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

     /* audit.c -- Auditing support
      * Gateway between the kernel (e.g., selinux) and the user-space audit daemon.
      * System-call specific features have moved to auditsc.c
      *
      * Copyright 2003-2007 Red Hat Inc., Durham, North Carolina.
      * All Rights Reserved.
      *
      * This program is free software; you can redistribute it and/or modify
      * it under the terms of the GNU General Public License as published by
     * the Free Software Foundation; either version 2 of the License, or
     * (at your option) any later version.
     *
     * This program is distributed in the hope that it will be useful,
     * but WITHOUT ANY WARRANTY; without even the implied warranty of
     * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
     * GNU General Public License for more details.
     *
     * You should have received a copy of the GNU General Public License
     * along with this program; if not, write to the Free Software
     * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
     *
     * Written by Rickard E. (Rik) Faith <faith@redhat.com>
     *
     * Goals: 1) Integrate fully with Security Modules.
     *        2) Minimal run-time overhead:
     *           a) Minimal when syscall auditing is disabled (audit_enable=0).
     *           b) Small when syscall auditing is enabled and no audit record
     *              is generated (defer as much work as possible to record
     *              generation time):
     *              i) context is allocated,
     *              ii) names from getname are stored without a copy, and
     *              iii) inode information stored from path_lookup.
     *        3) Ability to disable syscall auditing at boot time (audit=0).
     *        4) Usable by other parts of the kernel (if audit_log* is called,
     *           then a syscall record will be generated automatically for the
     *           current syscall).
     *        5) Netlink interface to user-space.
     *        6) Support low-overhead kernel-based filtering to minimize the
     *           information that must be passed to user-space.
     *
     * Example user-space utilities: http://people.redhat.com/sgrubb/audit/
     */
    
    #include <linux/init.h>
    #include <asm/types.h>
    #include <linux/atomic.h>
    #include <linux/mm.h>
    #include <linux/export.h>
    #include <linux/slab.h>
    #include <linux/err.h>
    #include <linux/kthread.h>
    
    #include <linux/audit.h>
    
    #include <net/sock.h>
    #include <net/netlink.h>
    #include <linux/skbuff.h>
    #ifdef CONFIG_SECURITY
    #include <linux/security.h>
    #endif
    #include <linux/netlink.h>
    #include <linux/freezer.h>
    #include <linux/tty.h>
    #include <linux/pid_namespace.h>
    
    #include "audit.h"
    
    /* No auditing will take place until audit_initialized == AUDIT_INITIALIZED.
     * (Initialization happens after skb_init is called.) */
    #define AUDIT_DISABLED          -1
    #define AUDIT_UNINITIALIZED     0
    #define AUDIT_INITIALIZED       1
    static int      audit_initialized;
    
    #define AUDIT_OFF       0
    #define AUDIT_ON        1
    #define AUDIT_LOCKED    2
    int             audit_enabled;
    int             audit_ever_enabled;
    
    EXPORT_SYMBOL_GPL(audit_enabled);
    
    /* Default state when kernel boots without any parameters. */
    static int      audit_default;
    
    /* If auditing cannot proceed, audit_failure selects what happens. */
    static int      audit_failure = AUDIT_FAIL_PRINTK;
    
    /*
     * If audit records are to be written to the netlink socket, audit_pid
     * contains the pid of the auditd process and audit_nlk_portid contains
     * the portid to use to send netlink messages to that process.
     */
    int             audit_pid;
    static int      audit_nlk_portid;
    
    /* If audit_rate_limit is non-zero, limit the rate of sending audit records
     * to that number per second.  This prevents DoS attacks, but results in
     * audit records being dropped. */
   static int      audit_rate_limit;
   
   /* Number of outstanding audit_buffers allowed. */
   static int      audit_backlog_limit = 64;
   static int      audit_backlog_wait_time = 60 * HZ;
   static int      audit_backlog_wait_overflow = 0;
   
   /* The identity of the user shutting down the audit system. */
   kuid_t          audit_sig_uid = INVALID_UID;
   pid_t           audit_sig_pid = -1;
   u32             audit_sig_sid = 0;
   
   /* Records can be lost in several ways:
      0) [suppressed in audit_alloc]
      1) out of memory in audit_log_start [kmalloc of struct audit_buffer]
      2) out of memory in audit_log_move [alloc_skb]
      3) suppressed due to audit_rate_limit
      4) suppressed due to audit_backlog_limit
   */
   static atomic_t    audit_lost = ATOMIC_INIT(0);
   
   /* The netlink socket. */
   static struct sock *audit_sock;
   
   /* Hash for inode-based rules */
   struct list_head audit_inode_hash[AUDIT_INODE_BUCKETS];
   
   /* The audit_freelist is a list of pre-allocated audit buffers (if more
    * than AUDIT_MAXFREE are in use, the audit buffer is freed instead of
    * being placed on the freelist). */
   static DEFINE_SPINLOCK(audit_freelist_lock);
   static int         audit_freelist_count;
   static LIST_HEAD(audit_freelist);
   
   static struct sk_buff_head audit_skb_queue;
   /* queue of skbs to send to auditd when/if it comes back */
   static struct sk_buff_head audit_skb_hold_queue;
   static struct task_struct *kauditd_task;
   static DECLARE_WAIT_QUEUE_HEAD(kauditd_wait);
   static DECLARE_WAIT_QUEUE_HEAD(audit_backlog_wait);
   
   /* Serialize requests from userspace. */
   DEFINE_MUTEX(audit_cmd_mutex);
   
   /* AUDIT_BUFSIZ is the size of the temporary buffer used for formatting
    * audit records.  Since printk uses a 1024 byte buffer, this buffer
    * should be at least that large. */
   #define AUDIT_BUFSIZ 1024
   
   /* AUDIT_MAXFREE is the number of empty audit_buffers we keep on the
    * audit_freelist.  Doing so eliminates many kmalloc/kfree calls. */
   #define AUDIT_MAXFREE  (2*NR_CPUS)
   
