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audit: Fix data races of skb_queue_len() readers on audit_queue

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commit c9a71daaec upstream.

Multiple readers access audit_queue.qlen via skb_queue_len() without
holding the queue lock or using READ_ONCE(), while kauditd writes to
this field via the skb_dequeue() → __skb_unlink() path with WRITE_ONCE()
protected by a spinlock. This constitutes data races.

All affected skb_queue_len(&audit_queue) call sites:
  - kauditd_thread() wait_event_freezable() condition
  - audit_receive_msg() AUDIT_GET handler (s.backlog assignment)
  - audit_receive() backlog check
  - audit_log_start() backlog check and pr_warn()

KCSAN reports the following conflicting access pattern (one example):
==================================================================
BUG: KCSAN: data-race in audit_log_start / skb_dequeue

write (marked) to 0xffffffff8512ee20 of 4 bytes by task 661 on cpu 57:
 skb_dequeue+0x70/0xf0
 kauditd_send_queue+0x71/0x220
 kauditd_thread+0x1cb/0x430
 kthread+0x1c2/0x210
 ret_from_fork+0x162/0x1a0
 ret_from_fork_asm+0x1a/0x30

read to 0xffffffff8512ee20 of 4 bytes by task 36586 on cpu 1:
 audit_log_start+0x2a0/0x6b0
 audit_core_dumps+0x64/0xa0
 do_coredump+0x14b/0x1260
 get_signal+0xeb2/0xf70
 arch_do_signal_or_restart+0x41/0x170
 exit_to_user_mode_loop+0xa2/0x1c0
 do_syscall_64+0x1a3/0x1c0
 entry_SYSCALL_64_after_hwframe+0x76/0xe0

value changed: 0x00000001 -> 0x00000000
==================================================================

Resolve the race by switching to lockless helper skb_queue_len_lockless(),
which internally uses READ_ONCE() and properly pairs with the WRITE_ONCE()
write accesses already present on the writer side.

Cc: stable@vger.kernel.org
Fixes: 3197542482 ("audit: rework audit_log_start()")
Signed-off-by: Chi Wang <wangchi@kylinos.cn>
Reviewed-by: Ricardo Robaina <rrobaina@redhat.com>
[PM: line length tweak]
Signed-off-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Chi Wang
2026-07-18 16:53:15 +02:00
committed by Greg Kroah-Hartman
parent e8417353cb
commit fe997a84a3
1 changed files with 5 additions and 5 deletions
Download Patch File Download Diff File Expand all files Collapse all files
kernel/audit.c
+5 -5
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@@ -946,7 +946,7 @@ main_queue:
* do the multicast send and rotate records from the
* main queue to the retry/hold queues */
wait_event_freezable(kauditd_wait,
(skb_queue_len(&audit_queue) ? 1 : 0));
(skb_queue_len_lockless(&audit_queue) ? 1 : 0));
}
return 0;
@@ -1279,7 +1279,7 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh,
s.rate_limit = audit_rate_limit;
s.backlog_limit = audit_backlog_limit;
s.lost = atomic_read(&audit_lost);
s.backlog = skb_queue_len(&audit_queue);
s.backlog = skb_queue_len_lockless(&audit_queue);
s.feature_bitmap = AUDIT_FEATURE_BITMAP_ALL;
s.backlog_wait_time = audit_backlog_wait_time;
s.backlog_wait_time_actual = atomic_read(&audit_backlog_wait_time_actual);
@@ -1622,7 +1622,7 @@ static void audit_receive(struct sk_buff *skb)
/* can't block with the ctrl lock, so penalize the sender now */
if (audit_backlog_limit &&
(skb_queue_len(&audit_queue) > audit_backlog_limit)) {
(skb_queue_len_lockless(&audit_queue) > audit_backlog_limit)) {
DECLARE_WAITQUEUE(wait, current);
/* wake kauditd to try and flush the queue */
@@ -1928,7 +1928,7 @@ struct audit_buffer *audit_log_start(struct audit_context *ctx, gfp_t gfp_mask,
long stime = audit_backlog_wait_time;
while (audit_backlog_limit &&
(skb_queue_len(&audit_queue) > audit_backlog_limit)) {
(skb_queue_len_lockless(&audit_queue) > audit_backlog_limit)) {
/* wake kauditd to try and flush the queue */
wake_up_interruptible(&kauditd_wait);
@@ -1948,7 +1948,7 @@ struct audit_buffer *audit_log_start(struct audit_context *ctx, gfp_t gfp_mask,
} else {
if (audit_rate_check() && printk_ratelimit())
pr_warn("audit_backlog=%d > audit_backlog_limit=%d\n",
skb_queue_len(&audit_queue),
skb_queue_len_lockless(&audit_queue),
audit_backlog_limit);
audit_log_lost("backlog limit exceeded");
return NULL;