[AUDIT] Requeue messages at head of queue, up to audit_backlog

[safe/jmp/linux-2.6] / 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 2003-2004 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 SELinux.
 *        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/atomic.h>
#include <asm/types.h>
#include <linux/mm.h>
#include <linux/module.h>

#include <linux/audit.h>

#include <net/sock.h>
#include <linux/skbuff.h>
#include <linux/netlink.h>

/* No auditing will take place until audit_initialized != 0.
 * (Initialization happens after skb_init is called.) */
static int      audit_initialized;

/* No syscall auditing will take place unless audit_enabled != 0. */
int             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 (non-zero) pid. */
static int      audit_pid;

/* If audit_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 atomic_t audit_backlog       = ATOMIC_INIT(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;

/* There are two lists of audit buffers.  The txlist contains audit
 * buffers that cannot be sent immediately to the netlink device because
 * we are in an irq context (these are sent later in a tasklet).
 *
 * The second list 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_txlist_lock);
static DEFINE_SPINLOCK(audit_freelist_lock);
static int         audit_freelist_count = 0;
static LIST_HEAD(audit_txlist);
static LIST_HEAD(audit_freelist);

/* There are three lists of rules -- one to search at task creation
 * time, one to search at syscall entry time, and another to search at
 * syscall exit time. */
static LIST_HEAD(audit_tsklist);
static LIST_HEAD(audit_entlist);
static LIST_HEAD(audit_extlist);

/* The netlink socket is only to be read by 1 CPU, which lets us assume
 * that list additions and deletions never happen simultaneiously in
 * auditsc.c */
static DECLARE_MUTEX(audit_netlink_sem);

/* 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_head  sklist;    /* formatted skbs ready to send */
        struct audit_context *ctx;      /* NULL or associated context */
        int                  len;       /* used area of tmp */
        char                 tmp[AUDIT_BUFSIZ];

                                /* Pointer to header and contents */
        struct nlmsghdr      *nlh;
        int                  total;
        int                  type;
        int                  pid;
};

void audit_set_type(struct audit_buffer *ab, int type)
{
        ab->type = type;
}

struct audit_entry {
        struct list_head  list;
        struct audit_rule rule;
};

static void audit_log_end_irq(struct audit_buffer *ab);
static void audit_log_end_fast(struct audit_buffer *ab);

static void audit_panic(const char *message)
{
        switch (audit_failure)
        {
        case AUDIT_FAIL_SILENT:
                break;
        case AUDIT_FAIL_PRINTK:
                printk(KERN_ERR "audit: %s\n", message);
                break;
        case AUDIT_FAIL_PANIC:
                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;
}

/* Emit at least 1 message per second, even if audit_rate_check is
 * throttling. */
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) {
                printk(KERN_WARNING
                       "audit: audit_lost=%d audit_backlog=%d"
                       " audit_rate_limit=%d audit_backlog_limit=%d\n",
                       atomic_read(&audit_lost),
                       atomic_read(&audit_backlog),
                       audit_rate_limit,
                       audit_backlog_limit);
                audit_panic(message);
        }

}

static int audit_set_rate_limit(int limit, uid_t loginuid)
{
        int old          = audit_rate_limit;
        audit_rate_limit = limit;
        audit_log(NULL, "audit_rate_limit=%d old=%d by auid %u",
                        audit_rate_limit, old, loginuid);
        return old;
}

static int audit_set_backlog_limit(int limit, uid_t loginuid)
{
        int old          = audit_backlog_limit;
        audit_backlog_limit = limit;
        audit_log(NULL, "audit_backlog_limit=%d old=%d by auid %u",
                        audit_backlog_limit, old, loginuid);
        return old;
}

static int audit_set_enabled(int state, uid_t loginuid)
{
        int old          = audit_enabled;
        if (state != 0 && state != 1)
                return -EINVAL;
        audit_enabled = state;
        audit_log(NULL, "audit_enabled=%d old=%d by auid %u",
                  audit_enabled, old, loginuid);
        return old;
}

static int audit_set_failure(int state, uid_t loginuid)
{
        int old          = audit_failure;
        if (state != AUDIT_FAIL_SILENT
            && state != AUDIT_FAIL_PRINTK
            && state != AUDIT_FAIL_PANIC)
                return -EINVAL;
        audit_failure = state;
        audit_log(NULL, "audit_failure=%d old=%d by auid %u",
                  audit_failure, old, loginuid);
        return old;
}

