In the Linux kernel, the following vulnerability has been resolved:
Bluetooth: btmtksdio: fix infinite loop in btmtksdio_txrx_work()
Every once in a while we see a hung btmtksdio_flush() task:
INFO: task kworker/u17:0:189 blocked for more than 122 seconds.
__cancel_work_timer+0x3f4/0x460
cancel_work_sync+0x1c/0x2c
btmtksdio_flush+0x2c/0x40
hci_dev_open_sync+0x10c4/0x2190
[..]
It all boils down to incorrect time_is_before_jiffies() usage in
btmtksdio_txrx_work(). The btmtksdio_txrx_work() loop is expected
to be terminated if running for longer than 5HZ. However the
timeout check is twisted: time_is_before_jiffies(old_jiffies + 5HZ)
evaluates to true when old_jiffies + 5*HZ is in the past i.e. when a
timeout has occurred. Using OR with time_is_before_jiffies(txrx_timeout)
means that:
- before the 5-second timeout: the condition is int_status || false,
so it loops as long as there are pending interrupts.
- after the 5-second timeout: the condition becomes int_status || true,
which is always true.
When the loop becomes infinite btmtksdio_txrx_work() loop never
terminates and never releases the SDIO host.
Fix loop termination condition to actually enforce a 5*HZ timeout.