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Fix GH-22480: phpdbg use-after-free re-watching a watched variable #22493

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Fix GH-22480: phpdbg use-after-free re-watching a watched variable #22493

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4 changes: 4 additions & 0 deletions NEWS
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Original file line number Diff line number Diff line change
Expand Up @@ -184,6 +184,10 @@ PHP NEWS
. Mark Phar::buildFromIterator() base directory argument as a path.
(ndossche)

- phpdbg:
. Fixed GH-22480 (Use-after-free when re-watching an already-watched
variable). (iliaal)

- Posix:
. Added validity check to the flags argument for posix_access(). (arshidkv12)

Expand Down
164 changes: 132 additions & 32 deletions sapi/phpdbg/phpdbg_watch.c
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Original file line number Diff line number Diff line change
Expand Up @@ -501,8 +501,39 @@ void phpdbg_free_watch_element(phpdbg_watch_element *element);
void phpdbg_remove_watchpoint(phpdbg_watchpoint_t *watch);
void phpdbg_watch_parent_ht(phpdbg_watch_element *element);

phpdbg_watch_element *phpdbg_add_watch_element(phpdbg_watchpoint_t *watch, phpdbg_watch_element *element) {
static bool phpdbg_watch_element_collides(void *addr, phpdbg_watchtype type, phpdbg_watch_element *element) {
phpdbg_watch_element *old;
phpdbg_btree_result *res = phpdbg_btree_find(&PHPDBG_G(watchpoint_tree), (zend_ulong) addr);

if (res) {
phpdbg_watchpoint_t *watch = res->ptr;
if (watch->type == type && (old = zend_hash_find_ptr(&watch->elements, element->str)) && old != element) {
return true;
}
}

return (old = zend_hash_find_ptr(&PHPDBG_G(watch_recreation), element->str)) && old != element;
}

static bool phpdbg_ht_watch_element_collides(zval *zv, phpdbg_watch_element *element) {
HashTable *ht = HT_FROM_ZVP(zv);

if (!ht) {
return false;
}

return phpdbg_watch_element_collides(HT_WATCH_OFFSET + (char *) ht, WATCH_ON_HASHTABLE, element);
}

static bool phpdbg_bucket_watch_element_collides(zval *zv, phpdbg_watch_element *element) {
return phpdbg_watch_element_collides((Bucket *) zv, WATCH_ON_BUCKET, element);
}

phpdbg_watch_element *phpdbg_add_watch_element(phpdbg_watchpoint_t *watch, phpdbg_watch_element *element, bool *is_new) {
phpdbg_btree_result *res;
if (is_new) {
*is_new = true;
}
if ((res = phpdbg_btree_find(&PHPDBG_G(watchpoint_tree), (zend_ulong) watch->addr.ptr)) == NULL) {
phpdbg_watchpoint_t *mem = emalloc(sizeof(*mem));
*mem = *watch;
Expand All @@ -520,6 +551,9 @@ phpdbg_watch_element *phpdbg_add_watch_element(phpdbg_watchpoint_t *watch, phpdb
if (element != old_element) {
phpdbg_free_watch_element(element);
}
if (is_new) {
*is_new = false;
}
return old_element;
}
}
Expand All @@ -534,25 +568,35 @@ phpdbg_watch_element *phpdbg_add_watch_element(phpdbg_watchpoint_t *watch, phpdb
return element;
}

phpdbg_watch_element *phpdbg_add_bucket_watch_element(Bucket *bucket, phpdbg_watch_element *element) {
phpdbg_watch_element *phpdbg_add_bucket_watch_element(Bucket *bucket, phpdbg_watch_element *element, bool *is_new) {
phpdbg_watchpoint_t watch;
phpdbg_set_bucket_watchpoint(bucket, &watch);
element = phpdbg_add_watch_element(&watch, element);
phpdbg_watch_parent_ht(element);
return element;
bool added_new;
phpdbg_watch_element *added = phpdbg_add_watch_element(&watch, element, &added_new);
if (added_new) {
phpdbg_watch_parent_ht(added);
}
if (is_new) {
*is_new = added_new;
}
return added;
}

phpdbg_watch_element *phpdbg_add_ht_watch_element(zval *zv, phpdbg_watch_element *element) {
phpdbg_watch_element *phpdbg_add_ht_watch_element(zval *zv, phpdbg_watch_element *element, bool *is_new) {
phpdbg_watchpoint_t watch;
HashTable *ht = HT_FROM_ZVP(zv);

if (is_new) {
*is_new = false;
}

if (!ht) {
return NULL;
}

element->flags |= Z_TYPE_P(zv) == IS_ARRAY ? PHPDBG_WATCH_ARRAY : PHPDBG_WATCH_OBJECT;
phpdbg_set_ht_watchpoint(ht, &watch);
return phpdbg_add_watch_element(&watch, element);
return phpdbg_add_watch_element(&watch, element, is_new);
}

