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

[Ben Hutchings]

On Mon, 2018-01-29 at 13:57 +0100, Greg Kroah-Hartman wrote:
> 4.4-stable review patch.ÂÂIf anyone has any objections, please let me know.
> 
> ------------------
> 
> From: Mike Maloney <maloney@xxxxxxxxxx>
> 
> 
> [ 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
> Â	v6_cork->tclass = tclass;
> Â	if (rt->dst.flags & DST_XFRM_TUNNEL)
> Â		mtu = np->pmtudisc >= IPV6_PMTUDISC_PROBE ?
> -		ÂÂÂÂÂÂrt->dst.dev->mtu : dst_mtu(&rt->dst);
> +		ÂÂÂÂÂÂREAD_ONCE(rt->dst.dev->mtu) : dst_mtu(&rt->dst);
> Â	else
> Â		mtu = np->pmtudisc >= IPV6_PMTUDISC_PROBE ?
> -		ÂÂÂÂÂÂrt->dst.dev->mtu : dst_mtu(rt->dst.path);
> +		ÂÂÂÂÂÂREAD_ONCE(rt->dst.dev->mtu) : dst_mtu(rt->dst.path);
> Â	if (np->frag_size < mtu) {
> Â		if (np->frag_size)
> Â			mtu = np->frag_size;
> Â	}
> +	if (mtu < IPV6_MIN_MTU)
> +		return -EINVAL;

This error path appears to leak a reference to rt->dst.

Ben.

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