batman-adv: Avoid nullptr derefence in batadv_v_neigh_is_sob

batadv_neigh_ifinfo_get can return NULL when it cannot find (even when only
temporarily) anymore the neigh_ifinfo in the list neigh->ifinfo_list. This
has to be checked to avoid kernel Oopses when the ifinfo is dereferenced.

This a situation which isn't expected but is already handled by functions
like batadv_v_neigh_cmp. The same kind of warning is therefore used before
the function returns without dereferencing the pointers.

Fixes: 9786906022eb ("batman-adv: B.A.T.M.A.N. V - implement neighbor comparison API calls")
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Marek Lindner <mareklindner@neomailbox.ch>
Signed-off-by: Antonio Quartulli <a@unstable.cc>

net/batman-adv/bat_v.c

@@ -27,6 +27,7 @@
 #include <linux/rculist.h>
 #include <linux/rcupdate.h>
 #include <linux/seq_file.h>
+#include <linux/stddef.h>
 #include <linux/types.h>
 #include <linux/workqueue.h>
 
@@ -276,6 +277,9 @@ static bool batadv_v_neigh_is_sob(struct batadv_neigh_node *neigh1,
 	ifinfo1 = batadv_neigh_ifinfo_get(neigh1, if_outgoing1);
 	ifinfo2 = batadv_neigh_ifinfo_get(neigh2, if_outgoing2);
 
+	if (WARN_ON(!ifinfo1 || !ifinfo2))
+		return false;
+
 	threshold = ifinfo1->bat_v.throughput / 4;
 	threshold = ifinfo1->bat_v.throughput - threshold;