linux-kernel - [PATCH 2/2] media: uvcvideo: Remove dangling pointers

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Message-Id: <20241127-uvc-fix-async-v1-2-eb8722531b8c@chromium.org>
Date: Wed, 27 Nov 2024 07:46:11 +0000
From: Ricardo Ribalda <ribalda@...omium.org>
To: Laurent Pinchart <laurent.pinchart@...asonboard.com>, 
 Hans de Goede <hdegoede@...hat.com>, 
 Mauro Carvalho Chehab <mchehab@...nel.org>, 
 Guennadi Liakhovetski <guennadi.liakhovetski@...el.com>
Cc: Mauro Carvalho Chehab <mchehab+samsung@...nel.org>, 
 linux-media@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Ricardo Ribalda <ribalda@...omium.org>, stable@...r.kernel.org
Subject: [PATCH 2/2] media: uvcvideo: Remove dangling pointers

When an async control is written, we copy a pointer to the file handle
that started the operation. That pointer will be used when the device is
done. Which could be anytime in the future.

If the user closes that file descriptor, its structure will be freed,
and there will be one dangling pointer per pending async control, that
the driver will try to use.

Clean all the dangling pointers during release().

To avoid adding a performance penalty in the most common case (no async
operation). A counter has been introduced with some logic to make sure
that it is properly handled.

Cc: stable@...r.kernel.org
Fixes: e5225c820c05 ("media: uvcvideo: Send a control event when a Control Change interrupt arrives")
Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
---
 drivers/media/usb/uvc/uvc_ctrl.c | 40 ++++++++++++++++++++++++++++++++++++++--
 drivers/media/usb/uvc/uvc_v4l2.c |  2 ++
 drivers/media/usb/uvc/uvcvideo.h |  3 +++
 3 files changed, 43 insertions(+), 2 deletions(-)

diff --git a/drivers/media/usb/uvc/uvc_ctrl.c b/drivers/media/usb/uvc/uvc_ctrl.c
index 5d3a28edf7f0..51a53ad25e9c 100644
--- a/drivers/media/usb/uvc/uvc_ctrl.c
+++ b/drivers/media/usb/uvc/uvc_ctrl.c
@@ -1589,7 +1589,12 @@ void uvc_ctrl_status_event(struct uvc_video_chain *chain,
 	mutex_lock(&chain->ctrl_mutex);
 
 	handle = ctrl->handle;
-	ctrl->handle = NULL;
+	if (handle) {
+		ctrl->handle = NULL;
+		WARN_ON(!handle->pending_async_ctrls);
+		if (handle->pending_async_ctrls)
+			handle->pending_async_ctrls--;
+	}
 
 	list_for_each_entry(mapping, &ctrl->info.mappings, list) {
 		s32 value = __uvc_ctrl_get_value(mapping, data);
@@ -2050,8 +2055,11 @@ int uvc_ctrl_set(struct uvc_fh *handle,
 	mapping->set(mapping, value,
 		uvc_ctrl_data(ctrl, UVC_CTRL_DATA_CURRENT));
 
-	if (ctrl->info.flags & UVC_CTRL_FLAG_ASYNCHRONOUS)
+	if (ctrl->info.flags & UVC_CTRL_FLAG_ASYNCHRONOUS) {
+		if (!ctrl->handle)
+			handle->pending_async_ctrls++;
 		ctrl->handle = handle;
+	}
 
 	ctrl->dirty = 1;
 	ctrl->modified = 1;
@@ -2774,6 +2782,34 @@ int uvc_ctrl_init_device(struct uvc_device *dev)
 	return 0;
 }
 
+void uvc_ctrl_cleanup_fh(struct uvc_fh *handle)
+{
+	struct uvc_entity *entity;
+
+	guard(mutex)(&handle->chain->ctrl_mutex);
+
+	if (!handle->pending_async_ctrls)
+		return;
+
+	list_for_each_entry(entity, &handle->chain->dev->entities, list) {
+		int i;
+
+		for (i = 0; i < entity->ncontrols; ++i) {
+			struct uvc_control *ctrl = &entity->controls[i];
+
+			if (!ctrl->handle || ctrl->handle != handle)
+				continue;
+
+			ctrl->handle = NULL;
+			if (WARN_ON(!handle->pending_async_ctrls))
+				continue;
+			handle->pending_async_ctrls--;
+		}
+	}
+
+	WARN_ON(handle->pending_async_ctrls);
+}
+
 /*
  * Cleanup device controls.
  */
diff --git a/drivers/media/usb/uvc/uvc_v4l2.c b/drivers/media/usb/uvc/uvc_v4l2.c
index 97c5407f6603..b425306a3b8c 100644
--- a/drivers/media/usb/uvc/uvc_v4l2.c
+++ b/drivers/media/usb/uvc/uvc_v4l2.c
@@ -652,6 +652,8 @@ static int uvc_v4l2_release(struct file *file)
 
 	uvc_dbg(stream->dev, CALLS, "%s\n", __func__);
 
+	uvc_ctrl_cleanup_fh(handle);
+
 	/* Only free resources if this is a privileged handle. */
 	if (uvc_has_privileges(handle))
 		uvc_queue_release(&stream->queue);
diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
index 07f9921d83f2..2f8a9c48e32a 100644
--- a/drivers/media/usb/uvc/uvcvideo.h
+++ b/drivers/media/usb/uvc/uvcvideo.h
@@ -612,6 +612,7 @@ struct uvc_fh {
 	struct uvc_video_chain *chain;
 	struct uvc_streaming *stream;
 	enum uvc_handle_state state;
+	unsigned int pending_async_ctrls; /* Protected by ctrl_mutex. */
 };
 
 struct uvc_driver {
@@ -797,6 +798,8 @@ int uvc_ctrl_is_accessible(struct uvc_video_chain *chain, u32 v4l2_id,
 int uvc_xu_ctrl_query(struct uvc_video_chain *chain,
 		      struct uvc_xu_control_query *xqry);
 
+void uvc_ctrl_cleanup_fh(struct uvc_fh *handle);
+
 /* Utility functions */
 struct usb_host_endpoint *uvc_find_endpoint(struct usb_host_interface *alts,
 					    u8 epaddr);

-- 
2.47.0.338.g60cca15819-goog