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Message-ID: <eaf2925504f14e9db946978a366fcbdf@realtek.com>
Date: Mon, 22 Sep 2025 01:18:38 +0000
From: Ping-Ke Shih <pkshih@...ltek.com>
To: Fedor Pchelkin <pchelkin@...ras.ru>,
Zong-Zhe Yang
<kevin_yang@...ltek.com>
CC: Bitterblue Smith <rtl8821cerfe2@...il.com>,
Bernie Huang
<phhuang@...ltek.com>,
"linux-wireless@...r.kernel.org"
<linux-wireless@...r.kernel.org>,
"linux-kernel@...r.kernel.org"
<linux-kernel@...r.kernel.org>,
"lvc-project@...uxtesting.org"
<lvc-project@...uxtesting.org>,
"stable@...r.kernel.org"
<stable@...r.kernel.org>
Subject: RE: [PATCH rtw-next v5 1/4] wifi: rtw89: fix use-after-free in rtw89_core_tx_kick_off_and_wait()
Fedor Pchelkin <pchelkin@...ras.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@...r.kernel.org
> Suggested-by: Zong-Zhe Yang <kevin_yang@...ltek.com>
> Signed-off-by: Fedor Pchelkin <pchelkin@...ras.ru>
Acked-by: Ping-Ke Shih <pkshih@...ltek.com>
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