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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
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