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

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Date:   Thu, 22 Apr 2021 18:03:32 +0200
From:   Sabrina Dubroca <sd@...asysnail.net>
To:     Florian Westphal <fw@...len.de>
Cc:     Phillip Potter <phil@...lpotter.co.uk>, davem@...emloft.net,
        kuba@...nel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, edumazet@...gle.com
Subject: Re: [PATCH] net: geneve: modify IP header check in geneve6_xmit_skb

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.

-- 
Sabrina