netdev - Re: [PATCH net] net: gso: fix tcp fraglist segmentation after pull from frag

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Message-ID: <66f522ae74384_84561294f8@willemb.c.googlers.com.notmuch>
Date: Thu, 26 Sep 2024 05:00:30 -0400
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Felix Fietkau <nbd@....name>, 
 netdev@...r.kernel.org, 
 Eric Dumazet <edumazet@...gle.com>, 
 "David S. Miller" <davem@...emloft.net>, 
 David Ahern <dsahern@...nel.org>, 
 Jakub Kicinski <kuba@...nel.org>, 
 Paolo Abeni <pabeni@...hat.com>, 
 Matthias Brugger <matthias.bgg@...il.com>, 
 AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>, 
 Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH net] net: gso: fix tcp fraglist segmentation after pull
 from frag_list

Felix Fietkau wrote:
> Detect tcp gso fraglist skbs with corrupted geometry (see below) and
> pass these to skb_segment instead of skb_segment_list, as the first
> can segment them correctly.
> 
> Valid SKB_GSO_FRAGLIST skbs
> - consist of two or more segments
> - the head_skb holds the protocol headers plus first gso_size
> - one or more frag_list skbs hold exactly one segment
> - all but the last must be gso_size
> 
> Optional datapath hooks such as NAT and BPF (bpf_skb_pull_data) can
> modify these skbs, breaking these invariants.
> 
> In extreme cases they pull all data into skb linear. For TCP, this
> causes a NULL ptr deref in __tcpv4_gso_segment_list_csum at
> tcp_hdr(seg->next).
> 
> Detect invalid geometry due to pull, by checking head_skb size.
> Don't just drop, as this may blackhole a destination. Convert to be
> able to pass to regular skb_segment.
> 
> Approach and description based on a patch by Willem de Bruijn.
> 
> Link: https://lore.kernel.org/netdev/20240428142913.18666-1-shiming.cheng@mediatek.com/
> Link: https://lore.kernel.org/netdev/20240922150450.3873767-1-willemdebruijn.kernel@gmail.com/
> Fixes: bee88cd5bd83 ("net: add support for segmenting TCP fraglist GSO packets")
> Cc: stable@...r.kernel.org
> Cc: Willem de Bruijn <willemb@...gle.com>
> Signed-off-by: Felix Fietkau <nbd@....name>

Reviewed-by: Willem de Bruijn <willemb@...gle.com>