4.2.8-ckt5 -stable review patch. If anyone has any objections, please let me
know.
---8<------------------------------------------------------------
From: Johannes Berg <johannes.b...@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 <dvyu...@google.com>
Signed-off-by: Johannes Berg <johannes.b...@intel.com>
Signed-off-by: Kamal Mostafa <ka...@canonical.com>
---
net/rfkill/core.c | 16 ++++------------
1 file changed, 4 insertions(+), 12 deletions(-)
diff --git a/net/rfkill/core.c b/net/rfkill/core.c
index 31b5c63..c20ea1b 100644
--- a/net/rfkill/core.c
+++ b/net/rfkill/core.c
@@ -1087,17 +1087,6 @@ 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)
{
@@ -1114,8 +1103,11 @@ 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)
--
2.7.0
