Re: [PATCH net] gso: fix gso fraglist segmentation after pull from frag_list

[Felix Fietkau <nbd@nbd.name>]

On 22.09.24 17:03, Willem de Bruijn wrote:
> From: Willem de Bruijn <willemb@google.com>
> 
> Detect 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 UDP, this
> causes a NULL ptr deref in __udpv4_gso_segment_list_csum at
> udp_hdr(seg->next)->dest.
> 
> 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.
> 
> Link: https://lore.kernel.org/netdev/20240428142913.18666-1-shiming.cheng@mediatek.com/
> Fixes: 3a1296a38d0c ("net: Support GRO/GSO fraglist chaining.")
> Signed-off-by: Willem de Bruijn <willemb@google.com>
> Cc: stable@vger.kernel.org

Reviewed-by: Felix Fietkau <nbd@nbd.name>