2025-12-08 00:46:21
Linux
PUBLISHED
In the Linux kernel, the following vulnerability has been resolved: net: bridge: fix use-after-free due to MST port state bypass syzbot reported[1] a use-after-free when deleting an expired fdb. It is due to a race condition between learning still happening and a port being deleted, after all its fdbs have been flushed. The ports state has been toggled to disabled so no learning should happen at that time, but if we have MST enabled, it will bypass the ports state, that together with VLAN filtering disabled can lead to fdb learning at a time when it shouldnt happen while the port is being deleted. VLAN filtering must be disabled because we flush the port VLANs when its being deleted which will stop learning. This fix adds a check for the ports vlan group which is initialized to NULL when the port is getting deleted, that avoids the port state bypass. When MST is enabled there would be a minimal new overhead in the fast-path because the ports vlan group pointer is cache-hot. [1] https://syzkaller.appspot.com/bug?extid=dd280197f0f7ab3917be