linux-kernel - [PATCH 2/5] media: uvc: don't do DMA on stack

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Date:   Mon, 21 Jun 2021 13:56:46 +0200
From:   Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
To:     unlisted-recipients:; (no To-header on input)
Cc:     linuxarm@...wei.com, mauro.chehab@...wei.com,
        Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-kernel@...r.kernel.org, linux-media@...r.kernel.org
Subject: [PATCH 2/5] media: uvc: don't do DMA on stack

As warned by smatch:
	drivers/media/usb/uvc/uvc_v4l2.c:911 uvc_ioctl_g_input() error: doing dma on the stack (&i)
	drivers/media/usb/uvc/uvc_v4l2.c:943 uvc_ioctl_s_input() error: doing dma on the stack (&i)

those two functions call uvc_query_ctrl passing a pointer to
a data at the DMA stack. those are used to send URBs via
usb_control_msg(). Using DMA stack is not supported and should
not work anymore on modern Linux versions.

So, use a temporary buffer, allocated together with
struct uvc_video_chain.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
---
 drivers/media/usb/uvc/uvc_v4l2.c | 10 ++++------
 drivers/media/usb/uvc/uvcvideo.h |  3 +++
 2 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/drivers/media/usb/uvc/uvc_v4l2.c b/drivers/media/usb/uvc/uvc_v4l2.c
index 252136cc885c..e60d4675881a 100644
--- a/drivers/media/usb/uvc/uvc_v4l2.c
+++ b/drivers/media/usb/uvc/uvc_v4l2.c
@@ -900,7 +900,6 @@ static int uvc_ioctl_g_input(struct file *file, void *fh, unsigned int *input)
 	struct uvc_fh *handle = fh;
 	struct uvc_video_chain *chain = handle->chain;
 	int ret;
-	u8 i;
 
 	if (chain->selector == NULL ||
 	    (chain->dev->quirks & UVC_QUIRK_IGNORE_SELECTOR_UNIT)) {
@@ -910,11 +909,11 @@ static int uvc_ioctl_g_input(struct file *file, void *fh, unsigned int *input)
 
 	ret = uvc_query_ctrl(chain->dev, UVC_GET_CUR, chain->selector->id,
 			     chain->dev->intfnum,  UVC_SU_INPUT_SELECT_CONTROL,
-			     &i, 1);
+			     &chain->input, 1);
 	if (ret < 0)
 		return ret;
 
-	*input = i - 1;
+	*input = chain->input - 1;
 	return 0;
 }
 
@@ -923,7 +922,6 @@ static int uvc_ioctl_s_input(struct file *file, void *fh, unsigned int input)
 	struct uvc_fh *handle = fh;
 	struct uvc_video_chain *chain = handle->chain;
 	int ret;
-	u32 i;
 
 	ret = uvc_acquire_privileges(handle);
 	if (ret < 0)
@@ -939,10 +937,10 @@ static int uvc_ioctl_s_input(struct file *file, void *fh, unsigned int input)
 	if (input >= chain->selector->bNrInPins)
 		return -EINVAL;
 
-	i = input + 1;
+	chain->input = input + 1;
 	return uvc_query_ctrl(chain->dev, UVC_SET_CUR, chain->selector->id,
 			      chain->dev->intfnum, UVC_SU_INPUT_SELECT_CONTROL,
-			      &i, 1);
+			      &chain->input, 1);
 }
 
 static int uvc_ioctl_queryctrl(struct file *file, void *fh,
diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
index cce5e38133cd..3c0ed90d6912 100644
--- a/drivers/media/usb/uvc/uvcvideo.h
+++ b/drivers/media/usb/uvc/uvcvideo.h
@@ -475,6 +475,9 @@ struct uvc_video_chain {
 	struct mutex ctrl_mutex;		/* Protects ctrl.info */
 
 	struct v4l2_prio_state prio;		/* V4L2 priority state */
+
+	u8 input;				/* buffer for set/get input */
+
 	u32 caps;				/* V4L2 chain-wide caps */
 };
 
-- 
2.31.1