[PATCH] usb: using mutex lock and supporting O_NONBLOCK flag in iowarrior_read()

[Jeongjun Park <aha310510@xxxxxxxxx>]

iowarrior_read() uses the iowarrior dev structure, but does not use any 
lock on the structure. This can cause various bugs including data-races,
so it is more appropriate to use a mutex lock to safely protect the 
iowarrior dev structure. When using a mutex lock, you should split the
branch to prevent blocking when the O_NONBLOCK flag is set.

In addition, it is unnecessary to check for NULL on the iowarrior dev 
structure obtained by reading file->private_data. Therefore, it is 
better to remove the check.

Fixes: 946b960d13c1 ("USB: add driver for iowarrior devices.")
Signed-off-by: Jeongjun Park <aha310510@xxxxxxxxx>
---
 drivers/usb/misc/iowarrior.c | 46 ++++++++++++++++++++++++++++--------
 1 file changed, 36 insertions(+), 10 deletions(-)

diff --git a/drivers/usb/misc/iowarrior.c b/drivers/usb/misc/iowarrior.c
index 6d28467ce352..a513766b4985 100644
--- a/drivers/usb/misc/iowarrior.c
+++ b/drivers/usb/misc/iowarrior.c
@@ -277,28 +277,45 @@ static ssize_t iowarrior_read(struct file *file, char __user *buffer,
 	struct iowarrior *dev;
 	int read_idx;
 	int offset;
+	int retval;
 
 	dev = file->private_data;
 
+	if (file->f_flags & O_NONBLOCK) {
+		retval = mutex_trylock(&dev->mutex);
+		if (!retval)
+			return -EAGAIN;
+	} else {
+		retval = mutex_lock_interruptible(&dev->mutex);
+		if (retval)
+			return -ERESTARTSYS;
+	}
+
 	/* verify that the device wasn't unplugged */
-	if (!dev || !dev->present)
-		return -ENODEV;
+	if (!dev->present) {
+		retval = -ENODEV;
+		goto exit;
+	}
 
 	dev_dbg(&dev->interface->dev, "minor %d, count = %zd\n",
 		dev->minor, count);
 
 	/* read count must be packet size (+ time stamp) */
 	if ((count != dev->report_size)
-	    && (count != (dev->report_size + 1)))
-		return -EINVAL;
+	    && (count != (dev->report_size + 1))) {
+		retval = -EINVAL;
+		goto exit;
+	}
 
 	/* repeat until no buffer overrun in callback handler occur */
 	do {
 		atomic_set(&dev->overflow_flag, 0);
 		if ((read_idx = read_index(dev)) == -1) {
 			/* queue empty */
-			if (file->f_flags & O_NONBLOCK)
-				return -EAGAIN;
+			if (file->f_flags & O_NONBLOCK) {
+				retval = -EAGAIN;
+				goto exit;
+			}
 			else {
 				//next line will return when there is either new data, or the device is unplugged
 				int r = wait_event_interruptible(dev->read_wait,
@@ -309,28 +326,37 @@ static ssize_t iowarrior_read(struct file *file, char __user *buffer,
 								  -1));
 				if (r) {
 					//we were interrupted by a signal
-					return -ERESTART;
+					retval = -ERESTART;
+					goto exit;
 				}
 				if (!dev->present) {
 					//The device was unplugged
-					return -ENODEV;
+					retval = -ENODEV;
+					goto exit;
 				}
 				if (read_idx == -1) {
 					// Can this happen ???
-					return 0;
+					retval = 0;
+					goto exit;
 				}
 			}
 		}
 
 		offset = read_idx * (dev->report_size + 1);
 		if (copy_to_user(buffer, dev->read_queue + offset, count)) {
-			return -EFAULT;
+			retval = -EFAULT;
+			goto exit;
 		}
 	} while (atomic_read(&dev->overflow_flag));
 
 	read_idx = ++read_idx == MAX_INTERRUPT_BUFFER ? 0 : read_idx;
 	atomic_set(&dev->read_idx, read_idx);
+	mutex_unlock(&dev->mutex);
 	return count;
+
+exit:
+	mutex_unlock(&dev->mutex);
+	return retval;
 }
 
 /*
--