[PATCH 3.16 004/366] drm/i915/cmdparser: Do not check past the cmd length.

[Ben Hutchings]

3.16.60-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Michal Srb <msrb@xxxxxxxx>

commit 3aec7f871c65eb5f76b4125fda432593c834a6f2 upstream.

The command MEDIA_VFE_STATE checks bits at offset +2 dwords. However, it is
possible to have MEDIA_VFE_STATE command with length = 0 + LENGTH_BIAS = 2.
In that case check_cmd will read bits from the following command, or even past
the end of the buffer.

If the offset ends up outside of the command length, reject the command.

Fixes: 351e3db2b363 ("drm/i915: Implement command buffer parsing logic")
Signed-off-by: Michal Srb <msrb@xxxxxxxx>
Link: https://patchwork.freedesktop.org/patch/msgid/20180205151745.29292-1-msrb@xxxxxxxx
Reviewed-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Link: https://patchwork.freedesktop.org/patch/msgid/20180205160438.3267-2-chris@xxxxxxxxxxxxxxxxxx
[bwh: Backported to 3.16: Log ring->id rather than engine->name]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 drivers/gpu/drm/i915/i915_cmd_parser.c | 6 ++++++
 1 file changed, 6 insertions(+)

--- a/drivers/gpu/drm/i915/i915_cmd_parser.c
+++ b/drivers/gpu/drm/i915/i915_cmd_parser.c
@@ -941,6 +941,12 @@ static bool check_cmd(const struct intel
 					continue;
 			}
 
+			if (desc->bits[i].offset >= length) {
+				DRM_DEBUG_DRIVER("CMD: Rejected command 0x%08X, too short to check bitmask (ring=%d)\n",
+						 *cmd, ring->id);
+				return false;
+			}
+
 			dword = cmd[desc->bits[i].offset] &
 				desc->bits[i].mask;