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

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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