[PATCH] media: s2255: bound JPEG frame size before copying into the buffer

[HyeongJun An]

s2255_fillbuff() memcpy()s vc->jpg_size bytes of a captured JPEG/MJPEG
frame into the vb2 plane.  vc->jpg_size is taken verbatim from the
S2255_MARKER_FRAME header the device sends (pdword[4] in save_frame())
and, unlike the frame payload length just above it, is never bounded:

	payload = le32_to_cpu(pdword[3]);
	if (payload > vc->req_image_size)	/* payload is checked ... */
		return -EINVAL;
	vc->pkt_size = payload;
	vc->jpg_size = le32_to_cpu(pdword[4]);	/* ... jpg_size is not */

A malicious or malfunctioning device can therefore report a jpg_size
larger than the destination vb2 plane, and the memcpy() writes past it.
jpg_size is a signed int, so a value with the top bit set also turns
into a huge length.

Reject a frame whose jpg_size is negative or exceeds the plane size
before copying it.

Fixes: 38f993ad8b1f ("V4L/DVB (8125): This driver adds support for the Sensoray 2255 devices.")
Cc: stable@xxxxxxxxxxxxxxx
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: HyeongJun An <sammiee5311@xxxxxxxxx>
---
 drivers/media/usb/s2255/s2255drv.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/media/usb/s2255/s2255drv.c b/drivers/media/usb/s2255/s2255drv.c
index 0b8182edf8e4..b34061ffe662 100644
--- a/drivers/media/usb/s2255/s2255drv.c
+++ b/drivers/media/usb/s2255/s2255drv.c
@@ -617,6 +617,12 @@ static void s2255_fillbuff(struct s2255_vc *vc,
 			break;
 		case V4L2_PIX_FMT_JPEG:
 		case V4L2_PIX_FMT_MJPEG:
+			if (jpgsize < 0 ||
+			    jpgsize > vb2_plane_size(&buf->vb.vb2_buf, 0)) {
+				dprintk(dev, 1, "bad JPEG frame size %d\n",
+					jpgsize);
+				break;
+			}
 			vb2_set_plane_payload(&buf->vb.vb2_buf, 0, jpgsize);
 			memcpy(vbuf, tmpbuf, jpgsize);
 			break;
-- 
2.43.0