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Date: Thu, 22 Feb 2024 13:57:38 +0100
From: Florian Westphal <fw@strlen.de>
To: Eric Dumazet <edumazet@google.com>
Cc: Florian Westphal <fw@strlen.de>,
	syzbot <syzbot+99d15fcdb0132a1e1a82@syzkaller.appspotmail.com>,
	davem@davemloft.net, dsahern@kernel.org, horms@kernel.org,
	kuba@kernel.org, linux-kernel@vger.kernel.org,
	netdev@vger.kernel.org, pabeni@redhat.com,
	syzkaller-bugs@googlegroups.com
Subject: Re: [syzbot] [net?] WARNING in mpls_gso_segment
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Eric Dumazet <edumazet@google.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?