media: uvcvideo: Enforce alignment of frame and interval

Struct uvc_frame and interval (u32*) are packaged together on
streaming->formats on a single contiguous allocation.

Right now they are allocated right after uvc_format, without taking into
consideration their required alignment.

This is working fine because both structures have a field with a
pointer, but it will stop working when the sizeof() of any of those
structs is not a multiple of the sizeof(void*).

Enforce that alignment during the allocation.
Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Link: https://lore.kernel.org/r/20240404-uvc-align-v2-1-9e104b0ecfbd@chromium.orgSigned-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

drivers/media/usb/uvc/uvc_driver.c

@@ -687,16 +687,26 @@ static int uvc_parse_streaming(struct uvc_device *dev,
 		goto error;
 	}
 
-	size = nformats * sizeof(*format) + nframes * sizeof(*frame)
+	/*
+	 * Allocate memory for the formats, the frames and the intervals,
+	 * plus any required padding to guarantee that everything has the
+	 * correct alignment.
+	 */
+	size = nformats * sizeof(*format);
+	size = ALIGN(size, __alignof__(*frame)) + nframes * sizeof(*frame);
+	size = ALIGN(size, __alignof__(*interval))
 	     + nintervals * sizeof(*interval);
+
 	format = kzalloc(size, GFP_KERNEL);
-	if (format == NULL) {
+	if (!format) {
 		ret = -ENOMEM;
 		goto error;
 	}
 
-	frame = (struct uvc_frame *)&format[nformats];
-	interval = (u32 *)&frame[nframes];
+	frame = (void *)format + nformats * sizeof(*format);
+	frame = PTR_ALIGN(frame, __alignof__(*frame));
+	interval = (void *)frame + nframes * sizeof(*frame);
+	interval = PTR_ALIGN(interval, __alignof__(*interval));
 
 	streaming->formats = format;
 	streaming->nformats = 0;