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Fix #81142: memory leak when unserialize()ing associative array #7160

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Fix #81142: memory leak when unserialize()ing associative array #7160

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12 changes: 12 additions & 0 deletions ext/standard/tests/serialize/bug81142.phpt
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Original file line number Diff line number Diff line change
@@ -0,0 +1,12 @@
--TEST--
Bug #81142 (memory leak when unserialize()ing associative array)
--FILE--
<?php
$mem0 = memory_get_usage();
$ctr = 0;
unserialize(serialize(["foo_$ctr" => 1]));
$mem1 = memory_get_usage();
var_dump($mem1 - $mem0);
?>
--EXPECT--
int(0)
8 changes: 7 additions & 1 deletion ext/standard/var_unserializer.re
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Expand Up @@ -947,7 +947,13 @@ use_double:
} else if (len == 1) {
ZVAL_INTERNED_STR(rval, ZSTR_CHAR((zend_uchar)*str));
} else if (as_key) {
ZVAL_STR(rval, zend_string_init_interned(str, len, 0));
zend_string *key = zend_string_init(str, len, 0);
zend_string *ikey = zend_interned_string_find_permanent(key);
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This will only work for strings that are created during startup, which is probably not terribly useful. We'd be mainly interested in strings that are either interned per-request or part of opcache. I think this would require adding a new hook for this purpose that can be replaced by opcache.

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I don't think this ought to use interned strings at all.

It looks simpler to add a table to unserialize data for keys.

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I think the idea here is specifically to reuse normal interned strings for things like object property names, which are usually available as interned strings.

Maybe @dstogov can comment.

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With opcache zend_string_init_interned() doesn't create new interned strings (just search for existing ones).
To implement the same behavior without opcache, we need to introduce a new callback in zend_string API.

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I don't think that we want to introduce a new callback in the stable PHP versions. So, postpone the fix to PHP 8.1?

if (ikey) {
zend_string_release(key);
key = ikey;
}
ZVAL_STR(rval, key);
} else {
ZVAL_STRINGL(rval, str, len);
}
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