[4.19,0/1] Fix UBSAN: undefined-behaviour in maybe_deliver

Message

Huang Guobin Jan. 26, 2022, 3:36 a.m. UTC

There is a syzkaller problem for Linux 4.19 last for over 1 year:
https://www.syzkaller.appspot.com/bug?id=288ae4752bb930c26369d675316de0310264ee34

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(+)