There is a bug observed when rtw89_core_tx_kick_off_and_wait() tries to access already freed skb_data:

BUG: KFENCE: use-after-free write in rtw89_core_tx_kick_off_and_wait drivers/net/wireless/realtek/rtw89/core.c:1110

CPU: 6 UID: 0 PID: 41377 Comm: kworker/u64:24 Not tainted 6.17.0-rc1+ #1 PREEMPT(lazy) Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS edk2-20250523-14.fc42 05/23/2025 Workqueue: events_unbound cfg80211_wiphy_work [cfg80211]

Use-after-free write at 0x0000000020309d9d (in kfence-#251): rtw89_core_tx_kick_off_and_wait drivers/net/wireless/realtek/rtw89/core.c:1110 rtw89_core_scan_complete drivers/net/wireless/realtek/rtw89/core.c:5338 rtw89_hw_scan_complete_cb drivers/net/wireless/realtek/rtw89/fw.c:7979 rtw89_chanctx_proceed_cb drivers/net/wireless/realtek/rtw89/chan.c:3165 rtw89_chanctx_proceed drivers/net/wireless/realtek/rtw89/chan.h:141 rtw89_hw_scan_complete drivers/net/wireless/realtek/rtw89/fw.c:8012 rtw89_mac_c2h_scanofld_rsp drivers/net/wireless/realtek/rtw89/mac.c:5059 rtw89_fw_c2h_work drivers/net/wireless/realtek/rtw89/fw.c:6758 process_one_work kernel/workqueue.c:3241 worker_thread kernel/workqueue.c:3400 kthread kernel/kthread.c:463 ret_from_fork arch/x86/kernel/process.c:154 ret_from_fork_asm arch/x86/entry/entry_64.S:258

kfence-#251: 0x0000000056e2393d-0x000000009943cb62, size=232, cache=skbuff_head_cache

allocated by task 41377 on cpu 6 at 77869.159548s (0.009551s ago): __alloc_skb net/core/skbuff.c:659 __netdev_alloc_skb net/core/skbuff.c:734 ieee80211_nullfunc_get net/mac80211/tx.c:5844 rtw89_core_send_nullfunc drivers/net/wireless/realtek/rtw89/core.c:3431 rtw89_core_scan_complete drivers/net/wireless/realtek/rtw89/core.c:5338 rtw89_hw_scan_complete_cb drivers/net/wireless/realtek/rtw89/fw.c:7979 rtw89_chanctx_proceed_cb drivers/net/wireless/realtek/rtw89/chan.c:3165 rtw89_chanctx_proceed drivers/net/wireless/realtek/rtw89/chan.c:3194 rtw89_hw_scan_complete drivers/net/wireless/realtek/rtw89/fw.c:8012 rtw89_mac_c2h_scanofld_rsp drivers/net/wireless/realtek/rtw89/mac.c:5059 rtw89_fw_c2h_work drivers/net/wireless/realtek/rtw89/fw.c:6758 process_one_work kernel/workqueue.c:3241 worker_thread kernel/workqueue.c:3400 kthread kernel/kthread.c:463 ret_from_fork arch/x86/kernel/process.c:154 ret_from_fork_asm arch/x86/entry/entry_64.S:258

freed by task 1045 on cpu 9 at 77869.168393s (0.001557s ago): ieee80211_tx_status_skb net/mac80211/status.c:1117 rtw89_pci_release_txwd_skb drivers/net/wireless/realtek/rtw89/pci.c:564 rtw89_pci_release_tx_skbs.isra.0 drivers/net/wireless/realtek/rtw89/pci.c:651 rtw89_pci_release_tx drivers/net/wireless/realtek/rtw89/pci.c:676 rtw89_pci_napi_poll drivers/net/wireless/realtek/rtw89/pci.c:4238 __napi_poll net/core/dev.c:7495 net_rx_action net/core/dev.c:7557 net/core/dev.c:7684 handle_softirqs kernel/softirq.c:580 do_softirq.part.0 kernel/softirq.c:480 __local_bh_enable_ip kernel/softirq.c:407 rtw89_pci_interrupt_threadfn drivers/net/wireless/realtek/rtw89/pci.c:927 irq_thread_fn kernel/irq/manage.c:1133 irq_thread kernel/irq/manage.c:1257 kthread kernel/kthread.c:463 ret_from_fork arch/x86/kernel/process.c:154 ret_from_fork_asm arch/x86/entry/entry_64.S:258

