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

     /*-
      * SPDX-License-Identifier: BSD-3-Clause
      *
      * Copyright (c) 1999-2005 Apple Inc.
      * Copyright (c) 2006-2007, 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/eventhandler.h>
    #include <sys/file.h>
    #include <sys/filedesc.h>
    #include <sys/fcntl.h>
    #include <sys/ipc.h>
    #include <sys/jail.h>
    #include <sys/kernel.h>
    #include <sys/kthread.h>
    #include <sys/malloc.h>
    #include <sys/mount.h>
    #include <sys/namei.h>
    #include <sys/priv.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/sysctl.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>
    
    FEATURE(audit, "BSM audit support");
    
    static uma_zone_t       audit_record_zone;
    static MALLOC_DEFINE(M_AUDITCRED, "audit_cred", "Audit cred storage");
    MALLOC_DEFINE(M_AUDITDATA, "audit_data", "Audit data storage");
    MALLOC_DEFINE(M_AUDITPATH, "audit_path", "Audit path storage");
    MALLOC_DEFINE(M_AUDITTEXT, "audit_text", "Audit text storage");
    MALLOC_DEFINE(M_AUDITGIDSET, "audit_gidset", "Audit GID set storage");
    
    static SYSCTL_NODE(_security, OID_AUTO, audit, CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
        "TrustedBSD audit controls");
    
    /*
     * Audit control settings that are set/read by system calls and are hence
     * non-static.
     *
    * Define the audit control flags.
    */
   int                     audit_trail_enabled;
   int                     audit_trail_suspended;
   #ifdef KDTRACE_HOOKS
   u_int                   audit_dtrace_enabled;
   #endif
   bool __read_frequently  audit_syscalls_enabled;
   
   /*
    * Flags controlling behavior in low storage situations.  Should we panic if
    * a write fails?  Should we fail stop if we're out of disk space?
    */
   int                     audit_panic_on_write_fail;
   int                     audit_fail_stop;
   int                     audit_argv;
   int                     audit_arge;
   
   /*
    * Are we currently "failing stop" due to out of disk space?
    */
   int                     audit_in_failure;
   
   /*
    * Global audit statistics.
    */
   struct audit_fstat      audit_fstat;
   
   /*
    * Preselection mask for non-attributable events.
    */
   struct au_mask          audit_nae_mask;
   
   /*
    * Mutex to protect global variables shared between various threads and
    * processes.
    */
   struct mtx              audit_mtx;
   
   /*
    * Queue of audit records ready for delivery to disk.  We insert new records
    * at the tail, and remove records from the head.  Also, a count of the
    * number of records used for checking queue depth.  In addition, a counter
    * of records that we have allocated but are not yet in the queue, which is
    * needed to estimate the total size of the combined set of records
    * outstanding in the system.
    */
   struct kaudit_queue     audit_q;
   int                     audit_q_len;
   int                     audit_pre_q_len;
   
   /*
    * Audit queue control settings (minimum free, low/high water marks, etc.)
    */
   struct au_qctrl         audit_qctrl;
   
   /*
    * Condition variable to signal to the worker that it has work to do: either
    * new records are in the queue, or a log replacement is taking place.
    */
   struct cv               audit_worker_cv;
   
   /*
    * Condition variable to flag when crossing the low watermark, meaning that
    * threads blocked due to hitting the high watermark can wake up and continue
    * to commit records.
    */
   struct cv               audit_watermark_cv;
   
   /*
    * Condition variable for  auditing threads wait on when in fail-stop mode.
    * Threads wait on this CV forever (and ever), never seeing the light of day
    * again.
    */
   static struct cv        audit_fail_cv;
   
   /*
    * Optional DTrace audit provider support: function pointers for preselection
    * and commit events.
    */
   #ifdef KDTRACE_HOOKS
   void    *(*dtaudit_hook_preselect)(au_id_t auid, au_event_t event,
               au_class_t class);
   int     (*dtaudit_hook_commit)(struct kaudit_record *kar, au_id_t auid,
               au_event_t event, au_class_t class, int sorf);
   void    (*dtaudit_hook_bsm)(struct kaudit_record *kar, au_id_t auid,
               au_event_t event, au_class_t class, int sorf,
               void *bsm_data, size_t bsm_lenlen);
   #endif
   
