Re: [PATCH v4 bpf 1/2] bpf: fix skb_do_redirect return values

[Jakub Sitnicki <jakub@cloudflare.com>]

On Tue, Jul 25, 2023 at 06:08 PM -07, Yan Zhai wrote:
> skb_do_redirect returns various of values: error code (negative),
> 0 (success), and some positive status code, e.g. NET_XMIT_CN,
> NET_RX_DROP. Commit 3a0af8fd61f9 ("bpf: BPF for lightweight tunnel
> infrastructure") didn't check the return code correctly, so positive
> values are propagated back along call chain:
>
>   ip_finish_output2
>     -> bpf_xmit
>       -> run_lwt_bpf
>         -> skb_do_redirect
>
> Inside ip_finish_output2, redirected skb will continue to neighbor
> subsystem as if LWTUNNEL_XMIT_CONTINUE is returned, despite that this
> skb could have been freed. The bug can trigger use-after-free warning
> and crashes kernel afterwards:
>
> https://gist.github.com/zhaiyan920/8fbac245b261fe316a7ef04c9b1eba48
>
> Convert positive statuses from skb_do_redirect eliminates this issue.
>
> Fixes: 3a0af8fd61f9 ("bpf: BPF for lightweight tunnel infrastructure")
> Tested-by: Jakub Sitnicki <jakub@cloudflare.com>
> Suggested-by: Markus Elfring <Markus.Elfring@web.de>
> Suggested-by: Stanislav Fomichev <sdf@google.com>
> Reported-by: Jordan Griege <jgriege@cloudflare.com>
> Signed-off-by: Yan Zhai <yan@cloudflare.com>
> ---

Reviewed-by: Jakub Sitnicki <jakub@cloudflare.com>