[PATCH] batman-adv: Fix NULL pointer dereference in DAT hash collision avoidance

[Pau Koning <paukoning@gmail.com>]

An entry in DAT with the hashed position of 0 can cause a NULL pointer
dereference when the first entry is checked by batadv_choose_next_candidate.
This first candidate automatically has the max value of 0 and the max_orig_node
of NULL. Not checking max_orig_node for NULL in batadv_is_orig_node_eligible
will lead to a NULL pointer dereference when checking for the lowest address.

This problem was added in 785ea1144182c341b8b85b0f8180291839d176a8
("batman-adv: Distributed ARP Table - create DHT helper functions").

Signed-off-by: Pau Koning <paukoning@gmail.com>
---
 net/batman-adv/distributed-arp-table.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/batman-adv/distributed-arp-table.c b/net/batman-adv/distributed-arp-table.c
index 0e05ad4..d54188a 100644
--- a/net/batman-adv/distributed-arp-table.c
+++ b/net/batman-adv/distributed-arp-table.c
@@ -439,7 +439,7 @@ static bool batadv_is_orig_node_eligible(struct batadv_dat_candidate *res,
 	/* this is an hash collision with the temporary selected node. Choose
 	 * the one with the lowest address
 	 */
-	if ((tmp_max == max) &&
+	if ((tmp_max == max) && max_orig_node &&
 	    (batadv_compare_eth(candidate->orig, max_orig_node->orig) > 0))
 		goto out;
 
-- 
1.7.10.4