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rfkill: fix rfkill_fop_read wait_event usage 

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: c64fb01627 ("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>
This commit is contained in:
Johannes Berg 2016-01-26 11:29:03 +01:00 committed by Greg Kroah-Hartman
parent eb80decbf0
commit 01e527fd4c
1 changed files with 4 additions and 12 deletions
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16
net/rfkill/core.c
View File

@ -1088,17 +1088,6 @@ 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)
{
@ -1115,8 +1104,11 @@ 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)