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Date:   Mon, 31 Jul 2023 17:26:53 +0300
From:   Dan Carpenter <dan.carpenter@linaro.org>
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>,
        Jakub Sitnicki <jakub@cloudflare.com>
Subject: Re: [PATCH v4 bpf 1/2] bpf: fix skb_do_redirect return values
Message-ID: <38c61917-98b5-4ca0-b04e-64f956ace6e4@kadam.mountain>
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Precedence: bulk

I'm not a networking person, but I was looking at some use after free
static checker warnings.

Apparently the rule with xmit functions is that if they return a value
> 15 then that means the skb was not freed.  Otherwise it's supposed to
be freed.  So like NETDEV_TX_BUSY is 0x10 so it's not freed.

This is checked with using the dev_xmit_complete() function.  So I feel
like it would make sense for LWTUNNEL_XMIT_CONTINUE to return higher
than 15.

Because that's the bug right?  The original code was assuming that
everything besides LWTUNNEL_XMIT_DONE was freed.

regards,
dan carpenter