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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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