bug symfony#24367 PdoSessionHandler: fix advisory lock for pgsql (Tobion)

This PR was merged into the 2.7 branch.

Discussion
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PdoSessionHandler: fix advisory lock for pgsql

when session.sid_bits per_character > 4 the session id can contain non-hex-characters which will be ignored by hexdec. this can potentially result in collisions on the lock key from different sessions, e.g. the session ids `aagh` and `aaij` would have the same pgsql lock because `hexdec('aagh') === hexdec('aaij')`

| Q             | A
| ------------- | ---
| Branch?       | 2.7
| Bug fix?      | yes
| New feature?  | no <!-- don't forget updating src/**/CHANGELOG.md files -->
| BC breaks?    | no
| Deprecations? | no <!-- don't forget updating UPGRADE-*.md files -->
| Tests pass?   | yes
| Fixed tickets | symfony#24095
| License       | MIT
| Doc PR        |

Commits
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0f0a6e8 PdoSessionHandler: fix advisory lock for pgsql when session.sid_bits_per_character > 4

Author: fabpot

src/Symfony/Component/HttpFoundation/Session/Storage/Handler/PdoSessionHandler.php

@@ -580,11 +580,11 @@ private function doAdvisoryLock($sessionId)
                 return $releaseStmt;
             case 'pgsql':
                 // Obtaining an exclusive session level advisory lock requires an integer key.
-                // So we convert the HEX representation of the session id to an integer.
-                // Since integers are signed, we have to skip one hex char to fit in the range.
-                if (4 === PHP_INT_SIZE) {
-                    $sessionInt1 = hexdec(substr($sessionId, 0, 7));
-                    $sessionInt2 = hexdec(substr($sessionId, 7, 7));
+                // When session.sid_bits_per_character > 4, the session id can contain non-hex-characters.
+                // So we cannot just use hexdec().
+                if (4 === \PHP_INT_SIZE) {
+                    $sessionInt1 = $this->convertStringToInt($sessionId);
+                    $sessionInt2 = $this->convertStringToInt(substr($sessionId, 4, 4));
 
                     $stmt = $this->pdo->prepare('SELECT pg_advisory_lock(:key1, :key2)');
                     $stmt->bindValue(':key1', $sessionInt1, \PDO::PARAM_INT);
@@ -595,7 +595,7 @@ private function doAdvisoryLock($sessionId)
                     $releaseStmt->bindValue(':key1', $sessionInt1, \PDO::PARAM_INT);
                     $releaseStmt->bindValue(':key2', $sessionInt2, \PDO::PARAM_INT);
                 } else {
-                    $sessionBigInt = hexdec(substr($sessionId, 0, 15));
+                    $sessionBigInt = $this->convertStringToInt($sessionId);
 
                     $stmt = $this->pdo->prepare('SELECT pg_advisory_lock(:key)');
                     $stmt->bindValue(':key', $sessionBigInt, \PDO::PARAM_INT);
@@ -613,6 +613,27 @@ private function doAdvisoryLock($sessionId)
         }
     }
 
+    /**
+     * Encodes the first 4 (when PHP_INT_SIZE == 4) or 8 characters of the string as an integer.
+     *
+     * Keep in mind, PHP integers are signed.
+     *
+     * @param string $string
+     *
+     * @return int
+     */
+    private function convertStringToInt($string)
+    {
+        if (4 === \PHP_INT_SIZE) {
+            return (ord($string[3]) << 24) + (ord($string[2]) << 16) + (ord($string[1]) << 8) + ord($string[0]);
+        }
+
+        $int1 = (ord($string[7]) << 24) + (ord($string[6]) << 16) + (ord($string[5]) << 8) + ord($string[4]);
+        $int2 = (ord($string[3]) << 24) + (ord($string[2]) << 16) + (ord($string[1]) << 8) + ord($string[0]);
+
+        return $int2 + ($int1 << 32);
+    }
+
     /**
      * Return a locking or nonlocking SQL query to read session information.
      *