From 43ce9bf0770f22048156e7b36fe812a3352da842 Mon Sep 17 00:00:00 2001
From: Ben Hutchings <ben@decadent.org.uk>
Date: Sat, 9 Dec 2017 19:24:58 +0000
Subject: [PATCH] ipsec: Fix aborted xfrm policy dump crash

commit 1137b5e2529a8f5ca8ee709288ecba3e68044df2 upstream.

This is a fix for CVE-2017-16939 suitable for older stable branches.
The upstream fix is commit 1137b5e2529a8f5ca8ee709288ecba3e68044df2,
from which the following explanation is taken:

    An independent security researcher, Mohamed Ghannam, has reported
    this vulnerability to Beyond Security's SecuriTeam Secure Disclosure
    program.

    The xfrm_dump_policy_done function expects xfrm_dump_policy to
    have been called at least once or it will crash.  This can be
    triggered if a dump fails because the target socket's receive
    buffer is full.

It was not possible to define a 'start' callback for netlink dumps
until Linux 4.5, so instead add a check for the initialisation flag in
the 'done' callback.

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
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