[PATCH] video: fbdev: kyro: Validate overlay viewport coordinates

[Danila Chernetsov <listdansp@mail.ru>]

The overlay viewport end coordinates are computed from the viewport
origin and dimensions using 32-bit unsigned arithmetic. Large input
values can cause these calculations to wrap around before the resulting
coordinates are passed to SetOverlayViewPort().

SetOverlayViewPort() packs the viewport coordinates into 16-bit
register fields. The X coordinates are additionally adjusted by +2
and +1 before being written. Validate the coordinate calculations
for 32-bit wraparound and ensure that the adjusted coordinates fit
within their 16-bit register fields before calling
SetOverlayViewPort().

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Danila Chernetsov <listdansp@mail.ru>
---
 drivers/video/fbdev/kyro/fbdev.c | 24 +++++++++++++++++++++++-
 1 file changed, 23 insertions(+), 1 deletion(-)

diff --git a/drivers/video/fbdev/kyro/fbdev.c b/drivers/video/fbdev/kyro/fbdev.c
index d756b3603fa6..133c91716c49 100644
--- a/drivers/video/fbdev/kyro/fbdev.c
+++ b/drivers/video/fbdev/kyro/fbdev.c
@@ -369,6 +369,9 @@ static int kyro_dev_overlay_create(u32 ulWidth,
 
 static int kyro_dev_overlay_viewport_set(u32 x, u32 y, u32 ulWidth, u32 ulHeight)
 {
+	u32 right;
+	u32 bottom;
+
 	if (deviceInfo.ulOverlayOffset == 0)
 		/* probably haven't called CreateOverlay yet */
 		return -EINVAL;
@@ -378,11 +381,30 @@ static int kyro_dev_overlay_viewport_set(u32 x, u32 y, u32 ulWidth, u32 ulHeight
 	    (x < 2 && ulWidth + 2 == 0))
 		return -EINVAL;
 
+	/*
+	 * SetOverlayViewPort() adjusts X coordinates by +2 (left) and +1
+	 * (right) before packing them into 16-bit register fields.
+	 */
+	if (x > U16_MAX - 2 || y > U16_MAX)
+		return -EINVAL;
+
+	right = x + ulWidth;
+	bottom = y + ulHeight;
+
+	if (right < x || bottom < y)
+		return -EINVAL;
+
+	right--;
+	bottom--;
+
+	if (right > U16_MAX - 1 || bottom > U16_MAX)
+		return -EINVAL;
+
 	/* Stop Ramdac Output */
 	DisableRamdacOutput(deviceInfo.pSTGReg);
 
 	SetOverlayViewPort(deviceInfo.pSTGReg,
-			   x, y, x + ulWidth - 1, y + ulHeight - 1);
+			x, y, right, bottom);
 
 	EnableOverlayPlane(deviceInfo.pSTGReg);
 	/* Start Ramdac Output */
-- 
2.25.1