocked;
           struct ucred *old_cred;
           struct vnode *old_vp;
   
           mtx_assert(&audit_mtx, MA_OWNED);
   
           do_replacement_signal = 0;
           while (audit_replacement_flag != 0) {
                   old_cred = *audit_credp;
                   old_vp = *audit_vpp;
                   *audit_credp = audit_replacement_cred;
                   *audit_vpp = audit_replacement_vp;
                   audit_replacement_cred = NULL;
                   audit_replacement_vp = NULL;
                   audit_replacement_flag = 0;
   
                   audit_enabled = (*audit_vpp != NULL);
   
                   if (old_vp != NULL) {
                           mtx_unlock(&audit_mtx);
                           vfslocked = VFS_LOCK_GIANT(old_vp->v_mount);
                           vn_close(old_vp, AUDIT_CLOSE_FLAGS, old_cred,
                               audit_td);
                           VFS_UNLOCK_GIANT(vfslocked);
                           crfree(old_cred);
                           mtx_lock(&audit_mtx);
                           old_cred = NULL;
                           old_vp = NULL;
                   }
                   do_replacement_signal = 1;
           }
   
           /*
            * Signal that replacement have occurred to wake up and start any
            * other replacements started in parallel.  We can continue about our
            * business in the mean time.  We broadcast so that both new
            * replacements can be inserted, but also so that the source(s) of
            * replacement can return successfully.
            */
           if (do_replacement_signal)
                   cv_broadcast(&audit_replacement_cv);
   }
   
   /*
    * 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 vnode *audit_vp, struct ucred *audit_cred,
       struct thread *audit_td, struct kaudit_record *ar)
   {
           struct au_record *bsm;
           au_class_t class;
           au_event_t event;
           au_id_t auid;
           int error, sorf;
   
           /*
            * 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_record_write(audit_vp, audit_cred, audit_td,
                       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))
                   return;
   
           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:
                   return;
   
           case BSM_FAILURE:
                   printf("audit_worker_process_record: BSM_FAILURE\n");
                   return;
   
           case BSM_SUCCESS:
                   break;
   
           default:
                   panic("kaudit_to_bsm returned %d", error);
           }
   
           if (ar->k_ar_commit & AR_PRESELECT_TRAIL)
                   audit_record_write(audit_vp, audit_cred, audit_td, 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);
   
           kau_free(bsm);
   }
   
   /*
    * 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.  In addition, the audit_work performs the
    * actual exchange of audit log vnode pointer, as audit_vp is a thread-local
    * variable.
    */
   static void
   audit_worker(void *arg)
   {
           struct kaudit_queue ar_worklist;
           struct kaudit_record *ar;
           struct ucred *audit_cred;
           struct thread *audit_td;
           struct vnode *audit_vp;
           int lowater_signal;
   
           /*
            * These are thread-local variables requiring no synchronization.
            */
           TAILQ_INIT(&ar_worklist);
           audit_cred = NULL;
           audit_td = curthread;
           audit_vp = NULL;
   
           mtx_lock(&audit_mtx);
           while (1) {
                   mtx_assert(&audit_mtx, MA_OWNED);
   
                   /*
                    * Wait for record or rotation events.
                    */
                   while (!audit_replacement_flag && TAILQ_EMPTY(&audit_q))
                           cv_wait(&audit_worker_cv, &audit_mtx);
   
                   /*
                    * First priority: replace the audit log target if requested.
                    */
                   audit_worker_rotate(&audit_cred, &audit_vp, audit_td);
   
                   /*
                    * 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(audit_vp, audit_cred,
                               audit_td, 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 and vnode 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.  The real work is done in the
    * audit_worker thread, but audit_rotate_vnode() waits synchronously for that
    * to complete.
    *
    * The vnode should be referenced and opened by the caller.  The credential
    * should be referenced.  audit_rotate_vnode() will own both references as of
    * this call, so the caller should not release either.
    *
    * XXXAUDIT: Review synchronize communication logic.  Really, this is a
    * message queue of depth 1.  We are essentially acquiring ownership of the
    * communications queue, inserting our message, and waiting for an
    * acknowledgement.
    */
   void
   audit_rotate_vnode(struct ucred *cred, struct vnode *vp)
   {
   
           /*
            * If other parallel log replacements have been requested, we wait
            * until they've finished before continuing.
            */
           mtx_lock(&audit_mtx);
           while (audit_replacement_flag != 0)
                   cv_wait(&audit_replacement_cv, &audit_mtx);
           audit_replacement_cred = cred;
           audit_replacement_flag = 1;
           audit_replacement_vp = vp;
   
           /*
            * Wake up the audit worker to perform the exchange once we release
            * the mutex.
            */
           cv_signal(&audit_worker_cv);
   
           /*
            * Wait for the audit_worker to broadcast that a replacement has
            * taken place; we know that once this has happened, our vnode has
            * been replaced in, so we can return successfully.
            */
           cv_wait(&audit_replacement_cv, &audit_mtx);
           audit_file_rotate_wait = 0; /* We can now request another rotation */
           mtx_unlock(&audit_mtx);
   }
   
   void
   audit_worker_init(void)
   {
           int error;
   
           cv_init(&audit_replacement_cv, "audit_replacement_cv");
           error = kthread_create(audit_worker, NULL, &audit_thread, RFHIGHPID,
               0, "audit");
           if (error)
                   panic("audit_worker_init: kthread_create returned %d", error);
   }

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