It is a consequence of a race between the waiting and the signaling side of the completion:

Waiting thread Completing thread

rtw89_core_tx_kick_off_and_wait() rcu_assign_pointer(skb_data->wait, wait) /* start waiting */ wait_for_completion_timeout() rtw89_pci_tx_status() rtw89_core_tx_wait_complete() rcu_read_lock() /* signals completion and * proceeds further */ complete(&wait->completion) rcu_read_unlock() ... /* frees skb_data */ ieee80211_tx_status_ni() /* returns (exit status doesn't matter) */ wait_for_completion_timeout() ... /* accesses the already freed skb_data */ rcu_assign_pointer(skb_data->wait, NULL)

The completing side might proceed and free the underlying skb even before the waiting side is fully awoken and run to execution. Actually the race happens regardless of wait_for_completion_timeout() exit status, e.g. the waiting side may hit a timeout and the concurrent completing side is still able to free the skb.

Skbs which are sent by rtw89_core_tx_kick_off_and_wait() are owned by the driver. They don't come from core ieee80211 stack so no need to pass them to ieee80211_tx_status_ni() on completing side.

Introduce a work function which will act as a garbage collector for rtw89_tx_wait_info objects and the associated skbs. Thus no potentially heavy locks are required on the completing side.

Found by Linux Verification Center (linuxtesting.org).

Fixes: 1ae5ca615285 ("wifi: rtw89: add function to wait for completion of TX skbs") Cc: stable@vger.kernel.org Suggested-by: Zong-Zhe Yang kevin_yang@realtek.com Signed-off-by: Fedor Pchelkin pchelkin@ispras.ru ---

v4: - fill wait's fields before publishing (Zong-Zhe) - leave dev_kfree_skb_any + kfree_rcu for tx_wait release (Zong-Zhe)

v3: - decrease waiting timeout in rtw89_tx_wait_work() (Zong-Zhe) - clear tx_waits list from rtw89_hci_reset(), too (Zong-Zhe) - keep RCU updating for skb_data->wait (Zong-Zhe) - keep the old order of calls in rtw89_pci_tx_status() (Zong-Zhe) - drop wait->finished as complete_all() would make the completion be done permanently

v2: - use a work function to manage release of tx_waits and associated skbs (Zong-Zhe)

drivers/net/wireless/realtek/rtw89/core.c | 29 ++++++++++++++---- drivers/net/wireless/realtek/rtw89/core.h | 36 +++++++++++++++++++++-- drivers/net/wireless/realtek/rtw89/pci.c | 3 +- drivers/net/wireless/realtek/rtw89/ser.c | 2 ++ 4 files changed, 61 insertions(+), 9 deletions(-)

diff --git a/drivers/net/wireless/realtek/rtw89/core.c b/drivers/net/wireless/realtek/rtw89/core.c index 57590f5577a3..438930b65631 100644 --- a/drivers/net/wireless/realtek/rtw89/core.c +++ b/drivers/net/wireless/realtek/rtw89/core.c @@ -1073,6 +1073,14 @@ rtw89_core_tx_update_desc_info(struct rtw89_dev *rtwdev, } }

+static void rtw89_tx_wait_work(struct wiphy *wiphy, struct wiphy_work *work) +{ + struct rtw89_dev *rtwdev = container_of(work, struct rtw89_dev, + tx_wait_work); + + rtw89_tx_wait_list_clear(rtwdev); +} + void rtw89_core_tx_kick_off(struct rtw89_dev *rtwdev, u8 qsel) { u8 ch_dma; @@ -1090,6 +1098,8 @@ int rtw89_core_tx_kick_off_and_wait(struct rtw89_dev *rtwdev, struct sk_buff *sk unsigned long time_left; int ret = 0;

