linux-kernel - Re: [PATCH 4.4 60/74] ipv6: fix udpv6 sendmsg crash caused by too small MTU

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Message-ID: <1519069941.3422.65.camel@codethink.co.uk>
Date:   Mon, 19 Feb 2018 20:52:21 +0100
From:   Ben Hutchings <ben.hutchings@...ethink.co.uk>
To:     Mike Maloney <maloney@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>
Cc:     stable@...r.kernel.org, syzbot <syzkaller@...glegroups.com>,
        "David S. Miller" <davem@...emloft.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4.4 60/74] ipv6: fix udpv6 sendmsg crash caused by too
 small MTU

On Mon, 2018-02-19 at 20:46 +0100, Ben Hutchings wrote:
> On Mon, 2018-01-29 at 13:57 +0100, Greg Kroah-Hartman wrote:
> > 4.4-stable review patch.  If anyone has any objections, please let me know.
> > 
> > ------------------
> > 
> > From: Mike Maloney <maloney@...gle.com>
> > 
> > 
> > [ Upstream commit 749439bfac6e1a2932c582e2699f91d329658196 ]
> 
> [...]
> > --- a/net/ipv6/ip6_output.c
> > +++ b/net/ipv6/ip6_output.c
> > @@ -1246,14 +1246,16 @@ static int ip6_setup_cork(struct sock *s
> >  	v6_cork->tclass = tclass;
> >  	if (rt->dst.flags & DST_XFRM_TUNNEL)
> >  		mtu = np->pmtudisc >= IPV6_PMTUDISC_PROBE ?
> > -		      rt->dst.dev->mtu : dst_mtu(&rt->dst);
> > +		      READ_ONCE(rt->dst.dev->mtu) : dst_mtu(&rt->dst);
> >  	else
> >  		mtu = np->pmtudisc >= IPV6_PMTUDISC_PROBE ?
> > -		      rt->dst.dev->mtu : dst_mtu(rt->dst.path);
> > +		      READ_ONCE(rt->dst.dev->mtu) : dst_mtu(rt->dst.path);
> >  	if (np->frag_size < mtu) {
> >  		if (np->frag_size)
> >  			mtu = np->frag_size;
> >  	}
> > +	if (mtu < IPV6_MIN_MTU)
> > +		return -EINVAL;
> 
> This error path appears to leak a reference to rt->dst.

Never mind, I see that the callers release it.

Ben.

> Ben.
> 
> > > >  	cork->base.fragsize = mtu;
> > > >  	if (dst_allfrag(rt->dst.path))
> > > >  		cork->base.flags |= IPCORK_ALLFRAG;
> > 
> > 
> > 
-- 
Ben Hutchings
Software Developer, Codethink Ltd.