netdev - Re: [PATCH net] geneve: fix header validation in geneve[6]_xmit

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date: Wed, 3 Apr 2024 16:59:52 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: Sabrina Dubroca <sd@...asysnail.net>
Cc: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org, eric.dumazet@...il.com, 
	syzbot+9ee20ec1de7b3168db09@...kaller.appspotmail.com, 
	Phillip Potter <phil@...lpotter.co.uk>
Subject: Re: [PATCH net] geneve: fix header validation in geneve[6]_xmit_skb

On Wed, Apr 3, 2024 at 4:55 PM Sabrina Dubroca <sd@...asysnail.net> wrote:
>
> 2024-04-03, 16:25:47 +0200, Eric Dumazet wrote:
> > On Wed, Apr 3, 2024 at 4:21 PM Sabrina Dubroca <sd@...asysnail.net> wrote:
> > >
> > > 2024-04-03, 11:38:53 +0000, Eric Dumazet wrote:
> > > > syzbot is able to trigger an uninit-value in geneve_xmit() [1]
> > > >
> > > > Problem : While most ip tunnel helpers (like ip_tunnel_get_dsfield())
> > > > uses skb_protocol(skb, true), pskb_inet_may_pull() is only using
> > > > skb->protocol.
> > > >
> > > > If anything else than ETH_P_IPV6 or ETH_P_IP is found in skb->protocol,
> > > > pskb_inet_may_pull() does nothing at all.
> > > >
> > > > If a vlan tag was provided by the caller (af_packet in the syzbot case),
> > > > the network header might not point to the correct location, and skb
> > > > linear part could be smaller than expected.
> > > >
> > > > Add skb_vlan_inet_prepare() to perform a complete validation and pull.
> > > > If no IPv4/IPv6 header is found, it returns 0.
> > >
> > > And then geneve_xmit_skb/geneve6_xmit_skb drops the packet, which
> > > breaks ARP over a geneve tunnel, and other valid things like macsec.
> >
> > geneve_xmit_skb() uses ip_hdr() blindly.
>
> Do those actually end up getting used? They get passed to
> {ip_tunnel_ecn_encap,ip_tunnel_get_ttl,ip_tunnel_get_dsfield}, and
> those helpers only look at their iph argument when skb_protocol(skb,
> true) is ETH_P_IP or ETH_P_IPV6. So, definitely not pretty, but I
> don't see a bug there. Am I missing something?

Please read my changelog, I explained that skb_protocol(skb, true) is
parsing the Ethernet header up to the non vlan proto.

syzbot buillt a vlan packet with final proto being IPv4.

So the helpers who are using skb_protocol() do not understand the IP
header has not been pulled.

>
> From a quick look, most users of those helpers seem to pass
> ip_hdr(skb) (except for ip_tunnel_ecn_encap called from
> ip_md_tunnel_xmit and ip_tunnel_xmit -- vxlan_xmit_one uses a cached
> version but I don't think it's needed). Would it be less confusing if
> we removed that argument and let the helper fetch ip_hdr?

If you look at the syzbot report, the ip header is definitely dereferenced.