netdev - Re: [PATCH bpf] bpf: avoid splat in pskb_pull

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Message-ID: <CANn89i+TRnT8E4fE-kKcUcF2LZ76yAsz=C-450sj54Z1Vq+zrQ@mail.gmail.com>
Date: Fri, 14 Jun 2024 14:11:26 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: Florian Westphal <fw@...len.de>
Cc: bpf@...r.kernel.org, martin.lau@...ux.dev, daniel@...earbox.net, 
	netdev@...r.kernel.org, syzbot+0c4150bff9fff3bf023c@...kaller.appspotmail.com
Subject: Re: [PATCH bpf] bpf: avoid splat in pskb_pull_reason

On Fri, Jun 14, 2024 at 12:41 PM Florian Westphal <fw@...len.de> wrote:
>
> syzkaller builds (CONFIG_DEBUG_NET=y) frequently trigger a debug
> hint in pskb_may_pull.
>
> We'd like to retain this debug check because it might hint at integer
> overflows and other issues (kernel code should pull headers, not huge
> value).
>
> In bpf case, this splat isn't interesting at all: such (nonsensical) bpf
> programs are typically generated by a fuzzer anyway.
>
> Do what Eric suggested and suppress such warning.
>
> For CONFIG_DEBUG_NET=n we don't need the extra check because
> pskb_may_pull will do the right thing: return an error without the
> WARN() backtrace.
>
> Reported-by: syzbot+0c4150bff9fff3bf023c@...kaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=0c4150bff9fff3bf023c
> Fixes: 219eee9c0d16 ("net: skbuff: add overflow debug check to pull/push helpers")
> Link: https://lore.kernel.org/netdev/9f254c96-54f2-4457-b7ab-1d9f6187939c@gmail.com/
> Suggested-by: Eric Dumazet <edumazet@...gle.com>
> Signed-off-by: Florian Westphal <fw@...len.de>
> ---

Thanks Florian

Reviewed-by: Eric Dumazet <edumazet@...gle.com>