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

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Message-ID: <9fae6b381dccd6566b6366c7090468bea1f5e1d7.camel@redhat.com>
Date: Thu, 18 Apr 2024 10:57:50 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Eric Dumazet <edumazet@...gle.com>, Kuniyuki Iwashima <kuniyu@...zon.com>
Cc: kuba@...nel.org, davem@...emloft.net, dsahern@...nel.org, 
 herbert@...dor.apana.org.au, kuni1840@...il.com, netdev@...r.kernel.org, 
 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().

On Thu, 2024-04-18 at 09:00 +0200, Eric Dumazet wrote:
> On Thu, Apr 18, 2024 at 8:56 AM Eric Dumazet <edumazet@...gle.com> wrote:
> > 
> > On Thu, Apr 18, 2024 at 5:32 AM Kuniyuki Iwashima <kuniyu@...zon.com> wrote:
> > > 
> > > 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.
> > 
> > I dislike this patch series. I had this NSH bug for a while in my
> > queue, the bug is in NSH.
> > 
> > Also I added skb_vlan_inet_prepare() recently for a similar issue.
> 
> Kuniyuki I am releasing the syzbot bug with a repro, if you have time to fix NSH
> all your patches can go away I think.

I agree a specific/smaller scope fix on in nsh should be preferred
here.

Thanks,

Paolo