[PATCH v2] media: uvc: don't do DMA on stack

[Mauro Carvalho Chehab <mchehab+huawei@xxxxxxxxxx>]

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.

Cc: stable@xxxxxxxxxxxxxxx	# Kernel 4.9 and upper
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@xxxxxxxxxx>
---
 drivers/media/usb/uvc/uvc_v4l2.c | 26 ++++++++++++++++++--------
 1 file changed, 18 insertions(+), 8 deletions(-)

diff --git a/drivers/media/usb/uvc/uvc_v4l2.c b/drivers/media/usb/uvc/uvc_v4l2.c
index 252136cc885c..d680ae8a5f87 100644
--- a/drivers/media/usb/uvc/uvc_v4l2.c
+++ b/drivers/media/usb/uvc/uvc_v4l2.c
@@ -899,8 +899,8 @@ 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;
+	char *buf;
 	int ret;
-	u8 i;
 
 	if (chain->selector == NULL ||
 	    (chain->dev->quirks & UVC_QUIRK_IGNORE_SELECTOR_UNIT)) {
@@ -908,13 +908,18 @@ static int uvc_ioctl_g_input(struct file *file, void *fh, unsigned int *input)
 		return 0;
 	}
 
+	buf = kmalloc(1, GFP_KERNEL);
+
 	ret = uvc_query_ctrl(chain->dev, UVC_GET_CUR, chain->selector->id,
 			     chain->dev->intfnum,  UVC_SU_INPUT_SELECT_CONTROL,
-			     &i, 1);
+			     buf, 1);
 	if (ret < 0)
 		return ret;
 
-	*input = i - 1;
+	*input = *buf;
+
+	kfree(buf);
+
 	return 0;
 }
 
@@ -922,8 +927,8 @@ 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;
+	char *buf;
 	int ret;
-	u32 i;
 
 	ret = uvc_acquire_privileges(handle);
 	if (ret < 0)
@@ -939,10 +944,15 @@ static int uvc_ioctl_s_input(struct file *file, void *fh, unsigned int input)
 	if (input >= chain->selector->bNrInPins)
 		return -EINVAL;
 
-	i = input + 1;
-	return uvc_query_ctrl(chain->dev, UVC_SET_CUR, chain->selector->id,
-			      chain->dev->intfnum, UVC_SU_INPUT_SELECT_CONTROL,
-			      &i, 1);
+	buf = kmalloc(1, GFP_KERNEL);
+
+	*buf = input + 1;
+	ret = uvc_query_ctrl(chain->dev, UVC_SET_CUR, chain->selector->id,
+			     chain->dev->intfnum, UVC_SU_INPUT_SELECT_CONTROL,
+			     buf, 1);
+	kfree(buf);
+
+	return ret;
 }
 
 static int uvc_ioctl_queryctrl(struct file *file, void *fh,
-- 
2.31.1