From: Jakub Kicinski <kuba@kernel.org>
To: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
Cc: netdev@vger.kernel.org, davem@davemloft.net, edumazet@google.com,
pabeni@redhat.com, Willem de Bruijn <willemb@google.com>,
syzbot <syzkaller@googlegroups.com>,
Alexander Duyck <alexander.duyck@gmail.com>
Subject: Re: [PATCH net] ip_gre: test csum_start instead of transport header
Date: Tue, 7 Jun 2022 17:18:21 -0700 [thread overview]
Message-ID: <20220607171821.74bc4f87@kernel.org> (raw)
In-Reply-To: <20220606132107.3582565-1-willemdebruijn.kernel@gmail.com>
On Mon, 6 Jun 2022 09:21:07 -0400 Willem de Bruijn wrote:
> From: Willem de Bruijn <willemb@google.com>
>
> GRE with TUNNEL_CSUM will apply local checksum offload on
> CHECKSUM_PARTIAL packets.
>
> ipgre_xmit must validate csum_start after an optional skb_pull,
> else lco_csum may trigger an overflow. The original check was
>
> if (csum && skb_checksum_start(skb) < skb->data)
> return -EINVAL;
>
> This had false positives when skb_checksum_start is undefined:
> when ip_summed is not CHECKSUM_PARTIAL. A discussed refinement
> was straightforward
>
> if (csum && skb->ip_summed == CHECKSUM_PARTIAL &&
> skb_checksum_start(skb) < skb->data)
> return -EINVAL;
>
> But was eventually revised more thoroughly:
> - restrict the check to the only branch where needed, in an
> uncommon GRE path that uses header_ops and calls skb_pull.
> - test skb_transport_header, which is set along with csum_start
> in skb_partial_csum_set in the normal header_ops datapath.
>
> Turns out skbs can arrive in this branch without the transport
> header set, e.g., through BPF redirection.
>
> Revise the check back to check csum_start directly, and only if
> CHECKSUM_PARTIAL. Do leave the check in the updated location.
> Check field regardless of whether TUNNEL_CSUM is configured.
>
> Link: https://lore.kernel.org/netdev/YS+h%2FtqCJJiQei+W@shredder/
> Link: https://lore.kernel.org/all/20210902193447.94039-2-willemdebruijn.kernel@gmail.com/T/#u
> Fixes: 8a0ed250f911 ("ip_gre: validate csum_start only on pull")
> Reported-by: syzbot <syzkaller@googlegroups.com>
> Signed-off-by: Willem de Bruijn <willemb@google.com>
Missing a CC for Alex, adding now.
next prev parent reply other threads:[~2022-06-08 2:46 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-06 13:21 [PATCH net] ip_gre: test csum_start instead of transport header Willem de Bruijn
2022-06-07 17:33 ` Eric Dumazet
2022-06-08 0:18 ` Jakub Kicinski [this message]
2022-06-08 14:54 ` Alexander H Duyck
2022-06-09 3:40 ` patchwork-bot+netdevbpf
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