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SubjectRe: [PATCH 4.4 60/74] ipv6: fix udpv6 sendmsg crash caused by too small MTU
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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@google.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.

Ben.

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

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