netdev - Re: [PATCH] net: check skb partial checksum offset after trim

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Date:   Sun, 13 Dec 2020 22:37:14 +0300
From:   Vasily Averin <vvs@...tuozzo.com>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Network Development <netdev@...r.kernel.org>
Subject: Re: [PATCH] net: check skb partial checksum offset after trim

On 12/13/20 2:49 AM, Willem de Bruijn wrote:
> On Sat, Dec 12, 2020 at 5:01 AM Vasily Averin <vvs@...tuozzo.com> wrote:
>>
>> On 12/11/20 6:37 PM, Vasily Averin wrote:
>>> It seems for me the similar problem can happen in __skb_trim_rcsum().
>>> Also I doubt that that skb_checksum_start_offset(skb) checks in
>>> __skb_postpull_rcsum() and skb_csum_unnecessary() are correct,
>>> becasue they do not guarantee that skb have correct CHECKSUM_PARTIAL.
>>> Could somebody confirm it?
>>
>> I've rechecked the code and I think now that other places are not affected,
>> i.e. skb_push_rcsum() only should be patched.
> 
> Thanks for investigating this. So tun was able to insert a packet with
> csum_start + csum_off + 2 beyond the packet after trimming, using
> virtio_net_hdr.csum_...
> 
> Any packet with an offset beyond the end of the packet is bogus
> really. No need to try to accept it by downgrading to CHECKSUM_NONE.

Do you mean it's better to force pskb_trim_rcsum() to return -EINVAL instead?

Thank you,
	Vasily Averin