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

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Message-ID: <daf225a9-8194-40c6-b797-8ab37de773a0@nbd.name>
Date: Thu, 26 Sep 2024 11:17:34 +0200
From: Felix Fietkau <nbd@....name>
To: Willem de Bruijn <willemdebruijn.kernel@...il.com>, netdev@...r.kernel.org
Cc: davem@...emloft.net, kuba@...nel.org, edumazet@...gle.com,
 pabeni@...hat.com, stable@...r.kernel.org, maze@...gle.com,
 shiming.cheng@...iatek.com, daniel@...earbox.net, lena.wang@...iatek.com,
 herbert@...dor.apana.org.au, Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH net] gso: fix gso fraglist segmentation after pull from
 frag_list

On 22.09.24 17:03, Willem de Bruijn wrote:
> From: Willem de Bruijn <willemb@...gle.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@...gle.com>
> Cc: stable@...r.kernel.org

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