[Devel] [PATCH vz10] bridge: stp: Fix a potential use-after-free when deleting a bridge

* [Devel] [PATCH vz10] bridge: stp: Fix a potential use-after-free when deleting a bridge
@ 2026-09-11 17:37 Konstantin Khorenko
  2026-09-14  8:14 ` Vasileios Almpanis
  2026-09-14 10:58 ` Konstantin Khorenko
  0 siblings, 2 replies; 3+ messages in thread
From: Konstantin Khorenko @ 2026-09-11 17:37 UTC (permalink / raw)
  To: Vasileios Almpanis, OpenVZ devel list; +Cc: Denis V. Lunev

From: Ido Schimmel <idosch@nvidia.com>

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

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reported-by: Noam Rathaus <noamr@ssd-disclosure.com>
Reported-by: Neil Young <contact@ssd-disclosure.com>
Acked-by: Nikolay Aleksandrov <nikolay@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Breno Leitao <leitao@debian.org>
Link: https://patch.msgid.link/20260629072117.497959-1-idosch@nvidia.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

(cherry picked from commit 2a00517db8de4be7df3d483b215c5544fb30a191)
https://virtuozzo.atlassian.net/browse/VSTOR-145092
Feature: fix ms/net

Signed-off-by: Konstantin Khorenko <khorenko@virtuozzo.com>
---
 net/bridge/br_if.c  | 3 +++
 net/bridge/br_stp.c | 3 ++-
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/net/bridge/br_if.c b/net/bridge/br_if.c
index b7bf3e0aced66..0fa4d5362d041 100644
--- a/net/bridge/br_if.c
+++ b/net/bridge/br_if.c
@@ -391,6 +391,9 @@ void br_dev_delete(struct net_device *dev, struct list_head *head)
 
 	br_fdb_delete_by_port(br, NULL, 0, 1);
 
+	timer_shutdown_sync(&br->hello_timer);
+	timer_shutdown_sync(&br->topology_change_timer);
+	timer_shutdown_sync(&br->tcn_timer);
 	cancel_delayed_work_sync(&br->gc_work);
 
 	br_sysfs_delbr(br->dev);
diff --git a/net/bridge/br_stp.c b/net/bridge/br_stp.c
index 024210f954683..76a2df165ffc8 100644
--- a/net/bridge/br_stp.c
+++ b/net/bridge/br_stp.c
@@ -371,7 +371,8 @@ void br_topology_change_detection(struct net_bridge *br)
 {
 	int isroot = br_is_root_bridge(br);
 
-	if (br->stp_enabled != BR_KERNEL_STP)
+	if (br->stp_enabled != BR_KERNEL_STP ||
+	    !(br->dev->flags & IFF_UP))
 		return;
 
 	br_info(br, "topology change detected, %s\n",
-- 
2.43.0

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