IB/cma: Fix a race condition in iboe_addr_get_sgid()

Code that dereferences the struct net_device ip_ptr member must be
protected with an in_dev_get() / in_dev_put() pair. Hence insert
calls to these functions.

Fixes: commit 7b85627b ("IB/cma: IBoE (RoCE) IP-based GID addressing")
Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Reviewed-by: Moni Shoua <monis@mellanox.com>
Cc: Or Gerlitz <ogerlitz@mellanox.com>
Cc: Roland Dreier <roland@purestorage.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Doug Ledford <dledford@redhat.com>

include/rdma/ib_addr.h

@@ -205,10 +205,12 @@ static inline void iboe_addr_get_sgid(struct rdma_dev_addr *dev_addr,
 
 	dev = dev_get_by_index(&init_net, dev_addr->bound_dev_if);
 	if (dev) {
-		ip4 = (struct in_device *)dev->ip_ptr;
-		if (ip4 && ip4->ifa_list && ip4->ifa_list->ifa_address)
+		ip4 = in_dev_get(dev);
+		if (ip4 && ip4->ifa_list && ip4->ifa_list->ifa_address) {
 			ipv6_addr_set_v4mapped(ip4->ifa_list->ifa_address,
 					       (struct in6_addr *)gid);
+			in_dev_put(ip4);
+		}
 		dev_put(dev);
 	}
 }