Re: [PATCH v3] skbuff: skb_segment, Call zero copy functions before using skbuff frags

[Eric Dumazet]

On Thu, Aug 31, 2023 at 10:17 AM Mohamed Khalfella
<mkhalfella@xxxxxxxxxxxxxxx> wrote:
>
> Commit bf5c25d60861 ("skbuff: in skb_segment, call zerocopy functions
> once per nskb") added the call to zero copy functions in skb_segment().
> The change introduced a bug in skb_segment() because skb_orphan_frags()
> may possibly change the number of fragments or allocate new fragments
> altogether leaving nrfrags and frag to point to the old values. This can
> cause a panic with stacktrace like the one below.
>
>

> In this case calling skb_orphan_frags() updated nr_frags leaving nrfrags
> local variable in skb_segment() stale. This resulted in the code hitting
> i >= nrfrags prematurely and trying to move to next frag_skb using
> list_skb pointer, which was NULL, and caused kernel panic. Move the call
> to zero copy functions before using frags and nr_frags.
>
> Fixes: bf5c25d60861 ("skbuff: in skb_segment, call zerocopy functions once per nskb")
> Signed-off-by: Mohamed Khalfella <mkhalfella@xxxxxxxxxxxxxxx>
> Reported-by: Amit Goyal <agoyal@xxxxxxxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> ---

Reviewed-by: Eric Dumazet <edumazet@xxxxxxxxxx>