   /*
    * Kernel audit information.  This will store the current audit address
    * or host information that the kernel will use when it's generating
    * audit records.  This data is modified by the A_GET{SET}KAUDIT auditon(2)
    * command.
    */
   static struct auditinfo_addr    audit_kinfo;
   static struct rwlock            audit_kinfo_lock;
   
   #define KINFO_LOCK_INIT()       rw_init(&audit_kinfo_lock, \
                                       "audit_kinfo_lock")
   #define KINFO_RLOCK()           rw_rlock(&audit_kinfo_lock)
   #define KINFO_WLOCK()           rw_wlock(&audit_kinfo_lock)
   #define KINFO_RUNLOCK()         rw_runlock(&audit_kinfo_lock)
   #define KINFO_WUNLOCK()         rw_wunlock(&audit_kinfo_lock)
   
   /*
    * Check various policies to see if we should enable system-call audit hooks.
    * Note that despite the mutex being held, we want to assign a value exactly
    * once, as checks of the flag are performed lock-free for performance
    * reasons.  The mutex is used to get a consistent snapshot of policy state --
    * e.g., safely accessing the two audit_trail flags.
    */
   void
   audit_syscalls_enabled_update(void)
   {
   
           mtx_lock(&audit_mtx);
   #ifdef KDTRACE_HOOKS
           if (audit_dtrace_enabled)
                   audit_syscalls_enabled = true;
           else {
   #endif
                   if (audit_trail_enabled && !audit_trail_suspended)
                           audit_syscalls_enabled = true;
                   else
                           audit_syscalls_enabled = false;
   #ifdef KDTRACE_HOOKS
           }
   #endif
           mtx_unlock(&audit_mtx);
   }
   
   void
   audit_set_kinfo(struct auditinfo_addr *ak)
   {
   
           KASSERT(ak->ai_termid.at_type == AU_IPv4 ||
               ak->ai_termid.at_type == AU_IPv6,
               ("audit_set_kinfo: invalid address type"));
   
           KINFO_WLOCK();
           audit_kinfo = *ak;
           KINFO_WUNLOCK();
   }
   
   void
   audit_get_kinfo(struct auditinfo_addr *ak)
   {
   
           KASSERT(audit_kinfo.ai_termid.at_type == AU_IPv4 ||
               audit_kinfo.ai_termid.at_type == AU_IPv6,
               ("audit_set_kinfo: invalid address type"));
   
           KINFO_RLOCK();
           *ak = audit_kinfo;
           KINFO_RUNLOCK();
   }
   
   /*
    * Construct an audit record for the passed thread.
    */
   static int
   audit_record_ctor(void *mem, int size, void *arg, int flags)
   {
           struct kaudit_record *ar;
           struct thread *td;
           struct ucred *cred;
           struct prison *pr;
   
           KASSERT(sizeof(*ar) == size, ("audit_record_ctor: wrong size"));
   
           td = arg;
           ar = mem;
           bzero(ar, sizeof(*ar));
           ar->k_ar.ar_magic = AUDIT_RECORD_MAGIC;
           nanotime(&ar->k_ar.ar_starttime);
   
