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media: cx231xx: reject geometry changes while the VBI queue is busy

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vidioc_s_fmt_vid_cap() and vidioc_s_std() change the device-wide
dev->width / dev->norm but only refuse the change when the *video* queue
(dev->vidq) is busy. The VBI queue (dev->vbiq) shares that same geometry:
cx231xx_init_vbi_isoc() latches dma_q->lines_per_field from dev->norm,
the VBI videobuf2 plane is sized from dev->width / dev->norm in
vbi_queue_setup() and vbi_buf_prepare(), and cx231xx_do_vbi_copy() then
recomputes the destination offset from the *live* dev->width and the
latched lines_per_field on every URB completion:

	offset = lines_completed * (dev->width << 1) + ...;
	if (dma_q->current_field == 2)
		offset += dev->width * 2 * dma_q->lines_per_field;
	memcpy(plane + offset, p_buffer, lencopy);

Because the VBI node shares video_ioctl_ops with the video node, an
application can size a small VBI plane (REQBUFS/QBUF with a small width,
or with the NTSC standard), then enlarge dev->width (or switch dev->norm
to PAL) through the video node while the VBI stream is running -- the
change is allowed because only dev->vidq is checked -- and let the device
deliver a field-2 VBI payload. cx231xx_do_vbi_copy() now computes the
offset with the larger geometry and memcpy()s past the end of the smaller
plane that was already allocated, a heap out-of-bounds write whose offset
is attacker-chosen and whose contents come from the device. The
per-field guard in cx231xx_copy_vbi_line() does not help: it bounds the
copy against the latched lines_per_field, not the plane's real capacity,
and vb2 does not re-run buf_prepare() for an already prepared buffer.

Refuse the format/standard change when the VBI queue is busy as well, so
the geometry cannot change underneath an allocated VBI buffer.

Fixes: 7c617138b8 ("media: cx231xx: convert to the vb2 framework")
Cc: stable@vger.kernel.org
Signed-off-by: Bryam Vargas <hexlabsecurity@proton.me>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>
This commit is contained in:
Bryam Vargas
2026-06-15 18:40:48 -05:00
committed by Hans Verkuil
parent 23b8b4cbd8
commit 627a121c15
1 changed files with 2 additions and 2 deletions
Download Patch File Download Diff File Expand all files Collapse all files

4
drivers/media/usb/cx231xx/cx231xx-video.c
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@@ -898,7 +898,7 @@ static int vidioc_s_fmt_vid_cap(struct file *file, void *priv,
if (rc)
return rc;
if (vb2_is_busy(&dev->vidq)) {
if (vb2_is_busy(&dev->vidq) || vb2_is_busy(&dev->vbiq)) {
dev_err(dev->dev, "%s: queue busy\n", __func__);
return -EBUSY;
}
@@ -933,7 +933,7 @@ static int vidioc_s_std(struct file *file, void *priv, v4l2_std_id norm)
if (dev->norm == norm)
return 0;
if (vb2_is_busy(&dev->vidq))
if (vb2_is_busy(&dev->vidq) || vb2_is_busy(&dev->vbiq))
return -EBUSY;
dev->norm = norm;