[PATCH] Reworked patch for labels on user space messages

[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/types.h>
#include <asm/atomic.h>
#include <linux/mm.h>
#include <linux/module.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>
#include <linux/netlink.h>
#include <linux/selinux.h>

#include "audit.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. */
int             audit_pid;

/* 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. */
uid_t           audit_sig_uid = -1;
pid_t           audit_sig_pid = -1;

/* 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;

/* 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;
static struct task_struct *kauditd_task;
static DECLARE_WAIT_QUEUE_HEAD(kauditd_wait);
static DECLARE_WAIT_QUEUE_HEAD(audit_backlog_wait);

/* The netlink socket is only to be read by 1 CPU, which lets us assume
 * that list additions and deletions never happen simultaneously in
 * auditsc.c */
DEFINE_MUTEX(audit_netlink_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;
};

static void audit_set_pid(struct audit_buffer *ab, pid_t pid)
{
        struct nlmsghdr *nlh = (struct nlmsghdr *)ab->skb->data;
        nlh->nlmsg_pid = pid;
}

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;
}

/**
 * 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) {
                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_set_rate_limit(int limit, uid_t loginuid)
{
        int old          = audit_rate_limit;
        audit_rate_limit = limit;
        audit_log(NULL, GFP_KERNEL, AUDIT_CONFIG_CHANGE, 
                        "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, GFP_KERNEL, AUDIT_CONFIG_CHANGE,
                        "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, GFP_KERNEL, AUDIT_CONFIG_CHANGE,
                        "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, GFP_KERNEL, AUDIT_CONFIG_CHANGE,
                        "audit_failure=%d old=%d by auid=%u",
                        audit_failure, old, loginuid);
        return old;
}

static int kauditd_thread(void *dummy)
{
        struct sk_buff *skb;

        while (1) {
                skb = skb_dequeue(&audit_skb_queue);
                wake_up(&audit_backlog_wait);
                if (skb) {
                        if (audit_pid) {
                                int err = netlink_unicast(audit_sock, skb, audit_pid, 0);
                                if (err < 0) {
                                        BUG_ON(err != -ECONNREFUSED); /* Shoudn't happen */
                                        printk(KERN_ERR "audit: *NO* daemon at audit_pid=%d\n", audit_pid);
                                        audit_pid = 0;
                                }
                        } else {
                                printk(KERN_NOTICE "%s\n", skb->data + NLMSG_SPACE(0));
                                kfree_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;
}

/**
 * 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.
 */
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)
                return;

        nlh              = NLMSG_PUT(skb, pid, seq, t, size);
        nlh->nlmsg_flags = flags;
        data             = NLMSG_DATA(nlh);
        memcpy(data, payload, size);

        /* Ignore failure. It'll only happen if the sender goes away,
           because our timeout is set to infinite. */
        netlink_unicast(audit_sock, skb, pid, 0);
        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_LIST_RULES:
        case AUDIT_SET:
        case AUDIT_ADD:
        case AUDIT_ADD_RULE:
        case AUDIT_DEL:
        case AUDIT_DEL_RULE:
        case AUDIT_SIGNAL_INFO:
                if (!cap_raised(eff_cap, 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 (!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, sid;
        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 */
        struct audit_sig_info   sig_data;

        err = audit_netlink_ok(NETLINK_CB(skb).eff_cap, 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;
        }

        pid  = NETLINK_CREDS(skb)->pid;
        uid  = NETLINK_CREDS(skb)->uid;
        loginuid = NETLINK_CB(skb).loginuid;
        sid  = NETLINK_CB(skb).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).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, GFP_KERNEL, AUDIT_CONFIG_CHANGE,
                                "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:
        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(&NETLINK_CB(skb), msg_type);
                if (err == 1) {
                        err = 0;
                        ab = audit_log_start(NULL, GFP_KERNEL, msg_type);
                        if (ab) {
                                audit_log_format(ab,
                                                 "user pid=%d uid=%u auid=%u",
                                                 pid, uid, loginuid);
                                if (sid) {
                                        char *ctx = NULL;
                                        u32 len;
                                        if (selinux_ctxid_to_string(
                                                        sid, &ctx, &len)) {
                                                audit_log_format(ab, 
                                                        " subj=%u", sid);
                                                /* Maybe call audit_panic? */
                                        } else
                                                audit_log_format(ab, 
                                                        " subj=%s", ctx);
                                        kfree(ctx);
                                }
                                audit_log_format(ab, " msg='%.1024s'",
                                         (char *)data);
                                audit_set_pid(ab, pid);
                                audit_log_end(ab);
                        }
                }
                break;
        case AUDIT_ADD:
        case AUDIT_DEL:
                if (nlmsg_len(nlh) < sizeof(struct audit_rule))
                        return -EINVAL;
                /* fallthrough */
        case AUDIT_LIST:
                err = audit_receive_filter(nlh->nlmsg_type, NETLINK_CB(skb).pid,
                                           uid, seq, data, nlmsg_len(nlh),
                                           loginuid);
                break;
        case AUDIT_ADD_RULE:
        case AUDIT_DEL_RULE:
                if (nlmsg_len(nlh) < sizeof(struct audit_rule_data))
                        return -EINVAL;
                /* fallthrough */
        case AUDIT_LIST_RULES:
                err = audit_receive_filter(nlh->nlmsg_type, NETLINK_CB(skb).pid,
                                           uid, seq, data, nlmsg_len(nlh),
                                           loginuid);
                break;
        case AUDIT_SIGNAL_INFO:
                sig_data.uid = audit_sig_uid;
                sig_data.pid = audit_sig_pid;
                audit_send_reply(NETLINK_CB(skb).pid, seq, AUDIT_SIGNAL_INFO, 
                                0, 0, &sig_data, sizeof(sig_data));
                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 void 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;
                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);
        }
}

