linux-kernel - Re: [PATCH] net: geneve: modify IP header check in geneve6_xmit

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Date:   Thu, 22 Apr 2021 22:03:05 +0100
From:   Phillip Potter <phil@...lpotter.co.uk>
To:     Sabrina Dubroca <sd@...asysnail.net>
Cc:     Florian Westphal <fw@...len.de>,
        Eric Dumazet <edumazet@...gle.com>,
        David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] net: geneve: modify IP header check in geneve6_xmit_skb

On Thu, Apr 22, 2021 at 07:18:49PM +0200, Sabrina Dubroca wrote:
> 2021-04-22, 18:52:10 +0200, Eric Dumazet wrote:
> > On Thu, Apr 22, 2021 at 6:04 PM Sabrina Dubroca <sd@...asysnail.net> wrote:
> > >
> > > 2021-04-22, 02:39:42 +0200, Florian Westphal wrote:
> > > > Phillip Potter <phil@...lpotter.co.uk> wrote:
> > > > > Modify the check in geneve6_xmit_skb to use the size of a struct iphdr
> > > > > rather than struct ipv6hdr. This fixes two kernel selftest failures
> > > > > introduced by commit 6628ddfec758
> > > > > ("net: geneve: check skb is large enough for IPv4/IPv6 header"), without
> > > > > diminishing the fix provided by that commit.
> > > >
> > > > What errors?
> > > >
> > > > > Reported-by: kernel test robot <oliver.sang@...el.com>
> > > > > Signed-off-by: Phillip Potter <phil@...lpotter.co.uk>
> > > > > ---
> > > > >  drivers/net/geneve.c | 2 +-
> > > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > > >
> > > > > diff --git a/drivers/net/geneve.c b/drivers/net/geneve.c
> > > > > index 42f31c681846..a57a5e6f614f 100644
> > > > > --- a/drivers/net/geneve.c
> > > > > +++ b/drivers/net/geneve.c
> > > > > @@ -988,7 +988,7 @@ static int geneve6_xmit_skb(struct sk_buff *skb, struct net_device *dev,
> > > > >     __be16 sport;
> > > > >     int err;
> > > > >
> > > > > -   if (!pskb_network_may_pull(skb, sizeof(struct ipv6hdr)))
> > > > > +   if (!pskb_network_may_pull(skb, sizeof(struct iphdr)))
> > > > >             return -EINVAL;
> > > >
> > > > Seems this is papering over some bug, this change makes no sense to
> > > > me.  Can you please explain this?
> > >
> > > I'm not sure the original commit (6628ddfec758 ("net: geneve: check
> > > skb is large enough for IPv4/IPv6 header")) is correct either. GENEVE
> > > isn't limited to carrying IP, I think an ethernet header with not much
> > > else on top should be valid.
> > 
> > Maybe, but we still attempt to use ip_hdr() in this case, from
> > geneve_get_v6_dst()
> > 
> > So there is something fishy.
> 
> In ip_tunnel_get_dsfield()? Only if there's IP in the packet. Other
> tunnel types (except vxlan, which probably has the same problem as
> geneve) ues pskb_inet_may_pull, that looks like what we need here as
> well.
> 
> -- 
> Sabrina
> 

Dear Sabrina,

Thank you for your feedback. I will try and rework the patch to fix my
original commit using the technique you suggest.

Regards,
Phil