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Commit 6736fde9 authored by Johannes Berg's avatar Johannes Berg
Browse files

rfkill: fix rfkill_fop_read wait_event usage 



The code within wait_event_interruptible() is called with
!TASK_RUNNING, so mustn't call any functions that can sleep,
like mutex_lock().

Since we re-check the list_empty() in a loop after the wait,
it's safe to simply use list_empty() without locking.

This bug has existed forever, but was only discovered now
because all userspace implementations, including the default
'rfkill' tool, use poll() or select() to get a readable fd
before attempting to read.

Cc: stable@vger.kernel.org
Fixes: c64fb016 ("rfkill: create useful userspace interface")
Reported-by: default avatarDmitry Vyukov <dvyukov@google.com>
Signed-off-by: default avatarJohannes Berg <johannes.berg@intel.com>
parent 4fa11ec7

net/rfkill/core.c

+4 −12
Original line number Diff line number Diff line
@@ -1095,17 +1095,6 @@ static unsigned int rfkill_fop_poll(struct file *file, poll_table *wait) 
	return res;

}



static bool rfkill_readable(struct rfkill_data *data)

{

	bool r;



	mutex_lock(&data->mtx);

	r = !list_empty(&data->events);

	mutex_unlock(&data->mtx);



	return r;

}



static ssize_t rfkill_fop_read(struct file *file, char __user *buf,

			       size_t count, loff_t *pos)

{
@@ -1122,8 +1111,11 @@ static ssize_t rfkill_fop_read(struct file *file, char __user *buf, 
			goto out;

		}

		mutex_unlock(&data->mtx);

		/* since we re-check and it just compares pointers,

		 * using !list_empty() without locking isn't a problem

		 */

		ret = wait_event_interruptible(data->read_wait,

					       rfkill_readable(data));

					       !list_empty(&data->events));

		mutex_lock(&data->mtx);



		if (ret)