           /*
            * Export the subject credential.
            */
           cred = td->td_ucred;
           cru2x(cred, &ar->k_ar.ar_subj_cred);
           ar->k_ar.ar_subj_ruid = cred->cr_ruid;
           ar->k_ar.ar_subj_rgid = cred->cr_rgid;
           ar->k_ar.ar_subj_egid = cred->cr_groups[0];
           ar->k_ar.ar_subj_auid = cred->cr_audit.ai_auid;
           ar->k_ar.ar_subj_asid = cred->cr_audit.ai_asid;
           ar->k_ar.ar_subj_pid = td->td_proc->p_pid;
           ar->k_ar.ar_subj_amask = cred->cr_audit.ai_mask;
           ar->k_ar.ar_subj_term_addr = cred->cr_audit.ai_termid;
           /*
            * If this process is jailed, make sure we capture the name of the
            * jail so we can use it to generate a zonename token when we covert
            * this record to BSM.
            */
           if (jailed(cred)) {
                   pr = cred->cr_prison;
                   (void) strlcpy(ar->k_ar.ar_jailname, pr->pr_name,
                       sizeof(ar->k_ar.ar_jailname));
           } else
                   ar->k_ar.ar_jailname[0] = '\0';
           return (0);
   }
   
   static void
   audit_record_dtor(void *mem, int size, void *arg)
   {
           struct kaudit_record *ar;
   
           KASSERT(sizeof(*ar) == size, ("audit_record_dtor: wrong size"));
   
           ar = mem;
           if (ar->k_ar.ar_arg_upath1 != NULL)
                   free(ar->k_ar.ar_arg_upath1, M_AUDITPATH);
           if (ar->k_ar.ar_arg_upath2 != NULL)
                   free(ar->k_ar.ar_arg_upath2, M_AUDITPATH);
           if (ar->k_ar.ar_arg_text != NULL)
                   free(ar->k_ar.ar_arg_text, M_AUDITTEXT);
           if (ar->k_udata != NULL)
                   free(ar->k_udata, M_AUDITDATA);
           if (ar->k_ar.ar_arg_argv != NULL)
                   free(ar->k_ar.ar_arg_argv, M_AUDITTEXT);
           if (ar->k_ar.ar_arg_envv != NULL)
                   free(ar->k_ar.ar_arg_envv, M_AUDITTEXT);
           if (ar->k_ar.ar_arg_groups.gidset != NULL)
                   free(ar->k_ar.ar_arg_groups.gidset, M_AUDITGIDSET);
   }
   
   /*
    * Initialize the Audit subsystem: configuration state, work queue,
    * synchronization primitives, worker thread, and trigger device node.  Also
    * call into the BSM assembly code to initialize it.
    */
   static void
   audit_init(void)
   {
   
           audit_trail_enabled = 0;
           audit_trail_suspended = 0;
           audit_syscalls_enabled = false;
           audit_panic_on_write_fail = 0;
           audit_fail_stop = 0;
           audit_in_failure = 0;
           audit_argv = 0;
           audit_arge = 0;
   
           audit_fstat.af_filesz = 0;      /* '' means unset, unbounded. */
           audit_fstat.af_currsz = 0;
           audit_nae_mask.am_success = 0;
           audit_nae_mask.am_failure = 0;
   
           TAILQ_INIT(&audit_q);
           audit_q_len = 0;
           audit_pre_q_len = 0;
           audit_qctrl.aq_hiwater = AQ_HIWATER;
           audit_qctrl.aq_lowater = AQ_LOWATER;
           audit_qctrl.aq_bufsz = AQ_BUFSZ;
           audit_qctrl.aq_minfree = AU_FS_MINFREE;
   
           audit_kinfo.ai_termid.at_type = AU_IPv4;
           audit_kinfo.ai_termid.at_addr[0] = INADDR_ANY;
   
           mtx_init(&audit_mtx, "audit_mtx", NULL, MTX_DEF);
           KINFO_LOCK_INIT();
           cv_init(&audit_worker_cv, "audit_worker_cv");
           cv_init(&audit_watermark_cv, "audit_watermark_cv");
           cv_init(&audit_fail_cv, "audit_fail_cv");
   
           audit_record_zone = uma_zcreate("audit_record",
               sizeof(struct kaudit_record), audit_record_ctor,
               audit_record_dtor, NULL, NULL, UMA_ALIGN_PTR, 0);
   
           /* First initialisation of audit_syscalls_enabled. */
           audit_syscalls_enabled_update();
   