   /* The audit_buffer is used when formatting an audit record.  The caller
    * locks briefly to get the record off the freelist or to allocate the
    * buffer, and locks briefly to send the buffer to the netlink layer or
    * to place it on a transmit queue.  Multiple audit_buffers can be in
    * use simultaneously. */
   struct audit_buffer {
           struct list_head     list;
           struct sk_buff       *skb;      /* formatted skb ready to send */
           struct audit_context *ctx;      /* NULL or associated context */
           gfp_t                gfp_mask;
   };
   
   struct audit_reply {
           int pid;
           struct sk_buff *skb;
   };
   
   static void audit_set_pid(struct audit_buffer *ab, pid_t pid)
   {
           if (ab) {
                   struct nlmsghdr *nlh = nlmsg_hdr(ab->skb);
                   nlh->nlmsg_pid = pid;
           }
   }
   
   void audit_panic(const char *message)
   {
           switch (audit_failure)
           {
           case AUDIT_FAIL_SILENT:
                   break;
           case AUDIT_FAIL_PRINTK:
                   if (printk_ratelimit())
                           printk(KERN_ERR "audit: %s\n", message);
                   break;
           case AUDIT_FAIL_PANIC:
                   /* test audit_pid since printk is always losey, why bother? */
                   if (audit_pid)
                           panic("audit: %s\n", message);
                   break;
           }
   }
   
   static inline int audit_rate_check(void)
   {
           static unsigned long    last_check = 0;
           static int              messages   = 0;
           static DEFINE_SPINLOCK(lock);
           unsigned long           flags;
           unsigned long           now;
           unsigned long           elapsed;
           int                     retval     = 0;
   
           if (!audit_rate_limit) return 1;
   
           spin_lock_irqsave(&lock, flags);
           if (++messages < audit_rate_limit) {
                   retval = 1;
           } else {
                   now     = jiffies;
                   elapsed = now - last_check;
                   if (elapsed > HZ) {
                           last_check = now;
                           messages   = 0;
                           retval     = 1;
                   }
           }
           spin_unlock_irqrestore(&lock, flags);
   
           return retval;
   }
   
   /**
    * audit_log_lost - conditionally log lost audit message event
    * @message: the message stating reason for lost audit message
    *
    * Emit at least 1 message per second, even if audit_rate_check is
    * throttling.
    * Always increment the lost messages counter.
   */
   void audit_log_lost(const char *message)
   {
           static unsigned long    last_msg = 0;
           static DEFINE_SPINLOCK(lock);
           unsigned long           flags;
           unsigned long           now;
           int                     print;
   
           atomic_inc(&audit_lost);
   
           print = (audit_failure == AUDIT_FAIL_PANIC || !audit_rate_limit);
   
           if (!print) {
                   spin_lock_irqsave(&lock, flags);
                   now = jiffies;
                   if (now - last_msg > HZ) {
                           print = 1;
                           last_msg = now;
                   }
                   spin_unlock_irqrestore(&lock, flags);
           }
   
           if (print) {
                   if (printk_ratelimit())
                           printk(KERN_WARNING
                                   "audit: audit_lost=%d audit_rate_limit=%d "
                                   "audit_backlog_limit=%d\n",
                                   atomic_read(&audit_lost),
                                   audit_rate_limit,
                                   audit_backlog_limit);
                   audit_panic(message);
           }
   }
   
   static int audit_log_config_change(char *function_name, int new, int old,
                                      kuid_t loginuid, u32 sessionid, u32 sid,
                                      int allow_changes)
   {
           struct audit_buffer *ab;
           int rc = 0;
   
           ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_CONFIG_CHANGE);
           if (unlikely(!ab))
                   return rc;
           audit_log_format(ab, "%s=%d old=%d auid=%u ses=%u", function_name, new,
                            old, from_kuid(&init_user_ns, loginuid), sessionid);
           if (sid) {
                   char *ctx = NULL;
                   u32 len;
   
                   rc = security_secid_to_secctx(sid, &ctx, &len);
                   if (rc) {
                           audit_log_format(ab, " sid=%u", sid);
                           allow_changes = 0; /* Something weird, deny request */
                   } else {
                           audit_log_format(ab, " subj=%s", ctx);
                           security_release_secctx(ctx, len);
                   }
           }
           audit_log_format(ab, " res=%d", allow_changes);
           audit_log_end(ab);
           return rc;
   }
   
   static int audit_do_config_change(char *function_name, int *to_change,
                                     int new, kuid_t loginuid, u32 sessionid,
                                     u32 sid)
   {
           int allow_changes, rc = 0, old = *to_change;
   
           /* check if we are locked */
           if (audit_enabled == AUDIT_LOCKED)
                   allow_changes = 0;
           else
                   allow_changes = 1;
   
           if (audit_enabled != AUDIT_OFF) {
                   rc = audit_log_config_change(function_name, new, old, loginuid,
                                                sessionid, sid, allow_changes);
                   if (rc)
                           allow_changes = 0;
           }
   
           /* If we are allowed, make the change */
           if (allow_changes == 1)
                   *to_change = new;
           /* Not allowed, update reason */
           else if (rc == 0)
                   rc = -EPERM;
           return rc;
   }
   
   static int audit_set_rate_limit(int limit, kuid_t loginuid, u32 sessionid,
                                   u32 sid)
   {
           return audit_do_config_change("audit_rate_limit", &audit_rate_limit,
                                         limit, loginuid, sessionid, sid);
   }
   
   static int audit_set_backlog_limit(int limit, kuid_t loginuid, u32 sessionid,
                                      u32 sid)
   {
           return audit_do_config_change("audit_backlog_limit", &audit_backlog_limit,
                                         limit, loginuid, sessionid, sid);
   }
   
   static int audit_set_enabled(int state, kuid_t loginuid, u32 sessionid, u32 sid)
   {
           int rc;
           if (state < AUDIT_OFF || state > AUDIT_LOCKED)
                   return -EINVAL;
   
           rc =  audit_do_config_change("audit_enabled", &audit_enabled, state,
                                        loginuid, sessionid, sid);
   
           if (!rc)
                   audit_ever_enabled |= !!state;
   
           return rc;
   }
   
   static int audit_set_failure(int state, kuid_t loginuid, u32 sessionid, u32 sid)
   {
           if (state != AUDIT_FAIL_SILENT
               && state != AUDIT_FAIL_PRINTK
               && state != AUDIT_FAIL_PANIC)
                   return -EINVAL;
   
           return audit_do_config_change("audit_failure", &audit_failure, state,
                                         loginuid, sessionid, sid);
   }
   
   /*
    * Queue skbs to be sent to auditd when/if it comes back.  These skbs should
    * already have been sent via prink/syslog and so if these messages are dropped
    * it is not a huge concern since we already passed the audit_log_lost()
    * notification and stuff.  This is just nice to get audit messages during
    * boot before auditd is running or messages generated while auditd is stopped.
    * This only holds messages is audit_default is set, aka booting with audit=1
    * or building your kernel that way.
    */
   static void audit_hold_skb(struct sk_buff *skb)
   {
           if (audit_default &&
               skb_queue_len(&audit_skb_hold_queue) < audit_backlog_limit)
                   skb_queue_tail(&audit_skb_hold_queue, skb);
           else
                   kfree_skb(skb);
   }
   
