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

[Bongani Hlope <developer@hlope.org.za>]

Sorry I had some down time on my mail server. I can confirm this patch
works for me, I have been running with it since you sent it through.

Regards

On Sat,  2 May 2026 19:46:13 -0500
Sean Wang <sean.wang@kernel.org> wrote:

> 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) {