Patch "rfkill: fix rfkill_fop_read wait_event usage" has been added to the 4.4-stable tree

[<gregkh@linuxfoundation.org>]

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 4.4-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-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 6736fde9672ff6717ac576e9bba2fd5f3dfec822 Mon Sep 17 00:00:00 2001
From: Johannes Berg <johannes.berg@intel.com>
Date: Tue, 26 Jan 2016 11:29:03 +0100
Subject: rfkill: fix rfkill_fop_read wait_event usage

From: Johannes Berg <johannes.berg@intel.com>

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.

Fixes: c64fb01627e24 ("rfkill: create useful userspace interface")
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

--- a/net/rfkill/core.c
+++ b/net/rfkill/core.c
@@ -1095,17 +1095,6 @@ 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)
 {
@@ -1122,8 +1111,11 @@ 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 johannes.berg@intel.com are

queue-4.4/mac80211-requeue-work-after-scan-complete-for-all-vif-types.patch
queue-4.4/rfkill-fix-rfkill_fop_read-wait_event-usage.patch