[PATCH 1/2] drm/i915/cmdparser: Check reg_table_count before derefencing.

[Michal Srb <msrb@suse.com>]

The find_reg function was assuming that there is always at least one table in
reg_tables. It is not always true.

In case of VCS or VECS, the reg_tables is NULL and reg_table_count is 0,
implying that no register-accessing commands are allowed. However, the command
tables include commands such as MI_STORE_REGISTER_MEM. When trying to check
such command, the find_reg would dereference NULL pointer.

Now it will just return NULL meaning that the register was not found and the
command will be rejected.

Signed-off-by: Michal Srb <msrb@suse.com>
---
 drivers/gpu/drm/i915/i915_cmd_parser.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_cmd_parser.c b/drivers/gpu/drm/i915/i915_cmd_parser.c
index 8ba932b22f7c..de7ec59433d1 100644
--- a/drivers/gpu/drm/i915/i915_cmd_parser.c
+++ b/drivers/gpu/drm/i915/i915_cmd_parser.c
@@ -1038,7 +1038,7 @@ find_reg(const struct intel_engine_cs *engine, bool is_master, u32 addr)
 	const struct drm_i915_reg_table *table = engine->reg_tables;
 	int count = engine->reg_table_count;
 
-	do {
+	for (; count > 0; ++table, --count) {
 		if (!table->master || is_master) {
 			const struct drm_i915_reg_descriptor *reg;
 
@@ -1046,7 +1046,7 @@ find_reg(const struct intel_engine_cs *engine, bool is_master, u32 addr)
 			if (reg != NULL)
 				return reg;
 		}
-	} while (table++, --count);
+	}
 
 	return NULL;
 }
-- 
2.13.6

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