   /*
    * For one reason or another this nlh isn't getting delivered to the userspace
    * audit daemon, just send it to printk.
    */
   static void audit_printk_skb(struct sk_buff *skb)
   {
           struct nlmsghdr *nlh = nlmsg_hdr(skb);
           char *data = nlmsg_data(nlh);
   
           if (nlh->nlmsg_type != AUDIT_EOE) {
                   if (printk_ratelimit())
                           printk(KERN_NOTICE "type=%d %s\n", nlh->nlmsg_type, data);
                   else
                           audit_log_lost("printk limit exceeded\n");
           }
   
           audit_hold_skb(skb);
   }
   
   static void kauditd_send_skb(struct sk_buff *skb)
   {
           int err;
           /* take a reference in case we can't send it and we want to hold it */
           skb_get(skb);
           err = netlink_unicast(audit_sock, skb, audit_nlk_portid, 0);
           if (err < 0) {
                   BUG_ON(err != -ECONNREFUSED); /* Shouldn't happen */
                   printk(KERN_ERR "audit: *NO* daemon at audit_pid=%d\n", audit_pid);
                   audit_log_lost("auditd disappeared\n");
                   audit_pid = 0;
                   /* we might get lucky and get this in the next auditd */
                   audit_hold_skb(skb);
           } else
                   /* drop the extra reference if sent ok */
                   consume_skb(skb);
   }
   
   static int kauditd_thread(void *dummy)
   {
           struct sk_buff *skb;
   
           set_freezable();
           while (!kthread_should_stop()) {
                   /*
                    * if auditd just started drain the queue of messages already
                    * sent to syslog/printk.  remember loss here is ok.  we already
                    * called audit_log_lost() if it didn't go out normally.  so the
                    * race between the skb_dequeue and the next check for audit_pid
                    * doesn't matter.
                    *
                    * if you ever find kauditd to be too slow we can get a perf win
                    * by doing our own locking and keeping better track if there
                    * are messages in this queue.  I don't see the need now, but
                    * in 5 years when I want to play with this again I'll see this
                    * note and still have no friggin idea what i'm thinking today.
                    */
                   if (audit_default && audit_pid) {
                           skb = skb_dequeue(&audit_skb_hold_queue);
                           if (unlikely(skb)) {
                                   while (skb && audit_pid) {
                                           kauditd_send_skb(skb);
                                           skb = skb_dequeue(&audit_skb_hold_queue);
                                   }
                           }
                   }
   
                   skb = skb_dequeue(&audit_skb_queue);
                   wake_up(&audit_backlog_wait);
                   if (skb) {
                           if (audit_pid)
                                   kauditd_send_skb(skb);
                           else
                                   audit_printk_skb(skb);
                   } else {
                           DECLARE_WAITQUEUE(wait, current);
                           set_current_state(TASK_INTERRUPTIBLE);
                           add_wait_queue(&kauditd_wait, &wait);
   
                           if (!skb_queue_len(&audit_skb_queue)) {
                                   try_to_freeze();
                                   schedule();
                           }
   
                           __set_current_state(TASK_RUNNING);
                           remove_wait_queue(&kauditd_wait, &wait);
                   }
           }
           return 0;
   }
   
   int audit_send_list(void *_dest)
   {
           struct audit_netlink_list *dest = _dest;
           int pid = dest->pid;
           struct sk_buff *skb;
   
           /* wait for parent to finish and send an ACK */
           mutex_lock(&audit_cmd_mutex);
           mutex_unlock(&audit_cmd_mutex);
   
           while ((skb = __skb_dequeue(&dest->q)) != NULL)
                   netlink_unicast(audit_sock, skb, pid, 0);
   
           kfree(dest);
   
           return 0;
   }
   
   struct sk_buff *audit_make_reply(int pid, int seq, int type, int done,
                                    int multi, const void *payload, int size)
   {
           struct sk_buff  *skb;
           struct nlmsghdr *nlh;
           void            *data;
           int             flags = multi ? NLM_F_MULTI : 0;
           int             t     = done  ? NLMSG_DONE  : type;
   
           skb = nlmsg_new(size, GFP_KERNEL);
           if (!skb)
                   return NULL;
   
           nlh     = nlmsg_put(skb, pid, seq, t, size, flags);
           if (!nlh)
                   goto out_kfree_skb;
           data = nlmsg_data(nlh);
           memcpy(data, payload, size);
           return skb;
   
   out_kfree_skb:
           kfree_skb(skb);
           return NULL;
   }
   
   static int audit_send_reply_thread(void *arg)
   {
           struct audit_reply *reply = (struct audit_reply *)arg;
   
           mutex_lock(&audit_cmd_mutex);
           mutex_unlock(&audit_cmd_mutex);
   
           /* Ignore failure. It'll only happen if the sender goes away,
              because our timeout is set to infinite. */
           netlink_unicast(audit_sock, reply->skb, reply->pid, 0);
           kfree(reply);
           return 0;
   }
   /**
    * audit_send_reply - send an audit reply message via netlink
    * @pid: process id to send reply to
    * @seq: sequence number
    * @type: audit message type
    * @done: done (last) flag
    * @multi: multi-part message flag
    * @payload: payload data
    * @size: payload size
    *
    * Allocates an skb, builds the netlink message, and sends it to the pid.
    * No failure notifications.
    */
   static void audit_send_reply(int pid, int seq, int type, int done, int multi,
                                const void *payload, int size)
   {
           struct sk_buff *skb;
           struct task_struct *tsk;
           struct audit_reply *reply = kmalloc(sizeof(struct audit_reply),
                                               GFP_KERNEL);
   
           if (!reply)
                   return;
   
           skb = audit_make_reply(pid, seq, type, done, multi, payload, size);
           if (!skb)
                   goto out;
   
           reply->pid = pid;
           reply->skb = skb;
   
           tsk = kthread_run(audit_send_reply_thread, reply, "audit_send_reply");
           if (!IS_ERR(tsk))
                   return;
           kfree_skb(skb);
   out:
           kfree(reply);
   }
   
   /*
    * Check for appropriate CAP_AUDIT_ capabilities on incoming audit
    * control messages.
    */
   static int audit_netlink_ok(struct sk_buff *skb, u16 msg_type)
   {
           int err = 0;
   
