netdev - Re: [PATCH 2/2] netfilter: ipvs/SIP: handle ip_vs_fill_iph_skb

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Date:	Thu, 28 Jan 2016 08:39:14 +0900
From:	Simon Horman <horms@...ge.net.au>
To:	Julian Anastasov <ja@....bg>
Cc:	Arnd Bergmann <arnd@...db.de>,
	Wensong Zhang <wensong@...ux-vs.org>,
	linux-arm-kernel@...ts.infradead.org,
	Pablo Neira Ayuso <pablo@...filter.org>,
	Patrick McHardy <kaber@...sh.net>,
	Jozsef Kadlecsik <kadlec@...ckhole.kfki.hu>,
	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
	lvs-devel@...r.kernel.org, netfilter-devel@...r.kernel.org,
	coreteam@...filter.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] netfilter: ipvs/SIP: handle ip_vs_fill_iph_skb_off
 failure

On Wed, Jan 27, 2016 at 10:56:08PM +0200, Julian Anastasov wrote:
> 
> 	Hello,
> 
> On Wed, 27 Jan 2016, Arnd Bergmann wrote:
> 
> > ip_vs_fill_iph_skb_off() may not find an IP header, and gcc has
> > determined that ip_vs_sip_fill_param() then incorrectly accesses
> > the protocol fields:
> > 
> > net/netfilter/ipvs/ip_vs_pe_sip.c: In function 'ip_vs_sip_fill_param':
> > net/netfilter/ipvs/ip_vs_pe_sip.c:76:5: error: 'iph.protocol' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> >   if (iph.protocol != IPPROTO_UDP)
> >      ^
> > net/netfilter/ipvs/ip_vs_pe_sip.c:81:10: error: 'iph.len' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> >   dataoff = iph.len + sizeof(struct udphdr);
> >           ^
> > 
> > This adds a check for the ip_vs_fill_iph_skb_off() return code
> > before looking at the ip header data returned from it.
> > 
> > Signed-off-by: Arnd Bergmann <arnd@...db.de>
> > Fixes: b0e010c527de ("ipvs: replace ip_vs_fill_ip4hdr with ip_vs_fill_iph_skb_off")
> 
> 	Looks ok to me,
> 
> Acked-by: Julian Anastasov <ja@....bg>

Thanks, I have queued this up.

> 	but see below...
> 
> > ---
> >  net/netfilter/ipvs/ip_vs_pe_sip.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/net/netfilter/ipvs/ip_vs_pe_sip.c b/net/netfilter/ipvs/ip_vs_pe_sip.c
> > index 1b8d594e493a..c4e9ca016a88 100644
> > --- a/net/netfilter/ipvs/ip_vs_pe_sip.c
> > +++ b/net/netfilter/ipvs/ip_vs_pe_sip.c
> > @@ -70,10 +70,10 @@ ip_vs_sip_fill_param(struct ip_vs_conn_param *p, struct sk_buff *skb)
> >  	const char *dptr;
> >  	int retc;
> >  
> > -	ip_vs_fill_iph_skb(p->af, skb, false, &iph);
> > +	retc = ip_vs_fill_iph_skb(p->af, skb, false, &iph);
> >  
> >  	/* Only useful with UDP */
> > -	if (iph.protocol != IPPROTO_UDP)
> > +	if (!retc || iph.protocol != IPPROTO_UDP)
> >  		return -EINVAL;
> >  	/* todo: IPv6 fragments:
> >  	 *       I think this only should be done for the first fragment. /HS
> 
> 	There are other places like this where result is not
> checked because there is always a guarding skb_header_pointer
> check, i.e. ip_vs_fill_iph_skb* should not fail at such point.
> 
> 	Let us know you want to extend this patch with other such
> calls (including ip_vs_fill_iph_skb_icmp)? May be they will
> need return NF_ACCEPT. I guess, all such changes should be
> for the ipvs-next/net-next tree when it opens.

I would suggest making such changes incrementally on top of this one.