RE: [PATCH rtw v3 1/5] wifi: rtw89: fix use-after-free in rtw89_core_tx_kick_off_and_wait()

Fedor Pchelkin pchelkin@ispras.ru wrote:

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

---

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 (me)

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

FWIW, I think RCU locking becomes unnecessary after the next patch [PATCH rtw v3 2/5] wifi: rtw89: fix tx_wait initialization race but let's keep it if you feel that's more safe.

Thanks. My thoughts are simple. 1. If it doesn't lead to bugs (i.e. not really necessary changes), keep it. 2. Keeping RCU gives us some room, if someday somehow we need to extend flow. Otherwise, we need to add it back again at that time. 3. Keep free side safe (kfree_rcu(@wait)) and doesn't depend on how complete() or wait_for_completion*() are implemented. (where completion is in @wait)

(If I change my mind after reading [PATCH v3 2/5], I will send my new comments.)

drivers/net/wireless/realtek/rtw89/core.c | 28 ++++++++++++++--- drivers/net/wireless/realtek/rtw89/core.h | 38 +++++++++++++++++++++-- drivers/net/wireless/realtek/rtw89/pci.c | 3 +- drivers/net/wireless/realtek/rtw89/ser.c | 2 ++ 4 files changed, 63 insertions(+), 8 deletions(-)

diff --git a/drivers/net/wireless/realtek/rtw89/core.c b/drivers/net/wireless/realtek/rtw89/core.c index 57590f5577a3..5c964283cd67 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); @@ -1098,17 +1108,22 @@ int

rtw89_core_tx_kick_off_and_wait(struct rtw89_dev *rtwdev, struct sk_buff *sk

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

• wait->skb = skb;

Generally, fill wait's fields before publishing it. (i.e. before rcu_assign_pointer(...))

rtw89_core_tx_kick_off(rtwdev, qsel); time_left = wait_for_completion_timeout(&wait->completion, msecs_to_jiffies(timeout));

• if (time_left == 0)

• if (time_left == 0) { ret = -ETIMEDOUT;

• else if (!wait->tx_done)

• ret = -EAGAIN;
  

• list_add_tail(&wait->list, &rtwdev->tx_waits);
  

• wiphy_work_queue(rtwdev->hw->wiphy, &rtwdev->tx_wait_work);
  
  

• rcu_assign_pointer(skb_data->wait, NULL);
• kfree_rcu(wait, rcu_head);

• } else {

• if (!wait->tx_done)
  

• 	ret = -EAGAIN;
  

• rtw89_tx_wait_release(&wait->rcu_head);
  

• }

  return ret;

} @@ -4972,6 +4987,7 @@ 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 +5219,7 @@ 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 +5250,7 @@ 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..9b22bb116af9 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 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 +6187,30 @@ 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 rcu_head *rcu_head) {

• struct rtw89_tx_wait_info *wait =

• container_of(rcu_head, struct rtw89_tx_wait_info, rcu_head);
  

• dev_kfree_skb_any(wait->skb);
• kfree(wait);

+}

+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);
  

• call_rcu(&wait->rcu_head, rtw89_tx_wait_release);
  

• }

+}

I feel dev_kfree_skb_any + kfree_rcu is fine at least for now.

For call_rcu, there is one problem to me. Can rtw89_tx_wait_release be invoked after rmmod ? e.g. one tx is never completed yet unfortunately -> user rmmod driver -> release pending skb -> rtw89_tx_wait_list_clear -> ...

So, how about the follow-up ?

rtw89_tx_wait_release(struct rtw89_tx_wait_info *wait): dev_kfree_skb_any(wait->skb) kfree_rcu(wait)

rtw89_tx_wait_list_clear(...): ... for each wait in list: ... list_del 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 +6220,7 @@ 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 +7289,12 @@ 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 +7302,13 @@ 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);

• complete_all(&wait->completion);

Maybe add a comment to hint. For example, /* Don't access skb anymore after completing */

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);

-- 2.51.0