CVE-2026-72389: bridge: stp: Fix a potential use-after-free when deleting a bridge

CVE-2026-72389: bridge: stp: Fix a potential use-after-free when deleting a bridge

[Greg Kroah-Hartman]

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

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

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

bridge: stp: Fix a potential use-after-free when deleting a bridge

The three STP timers are not supposed to be armed while the bridge is
administratively down. They are synchronously deactivated when the
bridge is put administratively down and the various call sites check for
'IFF_UP' before arming them.

This check is missing from br_topology_change_detection() and it is
possible to engineer a situation in which the topology change timer is
armed while the bridge is administratively down, resulting in a
use-after-free [1] when the bridge is deleted.

Fix by adding the missing check and for good measures synchronously
shutdown the three timers when the bridge is deleted.

[1]
ODEBUG: free active (active state 0) object: ffff88811662b9b0 object type: timer_list hint: br_topology_change_timer_expired (net/bridge/br_stp_timer.c:120)
WARNING: lib/debugobjects.c:629 at debug_print_object+0x1bc/0x450, CPU#9: ip/359

The Linux kernel CVE team has assigned CVE-2026-72389 to this issue.


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

	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 5.15.212 with commit c86579b0a2d201792bcb59316629f4ba4758cfc8
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 6.1.178 with commit 297a747f59bff6573196d7236178144d66524e68
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 6.6.145 with commit 4c40eec06eeac37c58e47a6058eb32901218d5d4
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 6.12.97 with commit 39283907a25e5caf0f2bd2947f6e56644b01e2b7
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 6.18.40 with commit b4b3458ef88df4798632619f018791d4344bcd92
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 7.1.5 with commit 40cbfa3a28e0919469d1b086629bb3ce38a83593
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 7.2-rc2 with commit 2a00517db8de4be7df3d483b215c5544fb30a191

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-2026-72389
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:
	net/bridge/br_if.c
	net/bridge/br_stp.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/c86579b0a2d201792bcb59316629f4ba4758cfc8
	https://git.kernel.org/stable/c/297a747f59bff6573196d7236178144d66524e68
	https://git.kernel.org/stable/c/4c40eec06eeac37c58e47a6058eb32901218d5d4
	https://git.kernel.org/stable/c/39283907a25e5caf0f2bd2947f6e56644b01e2b7
	https://git.kernel.org/stable/c/b4b3458ef88df4798632619f018791d4344bcd92
	https://git.kernel.org/stable/c/40cbfa3a28e0919469d1b086629bb3ce38a83593
	https://git.kernel.org/stable/c/2a00517db8de4be7df3d483b215c5544fb30a191