linux-kernel - [PATCH v2 4/5] media: uvcvideo: Protect uvc queue file operations against disconnect

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Message-Id: <20200908194557.198335-5-linux@roeck-us.net>
Date:   Tue,  8 Sep 2020 12:45:56 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        Sakari Ailus <sakari.ailus@....fi>,
        linux-uvc-devel@...ts.sourceforge.net, linux-usb@...r.kernel.org,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        Guenter Roeck <linux@...ck-us.net>,
        Alan Stern <stern@...land.harvard.edu>,
        Hans Verkuil <hverkuil-cisco@...all.nl>
Subject: [PATCH v2 4/5] media: uvcvideo: Protect uvc queue file operations against disconnect

uvc queue file operations have no mutex protection against USB
disconnect. This is questionable at least for the poll operation,
which has to wait for the uvc queue mutex. By the time that mutex
has been acquired, is it possible that the video device has been
unregistered.

Protect all file operations by using the queue mutex to avoid
possible race conditions. After acquiring the mutex, check if
the video device is still registered, and bail out if not.

Cc: Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc: Alan Stern <stern@...land.harvard.edu>
Cc: Hans Verkuil <hverkuil-cisco@...all.nl>
Signed-off-by: Guenter Roeck <linux@...ck-us.net>
---
v2: Return EPOLLERR instead of -ENODEV on poll errors

 drivers/media/usb/uvc/uvc_queue.c | 32 +++++++++++++++++++++++++++++--
 1 file changed, 30 insertions(+), 2 deletions(-)

diff --git a/drivers/media/usb/uvc/uvc_queue.c b/drivers/media/usb/uvc/uvc_queue.c
index cd60c6c1749e..b2c59ce38008 100644
--- a/drivers/media/usb/uvc/uvc_queue.c
+++ b/drivers/media/usb/uvc/uvc_queue.c
@@ -358,24 +358,52 @@ int uvc_queue_streamoff(struct uvc_video_queue *queue, enum v4l2_buf_type type)
 
 int uvc_queue_mmap(struct uvc_video_queue *queue, struct vm_area_struct *vma)
 {
-	return vb2_mmap(&queue->queue, vma);
+	struct uvc_streaming *stream = uvc_queue_to_stream(queue);
+	int ret;
+
+	mutex_lock(&queue->mutex);
+	if (!video_is_registered(&stream->vdev)) {
+		ret = -ENODEV;
+		goto unlock;
+	}
+	ret = vb2_mmap(&queue->queue, vma);
+unlock:
+	mutex_unlock(&queue->mutex);
+	return ret;
 }
 
 #ifndef CONFIG_MMU
 unsigned long uvc_queue_get_unmapped_area(struct uvc_video_queue *queue,
 		unsigned long pgoff)
 {
-	return vb2_get_unmapped_area(&queue->queue, 0, 0, pgoff, 0);
+	struct uvc_streaming *stream = uvc_queue_to_stream(queue);
+	unsigned long ret;
+
+	mutex_lock(&queue->mutex);
+	if (!video_is_registered(&stream->vdev)) {
+		ret = -ENODEV;
+		goto unlock;
+	}
+	ret = vb2_get_unmapped_area(&queue->queue, 0, 0, pgoff, 0);
+unlock:
+	mutex_unlock(&queue->mutex);
+	return ret;
 }
 #endif
 
 __poll_t uvc_queue_poll(struct uvc_video_queue *queue, struct file *file,
 			    poll_table *wait)
 {
+	struct uvc_streaming *stream = uvc_queue_to_stream(queue);
 	__poll_t ret;
 
 	mutex_lock(&queue->mutex);
+	if (!video_is_registered(&stream->vdev)) {
+		ret = EPOLLERR;
+		goto unlock;
+	}
 	ret = vb2_poll(&queue->queue, file, wait);
+unlock:
 	mutex_unlock(&queue->mutex);
 
 	return ret;
-- 
2.17.1