#ifdef CONFIG_NET
void audit_send_reply(int pid, int seq, int type, int done, int multi,
                      void *payload, int size)
{
        struct sk_buff  *skb;
        struct nlmsghdr *nlh;
        int             len = NLMSG_SPACE(size);
        void            *data;
        int             flags = multi ? NLM_F_MULTI : 0;
        int             t     = done  ? NLMSG_DONE  : type;

        skb = alloc_skb(len, GFP_KERNEL);
        if (!skb)
                goto nlmsg_failure;

        nlh              = NLMSG_PUT(skb, pid, seq, t, len - sizeof(*nlh));
        nlh->nlmsg_flags = flags;
        data             = NLMSG_DATA(nlh);
        memcpy(data, payload, size);
        netlink_unicast(audit_sock, skb, pid, MSG_DONTWAIT);
        return;

nlmsg_failure:                  /* Used by NLMSG_PUT */
        if (skb)
                kfree_skb(skb);
}

/*
 * Check for appropriate CAP_AUDIT_ capabilities on incoming audit
 * control messages.
 */
static int audit_netlink_ok(kernel_cap_t eff_cap, u16 msg_type)
{
        int err = 0;

        switch (msg_type) {
        case AUDIT_GET:
        case AUDIT_LIST:
        case AUDIT_SET:
        case AUDIT_ADD:
        case AUDIT_DEL:
                if (!cap_raised(eff_cap, CAP_AUDIT_CONTROL))
                        err = -EPERM;
                break;
        case AUDIT_USER:
                if (!cap_raised(eff_cap, CAP_AUDIT_WRITE))
                        err = -EPERM;
                break;
        default:  /* bad msg */
                err = -EINVAL;
        }

        return err;
}

static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
{
        u32                     uid, pid, seq;
        void                    *data;
        struct audit_status     *status_get, status_set;
        int                     err;
        struct audit_buffer     *ab;
        u16                     msg_type = nlh->nlmsg_type;
        uid_t                   loginuid; /* loginuid of sender */

        err = audit_netlink_ok(NETLINK_CB(skb).eff_cap, msg_type);
        if (err)
                return err;

        pid  = NETLINK_CREDS(skb)->pid;
        uid  = NETLINK_CREDS(skb)->uid;
        loginuid = NETLINK_CB(skb).loginuid;
        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       = atomic_read(&audit_backlog);
                audit_send_reply(NETLINK_CB(skb).pid, 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);
                        if (err < 0) return err;
                }
                if (status_get->mask & AUDIT_STATUS_FAILURE) {
                        err = audit_set_failure(status_get->failure, loginuid);
                        if (err < 0) return err;
                }
                if (status_get->mask & AUDIT_STATUS_PID) {
                        int old   = audit_pid;
                        audit_pid = status_get->pid;
                        audit_log(NULL, "audit_pid=%d old=%d by auid %u",
                                  audit_pid, old, loginuid);
                }
                if (status_get->mask & AUDIT_STATUS_RATE_LIMIT)
                        audit_set_rate_limit(status_get->rate_limit, loginuid);
                if (status_get->mask & AUDIT_STATUS_BACKLOG_LIMIT)
                        audit_set_backlog_limit(status_get->backlog_limit,
                                                        loginuid);
                break;
        case AUDIT_USER:
                ab = audit_log_start(NULL);
                if (!ab)
                        break;  /* audit_panic has been called */
                audit_log_format(ab,
                                 "user pid=%d uid=%d length=%d loginuid=%u"
                                 " msg='%.1024s'",
                                 pid, uid,
                                 (int)(nlh->nlmsg_len
                                       - ((char *)data - (char *)nlh)),
                                 loginuid, (char *)data);
                ab->type = AUDIT_USER;
                ab->pid  = pid;
                audit_log_end(ab);
                break;
        case AUDIT_ADD:
        case AUDIT_DEL:
                if (nlh->nlmsg_len < sizeof(struct audit_rule))
                        return -EINVAL;
                /* fallthrough */
        case AUDIT_LIST:
#ifdef CONFIG_AUDITSYSCALL
                err = audit_receive_filter(nlh->nlmsg_type, NETLINK_CB(skb).pid,
                                           uid, seq, data, loginuid);
#else
                err = -EOPNOTSUPP;
#endif
                break;
        default:
                err = -EINVAL;
                break;
        }

