linux-kernel - Re: [PATCH v4 bpf 1/2] bpf: fix skb_do

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Message-ID: <38c61917-98b5-4ca0-b04e-64f956ace6e4@kadam.mountain>
Date:   Mon, 31 Jul 2023 17:26:53 +0300
From:   Dan Carpenter <dan.carpenter@...aro.org>
To:     Yan Zhai <yan@...udflare.com>
Cc:     bpf@...r.kernel.org, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Mykola Lysenko <mykolal@...com>, Shuah Khan <shuah@...nel.org>,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        linux-kselftest@...r.kernel.org, kernel-team@...udflare.com,
        Jordan Griege <jgriege@...udflare.com>,
        Markus Elfring <Markus.Elfring@....de>,
        Jakub Sitnicki <jakub@...udflare.com>
Subject: Re: [PATCH v4 bpf 1/2] bpf: fix skb_do_redirect return values

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