On Mon, Dec 14, 2020 at 2:21 PM Vasily Averin [off-list ref] wrote:

syzbot reproduces BUG_ON in skb_checksum_help():
tun creates (bogus) skb with huge partial-checksummed area and
small ip packet inside. Then ip_rcv trims the skb based on size
of internal ip packet, after that csum offset points beyond of
trimmed skb. Then checksum_tg() called via netfilter hook
triggers BUG_ON:

        offset = skb_checksum_start_offset(skb);
        BUG_ON(offset >= skb_headlen(skb));

To work around the problem this patch forces pskb_trim_rcsum_slow()
to return -EINVAL in described scenario. It allows its callers to
drop such kind of packets.

Link: https://syzkaller.appspot.com/bug?id=b419a5ca95062664fe1a60b764621eb4526e2cd0
Reported-by: syzbot+7010af67ced6105e5ab6@syzkaller.appspotmail.com
Signed-off-by: Vasily Averin <redacted>
---
v2: drop bogus packets instead change its CHECKSUM_PARTIAL to CHECKSUM_NONE

Thanks for revising.

As far as I can tell, this goes back to the original introduction of
that user interface to set checksum offload, so

Fixes: 296f96fcfc16 ("Net driver using virtio")

For next time, please also mark network fixes as [PATCH net]. With that

Acked-by: Willem de Bruijn <willemb@google.com>