From: Will Deacon <will@xxxxxxxxxx> Date: Fri, 3 Apr 2020 16:13:21 +0100 > When an XDP program is installed, tun_build_skb() grabs a reference to > the current page fragment page if the program returns XDP_REDIRECT or > XDP_TX. However, since tun_xdp_act() passes through negative return > values from the XDP program, it is possible to trigger the error path by > mistake and accidentally drop a reference to the fragments page without > taking one, leading to a spurious free. This is believed to be the cause > of some KASAN use-after-free reports from syzbot [1], although without a > reproducer it is not possible to confirm whether this patch fixes the > problem. > > Ensure that we only drop a reference to the fragments page if the XDP > transmit or redirect operations actually fail. > > [1] https://syzkaller.appspot.com/bug?id=e76a6af1be4acd727ff6bbca669833f98cbf5d95 > > Cc: "David S. Miller" <davem@xxxxxxxxxxxxx> > Cc: Alexei Starovoitov <ast@xxxxxxxxxx> > Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx> > CC: Eric Dumazet <edumazet@xxxxxxxxxx> > Acked-by: Jason Wang <jasowang@xxxxxxxxxx> > Fixes: 8ae1aff0b331 ("tuntap: split out XDP logic") > Signed-off-by: Will Deacon <will@xxxxxxxxxx> Applied and queued up for -stable, thank you.
