[PATCH 4.19 223/243] drm/i810: Prevent underflow in ioctl

Greg Kroah-Hartman
2019-12-11T15:25:32Z

From: Dan Carpenter <dan.carpenter@oracle.com>

commit 4f69851fbaa26b155330be35ce8ac393e93e7442 upstream.

The "used" variables here come from the user in the ioctl and it can be
negative. It could result in an out of bounds write.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20191004102251.GC823@mwanda
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/gpu/drm/i810/i810_dma.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/gpu/drm/i810/i810_dma.c
+++ b/drivers/gpu/drm/i810/i810_dma.c
@@ -721,7 +721,7 @@ static void i810_dma_dispatch_vertex(str
if (nbox > I810_NR_SAREA_CLIPRECTS)
nbox = I810_NR_SAREA_CLIPRECTS;

- if (used > 4 * 1024)
+ if (used < 0 || used > 4 * 1024)
used = 0;

if (sarea_priv->dirty)
@@ -1041,7 +1041,7 @@ static void i810_dma_dispatch_mc(struct
if (u != I810_BUF_CLIENT)
DRM_DEBUG("MC found buffer that isn't mine!\n");

- if (used > 4 * 1024)
+ if (used < 0 || used > 4 * 1024)
used = 0;

sarea_priv->dirty = 0x7f;