[SRU][Xenial][PATCH 1/1] s390/qeth: fix L3 next-hop in xmit qeth hdr

[Joseph Salisbury]

From: Julian Wiedmann <jwi at linux.vnet.ibm.com>

BugLink: http://bugs.launchpad.net/bugs/1750813

On L3, the qeth_hdr struct needs to be filled with the next-hop
IP address.
The current code accesses rtable->rt_gateway without checking that
rtable is a valid address. The accidental access to a lowcore area
results in a random next-hop address in the qeth_hdr.
rtable (or more precisely, skb_dst(skb)) can be NULL in rare cases
(for instance together with AF_PACKET sockets).
This patch adds the missing NULL-ptr checks.

Signed-off-by: Julian Wiedmann <jwi at linux.vnet.ibm.com>
Signed-off-by: Ursula Braun <ubraun at linux.vnet.ibm.com>
Fixes: 87e7597b5a3 qeth: Move away from using neighbour entries in qeth_l3_fill_header()
Signed-off-by: David S. Miller <davem at davemloft.net>
(cherry picked from commit ec2c6726322f0d270bab477e4904bf9496f70ee5)
Signed-off-by: Joseph Salisbury <joseph.salisbury at canonical.com>
---
 drivers/s390/net/qeth_l3_main.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/s390/net/qeth_l3_main.c b/drivers/s390/net/qeth_l3_main.c
index bf3c1b2..84774c3 100644
--- a/drivers/s390/net/qeth_l3_main.c
+++ b/drivers/s390/net/qeth_l3_main.c
@@ -2727,7 +2727,7 @@ static void qeth_l3_fill_header(struct qeth_card *card, struct qeth_hdr *hdr,
 		struct rtable *rt = (struct rtable *) dst;
 		__be32 *pkey = &ip_hdr(skb)->daddr;
 
-		if (rt->rt_gateway)
+		if (rt && rt->rt_gateway)
 			pkey = &rt->rt_gateway;
 
 		/* IPv4 */
@@ -2738,7 +2738,7 @@ static void qeth_l3_fill_header(struct qeth_card *card, struct qeth_hdr *hdr,
 		struct rt6_info *rt = (struct rt6_info *) dst;
 		struct in6_addr *pkey = &ipv6_hdr(skb)->daddr;
 
-		if (!ipv6_addr_any(&rt->rt6i_gateway))
+		if (rt && !ipv6_addr_any(&rt->rt6i_gateway))
 			pkey = &rt->rt6i_gateway;
 
 		/* IPv6 */
-- 
2.7.4