           /* Only support the initial namespaces for now. */
           if ((current_user_ns() != &init_user_ns) ||
               (task_active_pid_ns(current) != &init_pid_ns))
                   return -EPERM;
   
           switch (msg_type) {
           case AUDIT_GET:
           case AUDIT_LIST:
           case AUDIT_LIST_RULES:
           case AUDIT_SET:
           case AUDIT_ADD:
           case AUDIT_ADD_RULE:
           case AUDIT_DEL:
           case AUDIT_DEL_RULE:
           case AUDIT_SIGNAL_INFO:
           case AUDIT_TTY_GET:
           case AUDIT_TTY_SET:
           case AUDIT_TRIM:
           case AUDIT_MAKE_EQUIV:
                   if (!capable(CAP_AUDIT_CONTROL))
                           err = -EPERM;
                   break;
           case AUDIT_USER:
           case AUDIT_FIRST_USER_MSG ... AUDIT_LAST_USER_MSG:
           case AUDIT_FIRST_USER_MSG2 ... AUDIT_LAST_USER_MSG2:
                   if (!capable(CAP_AUDIT_WRITE))
                           err = -EPERM;
                   break;
           default:  /* bad msg */
                   err = -EINVAL;
           }
   
           return err;
   }
   
   static int audit_log_common_recv_msg(struct audit_buffer **ab, u16 msg_type,
                                        kuid_t auid, u32 ses, u32 sid)
   {
           int rc = 0;
           char *ctx = NULL;
           u32 len;
   
           if (!audit_enabled) {
                   *ab = NULL;
                   return rc;
           }
   
           *ab = audit_log_start(NULL, GFP_KERNEL, msg_type);
           if (unlikely(!*ab))
                   return rc;
           audit_log_format(*ab, "pid=%d uid=%u auid=%u ses=%u",
                            task_tgid_vnr(current),
                            from_kuid(&init_user_ns, current_uid()),
                            from_kuid(&init_user_ns, auid), ses);
           if (sid) {
                   rc = security_secid_to_secctx(sid, &ctx, &len);
                   if (rc)
                           audit_log_format(*ab, " ssid=%u", sid);
                   else {
                           audit_log_format(*ab, " subj=%s", ctx);
                           security_release_secctx(ctx, len);
                   }
           }
   
           return rc;
   }
   
   static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
   {
           u32                     seq, sid;
           void                    *data;
           struct audit_status     *status_get, status_set;
           int                     err;
           struct audit_buffer     *ab;
           u16                     msg_type = nlh->nlmsg_type;
           kuid_t                  loginuid; /* loginuid of sender */
           u32                     sessionid;
           struct audit_sig_info   *sig_data;
           char                    *ctx = NULL;
           u32                     len;
   
           err = audit_netlink_ok(skb, msg_type);
           if (err)
                   return err;
   
           /* As soon as there's any sign of userspace auditd,
            * start kauditd to talk to it */
           if (!kauditd_task)
                   kauditd_task = kthread_run(kauditd_thread, NULL, "kauditd");
           if (IS_ERR(kauditd_task)) {
                   err = PTR_ERR(kauditd_task);
                   kauditd_task = NULL;
                   return err;
           }
   
           loginuid = audit_get_loginuid(current);
           sessionid = audit_get_sessionid(current);
           security_task_getsecid(current, &sid);
           seq  = nlh->nlmsg_seq;
           data = nlmsg_data(nlh);
   
           switch (msg_type) {
           case AUDIT_GET:
                   status_set.enabled       = audit_enabled;
                   status_set.failure       = audit_failure;
                   status_set.pid           = audit_pid;
                   status_set.rate_limit    = audit_rate_limit;
                   status_set.backlog_limit = audit_backlog_limit;
                   status_set.lost          = atomic_read(&audit_lost);
                   status_set.backlog       = skb_queue_len(&audit_skb_queue);
                   audit_send_reply(NETLINK_CB(skb).portid, seq, AUDIT_GET, 0, 0,
                                    &status_set, sizeof(status_set));
                   break;
           case AUDIT_SET:
                   if (nlh->nlmsg_len < sizeof(struct audit_status))
                           return -EINVAL;
                   status_get   = (struct audit_status *)data;
                   if (status_get->mask & AUDIT_STATUS_ENABLED) {
                           err = audit_set_enabled(status_get->enabled,
                                                   loginuid, sessionid, sid);
                           if (err < 0)
                                   return err;
                   }
                   if (status_get->mask & AUDIT_STATUS_FAILURE) {
                           err = audit_set_failure(status_get->failure,
                                                   loginuid, sessionid, sid);
                           if (err < 0)
                                   return err;
                   }
                   if (status_get->mask & AUDIT_STATUS_PID) {
                           int new_pid = status_get->pid;
   
                           if (audit_enabled != AUDIT_OFF)
                                   audit_log_config_change("audit_pid", new_pid,
                                                           audit_pid, loginuid,
                                                           sessionid, sid, 1);
   
                           audit_pid = new_pid;
                           audit_nlk_portid = NETLINK_CB(skb).portid;
                   }
                   if (status_get->mask & AUDIT_STATUS_RATE_LIMIT) {
                           err = audit_set_rate_limit(status_get->rate_limit,
                                                      loginuid, sessionid, sid);
                           if (err < 0)
                                   return err;
                   }
                   if (status_get->mask & AUDIT_STATUS_BACKLOG_LIMIT)
                           err = audit_set_backlog_limit(status_get->backlog_limit,
                                                         loginuid, sessionid, sid);
                   break;
           case AUDIT_USER:
           case AUDIT_FIRST_USER_MSG ... AUDIT_LAST_USER_MSG:
           case AUDIT_FIRST_USER_MSG2 ... AUDIT_LAST_USER_MSG2:
                   if (!audit_enabled && msg_type != AUDIT_USER_AVC)
                           return 0;
   
                   err = audit_filter_user();
                   if (err == 1) {
                           err = 0;
                           if (msg_type == AUDIT_USER_TTY) {
                                   err = tty_audit_push_task(current, loginuid,
                                                                sessionid);
                                   if (err)
                                           break;
                           }
                           audit_log_common_recv_msg(&ab, msg_type,
                                                     loginuid, sessionid, sid);
   
                           if (msg_type != AUDIT_USER_TTY)
                                   audit_log_format(ab, " msg='%.1024s'",
                                                    (char *)data);
                           else {
                                   int size;
   
                                   audit_log_format(ab, " msg=");
                                   size = nlmsg_len(nlh);
                                   if (size > 0 &&
                                       ((unsigned char *)data)[size - 1] == '\0')
                                           size--;
                                   audit_log_n_untrustedstring(ab, data, size);
                           }
                           audit_set_pid(ab, NETLINK_CB(skb).portid);
                           audit_log_end(ab);
                   }
                   break;
           case AUDIT_ADD:
           case AUDIT_DEL:
                   if (nlmsg_len(nlh) < sizeof(struct audit_rule))
                           return -EINVAL;
                   if (audit_enabled == AUDIT_LOCKED) {
                           audit_log_common_recv_msg(&ab, AUDIT_CONFIG_CHANGE,
                                                     loginuid, sessionid, sid);
   
