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 <e5d05e56bf41de82f10d33229b8a8f6b49290e98.1690332693.git.yan@cloudflare.com>
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From:   Jakub Sitnicki <jakub@cloudflare.com>
To:     Yan Zhai <yan@cloudflare.com>
Cc:     bpf@vger.kernel.org, Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>,
        Martin KaFai Lau <martin.lau@linux.dev>,
        Song Liu <song@kernel.org>, Yonghong Song <yhs@fb.com>,
        John Fastabend <john.fastabend@gmail.com>,
        KP Singh <kpsingh@kernel.org>,
        Stanislav Fomichev <sdf@google.com>,
        Hao Luo <haoluo@google.com>, Jiri Olsa <jolsa@kernel.org>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        Mykola Lysenko <mykolal@fb.com>, Shuah Khan <shuah@kernel.org>,
        linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
        linux-kselftest@vger.kernel.org, kernel-team@cloudflare.com,
        Jordan Griege <jgriege@cloudflare.com>,
        Markus Elfring <Markus.Elfring@web.de>
Subject: Re: [PATCH v4 bpf 1/2] bpf: fix skb_do_redirect return values
Date:   Wed, 26 Jul 2023 14:25:38 +0200
In-reply-to: <e5d05e56bf41de82f10d33229b8a8f6b49290e98.1690332693.git.yan@cloudflare.com>
Message-ID: <87ila6yi3l.fsf@cloudflare.com>
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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>