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

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>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/batman-adv/distributed-arp-table.c b/net/batman-adv/distributed-arp-table.c
index 183f97a86bb24c8099f4d3b7b7d4a5919d3432c4..553921511e4ee585cc9dd9e5bb52be59ef83298b 100644 (file)
--- a/net/batman-adv/distributed-arp-table.c
+++ b/net/batman-adv/distributed-arp-table.c
@@ -440,7 +440,7 @@ 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;