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

        mutex_lock(&audit_netlink_mutex);

        for (qlen = skb_queue_len(&sk->sk_receive_queue); qlen; qlen--) {
                skb = skb_dequeue(&sk->sk_receive_queue);
                audit_receive_skb(skb);
                kfree_skb(skb);
        }
        mutex_unlock(&audit_netlink_mutex);
}


/* 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, 0, audit_receive,
                                           THIS_MODULE);
        if (!audit_sock)
                audit_panic("cannot initialize netlink socket");
        else
                audit_sock->sk_sndtimeo = MAX_SCHEDULE_TIMEOUT;

        skb_queue_head_init(&audit_skb_queue);
        audit_initialized = 1;
        audit_enabled = audit_default;

        /* Register the callback with selinux.  This callback will be invoked
         * when a new policy is loaded. */
        selinux_audit_set_callback(&selinux_audit_rule_update);

        audit_log(NULL, GFP_KERNEL, AUDIT_KERNEL, "initialized");
        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);
        printk(KERN_INFO "audit: %s%s\n",
               audit_default ? "enabled" : "disabled",
               audit_initialized ? "" : " (after initialization)");
        if (audit_initialized)
                audit_enabled = audit_default;
        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
                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->skb = alloc_skb(AUDIT_BUFSIZ, gfp_mask);
        if (!ab->skb)
                goto err;

        ab->ctx = ctx;
        ab->gfp_mask = gfp_mask;
        nlh = (struct nlmsghdr *)skb_put(ab->skb, NLMSG_SPACE(0));
        nlh->nlmsg_type = type;
        nlh->nlmsg_flags = 0;
        nlh->nlmsg_pid = 0;
        nlh->nlmsg_seq = 0;
        return ab;
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 spinlock_t serial_lock = SPIN_LOCK_UNLOCKED;
        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);
        else {
                *t = CURRENT_TIME;
                *serial = audit_serial();
        }
}

/* 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            serial;
        int reserve;
        unsigned long timeout_start = jiffies;

        if (!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
                    && time_before(jiffies, timeout_start + audit_backlog_wait_time)) {

                        /* Wait for auditd to drain the queue a little */
                        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(timeout_start + audit_backlog_wait_time - jiffies);

                        __set_current_state(TASK_RUNNING);
                        remove_wait_queue(&audit_backlog_wait, &wait);
                        continue;
                }
                if (audit_rate_check())
                        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 ret = pskb_expand_head(skb, skb_headroom(skb), extra,
                                   ab->gfp_mask);
        if (ret < 0) {
                audit_log_lost("out of memory in audit_expand");
                return 0;
        }
        return skb_tailroom(skb);
}

/*
 * 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, 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;
                len = vsnprintf(skb->tail, avail, fmt, args2);
        }
        if (len > 0)
                skb_put(skb, len);
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_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";

        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;
        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 */
}

/**
 * audit_log_unstrustedstring - log a string that may contain random characters
 * @ab: audit_buffer
 * @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).
 */
void audit_log_untrustedstring(struct audit_buffer *ab, const char *string)
{
        const unsigned char *p = string;

        while (*p) {
                if (*p == '"' || *p < 0x21 || *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 escaped d_path */
void audit_log_d_path(struct audit_buffer *ab, const char *prefix,
                      struct dentry *dentry, struct vfsmount *vfsmnt)
{
        char *p, *path;

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

        /* We will allow 11 spaces for ' (deleted)' to be appended */
        path = kmalloc(PATH_MAX+11, ab->gfp_mask);
        if (!path) {
                audit_log_format(ab, "<no memory>");
                return;
        }
        p = d_path(dentry, vfsmnt, path, PATH_MAX+11);
        if (IS_ERR(p)) { /* Should never happen since we send PATH_MAX */
                /* FIXME: can we save some information here? */
                audit_log_format(ab, "<too long>");
        } else 
                audit_log_untrustedstring(ab, p);
        kfree(path);
}

/**
 * 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 {
                if (audit_pid) {
                        struct nlmsghdr *nlh = (struct nlmsghdr *)ab->skb->data;
                        nlh->nlmsg_len = ab->skb->len - NLMSG_SPACE(0);
                        skb_queue_tail(&audit_skb_queue, ab->skb);
                        ab->skb = NULL;
                        wake_up_interruptible(&kauditd_wait);
                } else {
                        printk(KERN_NOTICE "%s\n", ab->skb->data + NLMSG_SPACE(0));
                }
        }
        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);
        }
}

EXPORT_SYMBOL(audit_log_start);
EXPORT_SYMBOL(audit_log_end);
EXPORT_SYMBOL(audit_log_format);
EXPORT_SYMBOL(audit_log);