mfd: syscon: Add check for invalid resource size

Add a consistency check to avoid assigning an invalid value to
max_register due to a possible DT misconfiguration.

Suggested-by: Mark Langsdorf <mlangsdo@redhat.com>
Signed-off-by: Eder Zulian <ezulian@redhat.com>
Link: https://lore.kernel.org/r/20250212184524.585882-1-ezulian@redhat.com
Signed-off-by: Lee Jones <lee@kernel.org>

Author: efzrh

drivers/mfd/syscon.c

@@ -47,6 +47,7 @@ static struct syscon *of_syscon_register(struct device_node *np, bool check_res)
 	struct regmap_config syscon_config = syscon_regmap_config;
 	struct resource res;
 	struct reset_control *reset;
+	resource_size_t res_size;
 
 	WARN_ON(!mutex_is_locked(&syscon_list_lock));
 
@@ -96,14 +97,20 @@ static struct syscon *of_syscon_register(struct device_node *np, bool check_res)
 		}
 	}
 
+	res_size = resource_size(&res);
+	if (res_size < reg_io_width) {
+		ret = -EFAULT;
+		goto err_regmap;
+	}
+
 	syscon_config.name = kasprintf(GFP_KERNEL, "%pOFn@%pa", np, &res.start);
 	if (!syscon_config.name) {
 		ret = -ENOMEM;
 		goto err_regmap;
 	}
 	syscon_config.reg_stride = reg_io_width;
 	syscon_config.val_bits = reg_io_width * 8;
-	syscon_config.max_register = resource_size(&res) - reg_io_width;
+	syscon_config.max_register = res_size - reg_io_width;
 	if (!syscon_config.max_register)
 		syscon_config.max_register_is_0 = true;