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Fix shm corruption with coercion in options of unserialize() #20129

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Fix shm corruption with coercion in options of unserialize() #20129

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8b65954
Fix shm corruption with coercion in options of unserialize()
nielsdos Oct 10, 2025
332581e
fixup! lifetime
nielsdos Oct 11, 2025
e9b1d7a
Revert "fixup! lifetime"
nielsdos Oct 13, 2025
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8 changes: 8 additions & 0 deletions ext/standard/tests/serialize/shm_corruption_coercion_unserialize_options.phpt
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Original file line number Diff line number Diff line change
@@ -0,0 +1,8 @@
--TEST--
Shm corruption with coercion in options of unserialize()
--FILE--
<?php
unserialize("{}", ["allowed_classes" => [0]]);
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What happens if you have a non-stringable object as an option?

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That will work

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@nielsdos nielsdos Oct 11, 2025 •
edited
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In the sense that it will throw and exit out at the check after the loop

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Cool that's the thing I was wondering about.

?>
--EXPECTF--
Warning: unserialize(): Error at offset 0 of 2 bytes in %s on line %d
9 changes: 5 additions & 4 deletions ext/standard/var.c
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Expand Up @@ -1366,13 +1366,14 @@ PHPAPI void php_unserialize_with_options(zval *return_value, const char *buf, co
}
if(class_hash && Z_TYPE_P(classes) == IS_ARRAY) {
zval *entry;
zend_string *lcname;

ZEND_HASH_FOREACH_VAL(Z_ARRVAL_P(classes), entry) {
convert_to_string(entry);
lcname = zend_string_tolower(Z_STR_P(entry));
/* Note: cannot use zval_get_tmp_string() here as we need to keep it in class_hash for longer than this loop. */
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Is this comment accurate? zend_tmp_string_release() uses zend_string_release_ex() (i.e. not zend_string_free()), so it seems the allocation can still survive the loop. But it doesn't seem better, so maybe just remove the comment if my assuption is correct.

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@nielsdos nielsdos Oct 13, 2025 •
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Yeah my bad, you're right. I originally had a solution with the tmp string API (first commit). What I missed is that we actually take a strong reference via zend_string_tolower, so we can use that API. I'll revert my last commit and merge after CI passes

zend_string *str = zval_get_string(entry);
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Any reason for not using the try version of this API?

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Possible, but not necessary, as we will exit at the exception check a bit later.

zend_string *lcname = zend_string_tolower(str);
zend_hash_add_empty_element(class_hash, lcname);
zend_string_release_ex(lcname, 0);
zend_string_release_ex(lcname, false);
zend_string_release_ex(str, false);
} ZEND_HASH_FOREACH_END();

/* Exception during string conversion. */
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