On 8/21/2025 6:32 AM, Duoming Zhou wrote:
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 a critical
race condition:
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.
3.Subsequently, the brcmf_btcoex_info structure is freed.
4.Finally, the rescheduled worker attempts to execute, leading to
use-after-free bugs by accessing the freed brcmf_btcoex_info object.
Thanks for the patch. Being a nit picker just wanted to day that the
use-after-free happens a bit earlier as the worker itself is contained
in struct brcmf_btcoex_info. Also the diagram below does not add much
more than the textual description above.
The following diagram illustrates this sequence of events:
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-> //use
To resolve this race condition, 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.
However, no reason to stop this patch from going in so...
Acked-by: Arend van Spriel <arend.vanspriel@xxxxxxxxxxxx>
Fixes: 61730d4dfffc ("brcmfmac: support critical protocol API for DHCP")
Signed-off-by: Duoming Zhou <duoming@xxxxxxxxxx>
---
drivers/net/wireless/broadcom/brcm80211/brcmfmac/btcoex.c | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)
