netdev - Re: [PATCH v1 net 1/5] sit: Pull header after checking skb->protocol in sit_tunnel

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Date: Wed, 17 Apr 2024 20:31:45 -0700
From: Kuniyuki Iwashima <kuniyu@...zon.com>
To: <kuba@...nel.org>
CC: <davem@...emloft.net>, <dsahern@...nel.org>, <edumazet@...gle.com>,
	<herbert@...dor.apana.org.au>, <kuni1840@...il.com>, <kuniyu@...zon.com>,
	<netdev@...r.kernel.org>, <pabeni@...hat.com>,
	<steffen.klassert@...unet.com>, <syzkaller@...glegroups.com>,
	<willemb@...gle.com>
Subject: Re: [PATCH v1 net 1/5] sit: Pull header after checking skb->protocol in sit_tunnel_xmit().

From: Jakub Kicinski <kuba@...nel.org>
Date: Wed, 17 Apr 2024 19:04:32 -0700
> On Mon, 15 Apr 2024 15:20:37 -0700 Kuniyuki Iwashima wrote:
> > syzkaller crafted a GSO packet of ETH_P_8021AD + ETH_P_NSH and sent it
> > over sit0.
> > 
> > After nsh_gso_segment(), skb->data - skb->head was 138, on the other
> > hand, skb->network_header was 128.
> 
> is data offset > skb->network_header valid at this stage?
> Can't we drop these packets instead?

I think that needs another fix on the NSH side.

But even with that, we can still pass valid L2 skb to sit_tunnel_xmit()
and friends, and then we should just drop it there without calling
pskb_inet_may_pull() that should not be called for non-IP skb.