Ensure strncpy'ed strings are all null terminated

If there is no null byte among the first n bytes of the source the
resulting string will not be properly null terminated.
Ensure that all strings that are copied via strncpy are properly
terminated copy "sizeof (dest) - 1" bytes and manually terminate
the string in the cases the array was not initialized.

Example compiler warning:
  ../daemon/gamemode-tests.c: In function ‘run_cpu_governor_tests’:
  ../daemon/gamemode-tests.c:326:4: warning: ‘strncpy’ specified bound
      256 equals destination size [-Wstringop-truncation]
    strncpy(defaultgov, currentgov, CONFIG_VALUE_MAX);
    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

daemon/gamemode-gpu.c

@@ -224,7 +224,8 @@ int game_mode_get_gpu(GameModeGPUInfo *info)
 		}
 		break;
 	case Vendor_AMD:
-		strncpy(info->amd_performance_level, buffer, CONFIG_VALUE_MAX);
+		strncpy(info->amd_performance_level, buffer, sizeof(info->amd_performance_level) - 1);
+		info->amd_performance_level[sizeof(info->amd_performance_level) - 1] = '\0';
 		break;
 	}
 

daemon/gamemode-tests.c

@@ -323,7 +323,7 @@ static int run_cpu_governor_tests(struct GameModeConfig *config)
 	if (defaultgov[0] == '\0') {
 		const char *currentgov = get_gov_state();
 		if (currentgov) {
-			strncpy(defaultgov, currentgov, CONFIG_VALUE_MAX);
+			strncpy(defaultgov, currentgov, CONFIG_VALUE_MAX - 1);
 		} else {
 			LOG_ERROR(
 			    "Could not get current CPU governor state, this indicates an error! See rest "
@@ -445,16 +445,16 @@ int run_gpu_optimisation_tests(struct GameModeConfig *config)
 	long expected_core = gpuinfo->nv_core;
 	long expected_mem = gpuinfo->nv_mem;
 	long expected_nv_powermizer_mode = gpuinfo->nv_powermizer_mode;
-	char expected_amd_performance_level[CONFIG_VALUE_MAX];
-	strncpy(expected_amd_performance_level, gpuinfo->amd_performance_level, CONFIG_VALUE_MAX);
+	char expected_amd_performance_level[CONFIG_VALUE_MAX] = { 0 };
+	strncpy(expected_amd_performance_level, gpuinfo->amd_performance_level, CONFIG_VALUE_MAX - 1);
 
 	/* Get current stats */
 	game_mode_get_gpu(gpuinfo);
 	long original_nv_core = gpuinfo->nv_core;
 	long original_nv_mem = gpuinfo->nv_mem;
 	long original_nv_powermizer_mode = gpuinfo->nv_powermizer_mode;
-	char original_amd_performance_level[CONFIG_VALUE_MAX];
-	strncpy(original_amd_performance_level, gpuinfo->amd_performance_level, CONFIG_VALUE_MAX);
+	char original_amd_performance_level[CONFIG_VALUE_MAX] = { 0 };
+	strncpy(original_amd_performance_level, gpuinfo->amd_performance_level, CONFIG_VALUE_MAX - 1);
 
 	/* account for when settings are not set */
 	if (expected_nv_powermizer_mode == -1)

daemon/governors-query.c

@@ -134,7 +134,7 @@ const char *get_gov_state(void)
 				return "malformed";
 			}
 
-			strncpy(governor, contents, sizeof(governor));
+			strncpy(governor, contents, sizeof(governor) - 1);
 		} else {
 			LOG_ERROR("Failed to read contents of %s\n", gov);
 		}

daemon/gpuclockctl.c

@@ -289,7 +289,7 @@ static int get_gpu_state_amd(struct GameModeGPUInfo *info)
 		return -1;
 	}
 
-	char buff[CONFIG_VALUE_MAX];
+	char buff[CONFIG_VALUE_MAX] = { 0 };
 	if (!fgets(buff, CONFIG_VALUE_MAX, file)) {
 		LOG_ERROR("Could not read file %s (%s)!\n", path, strerror(errno));
 		return -1;
@@ -301,8 +301,8 @@ static int get_gpu_state_amd(struct GameModeGPUInfo *info)
 	}
 
 	/* Copy in the value from the file */
-	strncpy(info->amd_performance_level, buff, CONFIG_VALUE_MAX);
-
+	strncpy(info->amd_performance_level, buff, CONFIG_VALUE_MAX - 1);
+	info->amd_performance_level[CONFIG_VALUE_MAX - 1] = '\0';
 	return info == NULL;
 }
 
@@ -449,7 +449,7 @@ int main(int argc, char *argv[])
 				LOG_ERROR("Must pass performance level for AMD gpu!\n");
 				print_usage_and_exit();
 			}
-			strncpy(info.amd_performance_level, argv[3], CONFIG_VALUE_MAX);
+			strncpy(info.amd_performance_level, argv[3], CONFIG_VALUE_MAX - 1);
 			return set_gpu_state_amd(&info);
 			break;
 		default: