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>

diff --git a/net/xfrm/xfrm_user.c b/net/xfrm/xfrm_user.c
index 963222e..6723bb2 100644 (file)
--- a/net/xfrm/xfrm_user.c
+++ b/net/xfrm/xfrm_user.c
@@ -1530,7 +1530,8 @@ static int xfrm_dump_policy_done(struct netlink_callback *cb)
 {
        struct xfrm_policy_walk *walk = (struct xfrm_policy_walk *) &cb->args[1];
 
-       xfrm_policy_walk_done(walk);
+       if (cb->args[0])
+               xfrm_policy_walk_done(walk);
        return 0;
 }