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Commit ac4cec44 authored by David Woodhouse's avatar David Woodhouse
Browse files

AUDIT: Stop waiting for backlog after audit_panic() happens 



We force a rate-limit on auditable events by making them wait for space 
on the backlog queue. However, if auditd really is AWOL then this could 
potentially bring the entire system to a halt, depending on the audit 
rules in effect.

Firstly, make sure the wait time is honoured correctly -- it's the 
maximum time the process should wait, rather than the time to wait 
_each_ time round the loop. We were getting re-woken _each_ time a 
packet was dequeued, and the timeout was being restarted each time.

Secondly, reset the wait time after audit_panic() is called. In general 
this will be reset to zero, to allow progress to be made. If the system
is configured to _actually_ panic on audit_panic() then that will 
already have happened; otherwise we know that audit records are being 
lost anyway. 

These two tunables can't be exposed via AUDIT_GET and AUDIT_SET because 
those aren't particularly well-designed. It probably should have been 
done by sysctls or sysfs anyway -- one for a later patch.

Signed-off-by: default avatarDavid Woodhouse <dwmw2@infradead.org>
parent 7b430437

kernel/audit.c

+10 −5
Original line number Diff line number Diff line
@@ -79,6 +79,8 @@ 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;
@@ -655,6 +657,7 @@ struct audit_buffer *audit_log_start(struct audit_context *ctx, int gfp_mask, 
	struct timespec		t;

	unsigned int		serial;

	int reserve;

	unsigned long timeout_start = jiffies;



	if (!audit_initialized)

		return NULL;
@@ -667,8 +670,9 @@ struct audit_buffer *audit_log_start(struct audit_context *ctx, int gfp_mask, 


	while (audit_backlog_limit

	       && skb_queue_len(&audit_skb_queue) > audit_backlog_limit + reserve) {

		if (gfp_mask & __GFP_WAIT) {

			int ret = 1;

		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);
@@ -676,11 +680,10 @@ struct audit_buffer *audit_log_start(struct audit_context *ctx, int gfp_mask, 


			if (audit_backlog_limit &&

			    skb_queue_len(&audit_skb_queue) > audit_backlog_limit)

				ret = schedule_timeout(HZ * 60);

				schedule_timeout(timeout_start + audit_backlog_wait_time - jiffies);



			__set_current_state(TASK_RUNNING);

			remove_wait_queue(&audit_backlog_wait, &wait);

			if (ret)

			continue;

		}

		if (audit_rate_check())
@@ -690,6 +693,8 @@ struct audit_buffer *audit_log_start(struct audit_context *ctx, int gfp_mask, 
			       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;

	}