Re: [PATCH v2] net: drop bogus skb with CHECKSUM_PARTIAL and offset beyond end of trimmed packet

From: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
To: Vasily Averin <vvs@virtuozzo.com>
Cc: Willem de Bruijn <willemdebruijn.kernel@gmail.com>,
	"David S. Miller" <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>,
	Network Development <netdev@vger.kernel.org>
Subject: Re: [PATCH v2] net: drop bogus skb with CHECKSUM_PARTIAL and offset beyond end of trimmed packet
Date: Mon, 14 Dec 2020 15:59:24 -0500	[thread overview]
Message-ID: <CA+FuTSeicMroDHZGFuWQxhpwVBOztwWLMnzVTZKXPQ2EY9VmRA@mail.gmail.com> (raw)
In-Reply-To: <1b2494af-2c56-8ee2-7bc0-923fcad1cdf8@virtuozzo.com>

On Mon, Dec 14, 2020 at 2:21 PM Vasily Averin <vvs@virtuozzo.com> 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 <vvs@virtuozzo.com>
> ---
> 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>