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

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Message-ID: <CANn89i+raqGAERfsvxv9AM_AsgJNdnk3=YgLzf4guduj7G-s7Q@mail.gmail.com>
Date: Thu, 18 Apr 2024 09:00:32 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: 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, 
	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().

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.