           /* Initialize the BSM audit subsystem. */
           kau_init();
   
           audit_trigger_init();
   
           /* Register shutdown handler. */
           EVENTHANDLER_REGISTER(shutdown_pre_sync, audit_shutdown, NULL,
               SHUTDOWN_PRI_FIRST);
   
           /* Start audit worker thread. */
           audit_worker_init();
   }
   
   SYSINIT(audit_init, SI_SUB_AUDIT, SI_ORDER_FIRST, audit_init, NULL);
   
   /*
    * Drain the audit queue and close the log at shutdown.  Note that this can
    * be called both from the system shutdown path and also from audit
    * configuration syscalls, so 'arg' and 'howto' are ignored.
    *
    * XXXRW: In FreeBSD 7.x and 8.x, this fails to wait for the record queue to
    * drain before returning, which could lead to lost records on shutdown.
    */
   void
   audit_shutdown(void *arg, int howto)
   {
   
           audit_rotate_vnode(NULL, NULL);
   }
   
   /*
    * Return the current thread's audit record, if any.
    */
   struct kaudit_record *
   currecord(void)
   {
   
           return (curthread->td_ar);
   }
   
   /*
    * XXXAUDIT: Shouldn't there be logic here to sleep waiting on available
    * pre_q space, suspending the system call until there is room?
    */
   struct kaudit_record *
   audit_new(int event, struct thread *td)
   {
           struct kaudit_record *ar;
   
           /*
            * Note: the number of outstanding uncommitted audit records is
            * limited to the number of concurrent threads servicing system calls
            * in the kernel.
            */
           ar = uma_zalloc_arg(audit_record_zone, td, M_WAITOK);
           ar->k_ar.ar_event = event;
   
           mtx_lock(&audit_mtx);
           audit_pre_q_len++;
           mtx_unlock(&audit_mtx);
   
           return (ar);
   }
   
   void
   audit_free(struct kaudit_record *ar)
   {
   
           uma_zfree(audit_record_zone, ar);
   }
   
   void
   audit_commit(struct kaudit_record *ar, int error, int retval)
   {
           au_event_t event;
           au_class_t class;
           au_id_t auid;
           int sorf;
           struct au_mask *aumask;
   
           if (ar == NULL)
                   return;
   
           ar->k_ar.ar_errno = error;
           ar->k_ar.ar_retval = retval;
           nanotime(&ar->k_ar.ar_endtime);
   
           /*
            * Decide whether to commit the audit record by checking the error
            * value from the system call and using the appropriate audit mask.
            */
           if (ar->k_ar.ar_subj_auid == AU_DEFAUDITID)
                   aumask = &audit_nae_mask;
           else
                   aumask = &ar->k_ar.ar_subj_amask;
   
           if (error)
                   sorf = AU_PRS_FAILURE;
           else
                   sorf = AU_PRS_SUCCESS;
   
           /*
            * syscalls.master sometimes contains a prototype event number, which
            * we will transform into a more specific event number now that we
            * have more complete information gathered during the system call.
            */
           switch(ar->k_ar.ar_event) {
           case AUE_OPEN_RWTC:
                   ar->k_ar.ar_event = audit_flags_and_error_to_openevent(
                       ar->k_ar.ar_arg_fflags, error);
                   break;
   
           case AUE_OPENAT_RWTC:
                   ar->k_ar.ar_event = audit_flags_and_error_to_openatevent(
                       ar->k_ar.ar_arg_fflags, error);
                   break;
   
           case AUE_SYSCTL:
                   ar->k_ar.ar_event = audit_ctlname_to_sysctlevent(
                       ar->k_ar.ar_arg_ctlname, ar->k_ar.ar_valid_arg);
                   break;
   
           case AUE_AUDITON:
                   /* Convert the auditon() command to an event. */
                   ar->k_ar.ar_event = auditon_command_event(ar->k_ar.ar_arg_cmd);
                   break;
   