                           audit_log_format(ab, " audit_enabled=%d res=0",
                                            audit_enabled);
                           audit_log_end(ab);
                           return -EPERM;
                   }
                   /* fallthrough */
           case AUDIT_LIST:
                   err = audit_receive_filter(msg_type, NETLINK_CB(skb).portid,
                                              seq, data, nlmsg_len(nlh),
                                              loginuid, sessionid, sid);
                   break;
           case AUDIT_ADD_RULE:
           case AUDIT_DEL_RULE:
                   if (nlmsg_len(nlh) < sizeof(struct audit_rule_data))
                           return -EINVAL;
                   if (audit_enabled == AUDIT_LOCKED) {
                           audit_log_common_recv_msg(&ab, AUDIT_CONFIG_CHANGE,
                                                     loginuid, sessionid, sid);
   
                           audit_log_format(ab, " audit_enabled=%d res=0",
                                            audit_enabled);
                           audit_log_end(ab);
                           return -EPERM;
                   }
                   /* fallthrough */
           case AUDIT_LIST_RULES:
                   err = audit_receive_filter(msg_type, NETLINK_CB(skb).portid,
                                              seq, data, nlmsg_len(nlh),
                                              loginuid, sessionid, sid);
                   break;
           case AUDIT_TRIM:
                   audit_trim_trees();
   
                   audit_log_common_recv_msg(&ab, AUDIT_CONFIG_CHANGE,
                                             loginuid, sessionid, sid);
   
                   audit_log_format(ab, " op=trim res=1");
                   audit_log_end(ab);
                   break;
           case AUDIT_MAKE_EQUIV: {
                   void *bufp = data;
                   u32 sizes[2];
                   size_t msglen = nlmsg_len(nlh);
                   char *old, *new;
   
                   err = -EINVAL;
                   if (msglen < 2 * sizeof(u32))
                           break;
                   memcpy(sizes, bufp, 2 * sizeof(u32));
                   bufp += 2 * sizeof(u32);
                   msglen -= 2 * sizeof(u32);
                   old = audit_unpack_string(&bufp, &msglen, sizes[0]);
                   if (IS_ERR(old)) {
                           err = PTR_ERR(old);
                           break;
                   }
                   new = audit_unpack_string(&bufp, &msglen, sizes[1]);
                   if (IS_ERR(new)) {
                           err = PTR_ERR(new);
                           kfree(old);
                           break;
                   }
                   /* OK, here comes... */
                   err = audit_tag_tree(old, new);
   
                   audit_log_common_recv_msg(&ab, AUDIT_CONFIG_CHANGE,
                                             loginuid, sessionid, sid);
   
                   audit_log_format(ab, " op=make_equiv old=");
                   audit_log_untrustedstring(ab, old);
                   audit_log_format(ab, " new=");
                   audit_log_untrustedstring(ab, new);
                   audit_log_format(ab, " res=%d", !err);
                   audit_log_end(ab);
                   kfree(old);
                   kfree(new);
                   break;
           }
           case AUDIT_SIGNAL_INFO:
                   len = 0;
                   if (audit_sig_sid) {
                           err = security_secid_to_secctx(audit_sig_sid, &ctx, &len);
                           if (err)
                                   return err;
                   }
                   sig_data = kmalloc(sizeof(*sig_data) + len, GFP_KERNEL);
                   if (!sig_data) {
                           if (audit_sig_sid)
                                   security_release_secctx(ctx, len);
                           return -ENOMEM;
                   }
                   sig_data->uid = from_kuid(&init_user_ns, audit_sig_uid);
                   sig_data->pid = audit_sig_pid;
                   if (audit_sig_sid) {
                           memcpy(sig_data->ctx, ctx, len);
                           security_release_secctx(ctx, len);
                   }
                   audit_send_reply(NETLINK_CB(skb).portid, seq, AUDIT_SIGNAL_INFO,
                                   0, 0, sig_data, sizeof(*sig_data) + len);
                   kfree(sig_data);
                   break;
           case AUDIT_TTY_GET: {
                   struct audit_tty_status s;
                   struct task_struct *tsk = current;
   
                   spin_lock_irq(&tsk->sighand->siglock);
                   s.enabled = tsk->signal->audit_tty != 0;
                   spin_unlock_irq(&tsk->sighand->siglock);
   
                   audit_send_reply(NETLINK_CB(skb).portid, seq,
                                    AUDIT_TTY_GET, 0, 0, &s, sizeof(s));
                   break;
           }
           case AUDIT_TTY_SET: {
                   struct audit_tty_status *s;
                   struct task_struct *tsk = current;
   
                   if (nlh->nlmsg_len < sizeof(struct audit_tty_status))
                           return -EINVAL;
                   s = data;
                   if (s->enabled != 0 && s->enabled != 1)
                           return -EINVAL;
   
                   spin_lock_irq(&tsk->sighand->siglock);
                   tsk->signal->audit_tty = s->enabled != 0;
                   spin_unlock_irq(&tsk->sighand->siglock);
                   break;
           }
           default:
                   err = -EINVAL;
                   break;
           }
   
           return err < 0 ? err : 0;
   }
   
   /*
    * Get message from skb.  Each message is processed by audit_receive_msg.
    * Malformed skbs with wrong length are discarded silently.
    */
   static void audit_receive_skb(struct sk_buff *skb)
   {
           struct nlmsghdr *nlh;
           /*
            * len MUST be signed for NLMSG_NEXT to be able to dec it below 0
            * if the nlmsg_len was not aligned
            */
           int len;
           int err;
   
           nlh = nlmsg_hdr(skb);
           len = skb->len;
   
           while (NLMSG_OK(nlh, len)) {
                   err = audit_receive_msg(skb, nlh);
                   /* if err or if this message says it wants a response */
                   if (err || (nlh->nlmsg_flags & NLM_F_ACK))
                           netlink_ack(skb, nlh, err);
   
                   nlh = NLMSG_NEXT(nlh, len);
           }
   }
   
   /* Receive messages from netlink socket. */
   static void audit_receive(struct sk_buff  *skb)
   {
           mutex_lock(&audit_cmd_mutex);
           audit_receive_skb(skb);
           mutex_unlock(&audit_cmd_mutex);
   }
   
