From 627a121c15fe05a541f44d86016294b80bada75d Mon Sep 17 00:00:00 2001 From: Bryam Vargas Date: Mon, 15 Jun 2026 18:40:48 -0500 Subject: [PATCH] media: cx231xx: reject geometry changes while the VBI queue is busy 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: 7c617138b825 ("media: cx231xx: convert to the vb2 framework") Cc: stable@vger.kernel.org Signed-off-by: Bryam Vargas Signed-off-by: Hans Verkuil --- drivers/media/usb/cx231xx/cx231xx-video.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/media/usb/cx231xx/cx231xx-video.c b/drivers/media/usb/cx231xx/cx231xx-video.c index 2cd4e333bc4b..70aa99fead27 100644 --- a/drivers/media/usb/cx231xx/cx231xx-video.c +++ b/drivers/media/usb/cx231xx/cx231xx-video.c @@ -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;