           case AUE_MSGSYS:
                   if (ARG_IS_VALID(ar, ARG_SVIPC_WHICH))
                           ar->k_ar.ar_event =
                               audit_msgsys_to_event(ar->k_ar.ar_arg_svipc_which);
                   break;
   
           case AUE_SEMSYS:
                   if (ARG_IS_VALID(ar, ARG_SVIPC_WHICH))
                           ar->k_ar.ar_event =
                               audit_semsys_to_event(ar->k_ar.ar_arg_svipc_which);
                   break;
   
           case AUE_SHMSYS:
                   if (ARG_IS_VALID(ar, ARG_SVIPC_WHICH))
                           ar->k_ar.ar_event =
                               audit_shmsys_to_event(ar->k_ar.ar_arg_svipc_which);
                   break;
           }
   
           auid = ar->k_ar.ar_subj_auid;
           event = ar->k_ar.ar_event;
           class = au_event_class(event);
   
           ar->k_ar_commit |= AR_COMMIT_KERNEL;
           if (au_preselect(event, class, aumask, sorf) != 0)
                   ar->k_ar_commit |= AR_PRESELECT_TRAIL;
           if (audit_pipe_preselect(auid, event, class, sorf,
               ar->k_ar_commit & AR_PRESELECT_TRAIL) != 0)
                   ar->k_ar_commit |= AR_PRESELECT_PIPE;
   #ifdef KDTRACE_HOOKS
           /*
            * Expose the audit record to DTrace, both to allow the "commit" probe
            * to fire if it's desirable, and also to allow a decision to be made
            * about later firing with BSM in the audit worker.
            */
           if (dtaudit_hook_commit != NULL) {
                   if (dtaudit_hook_commit(ar, auid, event, class, sorf) != 0)
                           ar->k_ar_commit |= AR_PRESELECT_DTRACE;
           }
   #endif
   
           if ((ar->k_ar_commit & (AR_PRESELECT_TRAIL | AR_PRESELECT_PIPE |
               AR_PRESELECT_USER_TRAIL | AR_PRESELECT_USER_PIPE |
               AR_PRESELECT_DTRACE)) == 0) {
                   mtx_lock(&audit_mtx);
                   audit_pre_q_len--;
                   mtx_unlock(&audit_mtx);
                   audit_free(ar);
                   return;
           }
   
           /*
            * Note: it could be that some records initiated while audit was
            * enabled should still be committed?
            *
            * NB: The check here is not for audit_syscalls because any
            * DTrace-related obligations have been fulfilled above -- we're just
            * down to the trail and pipes now.
            */
           mtx_lock(&audit_mtx);
           if (audit_trail_suspended || !audit_trail_enabled) {
                   audit_pre_q_len--;
                   mtx_unlock(&audit_mtx);
                   audit_free(ar);
                   return;
           }
   
           /*
            * Constrain the number of committed audit records based on the
            * configurable parameter.
            */
           while (audit_q_len >= audit_qctrl.aq_hiwater)
                   cv_wait(&audit_watermark_cv, &audit_mtx);
   
           TAILQ_INSERT_TAIL(&audit_q, ar, k_q);
           audit_q_len++;
           audit_pre_q_len--;
           cv_signal(&audit_worker_cv);
           mtx_unlock(&audit_mtx);
   }
   
   /*
    * audit_syscall_enter() is called on entry to each system call.  It is
    * responsible for deciding whether or not to audit the call (preselection),
    * and if so, allocating a per-thread audit record.  audit_new() will fill in
    * basic thread/credential properties.
    *
    * This function will be entered only if audit_syscalls_enabled was set in the
    * macro wrapper for this function.  It could be cleared by the time this
    * function runs, but that is an acceptable race.
    */
   void
   audit_syscall_enter(unsigned short code, struct thread *td)
   {
           struct au_mask *aumask;
   #ifdef KDTRACE_HOOKS
           void *dtaudit_state;
   #endif
           au_class_t class;
           au_event_t event;
           au_id_t auid;
           int record_needed;
   
