[PATCH] iwlwifi: dvm: fix NULL pointer dereference in rxon

[dhyaan19022009-hue <dhyan19022009@gmail.com>]

When bringing up the wireless interface via virtual monitor mode,
iwlagn_bss_info_changed() can be called with a vif that has no
associated rxon context. This occurs during the
ieee80211_add_virtual_monitor() -> ieee80211_do_open() sequence.

The function iwl_rxon_ctx_from_vif() returns NULL for virtual monitor
interfaces, causing a NULL pointer dereference when the code attempts
to access ctx fields at offset +0x10.

Crash signature:
  BUG: kernel NULL pointer dereference, address: 0000000000000000
  RIP: 0010:iwlagn_bss_info_changed+0x19d/0x640 [iwldvm]
  Call Trace:
   drv_link_info_changed+0x2b5/0x2c0 [mac80211]
   ieee80211_link_info_change_notify+0x13d/0x160 [mac80211]
   ieee80211_recalc_txpower+0x5c/0x60 [mac80211]
   ieee80211_assign_link_chanctx+0x182/0x410 [mac80211]
   ieee80211_add_virtual_monitor+0x17c/0x2b0 [mac80211]
   ieee80211_do_open+0x6d8/0x740 [mac80211]

Add an early NULL check for ctx before accessing its members.

Hardware: Dell Latitude E6430
WiFi: Intel Centrino Advanced-N 6205 [8086:0085]
Kernel: 6.18.7-061807-generic

Reported-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Dhyan K Prajapati <dhyan19022009@gmail.com>
---
 drivers/net/wireless/intel/iwlwifi/dvm/rxon.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/net/wireless/intel/iwlwifi/dvm/rxon.c b/drivers/net/wireless/intel/iwlwifi/dvm/rxon.c
index e08e44cae..91dcf18b1 100644
--- a/drivers/net/wireless/intel/iwlwifi/dvm/rxon.c
+++ b/drivers/net/wireless/intel/iwlwifi/dvm/rxon.c
@@ -1392,6 +1392,11 @@ void iwlagn_bss_info_changed(struct ieee80211_hw *hw,
 
 	mutex_lock(&priv->mutex);
 
+
+        if (!ctx) {
+		mutex_unlock(&priv->mutex);
+		return;
+	}
 	if (changes & BSS_CHANGED_IDLE && vif->cfg.idle) {
 		/*
 		 * If we go idle, then clearly no "passive-no-rx"
-- 
2.43.0