From: Johannes Berg <johannes.berg@xxxxxxxxx>
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@xxxxxxxxxxxxxxx
Fixes: c64fb01627e24 ("rfkill: create useful userspace interface")
Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Signed-off-by: Johannes Berg <johannes.berg@xxxxxxxxx>
---
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 f53bf3b6558b..cf5b69ab1829 100644
--- a/net/rfkill/core.c
+++ b/net/rfkill/core.c
@@ -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)
--
2.6.2
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