[PATCH] media: cpia2: Fix integer overflow in mmap handling

[Takashi Iwai <tiwai@suse.de>]

The offset and size checks in cpia2_regmap_buffer() may ignore the
integer overflow and allow local users to obtain the access to the
kernel physical pages.

Fix it by modifying the check more carefully; the size value is
already checked beforehand and guaranteed to be smaller than
cam->frame_size*num_frames, so it's safe to subtract in the right
hand side.

This covers CVE-2019-18675.

Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
---

I'm submitting this since there hasn't been any action seen for this
bug over a month.  Let me know if there is already a fix.  Thanks.


 drivers/media/usb/cpia2/cpia2_core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/media/usb/cpia2/cpia2_core.c b/drivers/media/usb/cpia2/cpia2_core.c
index 20c50c2d042e..26ae7a5e3783 100644
--- a/drivers/media/usb/cpia2/cpia2_core.c
+++ b/drivers/media/usb/cpia2/cpia2_core.c
@@ -2401,7 +2401,7 @@ int cpia2_remap_buffer(struct camera_data *cam, struct vm_area_struct *vma)
 
 	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;
-- 
2.16.4