net80211: fix a NULL deref in ieee80211_sta_join1()

When ieee80211_sta_join1() gets an obss without ni_nt trying to lock
that will cause a NULL pointer deref.  Check for the table to be
valid and deal with the obss node accordingly.

This can happen if sta_newstate() calls ieee80211_reset_bss() for
nstate == INIT and ostate != INIT.  ieee80211_reset_bss() itself
calls ieee80211_node_table_reset() which calls node_reclaim()
which ends up in ieee80211_del_node_nt() which does remove the
node from the table and sets ni_table to NULL.
That node (former iv_bss) can then be returned as obss in the
(*iv_update_bss)() call in join1().

MFC after:	3 days
Reviewed by:	adrian, cc
Differential Revision: https://reviews.freebsd.org/D43469

1 files changed, 8 insertions, 5 deletions

diff --git a/sys/net80211/ieee80211_node.c b/sys/net80211/ieee80211_node.c
index 123da34ad3f1..f6bb4245f543 100644
--- a/sys/net80211/ieee80211_node.c
+++ b/sys/net80211/ieee80211_node.c
@@ -867,11 +867,14 @@ ieee80211_sta_join1(struct ieee80211_node *selbs)
 		struct ieee80211_node_table *nt = obss->ni_table;
 
 		copy_bss(selbs, obss);
-		ieee80211_node_decref(obss);	/* iv_bss reference */
-
-		IEEE80211_NODE_LOCK(nt);
-		node_reclaim(nt, obss);		/* station table reference */
-		IEEE80211_NODE_UNLOCK(nt);
+		if (nt != NULL) {
+			ieee80211_node_decref(obss);	/* iv_bss reference */
+			IEEE80211_NODE_LOCK(nt);
+			node_reclaim(nt, obss);		/* station table reference */
+			IEEE80211_NODE_UNLOCK(nt);
+		} else {
+			ieee80211_free_node(obss);	/* iv_bss reference */
+		}
 
 		obss = NULL;		/* NB: guard against later use */
 	}