+ lockdep_assert_wiphy(rtwdev->hw->wiphy); + wait = kzalloc(sizeof(*wait), GFP_KERNEL); if (!wait) { rtw89_core_tx_kick_off(rtwdev, qsel); @@ -1097,18 +1107,22 @@ int rtw89_core_tx_kick_off_and_wait(struct rtw89_dev *rtwdev, struct sk_buff *sk }

init_completion(&wait->completion); + wait->skb = skb; rcu_assign_pointer(skb_data->wait, wait);

rtw89_core_tx_kick_off(rtwdev, qsel); time_left = wait_for_completion_timeout(&wait->completion, msecs_to_jiffies(timeout)); - if (time_left == 0) - ret = -ETIMEDOUT; - else if (!wait->tx_done) - ret = -EAGAIN;

- rcu_assign_pointer(skb_data->wait, NULL); - kfree_rcu(wait, rcu_head); + if (time_left == 0) { + ret = -ETIMEDOUT; + list_add_tail(&wait->list, &rtwdev->tx_waits); + wiphy_work_queue(rtwdev->hw->wiphy, &rtwdev->tx_wait_work); + } else { + if (!wait->tx_done) + ret = -EAGAIN; + rtw89_tx_wait_release(wait); + }

return ret; } @@ -4972,6 +4986,7 @@ void rtw89_core_stop(struct rtw89_dev *rtwdev) clear_bit(RTW89_FLAG_RUNNING, rtwdev->flags);

wiphy_work_cancel(wiphy, &rtwdev->c2h_work); + wiphy_work_cancel(wiphy, &rtwdev->tx_wait_work); wiphy_work_cancel(wiphy, &rtwdev->cancel_6ghz_probe_work); wiphy_work_cancel(wiphy, &btc->eapol_notify_work); wiphy_work_cancel(wiphy, &btc->arp_notify_work); @@ -5203,6 +5218,7 @@ int rtw89_core_init(struct rtw89_dev *rtwdev) INIT_LIST_HEAD(&rtwdev->scan_info.pkt_list[band]); } INIT_LIST_HEAD(&rtwdev->scan_info.chan_list); + INIT_LIST_HEAD(&rtwdev->tx_waits); INIT_WORK(&rtwdev->ba_work, rtw89_core_ba_work); INIT_WORK(&rtwdev->txq_work, rtw89_core_txq_work); INIT_DELAYED_WORK(&rtwdev->txq_reinvoke_work, rtw89_core_txq_reinvoke_work); @@ -5233,6 +5249,7 @@ int rtw89_core_init(struct rtw89_dev *rtwdev) wiphy_work_init(&rtwdev->c2h_work, rtw89_fw_c2h_work); wiphy_work_init(&rtwdev->ips_work, rtw89_ips_work); wiphy_work_init(&rtwdev->cancel_6ghz_probe_work, rtw89_cancel_6ghz_probe_work); + wiphy_work_init(&rtwdev->tx_wait_work, rtw89_tx_wait_work); INIT_WORK(&rtwdev->load_firmware_work, rtw89_load_firmware_work);

skb_queue_head_init(&rtwdev->c2h_queue); diff --git a/drivers/net/wireless/realtek/rtw89/core.h b/drivers/net/wireless/realtek/rtw89/core.h index 43e10278e14d..b5586603f027 100644 --- a/drivers/net/wireless/realtek/rtw89/core.h +++ b/drivers/net/wireless/realtek/rtw89/core.h @@ -3506,9 +3506,12 @@ struct rtw89_phy_rate_pattern { bool enable; };

+#define RTW89_TX_WAIT_DEFAULT_TIMEOUT msecs_to_jiffies(10) struct rtw89_tx_wait_info { struct rcu_head rcu_head; + struct list_head list; struct completion completion; + struct sk_buff *skb; bool tx_done; };

@@ -5925,6 +5928,9 @@ struct rtw89_dev { /* used to protect rpwm */ spinlock_t rpwm_lock;

