[PATCH v2] media: uvcvideo: Enforce alignment of frame and interval

[Ricardo Ribalda <ribalda@chromium.org>]

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

Right now they 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>
---
This is better than 3 allocations, and do not have any performance
penalty.

I have tried this patch printing the size and the address of the
pointers in the old and the new mode, and it looks the same.

[    2.235223] drivers/media/usb/uvc/uvc_driver.c:694 uvc_parse_streaming 432
[    2.235249] drivers/media/usb/uvc/uvc_driver.c:704 uvc_parse_streaming 432
[    2.235256] drivers/media/usb/uvc/uvc_driver.c:714 uvc_parse_streaming 00000000d32087cc 00000000d3803788
[    2.235265] drivers/media/usb/uvc/uvc_driver.c:720 uvc_parse_streaming 00000000d32087cc 00000000d3803788
---
Changes in v2: Thanks Laurent.
- Enforce alignment during allocation instead of using __aligned()
  macros.
- Link to v1: https://lore.kernel.org/r/20230501-uvc-align-v1-1-0f713e4b84c3@chromium.org
---
 drivers/media/usb/uvc/uvc_driver.c | 20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c
index 7aefa76a42b31..7d9844ba3b205 100644
--- a/drivers/media/usb/uvc/uvc_driver.c
+++ b/drivers/media/usb/uvc/uvc_driver.c
@@ -663,16 +663,26 @@ static int uvc_parse_streaming(struct uvc_device *dev,
 		goto error;
 	}
 
-	size = nformats * sizeof(*format) + nframes * sizeof(*frame)
-	     + nintervals * sizeof(*interval);
+	/*
+	 * 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->format = format;
 	streaming->nformats = nformats;

---
base-commit: 58390c8ce1bddb6c623f62e7ed36383e7fa5c02f
change-id: 20230501-uvc-align-6ff202b68dab

Best regards,
-- 
Ricardo Ribalda <ribalda@chromium.org>