[PATCH v5 wireless] mac80211: fix NULL pointer dereference in monitor mode

[Dhyan K Prajapati <dhyan19022009@gmail.com>]

From: dhyaan19022009-hue <dhyaan19022009@gmail.com>

Crash trace:
  RIP: iwlagn_bss_info_changed+0x19d/0x640 [iwldvm]
  Code: 49 8b 46 10 <8b> 10
  RAX: 0000000000000000 (NULL link->conf->bss)
wifi: mac80211: fix NULL pointer deref regression in link notify
Commit c57e5b974514 ("wifi: mac80211: fix WARN_ON for monitor mode on
some devices") reorganized link change notifications. This caused a
regression for hardware using IEEE80211_HW_WANT_MONITOR_VIF. In monitor
mode, link->conf->bss is uninitialized, but current logic allows these
notifications to reach driver callbacks, causing a deterministic NULL
dereference in drivers like iwldvm. Fix this by validating the BSS
context before driver notification.
Device: Intel Centrino Advanced-n 6205
Fixes: c57e5b974514 ("wifi: mac80211: fix WARN_ON for monitor mode on some devices")
Cc: stable@vger.kernel.org
Cc: netdev@vger.kernel.org
Cc: linux-wireless@vger.kernel.org
Cc: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Dhyan K Prajapati <dhyaan19022009@gmail.com>
---
 net/mac80211/main.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/mac80211/main.c b/net/mac80211/main.c
index b05e313c7..190222c26 100644
--- a/net/mac80211/main.c
+++ b/net/mac80211/main.c
@@ -416,6 +416,8 @@ void ieee80211_link_info_change_notify(struct ieee80211_sub_if_data *sdata,
 	case NL80211_IFTYPE_MONITOR:
 		if (!ieee80211_hw_check(&local->hw, WANT_MONITOR_VIF))
 			return;
+		if (!link->conf->bss)
+			return;
 		break;
 	default:
 		break;
-- 
2.43.0