Patch "rfkill: fix rfkill_fop_read wait_event usage" has been added to the 3.14-stable tree

This is a note to let you know that I've just added the patch titled

rfkill: fix rfkill_fop_read wait_event usage

to the 3.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
rfkill-fix-rfkill_fop_read-wait_event-usage.patch
and it can be found in the queue-3.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Johannes Berg <[email protected]>
Date: Tue, 26 Jan 2016 11:29:03 +0100
Subject: rfkill: fix rfkill_fop_read wait_event usage

From: Johannes Berg <[email protected]>

commit 6736fde9672ff6717ac576e9bba2fd5f3dfec822 upstream.

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.

---
 net/rfkill/core.c |   16 ++++------------
 1 file changed, 4 insertions(+), 12 deletions(-)

@@ -1078,17 +1078,6 @@ static unsigned int rfkill_fop_poll(stru
 	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)
 {

@@ -1105,8 +1094,11 @@ static ssize_t rfkill_fop_read(struct fi
 			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)

Patches currently in stable-queue which might be from [email protected] are

queue-3.14/rfkill-copy-the-name-into-the-rfkill-struct.patch queue-3.14/mac80211-mesh-fix-call_rcu-usage.patch queue-3.14/rfkill-fix-rfkill_fop_read-wait_event-usage.patch