           KASSERT(td->td_ar == NULL, ("audit_syscall_enter: td->td_ar != NULL"));
           KASSERT((td->td_pflags & TDP_AUDITREC) == 0,
               ("audit_syscall_enter: TDP_AUDITREC set"));
   
           /*
            * In FreeBSD, each ABI has its own system call table, and hence
            * mapping of system call codes to audit events.  Convert the code to
            * an audit event identifier using the process system call table
            * reference.  In Darwin, there's only one, so we use the global
            * symbol for the system call table.  No audit record is generated
            * for bad system calls, as no operation has been performed.
            */
           if (code >= td->td_proc->p_sysent->sv_size)
                   return;
   
           event = td->td_proc->p_sysent->sv_table[code].sy_auevent;
           if (event == AUE_NULL)
                   return;
   
           /*
            * Check which audit mask to use; either the kernel non-attributable
            * event mask or the process audit mask.
            */
           auid = td->td_ucred->cr_audit.ai_auid;
           if (auid == AU_DEFAUDITID)
                   aumask = &audit_nae_mask;
           else
                   aumask = &td->td_ucred->cr_audit.ai_mask;
   
           /*
            * Determine whether trail or pipe preselection would like an audit
            * record allocated for this system call.
            */
           class = au_event_class(event);
           if (au_preselect(event, class, aumask, AU_PRS_BOTH)) {
                   /*
                    * If we're out of space and need to suspend unprivileged
                    * processes, do that here rather than trying to allocate
                    * another audit record.
                    *
                    * Note: we might wish to be able to continue here in the
                    * future, if the system recovers.  That should be possible
                    * by means of checking the condition in a loop around
                    * cv_wait().  It might be desirable to reevaluate whether an
                    * audit record is still required for this event by
                    * re-calling au_preselect().
                    */
                   if (audit_in_failure &&
                       priv_check(td, PRIV_AUDIT_FAILSTOP) != 0) {
                           cv_wait(&audit_fail_cv, &audit_mtx);
                           panic("audit_failing_stop: thread continued");
                   }
                   record_needed = 1;
           } else if (audit_pipe_preselect(auid, event, class, AU_PRS_BOTH, 0)) {
                   record_needed = 1;
           } else {
                   record_needed = 0;
           }
   
           /*
            * After audit trails and pipes have made their policy choices, DTrace
            * may request that records be generated as well.  This is a slightly
            * complex affair, as the DTrace audit provider needs the audit
            * framework to maintain some state on the audit record, which has not
            * been allocated at the point where the decision has to be made.
            * This hook must run even if we are not changing the decision, as
            * DTrace may want to stick event state onto a record we were going to
            * produce due to the trail or pipes.  The event state returned by the
            * DTrace provider must be safe without locks held between here and
            * below -- i.e., dtaudit_state must must refer to stable memory.
            */
   #ifdef KDTRACE_HOOKS
           dtaudit_state = NULL;
           if (dtaudit_hook_preselect != NULL) {
                   dtaudit_state = dtaudit_hook_preselect(auid, event, class);
                   if (dtaudit_state != NULL)
                           record_needed = 1;
           }
   #endif
   
           /*
            * If a record is required, allocate it and attach it to the thread
            * for use throughout the system call.  Also attach DTrace state if
            * required.
            *
            * XXXRW: If we decide to reference count the evname_elem underlying
            * dtaudit_state, we will need to free here if no record is allocated
            * or allocatable.
            */
           if (record_needed) {
                   td->td_ar = audit_new(event, td);
                   if (td->td_ar != NULL) {
                           td->td_pflags |= TDP_AUDITREC;
   #ifdef KDTRACE_HOOKS
                           td->td_ar->k_dtaudit_state = dtaudit_state;
   #endif
                   }
           } else
                   td->td_ar = NULL;
   }
   
   /*
    * audit_syscall_exit() is called from the return of every system call, or in
    * the event of exit1(), during the execution of exit1().  It is responsible
    * for committing the audit record, if any, along with return condition.
    */
   void
   audit_syscall_exit(int error, struct thread *td)
   {
           int retval;
   
