[PATCH v4] media: mc, v4l2: serialize REINIT and REQBUFS with req_queue_mutex

[Yuchan Nam <entropy1110@gmail.com>]

MEDIA_REQUEST_IOC_REINIT can run concurrently with VIDIOC_REQBUFS(0)
queue teardown paths. This can race request object cleanup against vb2
queue cancellation and lead to use-after-free reports.

We already serialize request queueing against STREAMON/OFF with
req_queue_mutex. Extend that serialization to REQBUFS, and also take
the same mutex in media_request_ioctl_reinit() so REINIT is in the
same exclusion domain.

This keeps request cleanup and queue cancellation from running in
parallel for request-capable devices.

Fixes: 6093d3002eab ("media: vb2: keep a reference to the request until dqbuf")
Cc: stable@vger.kernel.org
Signed-off-by: Yuchan Nam <entropy1110@gmail.com>
---
Changes since v3:
- Revert guard(mutex) usage in media_request_ioctl_reinit()
- Restore explicit mutex_unlock() calls in media_request_ioctl_reinit()

 drivers/media/mc/mc-request.c        | 5 +++++
 drivers/media/v4l2-core/v4l2-ioctl.c | 5 +++--
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/media/mc/mc-request.c b/drivers/media/mc/mc-request.c
index 8ad10c72f9db..4f632a9c292b 100644
--- a/drivers/media/mc/mc-request.c
+++ b/drivers/media/mc/mc-request.c
@@ -192,6 +192,8 @@ static long media_request_ioctl_reinit(struct media_request *req)
 	struct media_device *mdev = req->mdev;
 	unsigned long flags;
 
+	mutex_lock(&mdev->req_queue_mutex);
+
 	spin_lock_irqsave(&req->lock, flags);
 	if (req->state != MEDIA_REQUEST_STATE_IDLE &&
 	    req->state != MEDIA_REQUEST_STATE_COMPLETE) {
@@ -199,6 +201,7 @@ static long media_request_ioctl_reinit(struct media_request *req)
 			"request: %s not in idle or complete state, cannot reinit\n",
 			req->debug_str);
 		spin_unlock_irqrestore(&req->lock, flags);
+		mutex_unlock(&mdev->req_queue_mutex);
 		return -EBUSY;
 	}
 	if (req->access_count) {
@@ -206,6 +209,7 @@ static long media_request_ioctl_reinit(struct media_request *req)
 			"request: %s is being accessed, cannot reinit\n",
 			req->debug_str);
 		spin_unlock_irqrestore(&req->lock, flags);
+		mutex_unlock(&mdev->req_queue_mutex);
 		return -EBUSY;
 	}
 	req->state = MEDIA_REQUEST_STATE_CLEANING;
@@ -216,6 +220,7 @@ static long media_request_ioctl_reinit(struct media_request *req)
 	spin_lock_irqsave(&req->lock, flags);
 	req->state = MEDIA_REQUEST_STATE_IDLE;
 	spin_unlock_irqrestore(&req->lock, flags);
+	mutex_unlock(&mdev->req_queue_mutex);
 
 	return 0;
 }
diff --git a/drivers/media/v4l2-core/v4l2-ioctl.c b/drivers/media/v4l2-core/v4l2-ioctl.c
index 37d33d4a363d..a2b650f4ec3c 100644
--- a/drivers/media/v4l2-core/v4l2-ioctl.c
+++ b/drivers/media/v4l2-core/v4l2-ioctl.c
@@ -3082,13 +3082,14 @@ static long __video_do_ioctl(struct file *file,
 	}
 
 	/*
-	 * We need to serialize streamon/off with queueing new requests.
+	 * We need to serialize streamon/off/reqbufs with queueing new requests.
 	 * These ioctls may trigger the cancellation of a streaming
 	 * operation, and that should not be mixed with queueing a new
 	 * request at the same time.
 	 */
 	if (v4l2_device_supports_requests(vfd->v4l2_dev) &&
-	    (cmd == VIDIOC_STREAMON || cmd == VIDIOC_STREAMOFF)) {
+	    (cmd == VIDIOC_STREAMON || cmd == VIDIOC_STREAMOFF ||
+	     cmd == VIDIOC_REQBUFS)) {
 		req_queue_lock = &vfd->v4l2_dev->mdev->req_queue_mutex;
 
 		if (mutex_lock_interruptible(req_queue_lock))
-- 
2.52.0