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Fix GH-15210: phpdbg_print_changed_zvals working on a real copy instead. #15229

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Fix GH-15210: phpdbg_print_changed_zvals working on a real copy instead. #15229

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08e8a8f
Fix GH-15210: phpdbg_print_changed_zvals working on a real copy instead.
devnexen Aug 4, 2024
f845f7a
apply @nielsdos patches
devnexen Aug 9, 2024
a24ef06
adding tests
devnexen Aug 9, 2024
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13 changes: 10 additions & 3 deletions sapi/phpdbg/phpdbg_watch.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1168,8 +1168,9 @@ int phpdbg_print_changed_zvals(void) {

if (zend_hash_num_elements(PHPDBG_G(watchlist_mem)) > 0) {
/* we must not add elements to the hashtable while iterating over it (resize => read into freed memory) */
mem_list = PHPDBG_G(watchlist_mem);
PHPDBG_G(watchlist_mem) = PHPDBG_G(watchlist_mem_backup);
mem_list = malloc(phpdbg_pagesize > sizeof(HashTable) ? phpdbg_pagesize : sizeof(HashTable));
zend_hash_init(mem_list, zend_hash_num_elements(PHPDBG_G(watchlist_mem)), NULL, NULL, false);
zend_hash_copy(mem_list, PHPDBG_G(watchlist_mem), (copy_ctor_func_t) zval_add_ref);
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I don't totally understand why we need to duplicate the memory? Is it because the HashTable might be allocated with ZMM?

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in fact is to avoid the hashtable corruption of the original watchpoint list, working on a copy then copy back once all is done. it fixed the issue for me.

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Would increasing the refcounter on the HashTable also fix it or not?

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seems to work if I allow cow violation.

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That would be wrong, we need a temporary hash table so that resizes don't cause problems. Increasing the refcount won't protect you against that and only papers over the real issue.


ZEND_HASH_MAP_FOREACH_NUM_KEY(mem_list, page) {
phpdbg_btree_position pos = phpdbg_btree_find_between(&PHPDBG_G(watchpoint_tree), page, page + phpdbg_pagesize);
Expand All @@ -1192,7 +1193,13 @@ int phpdbg_print_changed_zvals(void) {
phpdbg_reenable_memory_watches();

if (mem_list) {
PHPDBG_G(watchlist_mem) = mem_list;
zend_hash_destroy(PHPDBG_G(watchlist_mem));
free(PHPDBG_G(watchlist_mem));
PHPDBG_G(watchlist_mem) = malloc(phpdbg_pagesize > sizeof(HashTable) ? phpdbg_pagesize : sizeof(HashTable));
zend_hash_init(PHPDBG_G(watchlist_mem), phpdbg_pagesize / (sizeof(Bucket) + sizeof(uint32_t)), NULL, NULL, true);
zend_hash_copy(PHPDBG_G(watchlist_mem), mem_list, (copy_ctor_func_t) zval_add_ref);
zend_hash_destroy(mem_list);
free(mem_list);
phpdbg_reenable_memory_watches();
}

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40 changes: 40 additions & 0 deletions sapi/phpdbg/tests/gh15210.phpt
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@@ -0,0 +1,40 @@
--TEST--
GH-15210 use after free after continue
--CREDITS--
YuanchengJiang
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We don't really use credit sections any longer, as those were more to go around the limitations of SVN

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okidoki

--PHPDBG--
b 4
r
w $a[0]
w r $b
c
q
--FILE--
<?php
header_register_callback(function() { echo "sent";});
$a = [0];
$a[0] = 1;
$b = &$a;
$a[0] = 2;
$a[1] = 3;
$c = [1];
$b = &$c;
?>
--EXPECTF--
[Successful compilation of %s]
prompt> [Breakpoint #0 added at %s:%d]
prompt> [Breakpoint #0 at %s:%d, hits: 1]
>00004: $a[0] = 1;
00005: $b = &$a;
00006: $a[0] = 2;
prompt> [Added watchpoint #0 for $a[0]]
prompt> [Added recursive watchpoint #1 for $b]
prompt> [Breaking on watchpoint $a[0]]
Old value: [Breaking on watchpoint $a[0]]
Old value: 0
New value: 1
>00002: header_register_callback(function() { echo "sent";});
00003: $a = [0];
00004: $a[0] = 1;
prompt> [$a[0] has been removed, removing watchpoint]
[$b has been removed, removing watchpoint recursively]