[PATCH] media:usb:cpia2: Properly check framebuffer mmap offsets

[Omer Shalev]

The cpai2 driver's mmap implementation wasn't properly check for all
possible offset values. Given a huge offset value , the calculation
start_offset + size can wrap around to a low value and pass the check

Signed-off-by: Omer Shalev <omerdeshalev@xxxxxxxxx>
---
 drivers/media/usb/cpia2/cpia2_core.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/media/usb/cpia2/cpia2_core.c b/drivers/media/usb/cpia2/cpia2_core.c
index 20c50c2d042e..9d621cfb2d74 100644
--- a/drivers/media/usb/cpia2/cpia2_core.c
+++ b/drivers/media/usb/cpia2/cpia2_core.c
@@ -2390,18 +2390,22 @@ int cpia2_remap_buffer(struct camera_data *cam, struct vm_area_struct *vma)
 {
 	const char *adr = (const char *)vma->vm_start;
 	unsigned long size = vma->vm_end-vma->vm_start;
-	unsigned long start_offset = vma->vm_pgoff << PAGE_SHIFT;
 	unsigned long start = (unsigned long) adr;
+	unsigned long start_offset;
 	unsigned long page, pos;
 
 	DBG("mmap offset:%ld size:%ld\n", start_offset, size);
 
 	if (!video_is_registered(&cam->vdev))
 		return -ENODEV;
+
+	if (vma->vm_pgoff > (~0UL >> PAGE_SHIFT))
+		return -EINVAL;
 
+	start_offset = vma->vm_pgoff << PAGE_SHIFT;
 	if (size > cam->frame_size*cam->num_frames  ||
 	    (start_offset % cam->frame_size) != 0 ||
-	    (start_offset+size > cam->frame_size*cam->num_frames))
+	    (start_offset > cam->frame_size*cam->num_frames - size))
 		return -EINVAL;
 
 	pos = ((unsigned long) (cam->frame_buffer)) + start_offset;
-- 
2.23.0