audit.c

/* audit.c -- Auditing support
 * Gateway between the kernel (e.g., selinux) and the user-space audit daemon.
 * System-call specific features have moved to auditsc.c
 *
 * Copyright 2003-2007 Red Hat Inc., Durham, North Carolina.
 * All Rights Reserved.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 * Written by Rickard E. (Rik) Faith <faith@redhat.com>
 *
 * Goals: 1) Integrate fully with Security Modules.
 *	  2) Minimal run-time overhead:
 *	     a) Minimal when syscall auditing is disabled (audit_enable=0).
 *	     b) Small when syscall auditing is enabled and no audit record
 *		is generated (defer as much work as possible to record
 *		generation time):
 *		i) context is allocated,
 *		ii) names from getname are stored without a copy, and
 *		iii) inode information stored from path_lookup.
 *	  3) Ability to disable syscall auditing at boot time (audit=0).
 *	  4) Usable by other parts of the kernel (if audit_log* is called,
 *	     then a syscall record will be generated automatically for the
 *	     current syscall).
 *	  5) Netlink interface to user-space.
 *	  6) Support low-overhead kernel-based filtering to minimize the
 *	     information that must be passed to user-space.
 *
 * Example user-space utilities: http://people.redhat.com/sgrubb/audit/
 */

#include <linux/init.h>
#include <asm/types.h>
#include <linux/atomic.h>
#include <linux/mm.h>
#include <linux/module.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 "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_pid contains
 * the pid to use to send netlink messages to that process.
 */
int		audit_pid;
static int	audit_nlk_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;
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;