This is a note to let you know that I've just added the patch titled
media: uvcvideo: Fix race condition with usb_kill_urb
to the 4.19-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
media-uvcvideo-fix-race-condition-with-usb_kill_urb.patch
and it can be found in the queue-4.19 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 619d9b710cf06f7a00a17120ca92333684ac45a8 Mon Sep 17 00:00:00 2001
From: Ricardo Ribalda <ribalda@xxxxxxxxxxxx>
Date: Thu, 5 Jan 2023 15:31:29 +0100
Subject: media: uvcvideo: Fix race condition with usb_kill_urb
From: Ricardo Ribalda <ribalda@xxxxxxxxxxxx>
commit 619d9b710cf06f7a00a17120ca92333684ac45a8 upstream.
usb_kill_urb warranties that all the handlers are finished when it
returns, but does not protect against threads that might be handling
asynchronously the urb.
For UVC, the function uvc_ctrl_status_event_async() takes care of
control changes asynchronously.
If the code is executed in the following order:
CPU 0 CPU 1
===== =====
uvc_status_complete()
uvc_status_stop()
uvc_ctrl_status_event_work()
uvc_status_start() -> FAIL
Then uvc_status_start will keep failing and this error will be shown:
<4>[ 5.540139] URB 0000000000000000 submitted while active
drivers/usb/core/urb.c:378 usb_submit_urb+0x4c3/0x528
Let's improve the current situation, by not re-submiting the urb if
we are stopping the status event. Also process the queued work
(if any) during stop.
CPU 0 CPU 1
===== =====
uvc_status_complete()
uvc_status_stop()
uvc_status_start()
uvc_ctrl_status_event_work() -> FAIL
Hopefully, with the usb layer protection this should be enough to cover
all the cases.
Cc: stable@xxxxxxxxxxxxxxx
Fixes: e5225c820c05 ("media: uvcvideo: Send a control event when a Control Change interrupt arrives")
Reviewed-by: Yunke Cao <yunkec@xxxxxxxxxxxx>
Signed-off-by: Ricardo Ribalda <ribalda@xxxxxxxxxxxx>
Reviewed-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
Signed-off-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/media/usb/uvc/uvc_ctrl.c | 5 +++++
drivers/media/usb/uvc/uvc_status.c | 37 +++++++++++++++++++++++++++++++++++++
drivers/media/usb/uvc/uvcvideo.h | 1 +
3 files changed, 43 insertions(+)
--- a/drivers/media/usb/uvc/uvc_ctrl.c
+++ b/drivers/media/usb/uvc/uvc_ctrl.c
@@ -11,6 +11,7 @@
*
*/
+#include <asm/barrier.h>
#include <linux/kernel.h>
#include <linux/list.h>
#include <linux/module.h>
@@ -1323,6 +1324,10 @@ static void uvc_ctrl_status_event_work(s
uvc_ctrl_status_event(w->chain, w->ctrl, w->data);
+ /* The barrier is needed to synchronize with uvc_status_stop(). */
+ if (smp_load_acquire(&dev->flush_status))
+ return;
+
/* Resubmit the URB. */
w->urb->interval = dev->int_ep->desc.bInterval;
ret = usb_submit_urb(w->urb, GFP_KERNEL);
--- a/drivers/media/usb/uvc/uvc_status.c
+++ b/drivers/media/usb/uvc/uvc_status.c
@@ -11,6 +11,7 @@
*
*/
+#include <asm/barrier.h>
#include <linux/kernel.h>
#include <linux/input.h>
#include <linux/slab.h>
@@ -315,5 +316,41 @@ int uvc_status_start(struct uvc_device *
void uvc_status_stop(struct uvc_device *dev)
{
+ struct uvc_ctrl_work *w = &dev->async_ctrl;
+
+ /*
+ * Prevent the asynchronous control handler from requeing the URB. The
+ * barrier is needed so the flush_status change is visible to other
+ * CPUs running the asynchronous handler before usb_kill_urb() is
+ * called below.
+ */
+ smp_store_release(&dev->flush_status, true);
+
+ /*
+ * Cancel any pending asynchronous work. If any status event was queued,
+ * process it synchronously.
+ */
+ if (cancel_work_sync(&w->work))
+ uvc_ctrl_status_event(w->chain, w->ctrl, w->data);
+
+ /* Kill the urb. */
usb_kill_urb(dev->int_urb);
+
+ /*
+ * The URB completion handler may have queued asynchronous work. This
+ * won't resubmit the URB as flush_status is set, but it needs to be
+ * cancelled before returning or it could then race with a future
+ * uvc_status_start() call.
+ */
+ if (cancel_work_sync(&w->work))
+ uvc_ctrl_status_event(w->chain, w->ctrl, w->data);
+
+ /*
+ * From this point, there are no events on the queue and the status URB
+ * is dead. No events will be queued until uvc_status_start() is called.
+ * The barrier is needed to make sure that flush_status is visible to
+ * uvc_ctrl_status_event_work() when uvc_status_start() will be called
+ * again.
+ */
+ smp_store_release(&dev->flush_status, false);
}
--- a/drivers/media/usb/uvc/uvcvideo.h
+++ b/drivers/media/usb/uvc/uvcvideo.h
@@ -603,6 +603,7 @@ struct uvc_device {
/* Status Interrupt Endpoint */
struct usb_host_endpoint *int_ep;
struct urb *int_urb;
+ bool flush_status;
u8 *status;
struct input_dev *input;
char input_phys[64];
Patches currently in stable-queue which might be from ribalda@xxxxxxxxxxxx are
queue-4.19/media-uvcvideo-handle-cameras-with-invalid-descripto.patch
queue-4.19/media-uvcvideo-fix-race-condition-with-usb_kill_urb.patch
queue-4.19/media-uvcvideo-provide-sync-and-async-uvc_ctrl_status_event.patch
