If a packet with bad checksum metadata gets into the ipv4 stack,
skb_checksum_help can corrupt the network header and cause a bunch of
mischief.
This was discovered and reported by Paulos, and has been reporoduced
by others independently since.
We really shouldn't allow such packets in, but as a defence
in depth measure, let's also check before we complete the checksum.
A more complete validation at input is forthcoming, but needs more work.
Cc: stable@vger.kernel.org
Fixes: f43798c276 ("tun: Allow GSO using virtio_net_hdr")
Fixes: bfd5f4a3d6 ("packet: Add GSO/csum offload support.")
Reported-by: Paulos Yibelo <habte.yibelo@gmail.com>
Closes: https://lore.kernel.org/netdev/20260922030310.8684-2-habte.yibelo@gmail.com/
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://patch.msgid.link/0a012b4923e189c4c593ef4f471e5ff0edbe9030.1791412497.git.mst@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
6785011f8b