        return err < 0 ? err : 0;
}

/* Get message from skb (based on rtnetlink_rcv_skb).  Each message is
 * processed by audit_receive_msg.  Malformed skbs with wrong length are
 * discarded silently.  */
static int audit_receive_skb(struct sk_buff *skb)
{
        int             err;
        struct nlmsghdr *nlh;
        u32             rlen;

        while (skb->len >= NLMSG_SPACE(0)) {
                nlh = (struct nlmsghdr *)skb->data;
                if (nlh->nlmsg_len < sizeof(*nlh) || skb->len < nlh->nlmsg_len)
                        return 0;
                rlen = NLMSG_ALIGN(nlh->nlmsg_len);
                if (rlen > skb->len)
                        rlen = skb->len;
                if ((err = audit_receive_msg(skb, nlh))) {
                        netlink_ack(skb, nlh, err);
                } else if (nlh->nlmsg_flags & NLM_F_ACK)
                        netlink_ack(skb, nlh, 0);
                skb_pull(skb, rlen);
        }
        return 0;
}

/* Receive messages from netlink socket. */
static void audit_receive(struct sock *sk, int length)
{
        struct sk_buff  *skb;

        if (down_trylock(&audit_netlink_sem))
                return;

                                /* FIXME: this must not cause starvation */
        while ((skb = skb_dequeue(&sk->sk_receive_queue))) {
                if (audit_receive_skb(skb) && skb->len)
                        skb_queue_head(&sk->sk_receive_queue, skb);
                else
                        kfree_skb(skb);
        }
        up(&audit_netlink_sem);
}

/* Move data from tmp buffer into an skb.  This is an extra copy, and
 * that is unfortunate.  However, the copy will only occur when a record
 * is being written to user space, which is already a high-overhead
 * operation.  (Elimination of the copy is possible, for example, by
 * writing directly into a pre-allocated skb, at the cost of wasting
 * memory. */
static void audit_log_move(struct audit_buffer *ab)
{
        struct sk_buff  *skb;
        char            *start;
        int             extra = ab->nlh ? 0 : NLMSG_SPACE(0);

        /* possible resubmission */
        if (ab->len == 0)
                return;

        skb = skb_peek(&ab->sklist);
        if (!skb || skb_tailroom(skb) <= ab->len + extra) {
                skb = alloc_skb(2 * ab->len + extra, GFP_ATOMIC);
                if (!skb) {
                        ab->len = 0; /* Lose information in ab->tmp */
                        audit_log_lost("out of memory in audit_log_move");
                        return;
                }
                __skb_queue_tail(&ab->sklist, skb);
                if (!ab->nlh)
                        ab->nlh = (struct nlmsghdr *)skb_put(skb,
                                                             NLMSG_SPACE(0));
        }
        start = skb_put(skb, ab->len);
        memcpy(start, ab->tmp, ab->len);
        ab->len = 0;
}

/* Iterate over the skbuff in the audit_buffer, sending their contents
 * to user space. */
static inline int audit_log_drain(struct audit_buffer *ab)
{
        struct sk_buff *skb;

        while ((skb = skb_dequeue(&ab->sklist))) {
                int retval = 0;

                if (audit_pid) {
                        if (ab->nlh) {
                                ab->nlh->nlmsg_len   = ab->total;
                                ab->nlh->nlmsg_type  = ab->type;
                                ab->nlh->nlmsg_flags = 0;
                                ab->nlh->nlmsg_seq   = 0;
                                ab->nlh->nlmsg_pid   = ab->pid;
                        }
                        skb_get(skb); /* because netlink_* frees */
                        retval = netlink_unicast(audit_sock, skb, audit_pid,
                                                 MSG_DONTWAIT);
                }
                if (retval == -EAGAIN &&
                    (atomic_read(&audit_backlog)) < audit_backlog_limit) {
                        skb_queue_head(&ab->sklist, skb);
                        audit_log_end_irq(ab);
                        return 1;
                }
                if (retval < 0) {
                        if (retval == -ECONNREFUSED) {
                                printk(KERN_ERR
                                       "audit: *NO* daemon at audit_pid=%d\n",
                                       audit_pid);
                                audit_pid = 0;
                        } else
                                audit_log_lost("netlink socket too busy");
                }
                if (!audit_pid) { /* No daemon */
                        int offset = ab->nlh ? NLMSG_SPACE(0) : 0;
                        int len    = skb->len - offset;
                        skb->data[offset + len] = '\0';
                        printk(KERN_ERR "%s\n", skb->data + offset);
                }
                kfree_skb(skb);
                ab->nlh = NULL;
        }
        return 0;
}

