linux-cve-announce - CVE-2025-39773: net: bridge: fix soft lockup in br_multicast_query

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Message-ID: <2025091146-CVE-2025-39773-e511@gregkh>
Date: Thu, 11 Sep 2025 18:56:52 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-39773: net: bridge: fix soft lockup in br_multicast_query_expired()

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

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

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

net: bridge: fix soft lockup in br_multicast_query_expired()

When set multicast_query_interval to a large value, the local variable
'time' in br_multicast_send_query() may overflow. If the time is smaller
than jiffies, the timer will expire immediately, and then call mod_timer()
again, which creates a loop and may trigger the following soft lockup
issue.

  watchdog: BUG: soft lockup - CPU#1 stuck for 221s! [rb_consumer:66]
  CPU: 1 UID: 0 PID: 66 Comm: rb_consumer Not tainted 6.16.0+ #259 PREEMPT(none)
  Call Trace:
   <IRQ>
   __netdev_alloc_skb+0x2e/0x3a0
   br_ip6_multicast_alloc_query+0x212/0x1b70
   __br_multicast_send_query+0x376/0xac0
   br_multicast_send_query+0x299/0x510
   br_multicast_query_expired.constprop.0+0x16d/0x1b0
   call_timer_fn+0x3b/0x2a0
   __run_timers+0x619/0x950
   run_timer_softirq+0x11c/0x220
   handle_softirqs+0x18e/0x560
   __irq_exit_rcu+0x158/0x1a0
   sysvec_apic_timer_interrupt+0x76/0x90
   </IRQ>

This issue can be reproduced with:
  ip link add br0 type bridge
  echo 1 > /sys/class/net/br0/bridge/multicast_querier
  echo 0xffffffffffffffff >
  	/sys/class/net/br0/bridge/multicast_query_interval
  ip link set dev br0 up

The multicast_startup_query_interval can also cause this issue. Similar to
the commit 99b40610956a ("net: bridge: mcast: add and enforce query
interval minimum"), add check for the query interval maximum to fix this
issue.

The Linux kernel CVE team has assigned CVE-2025-39773 to this issue.

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

	Issue introduced in 2.6.34 with commit d902eee43f1951b358d7347d9165c6af21cf7b1b and fixed in 5.15.190 with commit 34171b9e53bd1dc264f5556579f2b04f04435c73
	Issue introduced in 2.6.34 with commit d902eee43f1951b358d7347d9165c6af21cf7b1b and fixed in 6.1.149 with commit 43e281fde5e76a866a4d10780c35023f16c0e432
	Issue introduced in 2.6.34 with commit d902eee43f1951b358d7347d9165c6af21cf7b1b and fixed in 6.6.103 with commit 96476b043efb86a94f2badd260f7f99c97bd5893
	Issue introduced in 2.6.34 with commit d902eee43f1951b358d7347d9165c6af21cf7b1b and fixed in 6.12.44 with commit bdb19cd0de739870bb3494c815138b9dc30875c4
	Issue introduced in 2.6.34 with commit d902eee43f1951b358d7347d9165c6af21cf7b1b and fixed in 6.16.4 with commit 5bf5fce8a0c2a70d063af778fdb5b27238174cdd
	Issue introduced in 2.6.34 with commit d902eee43f1951b358d7347d9165c6af21cf7b1b and fixed in 6.17-rc3 with commit d1547bf460baec718b3398365f8de33d25c5f36f

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-2025-39773
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_multicast.c
	net/bridge/br_private.h

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/34171b9e53bd1dc264f5556579f2b04f04435c73
	https://git.kernel.org/stable/c/43e281fde5e76a866a4d10780c35023f16c0e432
	https://git.kernel.org/stable/c/96476b043efb86a94f2badd260f7f99c97bd5893
	https://git.kernel.org/stable/c/bdb19cd0de739870bb3494c815138b9dc30875c4
	https://git.kernel.org/stable/c/5bf5fce8a0c2a70d063af778fdb5b27238174cdd
	https://git.kernel.org/stable/c/d1547bf460baec718b3398365f8de33d25c5f36f