CVE-2026-64435: audit: Fix data races of skb_queue_len() readers on audit_queue

From: Greg Kroah-Hartman <[email protected]>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

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

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.

[PM: line length tweak]

The Linux kernel CVE team has assigned CVE-2026-64435 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 4.10 with commit 3197542482df22c2a131d4a813280bd7c54cedf5 and fixed in 5.10.261 with commit 69f98fff30bdaa72b0cb0e7e078ab6456a0a59b0
	Issue introduced in 4.10 with commit 3197542482df22c2a131d4a813280bd7c54cedf5 and fixed in 5.15.212 with commit b35597bdae1a5d8395da4b9baa993b9b71f74d68
	Issue introduced in 4.10 with commit 3197542482df22c2a131d4a813280bd7c54cedf5 and fixed in 6.1.178 with commit e575dabb805252e3113fdc3f56f6ecacfde422d0
	Issue introduced in 4.10 with commit 3197542482df22c2a131d4a813280bd7c54cedf5 and fixed in 6.6.145 with commit 7ff42312ccde549f8c698723822c7db35107a39b
	Issue introduced in 4.10 with commit 3197542482df22c2a131d4a813280bd7c54cedf5 and fixed in 6.12.96 with commit a3d85dec60bb0622360fc176b2a51abdbe2ff0ad
	Issue introduced in 4.10 with commit 3197542482df22c2a131d4a813280bd7c54cedf5 and fixed in 6.18.39 with commit fe997a84a385f840b593ead92e575503a5046cee
	Issue introduced in 4.10 with commit 3197542482df22c2a131d4a813280bd7c54cedf5 and fixed in 7.1.4 with commit c5186201fa7030289cc4fe23fae87a3fcb566856
	Issue introduced in 4.10 with commit 3197542482df22c2a131d4a813280bd7c54cedf5 and fixed in 7.2-rc3 with commit c9a71daaecb2fb1d8c704545cc0b1c920b9bf5d7

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-64435
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	kernel/audit.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/69f98fff30bdaa72b0cb0e7e078ab6456a0a59b0
	https://git.kernel.org/stable/c/b35597bdae1a5d8395da4b9baa993b9b71f74d68
	https://git.kernel.org/stable/c/e575dabb805252e3113fdc3f56f6ecacfde422d0
	https://git.kernel.org/stable/c/7ff42312ccde549f8c698723822c7db35107a39b
	https://git.kernel.org/stable/c/a3d85dec60bb0622360fc176b2a51abdbe2ff0ad
	https://git.kernel.org/stable/c/fe997a84a385f840b593ead92e575503a5046cee
	https://git.kernel.org/stable/c/c5186201fa7030289cc4fe23fae87a3fcb566856
	https://git.kernel.org/stable/c/c9a71daaecb2fb1d8c704545cc0b1c920b9bf5d7