   /* Initialize audit support at boot time. */
   static int __init audit_init(void)
   {
           int i;
           struct netlink_kernel_cfg cfg = {
                   .input  = audit_receive,
           };
   
           if (audit_initialized == AUDIT_DISABLED)
                   return 0;
   
           printk(KERN_INFO "audit: initializing netlink socket (%s)\n",
                  audit_default ? "enabled" : "disabled");
           audit_sock = netlink_kernel_create(&init_net, NETLINK_AUDIT, &cfg);
           if (!audit_sock)
                   audit_panic("cannot initialize netlink socket");
           else
                   audit_sock->sk_sndtimeo = MAX_SCHEDULE_TIMEOUT;
   
           skb_queue_head_init(&audit_skb_queue);
           skb_queue_head_init(&audit_skb_hold_queue);
           audit_initialized = AUDIT_INITIALIZED;
           audit_enabled = audit_default;
           audit_ever_enabled |= !!audit_default;
   
           audit_log(NULL, GFP_KERNEL, AUDIT_KERNEL, "initialized");
   
           for (i = 0; i < AUDIT_INODE_BUCKETS; i++)
                   INIT_LIST_HEAD(&audit_inode_hash[i]);
   
           return 0;
   }
   __initcall(audit_init);
   
   /* Process kernel command-line parameter at boot time.  audit=0 or audit=1. */
   static int __init audit_enable(char *str)
   {
           audit_default = !!simple_strtol(str, NULL, 0);
           if (!audit_default)
                   audit_initialized = AUDIT_DISABLED;
   
           printk(KERN_INFO "audit: %s", audit_default ? "enabled" : "disabled");
   
           if (audit_initialized == AUDIT_INITIALIZED) {
                   audit_enabled = audit_default;
                   audit_ever_enabled |= !!audit_default;
           } else if (audit_initialized == AUDIT_UNINITIALIZED) {
                   printk(" (after initialization)");
           } else {
                   printk(" (until reboot)");
           }
           printk("\n");
   
           return 1;
   }
   
   __setup("audit=", audit_enable);
   
   static void audit_buffer_free(struct audit_buffer *ab)
   {
          unsigned long flags;
  
          if (!ab)
                  return;
  
          if (ab->skb)
                  kfree_skb(ab->skb);
  
          spin_lock_irqsave(&audit_freelist_lock, flags);
          if (audit_freelist_count > AUDIT_MAXFREE)
                  kfree(ab);
          else {
                  audit_freelist_count++;
                  list_add(&ab->list, &audit_freelist);
          }
          spin_unlock_irqrestore(&audit_freelist_lock, flags);
  }
  
  static struct audit_buffer * audit_buffer_alloc(struct audit_context *ctx,
                                                  gfp_t gfp_mask, int type)
  {
          unsigned long flags;
          struct audit_buffer *ab = NULL;
          struct nlmsghdr *nlh;
  
          spin_lock_irqsave(&audit_freelist_lock, flags);
          if (!list_empty(&audit_freelist)) {
                  ab = list_entry(audit_freelist.next,
                                  struct audit_buffer, list);
                  list_del(&ab->list);
                  --audit_freelist_count;
          }
          spin_unlock_irqrestore(&audit_freelist_lock, flags);
  
          if (!ab) {
                  ab = kmalloc(sizeof(*ab), gfp_mask);
                  if (!ab)
                          goto err;
          }
  
          ab->ctx = ctx;
          ab->gfp_mask = gfp_mask;
  
          ab->skb = nlmsg_new(AUDIT_BUFSIZ, gfp_mask);
          if (!ab->skb)
                  goto err;
  
          nlh = nlmsg_put(ab->skb, 0, 0, type, 0, 0);
          if (!nlh)
                  goto out_kfree_skb;
  
          return ab;
  
  out_kfree_skb:
          kfree_skb(ab->skb);
          ab->skb = NULL;
  err:
          audit_buffer_free(ab);
          return NULL;
  }
  
  /**
   * audit_serial - compute a serial number for the audit record
   *
   * Compute a serial number for the audit record.  Audit records are
   * written to user-space as soon as they are generated, so a complete
   * audit record may be written in several pieces.  The timestamp of the
   * record and this serial number are used by the user-space tools to
   * determine which pieces belong to the same audit record.  The
   * (timestamp,serial) tuple is unique for each syscall and is live from
   * syscall entry to syscall exit.
   *
   * NOTE: Another possibility is to store the formatted records off the
   * audit context (for those records that have a context), and emit them
   * all at syscall exit.  However, this could delay the reporting of
   * significant errors until syscall exit (or never, if the system
   * halts).
   */
  unsigned int audit_serial(void)
  {
          static DEFINE_SPINLOCK(serial_lock);
          static unsigned int serial = 0;
  
          unsigned long flags;
          unsigned int ret;
  
          spin_lock_irqsave(&serial_lock, flags);
          do {
                  ret = ++serial;
          } while (unlikely(!ret));
          spin_unlock_irqrestore(&serial_lock, flags);
  
          return ret;
  }
  
  static inline void audit_get_stamp(struct audit_context *ctx,
                                     struct timespec *t, unsigned int *serial)
  {
          if (!ctx || !auditsc_get_stamp(ctx, t, serial)) {
                  *t = CURRENT_TIME;
                  *serial = audit_serial();
          }
  }
  
  /*
   * Wait for auditd to drain the queue a little
   */
  static void wait_for_auditd(unsigned long sleep_time)
  {
          DECLARE_WAITQUEUE(wait, current);
          set_current_state(TASK_INTERRUPTIBLE);
          add_wait_queue(&audit_backlog_wait, &wait);
  
          if (audit_backlog_limit &&
              skb_queue_len(&audit_skb_queue) > audit_backlog_limit)
                  schedule_timeout(sleep_time);
  
          __set_current_state(TASK_RUNNING);
          remove_wait_queue(&audit_backlog_wait, &wait);
  }
  
  /* Obtain an audit buffer.  This routine does locking to obtain the
   * audit buffer, but then no locking is required for calls to
   * audit_log_*format.  If the tsk is a task that is currently in a
   * syscall, then the syscall is marked as auditable and an audit record
   * will be written at syscall exit.  If there is no associated task, tsk
   * should be NULL. */
  
  /**
   * audit_log_start - obtain an audit buffer
   * @ctx: audit_context (may be NULL)
   * @gfp_mask: type of allocation
   * @type: audit message type
   *
   * Returns audit_buffer pointer on success or NULL on error.
   *
   * Obtain an audit buffer.  This routine does locking to obtain the
   * audit buffer, but then no locking is required for calls to
   * audit_log_*format.  If the task (ctx) is a task that is currently in a
   * syscall, then the syscall is marked as auditable and an audit record
   * will be written at syscall exit.  If there is no associated task, then
   * task context (ctx) should be NULL.
   */
  struct audit_buffer *audit_log_start(struct audit_context *ctx, gfp_t gfp_mask,
                                       int type)
  {
          struct audit_buffer     *ab     = NULL;
          struct timespec         t;
          unsigned int            uninitialized_var(serial);
          int reserve;
          unsigned long timeout_start = jiffies;
  
          if (audit_initialized != AUDIT_INITIALIZED)
                  return NULL;
  
          if (unlikely(audit_filter_type(type)))
                  return NULL;
  
          if (gfp_mask & __GFP_WAIT)
                  reserve = 0;
          else
                  reserve = 5; /* Allow atomic callers to go up to five
                                  entries over the normal backlog limit */
  
          while (audit_backlog_limit
                 && skb_queue_len(&audit_skb_queue) > audit_backlog_limit + reserve) {
                  if (gfp_mask & __GFP_WAIT && audit_backlog_wait_time) {
                          unsigned long sleep_time;
  
