netdev - Re: [PATCH net] net: validate untrusted gso packets without csum offload

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Date:   Fri, 15 Feb 2019 09:36:36 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        netdev@...r.kernel.org
Cc:     davem@...emloft.net, edumazet@...gle.com, jasowang@...hat.com,
        maximmi@...lanox.com, Willem de Bruijn <willemb@...gle.com>,
        syzbot <syzkaller@...glegroups.com>
Subject: Re: [PATCH net] net: validate untrusted gso packets without csum
 offload



On 02/15/2019 09:15 AM, Willem de Bruijn wrote:
> From: Willem de Bruijn <willemb@...gle.com>
> 
> Syzkaller again found a path to a kernel crash through bad gso input.
> By building an excessively large packet to cause an skb field to wrap.
> 
> If VIRTIO_NET_HDR_F_NEEDS_CSUM was set this would have been dropped in
> skb_partial_csum_set.
> 
> GSO packets that do not set checksum offload are suspicious and rare.
> Most callers of virtio_net_hdr_to_skb already pass them to
> skb_probe_transport_header.
> 
> Move that test forward, change it to detect parse failure and drop
> packets on failure as those cleary are not one of the legitimate
> VIRTIO_NET_HDR_GSO types.
> 
> Fixes: bfd5f4a3d605 ("packet: Add GSO/csum offload support.")
> Fixes: f43798c27684 ("tun: Allow GSO using virtio_net_hdr")
> Reported-by: syzbot <syzkaller@...glegroups.com>
> Signed-off-by: Willem de Bruijn <willemb@...gle.com>

Reviewed-by: Eric Dumazet <edumazet@...gle.com>