[PATCH v2 2/2] drm/i915/cmdparser: Do not check past the cmd length.

[Michal Srb <msrb@suse.com>]

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.

Signed-off-by: Michal Srb <msrb@suse.com>
---

 v2: Return false instead of continuing - reject the command instead of
     ignoring.

 drivers/gpu/drm/i915/i915_cmd_parser.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_cmd_parser.c b/drivers/gpu/drm/i915/i915_cmd_parser.c
index de7ec59433d1..ef7ad016d67c 100644
--- a/drivers/gpu/drm/i915/i915_cmd_parser.c
+++ b/drivers/gpu/drm/i915/i915_cmd_parser.c
@@ -1218,6 +1218,12 @@ static bool check_cmd(const struct intel_engine_cs *engine,
 					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;
 
-- 
2.13.6

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