Commit 01e527fd authored by Johannes Berg's avatar Johannes Berg Committed by Greg Kroah-Hartman

rfkill: fix rfkill_fop_read wait_event usage

commit 6736fde9 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: c64fb016 ("rfkill: create useful userspace interface")
Reported-by: default avatarDmitry Vyukov <dvyukov@google.com>
Signed-off-by: default avatarJohannes Berg <johannes.berg@intel.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent eb80decb
...@@ -1088,17 +1088,6 @@ static unsigned int rfkill_fop_poll(struct file *file, poll_table *wait) ...@@ -1088,17 +1088,6 @@ static unsigned int rfkill_fop_poll(struct file *file, poll_table *wait)
return res; 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, static ssize_t rfkill_fop_read(struct file *file, char __user *buf,
size_t count, loff_t *pos) size_t count, loff_t *pos)
{ {
...@@ -1115,8 +1104,11 @@ static ssize_t rfkill_fop_read(struct file *file, char __user *buf, ...@@ -1115,8 +1104,11 @@ static ssize_t rfkill_fop_read(struct file *file, char __user *buf,
goto out; goto out;
} }
mutex_unlock(&data->mtx); 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, ret = wait_event_interruptible(data->read_wait,
rfkill_readable(data)); !list_empty(&data->events));
mutex_lock(&data->mtx); mutex_lock(&data->mtx);
if (ret) if (ret)
......
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