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[Session] limiting :key for GET_LOCK to 64 chars #27250

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May 15, 2018
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[Session] limiting :key for GET_LOCK to 64 chars #27250

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6 changes: 4 additions & 2 deletions src/Symfony/Component/HttpFoundation/Session/Storage/Handler/PdoSessionHandler.php
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Original file line number Diff line number Diff line change
Expand Up @@ -552,14 +552,16 @@ private function doAdvisoryLock($sessionId)
{
switch ($this->driver) {
case 'mysql':
// MySQL 5.7.5 and later enforces a maximum length on lock names of 64 characters. Previously, no limit was enforced.
$lockId = \substr($sessionId, 0, 64);
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I'd recommend to hash the session id instead (or doing something similar) as keeping just the first 64 chars could lead to conflicts depending on how the session id is generated.

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The session id is just a random string. So hashing that does not reduce the likeliness of collisions compared to just using the first 64 bytes.

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@fabian, @Tobion is right, session_id is just a random string, which is result of http://php.net/manual/en/session.configuration.php#ini.session.hash-function and by default it's md5

// should we handle the return value? 0 on timeout, null on error
// we use a timeout of 50 seconds which is also the default for innodb_lock_wait_timeout
$stmt = $this->pdo->prepare('SELECT GET_LOCK(:key, 50)');
$stmt->bindValue(':key', $sessionId, \PDO::PARAM_STR);
$stmt->bindValue(':key', $lockId, \PDO::PARAM_STR);
$stmt->execute();

$releaseStmt = $this->pdo->prepare('DO RELEASE_LOCK(:key)');
$releaseStmt->bindValue(':key', $sessionId, \PDO::PARAM_STR);
$releaseStmt->bindValue(':key', $lockId, \PDO::PARAM_STR);

return $releaseStmt;
case 'pgsql':
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