[PATCH v2] mac80211: Fix NULL-pointer deference on ibss merge when not ready

[Tim Harvey <harvey.tim@gmail.com>]

dev_open will eventually call ieee80211_ibss_join which sets up the
skb used for beacons/probe-responses however it is possible to
receive beacons that attempt to merge before this occurs causing
a null pointer dereference.  Check ssid_len as that is the last
thing set in ieee80211_ibss_join.

This occurs quite easily in the presence of adhoc nodes with hidden SSID's

Signed-off-by: Tim Harvey <harvey.tim@gmail.com>
---
 net/mac80211/ibss.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/net/mac80211/ibss.c b/net/mac80211/ibss.c
index 410d104..93926c0 100644
--- a/net/mac80211/ibss.c
+++ b/net/mac80211/ibss.c
@@ -85,6 +85,8 @@ static void __ieee80211_sta_join_ibss(struct ieee80211_sub_if_data *sdata,
 	/* Reset own TSF to allow time synchronization work. */
 	drv_reset_tsf(local);
 
+	if (!ifibss->ssid_len)
+		return; /* not ready to merge yet */
 	skb = ifibss->skb;
 	rcu_assign_pointer(ifibss->presp, NULL);
 	synchronize_rcu();
-- 
1.7.0.4