/* Initialize audit support at boot time. */
static int __init audit_init(void)
{
        printk(KERN_INFO "audit: initializing netlink socket (%s)\n",
               audit_default ? "enabled" : "disabled");
        audit_sock = netlink_kernel_create(NETLINK_AUDIT, audit_receive);
        if (!audit_sock)
                audit_panic("cannot initialize netlink socket");

        audit_initialized = 1;
        audit_enabled = audit_default;
        audit_log(NULL, "initialized");
        return 0;
}

#else
/* Without CONFIG_NET, we have no skbuffs.  For now, print what we have
 * in the buffer. */
static void audit_log_move(struct audit_buffer *ab)
{
        printk(KERN_ERR "%*.*s\n", ab->len, ab->len, ab->tmp);
        ab->len = 0;
}

static inline int audit_log_drain(struct audit_buffer *ab)
{
        return 0;
}

/* Initialize audit support at boot time. */
int __init audit_init(void)
{
        printk(KERN_INFO "audit: initializing WITHOUT netlink support\n");
        audit_sock = NULL;
        audit_pid  = 0;

        audit_initialized = 1;
        audit_enabled = audit_default;
        audit_log(NULL, "initialized");
        return 0;
}
#endif

__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);
        printk(KERN_INFO "audit: %s%s\n",
               audit_default ? "enabled" : "disabled",
               audit_initialized ? "" : " (after initialization)");
        if (audit_initialized)
                audit_enabled = audit_default;
        return 0;
}

__setup("audit=", audit_enable);


/* 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. */
struct audit_buffer *audit_log_start(struct audit_context *ctx)
{
        struct audit_buffer     *ab     = NULL;
        unsigned long           flags;
        struct timespec         t;
        unsigned int            serial;

        if (!audit_initialized)
                return NULL;

        if (audit_backlog_limit
            && atomic_read(&audit_backlog) > audit_backlog_limit) {
                if (audit_rate_check())
                        printk(KERN_WARNING
                               "audit: audit_backlog=%d > "
                               "audit_backlog_limit=%d\n",
                               atomic_read(&audit_backlog),
                               audit_backlog_limit);
                audit_log_lost("backlog limit exceeded");
                return NULL;
        }

        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_ATOMIC);
        if (!ab) {
                audit_log_lost("out of memory in audit_log_start");
                return NULL;
        }

        atomic_inc(&audit_backlog);
        skb_queue_head_init(&ab->sklist);

        ab->ctx   = ctx;
        ab->len   = 0;
        ab->nlh   = NULL;
        ab->total = 0;
        ab->type  = AUDIT_KERNEL;
        ab->pid   = 0;

#ifdef CONFIG_AUDITSYSCALL
        if (ab->ctx)
                audit_get_stamp(ab->ctx, &t, &serial);
        else
#endif
        {
                t = CURRENT_TIME;
                serial = 0;
        }
        audit_log_format(ab, "audit(%lu.%03lu:%u): ",
                         t.tv_sec, t.tv_nsec/1000000, serial);
        return ab;
}


/* 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;

        if (!ab)
                return;

        avail = sizeof(ab->tmp) - ab->len;
        if (avail <= 0) {
                audit_log_move(ab);
                avail = sizeof(ab->tmp) - ab->len;
        }
        len   = vsnprintf(ab->tmp + ab->len, 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. */
                audit_log_move(ab);
                avail = sizeof(ab->tmp) - ab->len;
                len   = vsnprintf(ab->tmp + ab->len, avail, fmt, args);
        }
        ab->len   += (len < avail) ? len : avail;
        ab->total += (len < avail) ? len : avail;
}

