netdev - Re: [syzbot] [net?] WARNING in mpls_gso

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Message-ID: <20240222125738.GC28098@breakpoint.cc>
Date: Thu, 22 Feb 2024 13:57:38 +0100
From: Florian Westphal <fw@...len.de>
To: Eric Dumazet <edumazet@...gle.com>
Cc: Florian Westphal <fw@...len.de>,
	syzbot <syzbot+99d15fcdb0132a1e1a82@...kaller.appspotmail.com>,
	davem@...emloft.net, dsahern@...nel.org, horms@...nel.org,
	kuba@...nel.org, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org, pabeni@...hat.com,
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [net?] WARNING in mpls_gso_segment

Eric Dumazet <edumazet@...gle.com> wrote:
> I was thinking about adding a debug check in skb_inner_network_header(skb)
> if inner_network_header is zero (that would mean it is not 'set' yet),
> but this would trigger even after your patch.

What about adding:

static inline bool skb_inner_network_header_was_set(const struct sk_buff *skb)
{
	return skb->inner_network_header > 0;
}

... and using that instead of checking for negative header length
post-subtraction?