           /*
            * Commit the audit record as desired; once we pass the record into
            * audit_commit(), the memory is owned by the audit subsystem.  The
            * return value from the system call is stored on the user thread.
            * If there was an error, the return value is set to -1, imitating
            * the behavior of the cerror routine.
            */
           if (error)
                   retval = -1;
           else
                   retval = td->td_retval[0];
   
           audit_commit(td->td_ar, error, retval);
           td->td_ar = NULL;
           td->td_pflags &= ~TDP_AUDITREC;
   }
   
   void
   audit_cred_copy(struct ucred *src, struct ucred *dest)
   {
   
           bcopy(&src->cr_audit, &dest->cr_audit, sizeof(dest->cr_audit));
   }
   
   void
   audit_cred_destroy(struct ucred *cred)
   {
   
   }
   
   void
   audit_cred_init(struct ucred *cred)
   {
   
           bzero(&cred->cr_audit, sizeof(cred->cr_audit));
   }
   
   /*
    * Initialize audit information for the first kernel process (proc 0) and for
    * the first user process (init).
    */
   void
   audit_cred_kproc0(struct ucred *cred)
   {
   
           cred->cr_audit.ai_auid = AU_DEFAUDITID;
           cred->cr_audit.ai_termid.at_type = AU_IPv4;
   }
   
   void
   audit_cred_proc1(struct ucred *cred)
   {
   
           cred->cr_audit.ai_auid = AU_DEFAUDITID;
           cred->cr_audit.ai_termid.at_type = AU_IPv4;
   }
   
   void
   audit_thread_alloc(struct thread *td)
   {
   
           td->td_ar = NULL;
   }
   
   void
   audit_thread_free(struct thread *td)
   {
   
           KASSERT(td->td_ar == NULL, ("audit_thread_free: td_ar != NULL"));
           KASSERT((td->td_pflags & TDP_AUDITREC) == 0,
               ("audit_thread_free: TDP_AUDITREC set"));
   }
   
   void
   audit_proc_coredump(struct thread *td, char *path, int errcode)
   {
           struct kaudit_record *ar;
           struct au_mask *aumask;
           struct ucred *cred;
           au_class_t class;
           int ret, sorf;
           char **pathp;
           au_id_t auid;
   
           ret = 0;
   
           /*
            * Make sure we are using the correct preselection mask.
            */
           cred = td->td_ucred;
           auid = cred->cr_audit.ai_auid;
           if (auid == AU_DEFAUDITID)
                   aumask = &audit_nae_mask;
           else
                   aumask = &cred->cr_audit.ai_mask;
           /*
            * It's possible for coredump(9) generation to fail.  Make sure that
            * we handle this case correctly for preselection.
            */
           if (errcode != 0)
                   sorf = AU_PRS_FAILURE;
           else
                   sorf = AU_PRS_SUCCESS;
           class = au_event_class(AUE_CORE);
           if (au_preselect(AUE_CORE, class, aumask, sorf) == 0 &&
               audit_pipe_preselect(auid, AUE_CORE, class, sorf, 0) == 0)
                   return;
   
           /*
            * If we are interested in seeing this audit record, allocate it.
            * Where possible coredump records should contain a pathname and arg32
            * (signal) tokens.
            */
           ar = audit_new(AUE_CORE, td);
           if (ar == NULL)
                   return;
           if (path != NULL) {
                   pathp = &ar->k_ar.ar_arg_upath1;
                   *pathp = malloc(MAXPATHLEN, M_AUDITPATH, M_WAITOK);
                   audit_canon_path(td, AT_FDCWD, path, *pathp);
                   ARG_SET_VALID(ar, ARG_UPATH1);
           }
           ar->k_ar.ar_arg_signum = td->td_proc->p_sig;
           ARG_SET_VALID(ar, ARG_SIGNUM);
           if (errcode != 0)
                   ret = 1;
           audit_commit(ar, errcode, ret);
   }

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