tun: Don't put_page() for all negative return values from XDP program

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" <[email protected]>
Cc: Alexei Starovoitov <[email protected]>
Cc: Daniel Borkmann <[email protected]>
CC: Eric Dumazet <[email protected]>
Acked-by: Jason Wang <[email protected]>
Fixes: 8ae1aff0b331 ("tuntap: split out XDP logic")
Signed-off-by: Will Deacon <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

0 files changed, 0 insertions, 0 deletions