bug #19666 Verify explicitly that the request IP is a valid IPv4 address (nesk)

This PR was squashed before being merged into the 2.7 branch (closes #19666).

Discussion
----------

Verify explicitly that the request IP is a valid IPv4 address

| Q             | A
| ------------- | ---
| Branch?       | 2.7
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

Take the following base code (the array is based on [CloudFlare IP Ranges](https://www.cloudflare.com/ips/)):

```php
use Symfony\Component\HttpFoundation\IpUtils;

$ips = [
   "103.21.244.0/22",
   "103.22.200.0/22",
   "103.31.4.0/22",
   "104.16.0.0/12",
   "108.162.192.0/18",
   "131.0.72.0/22",
   "141.101.64.0/18",
   "162.158.0.0/15",
   "172.64.0.0/13",
   "173.245.48.0/20",
   "188.114.96.0/20",
   "190.93.240.0/20",
   "197.234.240.0/22",
   "198.41.128.0/17",
   "199.27.128.0/21",
   "2400:cb00::/32",
   "2405:8100::/32",
   "2405:b500::/32",
   "2606:4700::/32",
   "2803:f800::/32",
   "2c0f:f248::/32",
   "2a06:98c0::/29",
];
```

Before this PR, the following code would have returned `true` instead of the expected `false` value:

```php
IpUtils::checkIp('blablabla', $ips);
```

This due to the `ip2long` function returning `false` for an invalid IP address, thus returning `"00000000000000000000000000000000"` with the following code:

```php
sprintf('%032b', ip2long('blablabla'));
```

To fix this I simply check if the `$requestIp` variable contains a valid IP address.

Commits
-------

17e418c Verify explicitly that the request IP is a valid IPv4 address

Author: fabpot

src/Symfony/Component/HttpFoundation/IpUtils.php

@@ -61,11 +61,14 @@ public static function checkIp($requestIp, $ips)
      */
     public static function checkIp4($requestIp, $ip)
     {
+        if (!filter_var($requestIp, FILTER_VALIDATE_IP, FILTER_FLAG_IPV4)) {
+            return false;
+        }
+
         if (false !== strpos($ip, '/')) {
             list($address, $netmask) = explode('/', $ip, 2);
 
             if ($netmask === '0') {
-                // Ensure IP is valid - using ip2long below implicitly validates, but we need to do it manually here
                 return filter_var($address, FILTER_VALIDATE_IP, FILTER_FLAG_IPV4);
             }
 

src/Symfony/Component/HttpFoundation/Tests/IpUtilsTest.php

@@ -37,6 +37,7 @@ public function testIpv4Provider()
             array(true, '1.2.3.4', '0.0.0.0/0'),
             array(true, '1.2.3.4', '192.168.1.0/0'),
             array(false, '1.2.3.4', '256.256.256/0'), // invalid CIDR notation
+            array(false, 'an_invalid_ip', '192.168.1.0/24'),
         );
     }