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Fix GH-8556: FFI\CData use-after-free after FFI object destroyed #10574

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Fix GH-8556: FFI\CData use-after-free after FFI object destroyed #10574

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15 changes: 13 additions & 2 deletions ext/ffi/ffi.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2777,7 +2777,17 @@ static ZEND_FUNCTION(ffi_trampoline) /* {{{ */
free_alloca(arg_values, arg_values_use_heap);
}

zend_ffi_cdata_to_zval(NULL, ret, ZEND_FFI_TYPE(type->func.ret_type), BP_VAR_R, return_value, 0, 1, 0);
zend_ffi_type *func_ret_type = type->func.ret_type;

if (ZEND_FFI_TYPE_IS_OWNED(func_ret_type)) {
func_ret_type = ZEND_FFI_TYPE(func_ret_type);
if (!(func_ret_type->attr & ZEND_FFI_ATTR_STORED)
&& func_ret_type->kind == ZEND_FFI_TYPE_POINTER) {
type->func.ret_type = func_ret_type = zend_ffi_remember_type(func_ret_type);
}
}

zend_ffi_cdata_to_zval(NULL, ret, func_ret_type, BP_VAR_R, return_value, 0, 1, 0);
free_alloca(ret, ret_use_heap);

exit:
Expand Down Expand Up @@ -2919,7 +2929,7 @@ ZEND_METHOD(FFI, cdef) /* {{{ */

if (code && ZSTR_LEN(code)) {
/* Parse C definitions */
FFI_G(default_type_attr) = ZEND_FFI_ATTR_STORED;
FFI_G(default_type_attr) = 0;
Comment on lines -2922 to +2932
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I afraid this was a design decision - cdef should relive all CData objects. Otherwise almost any type has to be remembered. The problem is not limited to return type, but to any declared type.

<?php
$cdef = FFI::cdef("typedef int T[5];");
$a = $cdef->new("T");
var_dump($a);
unset($cdef);
var_dump($a);

It would be great to find a common efficient solution. Fixing this only for return type doesn't make a lot of sense.

I would agree to merge this fix only for return type without this s/ZEND_FFI_ATTR_STORED/0/ hunk.

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Oh I see, thanks for checking. I'll see later this week if I can come up with something.

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Thanks for looking into this :)


if (zend_ffi_parse_decl(ZSTR_VAL(code), ZSTR_LEN(code)) != SUCCESS) {
if (FFI_G(symbols)) {
Expand Down Expand Up @@ -3144,6 +3154,7 @@ static void zend_ffi_cleanup_type(zend_ffi_type *old, zend_ffi_type *type) /* {{

static zend_ffi_type *zend_ffi_remember_type(zend_ffi_type *type) /* {{{ */
{
ZEND_ASSERT(!ZEND_FFI_TYPE_IS_OWNED(type) && "type argument must not be a tagged pointer");
if (!FFI_G(weak_types)) {
FFI_G(weak_types) = emalloc(sizeof(HashTable));
zend_hash_init(FFI_G(weak_types), 0, NULL, zend_ffi_type_hash_dtor, 0);
Expand Down
39 changes: 39 additions & 0 deletions ext/ffi/tests/gh8556.phpt
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Original file line number Diff line number Diff line change
@@ -0,0 +1,39 @@
--TEST--
GH-8556 (FFI\CData use-after-free after FFI object destroyed)
--EXTENSIONS--
ffi
--SKIPIF--
<?php
try {
$libc = FFI::cdef("char *getenv(char *);", "libc.so.6");
} catch (Throwable $_) {
die('skip libc.so.6 not available');
}
?>
--INI--
ffi.enable=1
--FILE--
<?php

putenv("TEST=123");

// Original
$c = (FFI::cdef("char *getenv(char *);", "libc.so.6"))->getenv("TEST");
var_dump($c);

// Variant on the original
$libc = FFI::cdef("char *getenv(char *);", "libc.so.6");
$result = $libc->getenv("TEST");
unset($libc); // Frees ffi cdata ->type member
var_dump($result);

?>
--EXPECT--
object(FFI\CData:char*)#2 (1) {
[0]=>
string(1) "1"
}
object(FFI\CData:char*)#3 (1) {
[0]=>
string(1) "1"
}