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From:   Yan Zhai <yan@cloudflare.com>
Date:   Tue, 1 Aug 2023 17:18:36 -0500
Message-ID: <CAO3-Pbpx8vmC_-o59s61mU=TzYLb+VpZ2qk+QhTMjVM6jf=71g@mail.gmail.com>
Subject: Re: [PATCH v4 bpf 1/2] bpf: fix skb_do_redirect return values
To:     Dan Carpenter <dan.carpenter@linaro.org>
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>,
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On Mon, Jul 31, 2023 at 9:26=E2=80=AFAM Dan Carpenter <dan.carpenter@linaro=
.org> wrote:
>
> I'm not a networking person, but I was looking at some use after free
> static checker warnings.

Did you refer to the gist I posted or something new?

>
> 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.

Yes I am adopting your suggestion in v5. Dealing with NETDEV_TX_BUSY
would be left as another item (potentially more suited for netdev
rather than bpf). Would be great to find a reproduction of memleak.

>
> Because that's the bug right?  The original code was assuming that
> everything besides LWTUNNEL_XMIT_DONE was freed.
>
> regards,
> dan carpenter
>


--=20

Yan