[PATCH] wifi: mt76: mt792x: fix NULL dereference during CSA beacon handling

[Sean Wang <sean.wang@kernel.org>]

From: Sean Wang <sean.wang@mediatek.com>

mac80211 may call channel_switch_rx_beacon() while CSA is active, but
mt76's cached dev->new_ctx is not guaranteed to be valid at that point.

Avoid dereferencing dev->new_ctx when the target channel context is not
available and leave the existing CSA timer unchanged.

kernel: Workqueue: events_unbound cfg80211_wiphy_work [cfg80211]
kernel: RIP: 0010:mt7921_channel_switch_rx_beacon+0x1f/0x100
[mt7921_common]
kernel: RAX: 0000000000000000
kernel: CR2: 0000000000000000
kernel: Call Trace:
kernel:  <TASK>
kernel:  ieee80211_sta_process_chanswitch+0x67c/0xee0 [mac80211]
kernel:  ieee80211_rx_mgmt_beacon+0x842/0x22a0 [mac80211]
kernel:  ieee80211_sta_rx_queued_mgmt+0xa7/0xbb0 [mac80211]
kernel:  ieee80211_iface_work+0x62e/0x890 [mac80211]
kernel:  cfg80211_wiphy_work+0x1ee/0x280 [cfg80211]
kernel:  process_scheduled_works+0x180/0x680
kernel:  worker_thread+0x1aa/0x450
kernel:  kthread+0x181/0x1e0
kernel:  ret_from_fork+0x405/0x600
kernel:  ret_from_fork_asm+0x11/0x20
kernel:  </TASK>
kernel: CR2: 0000000000000000
kernel: ---[ end trace 0000000000000000 ]---

mt7925 has the same unsafe dev->new_ctx dereference in its CSA beacon
handling path, so guard both drivers against the missing target channel
context and leave the existing CSA timer unchanged.

Reported-by: Bongani Hlope <developer@hlope.org.za>
Closes: https://lore.kernel.org/linux-wireless/20260502140616.7672da98@bongani-mini.home.org.za/
Fixes: 8aa2f59260eb ("wifi: mt76: mt7921: introduce CSA support")
Fixes: 7900da40e315 ("wifi: mt76: mt7925: introduce CSA support in non-MLO mode")
Signed-off-by: Sean Wang <sean.wang@mediatek.com>
---
 drivers/net/wireless/mediatek/mt76/mt7921/main.c | 3 +++
 drivers/net/wireless/mediatek/mt76/mt7925/main.c | 3 +++
 2 files changed, 6 insertions(+)

diff --git a/drivers/net/wireless/mediatek/mt76/mt7921/main.c b/drivers/net/wireless/mediatek/mt76/mt7921/main.c
index 3d74fabe7408..a326f4c95c7c 100644
--- a/drivers/net/wireless/mediatek/mt76/mt7921/main.c
+++ b/drivers/net/wireless/mediatek/mt76/mt7921/main.c
@@ -1508,6 +1508,9 @@ static void mt7921_channel_switch_rx_beacon(struct ieee80211_hw *hw,
 	struct mt792x_vif *mvif = (struct mt792x_vif *)vif->drv_priv;
 	u16 beacon_interval = vif->bss_conf.beacon_int;
 
+	if (!dev->new_ctx)
+		return;
+
 	if (cfg80211_chandef_identical(&chsw->chandef,
 				       &dev->new_ctx->def) &&
 				       chsw->count) {
diff --git a/drivers/net/wireless/mediatek/mt76/mt7925/main.c b/drivers/net/wireless/mediatek/mt76/mt7925/main.c
index 73d3722739d0..b96a8e2efcbc 100644
--- a/drivers/net/wireless/mediatek/mt76/mt7925/main.c
+++ b/drivers/net/wireless/mediatek/mt76/mt7925/main.c
@@ -2402,6 +2402,9 @@ static void mt7925_channel_switch_rx_beacon(struct ieee80211_hw *hw,
 
 	beacon_interval = vif->bss_conf.beacon_int;
 
+	if (!dev->new_ctx)
+		return;
+
 	if (cfg80211_chandef_identical(&chsw->chandef,
 				       &dev->new_ctx->def) &&
 				       chsw->count) {
-- 
2.43.0