platform/x86: alienware-wmi: fix format string overflow warning

gcc points out a possible format string overflow for a large value of 'zone':

drivers/platform/x86/alienware-wmi.c: In function 'alienware_wmi_init':
drivers/platform/x86/alienware-wmi.c:461:24: error: '%02X' directive writing between 2 and 8 bytes into a region of size 6 [-Werror=format-overflow=]
   sprintf(buffer, "zone%02X", i);
                        ^~~~
drivers/platform/x86/alienware-wmi.c:461:19: note: directive argument in the range [0, 2147483646]
   sprintf(buffer, "zone%02X", i);
                   ^~~~~~~~~~
drivers/platform/x86/alienware-wmi.c:461:3: note: 'sprintf' output between 7 and 13 bytes into a destination of size 10

This replaces the 'int' variable with an 'u8' to make sure
it always fits, renaming the variable to 'zone' for clarity.

Unfortunately, gcc-7.1.1 still warns about it with that change, which
seems to be unintended by the gcc developers. I have opened a bug
against gcc with a reduced test case. As a workaround, I also
change the format string to use "%02hhX", which shuts up the
warning in that version.

Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81483
Link: https://patchwork.ozlabs.org/patch/788415/
Suggested-by: Andy Shevchenko <andy@infradead.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
[andy: added empty lines after u8 zone; definitions]
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

diff --git a/drivers/platform/x86/alienware-wmi.c b/drivers/platform/x86/alienware-wmi.c
index 0831b428c217549f6d42a6d1543d4ed0cb539535..4eb8e1a472b23821280fae17f91df35a8ce8737e 100644 (file)
--- a/drivers/platform/x86/alienware-wmi.c
+++ b/drivers/platform/x86/alienware-wmi.c
@@ -255,12 +255,13 @@ static int parse_rgb(const char *buf, struct platform_zone *zone)
 
 static struct platform_zone *match_zone(struct device_attribute *attr)
 {
-       int i;
-       for (i = 0; i < quirks->num_zones; i++) {
-               if ((struct device_attribute *)zone_data[i].attr == attr) {
+       u8 zone;
+
+       for (zone = 0; zone < quirks->num_zones; zone++) {
+               if ((struct device_attribute *)zone_data[zone].attr == attr) {
                        pr_debug("alienware-wmi: matched zone location: %d\n",
-                                zone_data[i].location);
-                       return &zone_data[i];
+                                zone_data[zone].location);
+                       return &zone_data[zone];
                }
        }
        return NULL;
@@ -420,7 +421,7 @@ static DEVICE_ATTR(lighting_control_state, 0644, show_control_state,
 
 static int alienware_zone_init(struct platform_device *dev)
 {
-       int i;
+       u8 zone;
        char buffer[10];
        char *name;
 
@@ -457,19 +458,19 @@ static int alienware_zone_init(struct platform_device *dev)
        if (!zone_data)
                return -ENOMEM;
 
-       for (i = 0; i < quirks->num_zones; i++) {
-               sprintf(buffer, "zone%02X", i);
+       for (zone = 0; zone < quirks->num_zones; zone++) {
+               sprintf(buffer, "zone%02hhX", zone);
                name = kstrdup(buffer, GFP_KERNEL);
                if (name == NULL)
                        return 1;
-               sysfs_attr_init(&zone_dev_attrs[i].attr);
-               zone_dev_attrs[i].attr.name = name;
-               zone_dev_attrs[i].attr.mode = 0644;
-               zone_dev_attrs[i].show = zone_show;
-               zone_dev_attrs[i].store = zone_set;
-               zone_data[i].location = i;
-               zone_attrs[i] = &zone_dev_attrs[i].attr;
-               zone_data[i].attr = &zone_dev_attrs[i];
+               sysfs_attr_init(&zone_dev_attrs[zone].attr);
+               zone_dev_attrs[zone].attr.name = name;
+               zone_dev_attrs[zone].attr.mode = 0644;
+               zone_dev_attrs[zone].show = zone_show;
+               zone_dev_attrs[zone].store = zone_set;
+               zone_data[zone].location = zone;
+               zone_attrs[zone] = &zone_dev_attrs[zone].attr;
+               zone_data[zone].attr = &zone_dev_attrs[zone];
        }
        zone_attrs[quirks->num_zones] = &dev_attr_lighting_control_state.attr;
        zone_attribute_group.attrs = zone_attrs;
@@ -481,12 +482,13 @@ static int alienware_zone_init(struct platform_device *dev)
 
 static void alienware_zone_exit(struct platform_device *dev)
 {
+       u8 zone;
+
        sysfs_remove_group(&dev->dev.kobj, &zone_attribute_group);
        led_classdev_unregister(&global_led);
        if (zone_dev_attrs) {
-               int i;
-               for (i = 0; i < quirks->num_zones; i++)
-                       kfree(zone_dev_attrs[i].attr.name);
+               for (zone = 0; zone < quirks->num_zones; zone++)
+                       kfree(zone_dev_attrs[zone].attr.name);
        }
        kfree(zone_dev_attrs);
        kfree(zone_data);