wifi: ipw2x00: refactor to use kstrtoul

The current implementation seems to reinvent what `kstrtoul` already does
in terms of functionality and error handling. Remove uses of `simple_strtoul()`
in favor of `kstrtoul()`.

There is the following note at `lib/vsprintf.c:simple_strtoull()` which
further backs this change:
| * This function has caveats. Please use kstrtoull (or kstrtoul) instead.

And here, simple_str* are explicitly deprecated [3].

This patch also removes an instance of the deprecated `strncpy` which helps [2].

Compile tested only.

Link: https://lore.kernel.org/all/202308011602.3CC1C0244C@keescook/ [1]
Link: https://github.com/KSPP/linux/issues/90 [2]
Link: https://docs.kernel.org/process/deprecated.html#simple-strtol-simple-strtoll-simple-strtoul-simple-strtoull [3]
Cc: linux-hardening@vger.kernel.org
Suggested-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Justin Stitt <justinstitt@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20230802-wifi-ipw2x00-refactor-v2-1-d33f765e9cd5@google.com

drivers/net/wireless/intel/ipw2x00/ipw2200.c

@@ -1176,23 +1176,20 @@ static ssize_t debug_level_show(struct device_driver *d, char *buf)
 static ssize_t debug_level_store(struct device_driver *d, const char *buf,
 				 size_t count)
 {
-	char *p = (char *)buf;
-	u32 val;
+	unsigned long val;
 
-	if (p[1] == 'x' || p[1] == 'X' || p[0] == 'x' || p[0] == 'X') {
-		p++;
-		if (p[0] == 'x' || p[0] == 'X')
-			p++;
-		val = simple_strtoul(p, &p, 16);
-	} else
-		val = simple_strtoul(p, &p, 10);
-	if (p == buf)
+	int result = kstrtoul(buf, 0, &val);
+
+	if (result == -EINVAL)
 		printk(KERN_INFO DRV_NAME
 		       ": %s is not in hex or decimal form.\n", buf);
+	else if (result == -ERANGE)
+		printk(KERN_INFO DRV_NAME
+			 ": %s has overflowed.\n", buf);
 	else
 		ipw_debug_level = val;
 
-	return strnlen(buf, count);
+	return count;
 }
 static DRIVER_ATTR_RW(debug_level);
 
@@ -1461,25 +1458,13 @@ static ssize_t scan_age_store(struct device *d, struct device_attribute *attr,
 {
 	struct ipw_priv *priv = dev_get_drvdata(d);
 	struct net_device *dev = priv->net_dev;
-	char buffer[] = "00000000";
-	unsigned long len =
-	    (sizeof(buffer) - 1) > count ? count : sizeof(buffer) - 1;
-	unsigned long val;
-	char *p = buffer;
 
 	IPW_DEBUG_INFO("enter\n");
 
-	strncpy(buffer, buf, len);
-	buffer[len] = 0;
+	unsigned long val;
+	int result = kstrtoul(buf, 0, &val);
 
-	if (p[1] == 'x' || p[1] == 'X' || p[0] == 'x' || p[0] == 'X') {
-		p++;
-		if (p[0] == 'x' || p[0] == 'X')
-			p++;
-		val = simple_strtoul(p, &p, 16);
-	} else
-		val = simple_strtoul(p, &p, 10);
-	if (p == buffer) {
+	if (result == -EINVAL || result == -ERANGE) {
 		IPW_DEBUG_INFO("%s: user supplied invalid value.\n", dev->name);
 	} else {
 		priv->ieee->scan_age = val;
@@ -1487,7 +1472,7 @@ static ssize_t scan_age_store(struct device *d, struct device_attribute *attr,
 	}
 
 	IPW_DEBUG_INFO("exit\n");
-	return len;
+	return count;
 }
 
 static DEVICE_ATTR_RW(scan_age);