Re: [PATCH net] bridge: stp: Fix a potential use-after-free when deleting a bridge

[Breno Leitao <leitao@debian.org>]

On Mon, Jun 29, 2026 at 10:21:17AM +0300, Ido Schimmel wrote:
> 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>