There is a syzkaller problem for Linux 4.19 last for over 1 year: https://www.syzkaller.appspot.com/bug?id=288ae4752bb930c26369d675316de031026...
Mainline patch 7d850abd5f4e(net: bridge: add support for port isolation) introduces the BR_ISOLATED feature, a pair of ports with the BR_ISOLATED option set cannot communicate with each other. This feature applies only to ingress flow, not egress flow. However, the function br_skb_isolated that checks if an interface is isolated will be used not only for the ingress path, but also for the egress path. Since Linux-4.19 not merge the mainline patch fd65e5a95d0838(net: bridge: clear bridge's private skb space on xmit), the value of skb->cb is unde- fined because it is not initialized. Therefore, checking BR_INPUT_SKB_CB(skb)->src_port_isolated on the egress path will access an undefined value, resulting in an error in the judgment of br_skb_isolated. UBSAN triggers an alarm by finding undefined BR_INPUT_SKB_CB(skb)->src_port_isolated. So cherry-pick mainline patch fd65e5a95d0838(net: bridge: clear bridge's private skb space on xmit) to Linux 4.19 to fix it.
Nikolay Aleksandrov (1): net: bridge: clear bridge's private skb space on xmit
net/bridge/br_device.c | 2 ++ 1 file changed, 2 insertions(+)