6.12-stable review patch. If anyone has any objections, please let me know.
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From: Duoming Zhou duoming@zju.edu.cn
[ Upstream commit 9cb83d4be0b9b697eae93d321e0da999f9cdfcfc ]
The brcmf_btcoex_detach() only shuts down the btcoex timer, if the flag timer_on is false. However, the brcmf_btcoex_timerfunc(), which runs as timer handler, sets timer_on to false. This creates critical race conditions:
1.If brcmf_btcoex_detach() is called while brcmf_btcoex_timerfunc() is executing, it may observe timer_on as false and skip the call to timer_shutdown_sync().
2.The brcmf_btcoex_timerfunc() may then reschedule the brcmf_btcoex_info worker after the cancel_work_sync() has been executed, resulting in use-after-free bugs.
The use-after-free bugs occur in two distinct scenarios, depending on the timing of when the brcmf_btcoex_info struct is freed relative to the execution of its worker thread.
Scenario 1: Freed before the worker is scheduled
The brcmf_btcoex_info is deallocated before the worker is scheduled. A race condition can occur when schedule_work(&bt_local->work) is called after the target memory has been freed. The sequence of events is detailed below:
CPU0 | CPU1 brcmf_btcoex_detach | brcmf_btcoex_timerfunc | bt_local->timer_on = false; if (cfg->btcoex->timer_on) | ... | cancel_work_sync(); | ... | kfree(cfg->btcoex); // FREE | | schedule_work(&bt_local->work); // USE
Scenario 2: Freed after the worker is scheduled
The brcmf_btcoex_info is freed after the worker has been scheduled but before or during its execution. In this case, statements within the brcmf_btcoex_handler() — such as the container_of macro and subsequent dereferences of the brcmf_btcoex_info object will cause a use-after-free access. The following timeline illustrates this scenario:
CPU0 | CPU1 brcmf_btcoex_detach | brcmf_btcoex_timerfunc | bt_local->timer_on = false; if (cfg->btcoex->timer_on) | ... | cancel_work_sync(); | ... | schedule_work(); // Reschedule | kfree(cfg->btcoex); // FREE | brcmf_btcoex_handler() // Worker /* | btci = container_of(....); // USE The kfree() above could | ... also occur at any point | btci-> // USE during the worker's execution| */ |
To resolve the race conditions, drop the conditional check and call timer_shutdown_sync() directly. It can deactivate the timer reliably, regardless of its current state. Once stopped, the timer_on state is then set to false.
Fixes: 61730d4dfffc ("brcmfmac: support critical protocol API for DHCP") Acked-by: Arend van Spriel arend.vanspriel@broadcom.com Signed-off-by: Duoming Zhou duoming@zju.edu.cn Link: https://patch.msgid.link/20250822050839.4413-1-duoming@zju.edu.cn Signed-off-by: Johannes Berg johannes.berg@intel.com Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/net/wireless/broadcom/brcm80211/brcmfmac/btcoex.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-)
diff --git a/drivers/net/wireless/broadcom/brcm80211/brcmfmac/btcoex.c b/drivers/net/wireless/broadcom/brcm80211/brcmfmac/btcoex.c index 1e8495f50c16a..6531cff58ae9f 100644 --- a/drivers/net/wireless/broadcom/brcm80211/brcmfmac/btcoex.c +++ b/drivers/net/wireless/broadcom/brcm80211/brcmfmac/btcoex.c @@ -392,10 +392,8 @@ void brcmf_btcoex_detach(struct brcmf_cfg80211_info *cfg) if (!cfg->btcoex) return;
- if (cfg->btcoex->timer_on) { - cfg->btcoex->timer_on = false; - timer_shutdown_sync(&cfg->btcoex->timer); - } + timer_shutdown_sync(&cfg->btcoex->timer); + cfg->btcoex->timer_on = false;
cancel_work_sync(&cfg->btcoex->work);