                          sleep_time = timeout_start + audit_backlog_wait_time -
                                          jiffies;
                          if ((long)sleep_time > 0)
                                  wait_for_auditd(sleep_time);
                          continue;
                  }
                  if (audit_rate_check() && printk_ratelimit())
                          printk(KERN_WARNING
                                 "audit: audit_backlog=%d > "
                                 "audit_backlog_limit=%d\n",
                                 skb_queue_len(&audit_skb_queue),
                                 audit_backlog_limit);
                  audit_log_lost("backlog limit exceeded");
                  audit_backlog_wait_time = audit_backlog_wait_overflow;
                  wake_up(&audit_backlog_wait);
                  return NULL;
          }
  
          ab = audit_buffer_alloc(ctx, gfp_mask, type);
          if (!ab) {
                  audit_log_lost("out of memory in audit_log_start");
                  return NULL;
          }
  
          audit_get_stamp(ab->ctx, &t, &serial);
  
          audit_log_format(ab, "audit(%lu.%03lu:%u): ",
                           t.tv_sec, t.tv_nsec/1000000, serial);
          return ab;
  }
  
  /**
   * audit_expand - expand skb in the audit buffer
   * @ab: audit_buffer
   * @extra: space to add at tail of the skb
   *
   * Returns 0 (no space) on failed expansion, or available space if
   * successful.
   */
  static inline int audit_expand(struct audit_buffer *ab, int extra)
  {
          struct sk_buff *skb = ab->skb;
          int oldtail = skb_tailroom(skb);
          int ret = pskb_expand_head(skb, 0, extra, ab->gfp_mask);
          int newtail = skb_tailroom(skb);
  
          if (ret < 0) {
                  audit_log_lost("out of memory in audit_expand");
                  return 0;
          }
  
          skb->truesize += newtail - oldtail;
          return newtail;
  }
  
  /*
   * Format an audit message into the audit buffer.  If there isn't enough
   * room in the audit buffer, more room will be allocated and vsnprint
   * will be called a second time.  Currently, we assume that a printk
   * can't format message larger than 1024 bytes, so we don't either.
   */
  static void audit_log_vformat(struct audit_buffer *ab, const char *fmt,
                                va_list args)
  {
          int len, avail;
          struct sk_buff *skb;
          va_list args2;
  
          if (!ab)
                  return;
  
          BUG_ON(!ab->skb);
          skb = ab->skb;
          avail = skb_tailroom(skb);
          if (avail == 0) {
                  avail = audit_expand(ab, AUDIT_BUFSIZ);
                  if (!avail)
                          goto out;
          }
          va_copy(args2, args);
          len = vsnprintf(skb_tail_pointer(skb), avail, fmt, args);
          if (len >= avail) {
                  /* The printk buffer is 1024 bytes long, so if we get
                   * here and AUDIT_BUFSIZ is at least 1024, then we can
                   * log everything that printk could have logged. */
                  avail = audit_expand(ab,
                          max_t(unsigned, AUDIT_BUFSIZ, 1+len-avail));
                  if (!avail)
                          goto out_va_end;
                  len = vsnprintf(skb_tail_pointer(skb), avail, fmt, args2);
          }
          if (len > 0)
                  skb_put(skb, len);
  out_va_end:
          va_end(args2);
  out:
          return;
  }
  
  /**
   * audit_log_format - format a message into the audit buffer.
   * @ab: audit_buffer
   * @fmt: format string
   * @...: optional parameters matching @fmt string
   *
   * All the work is done in audit_log_vformat.
   */
  void audit_log_format(struct audit_buffer *ab, const char *fmt, ...)
  {
          va_list args;
  
          if (!ab)
                  return;
          va_start(args, fmt);
          audit_log_vformat(ab, fmt, args);
          va_end(args);
  }
  
  /**
   * audit_log_hex - convert a buffer to hex and append it to the audit skb
   * @ab: the audit_buffer
   * @buf: buffer to convert to hex
   * @len: length of @buf to be converted
   *
   * No return value; failure to expand is silently ignored.
   *
   * This function will take the passed buf and convert it into a string of
   * ascii hex digits. The new string is placed onto the skb.
   */
  void audit_log_n_hex(struct audit_buffer *ab, const unsigned char *buf,
                  size_t len)
  {
          int i, avail, new_len;
          unsigned char *ptr;
          struct sk_buff *skb;
          static const unsigned char *hex = "0123456789ABCDEF";
  
          if (!ab)
                  return;
  
          BUG_ON(!ab->skb);
          skb = ab->skb;
          avail = skb_tailroom(skb);
          new_len = len<<1;
          if (new_len >= avail) {
                  /* Round the buffer request up to the next multiple */
                  new_len = AUDIT_BUFSIZ*(((new_len-avail)/AUDIT_BUFSIZ) + 1);
                  avail = audit_expand(ab, new_len);
                  if (!avail)
                          return;
          }
  
          ptr = skb_tail_pointer(skb);
          for (i=0; i<len; i++) {
                  *ptr++ = hex[(buf[i] & 0xF0)>>4]; /* Upper nibble */
                  *ptr++ = hex[buf[i] & 0x0F];      /* Lower nibble */
          }
          *ptr = 0;
          skb_put(skb, len << 1); /* new string is twice the old string */
  }
  
  /*
   * Format a string of no more than slen characters into the audit buffer,
   * enclosed in quote marks.
   */
  void audit_log_n_string(struct audit_buffer *ab, const char *string,
                          size_t slen)
  {
          int avail, new_len;
          unsigned char *ptr;
          struct sk_buff *skb;
  
          if (!ab)
                  return;
  
          BUG_ON(!ab->skb);
          skb = ab->skb;
          avail = skb_tailroom(skb);
          new_len = slen + 3;     /* enclosing quotes + null terminator */
          if (new_len > avail) {
                  avail = audit_expand(ab, new_len);
                  if (!avail)
                          return;
          }
          ptr = skb_tail_pointer(skb);
          *ptr++ = '"';
          memcpy(ptr, string, slen);
          ptr += slen;
          *ptr++ = '"';
          *ptr = 0;
          skb_put(skb, slen + 2); /* don't include null terminator */
  }
  
