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Fix circumvented type check with return by ref + finally #19172

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Fix circumvented type check with return by ref + finally #19172

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24 changes: 24 additions & 0 deletions Zend/tests/gh18736.phpt
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Original file line number Diff line number Diff line change
@@ -0,0 +1,24 @@
--TEST--
GH-18736: Circumvented type check with return by ref + finally
--FILE--
<?php

function &test(): int {
$x = 0;
try {
return $x;
} finally {
$x = 'test';
}
}

try {
$x = &test();
var_dump($x);
} catch (Error $e) {
echo $e->getMessage(), "\n";
}

?>
--EXPECT--
test(): Return value must be of type int, string returned
9 changes: 9 additions & 0 deletions Zend/zend_compile.c
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Original file line number Diff line number Diff line change
Expand Up @@ -5703,6 +5703,15 @@ static void zend_compile_return(zend_ast *ast) /* {{{ */

zend_handle_loops_and_finally((expr_node.op_type & (IS_TMP_VAR | IS_VAR)) ? &expr_node : NULL);

/* Content of reference might have changed in finally, repeat type check. */
if (by_ref
&& !zend_stack_is_empty(&CG(loop_var_stack))
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Why is this check needed? The by_ref makes sense because that is how the type of the returned variable changes, and the is_generator and ZEND_ACC_HAS_RETURN_TYPE make sense because those are the conditions used above, but this condition (empty loop variable stack) isn't checked above - maybe add a comment about why it is needed here but not previously?

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It's just a fast way to check whether we're in a try. We could use zend_has_finally(), but technically even loop/switch var FREEs could change the content of the reference. It's very unlikely to matter in practice, but given return-by-ref with finally/loops should be rare enough I didn't bother optimizing this more.

&& !is_generator
&& (CG(active_op_array)->fn_flags & ZEND_ACC_HAS_RETURN_TYPE)) {
zend_emit_return_type_check(
expr_ast ? &expr_node : NULL, CG(active_op_array)->arg_info - 1, 0);
}

opline = zend_emit_op(NULL, by_ref ? ZEND_RETURN_BY_REF : ZEND_RETURN,
&expr_node, NULL);

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