/* Format a message into the audit buffer.  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);
}

void audit_log_hex(struct audit_buffer *ab, const unsigned char *buf, size_t len)
{
        int i;

        for (i=0; i<len; i++)
                audit_log_format(ab, "%02x", buf[i]);
}

void audit_log_untrustedstring(struct audit_buffer *ab, const char *string)
{
        const unsigned char *p = string;

        while (*p) {
                if (*p == '"' || *p == ' ' || *p < 0x20 || *p > 0x7f) {
                        audit_log_hex(ab, string, strlen(string));
                        return;
                }
                p++;
        }
        audit_log_format(ab, "\"%s\"", string);
}


/* This is a helper-function to print the d_path without using a static
 * buffer or allocating another buffer in addition to the one in
 * audit_buffer. */
void audit_log_d_path(struct audit_buffer *ab, const char *prefix,
                      struct dentry *dentry, struct vfsmount *vfsmnt)
{
        char *p;
        int  len, avail;

        if (prefix) audit_log_format(ab, " %s", prefix);

        if (ab->len > 128)
                audit_log_move(ab);
        avail = sizeof(ab->tmp) - ab->len;
        p = d_path(dentry, vfsmnt, ab->tmp + ab->len, avail);
        if (IS_ERR(p)) {
                /* FIXME: can we save some information here? */
                audit_log_format(ab, "<toolong>");
        } else {
                                /* path isn't at start of buffer */
                len        = (ab->tmp + sizeof(ab->tmp) - 1) - p;
                memmove(ab->tmp + ab->len, p, len);
                ab->len   += len;
                ab->total += len;
        }
}

/* Remove queued messages from the audit_txlist and send them to userspace. */
static void audit_tasklet_handler(unsigned long arg)
{
        LIST_HEAD(list);
        struct audit_buffer *ab;
        unsigned long       flags;

        spin_lock_irqsave(&audit_txlist_lock, flags);
        list_splice_init(&audit_txlist, &list);
        spin_unlock_irqrestore(&audit_txlist_lock, flags);

        while (!list_empty(&list)) {
                ab = list_entry(list.next, struct audit_buffer, list);
                list_del(&ab->list);
                audit_log_end_fast(ab);
        }
}

static DECLARE_TASKLET(audit_tasklet, audit_tasklet_handler, 0);

/* The netlink_* functions cannot be called inside an irq context, so
 * the audit buffer is places on a queue and a tasklet is scheduled to
 * remove them from the queue outside the irq context.  May be called in
 * any context. */
static void audit_log_end_irq(struct audit_buffer *ab)
{
        unsigned long flags;

        if (!ab)
                return;
        spin_lock_irqsave(&audit_txlist_lock, flags);
        list_add_tail(&ab->list, &audit_txlist);
        spin_unlock_irqrestore(&audit_txlist_lock, flags);

        tasklet_schedule(&audit_tasklet);
}

/* Send the message in the audit buffer directly to user space.  May not
 * be called in an irq context. */
static void audit_log_end_fast(struct audit_buffer *ab)
{
        unsigned long flags;

        BUG_ON(in_irq());
        if (!ab)
                return;
        if (!audit_rate_check()) {
                audit_log_lost("rate limit exceeded");
        } else {
                audit_log_move(ab);
                if (audit_log_drain(ab))
                        return;
        }

        atomic_dec(&audit_backlog);
        spin_lock_irqsave(&audit_freelist_lock, flags);
        if (++audit_freelist_count > AUDIT_MAXFREE)
                kfree(ab);
        else
                list_add(&ab->list, &audit_freelist);
        spin_unlock_irqrestore(&audit_freelist_lock, flags);
}

/* Send or queue the message in the audit buffer, depending on the
 * current context.  (A convenience function that may be called in any
 * context.) */
void audit_log_end(struct audit_buffer *ab)
{
        if (in_irq())
                audit_log_end_irq(ab);
        else
                audit_log_end_fast(ab);
}

/* Log an audit record.  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, const char *fmt, ...)
{
        struct audit_buffer *ab;
        va_list args;

        ab = audit_log_start(ctx);
        if (ab) {
                va_start(args, fmt);
                audit_log_vformat(ab, fmt, args);
                va_end(args);
                audit_log_end(ab);
        }
}