From b3ad99ed45917f42884fee731fa3cf9b8229a26c Mon Sep 17 00:00:00 2001
From: Michal Srb <msrb@suse.com>
Date: Mon, 5 Feb 2018 16:04:38 +0000
Subject: [PATCH] drm/i915/cmdparser: Do not check past the cmd length.
Git-commit: b3ad99ed45917f42884fee731fa3cf9b8229a26c
Patch-mainline: v4.16-rc1
References: FATE#322643 bsc#1055900
No-fix: 3aec7f871c65eb5f76b4125fda432593c834a6f2

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@suse.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180205151745.29292-1-msrb@suse.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/20180205160438.3267-2-chris@chris-wilson.co.uk
(cherry picked from commit 3aec7f871c65eb5f76b4125fda432593c834a6f2)

Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 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
@@ -1212,6 +1212,12 @@ 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 (%s)\n",
+						 *cmd, engine->name);
+				return false;
+			}
+
 			dword = cmd[desc->bits[i].offset] &
 				desc->bits[i].mask;