| From | Kamal Mostafa <> | Subject | [PATCH 3.19.y-ckt 017/196] rfkill: fix rfkill_fop_read wait_event usage | Date | Tue, 8 Mar 2016 16:27:55 -0800 |
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3.19.8-ckt16 -stable review patch. If anyone has any objections, please let me know.
---8<------------------------------------------------------------
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: Kamal Mostafa <kamal@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 4b333ed..11c5d22 100644 --- a/net/rfkill/core.c +++ b/net/rfkill/core.c @@ -1081,17 +1081,6 @@ 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) { @@ -1108,8 +1097,11 @@ 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
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