  /**
   * audit_string_contains_control - does a string need to be logged in hex
   * @string: string to be checked
   * @len: max length of the string to check
   */
  int audit_string_contains_control(const char *string, size_t len)
  {
          const unsigned char *p;
          for (p = string; p < (const unsigned char *)string + len; p++) {
                  if (*p == '"' || *p < 0x21 || *p > 0x7e)
                          return 1;
          }
          return 0;
  }
  
  /**
   * audit_log_n_untrustedstring - log a string that may contain random characters
   * @ab: audit_buffer
   * @len: length of string (not including trailing null)
   * @string: string to be logged
   *
   * This code will escape a string that is passed to it if the string
   * contains a control character, unprintable character, double quote mark,
   * or a space. Unescaped strings will start and end with a double quote mark.
   * Strings that are escaped are printed in hex (2 digits per char).
   *
   * The caller specifies the number of characters in the string to log, which may
   * or may not be the entire string.
   */
  void audit_log_n_untrustedstring(struct audit_buffer *ab, const char *string,
                                   size_t len)
  {
          if (audit_string_contains_control(string, len))
                  audit_log_n_hex(ab, string, len);
          else
                  audit_log_n_string(ab, string, len);
  }
  
  /**
   * audit_log_untrustedstring - log a string that may contain random characters
   * @ab: audit_buffer
   * @string: string to be logged
   *
   * Same as audit_log_n_untrustedstring(), except that strlen is used to
   * determine string length.
   */
  void audit_log_untrustedstring(struct audit_buffer *ab, const char *string)
  {
          audit_log_n_untrustedstring(ab, string, strlen(string));
  }
  
  /* This is a helper-function to print the escaped d_path */
  void audit_log_d_path(struct audit_buffer *ab, const char *prefix,
                        const struct path *path)
  {
          char *p, *pathname;
  
          if (prefix)
                  audit_log_format(ab, "%s", prefix);
  
          /* We will allow 11 spaces for ' (deleted)' to be appended */
          pathname = kmalloc(PATH_MAX+11, ab->gfp_mask);
          if (!pathname) {
                  audit_log_string(ab, "<no_memory>");
                  return;
          }
          p = d_path(path, pathname, PATH_MAX+11);
          if (IS_ERR(p)) { /* Should never happen since we send PATH_MAX */
                  /* FIXME: can we save some information here? */
                  audit_log_string(ab, "<too_long>");
          } else
                  audit_log_untrustedstring(ab, p);
          kfree(pathname);
  }
  
  void audit_log_key(struct audit_buffer *ab, char *key)
  {
          audit_log_format(ab, " key=");
          if (key)
                  audit_log_untrustedstring(ab, key);
          else
                  audit_log_format(ab, "(null)");
  }
  
  /**
   * audit_log_link_denied - report a link restriction denial
   * @operation: specific link opreation
   * @link: the path that triggered the restriction
   */
  void audit_log_link_denied(const char *operation, struct path *link)
  {
          struct audit_buffer *ab;
  
          ab = audit_log_start(current->audit_context, GFP_KERNEL,
                               AUDIT_ANOM_LINK);
          if (!ab)
                  return;
          audit_log_format(ab, "op=%s action=denied", operation);
          audit_log_format(ab, " pid=%d comm=", current->pid);
          audit_log_untrustedstring(ab, current->comm);
          audit_log_d_path(ab, " path=", link);
          audit_log_format(ab, " dev=");
          audit_log_untrustedstring(ab, link->dentry->d_inode->i_sb->s_id);
          audit_log_format(ab, " ino=%lu", link->dentry->d_inode->i_ino);
          audit_log_end(ab);
  }
  
  /**
   * audit_log_end - end one audit record
   * @ab: the audit_buffer
   *
   * The netlink_* functions cannot be called inside an irq context, so
   * the audit buffer is placed on a queue and a tasklet is scheduled to
   * remove them from the queue outside the irq context.  May be called in
   * any context.
   */
  void audit_log_end(struct audit_buffer *ab)
  {
          if (!ab)
                  return;
          if (!audit_rate_check()) {
                  audit_log_lost("rate limit exceeded");
          } else {
                  struct nlmsghdr *nlh = nlmsg_hdr(ab->skb);
                  nlh->nlmsg_len = ab->skb->len - NLMSG_SPACE(0);
  
                  if (audit_pid) {
                          skb_queue_tail(&audit_skb_queue, ab->skb);
                          wake_up_interruptible(&kauditd_wait);
                  } else {
                          audit_printk_skb(ab->skb);
                  }
                  ab->skb = NULL;
          }
          audit_buffer_free(ab);
  }
  
  /**
   * audit_log - Log an audit record
   * @ctx: audit context
   * @gfp_mask: type of allocation
   * @type: audit message type
   * @fmt: format string to use
   * @...: variable parameters matching the format string
   *
   * This is a convenience function that calls audit_log_start,
   * audit_log_vformat, and audit_log_end.  It may be called
   * in any context.
   */
  void audit_log(struct audit_context *ctx, gfp_t gfp_mask, int type,
                 const char *fmt, ...)
  {
          struct audit_buffer *ab;
          va_list args;
  
          ab = audit_log_start(ctx, gfp_mask, type);
          if (ab) {
                  va_start(args, fmt);
                  audit_log_vformat(ab, fmt, args);
                  va_end(args);
                  audit_log_end(ab);
          }
  }
  
  #ifdef CONFIG_SECURITY
  /**
   * audit_log_secctx - Converts and logs SELinux context
   * @ab: audit_buffer
   * @secid: security number
   *
   * This is a helper function that calls security_secid_to_secctx to convert
   * secid to secctx and then adds the (converted) SELinux context to the audit
   * log by calling audit_log_format, thus also preventing leak of internal secid
   * to userspace. If secid cannot be converted audit_panic is called.
   */
  void audit_log_secctx(struct audit_buffer *ab, u32 secid)
  {
          u32 len;
          char *secctx;
  
          if (security_secid_to_secctx(secid, &secctx, &len)) {
                  audit_panic("Cannot convert secid to context");
          } else {
                  audit_log_format(ab, " obj=%s", secctx);
                  security_release_secctx(secctx, len);
          }
  }
  EXPORT_SYMBOL(audit_log_secctx);
  #endif
  
  EXPORT_SYMBOL(audit_log_start);
  EXPORT_SYMBOL(audit_log_end);
  EXPORT_SYMBOL(audit_log_format);
  EXPORT_SYMBOL(audit_log);

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