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Date:   Tue, 21 Mar 2017 00:36:01 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     Eric Dumazet <eric.dumazet@...il.com>,
        Anarcheuz Fritz <anarcheuz@...il.com>
Cc:     davem@...emloft.net, security@...nel.org, netdev@...r.kernel.org
Subject: Re: PROBLEM: null-ptr deref in ip_options_echo may lead to denial
 of service

On Tue, 2017-03-21 at 00:33 +0000, Ben Hutchings wrote:
> On Sun, 2017-03-19 at 22:25 -0700, Eric Dumazet wrote:
> > On Mon, 2017-03-20 at 12:59 +0800, Anarcheuz Fritz wrote:
> > > Hi David,
> > > 
> > > 
> > > While working on some legacy kernel I stumbled upon a null-ptr deref in
> > > ip_options_echo. The bug has been verified on the latest version
> > > 3.2.87 from the supported long-term branch.
> > > 
> > 
> > Fixed in commit 34b2cef20f19c87999fff3da4071e66937db9644
> > ("ipv4: keep skb->dst around in presence of IP options")
> > 
> > For 3.2, since d826eb14ecef was not backported, following patch should
> > do it.
> > 
> > (Bug origin was f84af32cbca70 ("net: ip_queue_rcv_skb() helper"))
> 
> I see, I thought the vulnerability was introduced by d826eb14ecef.
> 
> > diff --git a/net/ipv4/ip_sockglue.c b/net/ipv4/ip_sockglue.c
> > index b3648bbef0da..a6e1eeb02267 100644
> > --- a/net/ipv4/ip_sockglue.c
> > +++ b/net/ipv4/ip_sockglue.c
> > @@ -1009,7 +1009,8 @@ e_inval:
> >   */
> >  int ip_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
> >  {
> > -	if (!(inet_sk(sk)->cmsg_flags & IP_CMSG_PKTINFO))
> > +	if (!(inet_sk(sk)->cmsg_flags & IP_CMSG_PKTINFO) &&
> > +	    !IPCB(skb)->opt.optlen)
> >  		skb_dst_drop(skb);
> >  	return sock_queue_rcv_skb(sk, skb);
> >  }
> 
> Thanks to both of you; I'll queue this up for 3.2.

Actually, could I have a Signed-off-by for this, Eric?

Ben.

-- 
Ben Hutchings
Power corrupts.  Absolute power is kind of neat.
                           - John Lehman, Secretary of the US Navy
1981-1987


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