audit.c

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/* 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 <[email protected]>
 *
 * 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;
}

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);
    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;
}
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);
    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;
}

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();
    }
}

/* 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, 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
            && 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_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;
}

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;
}

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_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 */
}

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;
}

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);
}

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)");
}

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);
}

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);
}

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

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);