+ struct list_head tx_waits; + struct wiphy_work tx_wait_work; + struct rtw89_cam_info cam_info;

struct sk_buff_head c2h_queue; @@ -6181,6 +6187,27 @@ rtw89_assoc_link_rcu_dereference(struct rtw89_dev *rtwdev, u8 macid) list_first_entry_or_null(&p->dlink_pool, typeof(*p->links_inst), dlink_schd); \ })

+static inline void rtw89_tx_wait_release(struct rtw89_tx_wait_info *wait) +{ + dev_kfree_skb_any(wait->skb); + kfree_rcu(wait, rcu_head); +} + +static inline void rtw89_tx_wait_list_clear(struct rtw89_dev *rtwdev) +{ + struct rtw89_tx_wait_info *wait, *tmp; + + lockdep_assert_wiphy(rtwdev->hw->wiphy); + + list_for_each_entry_safe(wait, tmp, &rtwdev->tx_waits, list) { + if (!wait_for_completion_timeout(&wait->completion, + RTW89_TX_WAIT_DEFAULT_TIMEOUT)) + continue; + list_del(&wait->list); + rtw89_tx_wait_release(wait); + } +} + static inline int rtw89_hci_tx_write(struct rtw89_dev *rtwdev, struct rtw89_core_tx_request *tx_req) { @@ -6190,6 +6217,7 @@ static inline int rtw89_hci_tx_write(struct rtw89_dev *rtwdev, static inline void rtw89_hci_reset(struct rtw89_dev *rtwdev) { rtwdev->hci.ops->reset(rtwdev); + rtw89_tx_wait_list_clear(rtwdev); }

static inline int rtw89_hci_start(struct rtw89_dev *rtwdev) @@ -7258,11 +7286,12 @@ static inline struct sk_buff *rtw89_alloc_skb_for_rx(struct rtw89_dev *rtwdev, return dev_alloc_skb(length); }

-static inline void rtw89_core_tx_wait_complete(struct rtw89_dev *rtwdev, +static inline bool rtw89_core_tx_wait_complete(struct rtw89_dev *rtwdev, struct rtw89_tx_skb_data *skb_data, bool tx_done) { struct rtw89_tx_wait_info *wait; + bool ret = false;

rcu_read_lock();

@@ -7270,11 +7299,14 @@ static inline void rtw89_core_tx_wait_complete(struct rtw89_dev *rtwdev, if (!wait) goto out;

+ ret = true; wait->tx_done = tx_done; - complete(&wait->completion); + /* Don't access skb anymore after completion */ + complete_all(&wait->completion);

out: rcu_read_unlock(); + return ret; }

static inline bool rtw89_is_mlo_1_1(struct rtw89_dev *rtwdev) diff --git a/drivers/net/wireless/realtek/rtw89/pci.c b/drivers/net/wireless/realtek/rtw89/pci.c index a669f2f843aa..4e3034b44f56 100644 --- a/drivers/net/wireless/realtek/rtw89/pci.c +++ b/drivers/net/wireless/realtek/rtw89/pci.c @@ -464,7 +464,8 @@ static void rtw89_pci_tx_status(struct rtw89_dev *rtwdev, struct rtw89_tx_skb_data *skb_data = RTW89_TX_SKB_CB(skb); struct ieee80211_tx_info *info;

- rtw89_core_tx_wait_complete(rtwdev, skb_data, tx_status == RTW89_TX_DONE); + if (rtw89_core_tx_wait_complete(rtwdev, skb_data, tx_status == RTW89_TX_DONE)) + return;

info = IEEE80211_SKB_CB(skb); ieee80211_tx_info_clear_status(info); diff --git a/drivers/net/wireless/realtek/rtw89/ser.c b/drivers/net/wireless/realtek/rtw89/ser.c index bb39fdbcba0d..fe7beff8c424 100644 --- a/drivers/net/wireless/realtek/rtw89/ser.c +++ b/drivers/net/wireless/realtek/rtw89/ser.c @@ -502,7 +502,9 @@ static void ser_reset_trx_st_hdl(struct rtw89_ser *ser, u8 evt) }

drv_stop_rx(ser); + wiphy_lock(wiphy); drv_trx_reset(ser); + wiphy_unlock(wiphy);

/* wait m3 */ hal_send_m2_event(ser);