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Date: Mon, 22 Apr 2024 16:52:55 +0200
From: Florian Westphal <fw@strlen.de>
To: Eric Dumazet <edumazet@google.com>
Cc: syzbot <syzbot+0c4150bff9fff3bf023c@syzkaller.appspotmail.com>,
	andrii@kernel.org, ast@kernel.org, bpf@vger.kernel.org,
	daniel@iogearbox.net, davem@davemloft.net, eddyz87@gmail.com,
	fw@strlen.de, haoluo@google.com, horms@kernel.org,
	john.fastabend@gmail.com, jolsa@kernel.org, kpsingh@kernel.org,
	kuba@kernel.org, linux-kernel@vger.kernel.org, martin.lau@linux.dev,
	netdev@vger.kernel.org, pabeni@redhat.com, sdf@google.com,
	song@kernel.org, syzkaller-bugs@googlegroups.com,
	yonghong.song@linux.dev
Subject: Re: [syzbot] [bpf?] [net?] WARNING in skb_ensure_writable
Message-ID: <20240422145255.GA13918@breakpoint.cc>
References: <000000000000eac28e0616b026d1@google.com>
 <CANn89iKr4pY3wcMb=ONr8f5DU1X300XG8RoX7HU4_FEWSAJ9_w@mail.gmail.com>
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Eric Dumazet <edumazet@google.com> wrote:
> Hmm... Not sure how to deal with this one... this is a 'false positive'
> 
> diff --git a/net/core/filter.c b/net/core/filter.c
> index 58e8e1a70aa752a2c045117e00d8797478da4738..a7cea6d717ef321215bc4cf9ab3b83535c4eec98
> 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -1662,6 +1662,11 @@ static DEFINE_PER_CPU(struct bpf_scratchpad, bpf_sp);
>  static inline int __bpf_try_make_writable(struct sk_buff *skb,
>                                           unsigned int write_len)
>  {
> +#if defined(CONFIG_DEBUG_NET)
> +       /* Avoid a splat in pskb_may_pull_reason() */
> +       if (write_len > INT_MAX)
> +               return -EINVAL;
> +#endif
>         return skb_ensure_writable(skb, write_len);
>  }
> 

LGTM, thanks Eric.  I think the current 'warn on > INT_MAX' makes sense
for normal (non-bpf) callers.