linux-cve-announce - CVE-2025-71132: smc91x: fix broken irq-context in PREEMPT

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Message-ID: <2026011452-CVE-2025-71132-b03b@gregkh>
Date: Wed, 14 Jan 2026 16:07:56 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-71132: smc91x: fix broken irq-context in PREEMPT_RT

From: Greg Kroah-Hartman <gregkh@...nel.org>

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

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

smc91x: fix broken irq-context in PREEMPT_RT

When smc91x.c is built with PREEMPT_RT, the following splat occurs
in FVP_RevC:

[   13.055000] smc91x LNRO0003:00 eth0: link up, 10Mbps, half-duplex, lpa 0x0000
[   13.062137] BUG: workqueue leaked atomic, lock or RCU: kworker/2:1[106]
[   13.062137]      preempt=0x00000000 lock=0->0 RCU=0->1 workfn=mld_ifc_work
[   13.062266] C
** replaying previous printk message **
[   13.062266] CPU: 2 UID: 0 PID: 106 Comm: kworker/2:1 Not tainted 6.18.0-dirty #179 PREEMPT_{RT,(full)}
[   13.062353] Hardware name:  , BIOS
[   13.062382] Workqueue: mld mld_ifc_work
[   13.062469] Call trace:
[   13.062494]  show_stack+0x24/0x40 (C)
[   13.062602]  __dump_stack+0x28/0x48
[   13.062710]  dump_stack_lvl+0x7c/0xb0
[   13.062818]  dump_stack+0x18/0x34
[   13.062926]  process_scheduled_works+0x294/0x450
[   13.063043]  worker_thread+0x260/0x3d8
[   13.063124]  kthread+0x1c4/0x228
[   13.063235]  ret_from_fork+0x10/0x20

This happens because smc_special_trylock() disables IRQs even on PREEMPT_RT,
but smc_special_unlock() does not restore IRQs on PREEMPT_RT.
The reason is that smc_special_unlock() calls spin_unlock_irqrestore(),
and rcu_read_unlock_bh() in __dev_queue_xmit() cannot invoke
rcu_read_unlock() through __local_bh_enable_ip() when current->softirq_disable_cnt becomes zero.

To address this issue, replace smc_special_trylock() with spin_trylock_irqsave().

The Linux kernel CVE team has assigned CVE-2025-71132 to this issue.


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

	Issue introduced in 5.15 with commit 342a93247e0837101f27bbcca26f402902df98dc and fixed in 6.1.160 with commit 9d222141b00156509d67d80c771fbefa92c43ace
	Issue introduced in 5.15 with commit 342a93247e0837101f27bbcca26f402902df98dc and fixed in 6.6.120 with commit ef277ae121b3249c99994652210a326b52d527b0
	Issue introduced in 5.15 with commit 342a93247e0837101f27bbcca26f402902df98dc and fixed in 6.12.64 with commit 36561b86cb2501647662cfaf91286dd6973804a6
	Issue introduced in 5.15 with commit 342a93247e0837101f27bbcca26f402902df98dc and fixed in 6.18.4 with commit b6018d5c1a8f09d5efe4d6961d7ee45fdf3a7ce3
	Issue introduced in 5.15 with commit 342a93247e0837101f27bbcca26f402902df98dc and fixed in 6.19-rc4 with commit 6402078bd9d1ed46e79465e1faaa42e3458f8a33

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-2025-71132
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:
	drivers/net/ethernet/smsc/smc91x.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/9d222141b00156509d67d80c771fbefa92c43ace
	https://git.kernel.org/stable/c/ef277ae121b3249c99994652210a326b52d527b0
	https://git.kernel.org/stable/c/36561b86cb2501647662cfaf91286dd6973804a6
	https://git.kernel.org/stable/c/b6018d5c1a8f09d5efe4d6961d7ee45fdf3a7ce3
	https://git.kernel.org/stable/c/6402078bd9d1ed46e79465e1faaa42e3458f8a33