bool phpdbg_is_recursively_watched(void *ptr, phpdbg_watch_element *element) {
Expand Down Expand Up @@ -588,8 +632,15 @@ void phpdbg_add_recursive_watch_from_ht(phpdbg_watch_element *element, zend_long
child->parent = element;
child->child = NULL;
child->parent_container = HT_WATCH_HT(element->watch);
zend_hash_add_ptr(&element->child_container, child->str, child);
phpdbg_add_bucket_watch_element((Bucket *) zv, child);
if (phpdbg_bucket_watch_element_collides(zv, child)) {
phpdbg_free_watch_element(child);
return;
}
bool added_new;
phpdbg_add_bucket_watch_element((Bucket *) zv, child, &added_new);
if (added_new) {
zend_hash_add_ptr(&element->child_container, child->str, child);
}
}

void phpdbg_recurse_watch_element(phpdbg_watch_element *element) {
Expand Down Expand Up @@ -627,8 +678,13 @@ void phpdbg_recurse_watch_element(phpdbg_watch_element *element) {
child->child = NULL;
element->child = child;
}
if (phpdbg_ht_watch_element_collides(zv, child)) {
phpdbg_free_watch_element(child);
element->child = NULL;
return;
}
zend_hash_init(&child->child_container, 8, NULL, NULL, 0);
phpdbg_add_ht_watch_element(zv, child);
phpdbg_add_ht_watch_element(zv, child, NULL);
} else if (zend_hash_num_elements(&element->child_container) == 0) {
zend_string *str;
zend_long idx;
Expand Down Expand Up @@ -727,7 +783,10 @@ bool phpdbg_try_re_adding_watch_element(zval *parent, phpdbg_watch_element *elem
phpdbg_print_watch_diff(WATCH_ON_HASHTABLE, element->str, oldPtr, htPtr);
}

phpdbg_add_ht_watch_element(parent, element);
if ((element->flags & PHPDBG_WATCH_RECURSIVE) && phpdbg_ht_watch_element_collides(parent, element)) {
return false;
}
element = phpdbg_add_ht_watch_element(parent, element, NULL);
} else if ((zv = zend_symtable_find(ht, element->name_in_parent))) {
if (element->flags & PHPDBG_WATCH_IMPLICIT) {
zval *next = zv;
Expand All @@ -746,9 +805,11 @@ bool phpdbg_try_re_adding_watch_element(zval *parent, phpdbg_watch_element *elem
phpdbg_print_watch_diff(WATCH_ON_ZVAL, element->str, &element->backup.zv, zv);
}

if ((element->flags & PHPDBG_WATCH_RECURSIVE) && phpdbg_bucket_watch_element_collides(zv, element)) {
return false;
}
element->parent_container = ht;
phpdbg_add_bucket_watch_element((Bucket *) zv, element);
phpdbg_watch_parent_ht(element);
element = phpdbg_add_bucket_watch_element((Bucket *) zv, element, NULL);
} else {
return false;
}
Expand Down Expand Up @@ -1248,14 +1309,23 @@ void phpdbg_list_watchpoints(void) {
} ZEND_HASH_FOREACH_END();
}

static int phpdbg_create_simple_watchpoint(zval *zv, phpdbg_watch_element *element) {
element->flags = PHPDBG_WATCH_SIMPLE;
phpdbg_add_bucket_watch_element((Bucket *) zv, element);
#define PHPDBG_WATCH_DUPLICATE 1

@ndossche ndossche Jul 13, 2026

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Instead of mixing SUCCESS / this define; it would be cleaner if we had an enum and used that enum as a return type.


static int phpdbg_create_simple_watchpoint(zval *zv, phpdbg_watch_element **element) {
phpdbg_watch_element *added;
(*element)->flags = PHPDBG_WATCH_SIMPLE;
bool added_new;
added = phpdbg_add_bucket_watch_element((Bucket *) zv, *element, &added_new);
if (!added_new) {
*element = added;
return PHPDBG_WATCH_DUPLICATE;
}
return SUCCESS;
}

static int phpdbg_create_array_watchpoint(zval *zv, phpdbg_watch_element *element) {
phpdbg_watch_element *new;
static int phpdbg_create_array_watchpoint(zval *zv, phpdbg_watch_element **element_ptr) {
phpdbg_watch_element *element = *element_ptr;
phpdbg_watch_element *new, *added;
zend_string *str;
zval *orig_zv = zv;

Expand All @@ -1264,30 +1334,48 @@ static int phpdbg_create_array_watchpoint(zval *zv, phpdbg_watch_element *elemen
return FAILURE;
}

new = ecalloc(1, sizeof(phpdbg_watch_element));

str = strpprintf(0, "%.*s[]", (int) ZSTR_LEN(element->str), ZSTR_VAL(element->str));
zend_string_release(element->str);
element->str = str;
element->flags = PHPDBG_WATCH_IMPLICIT;
phpdbg_add_bucket_watch_element((Bucket *) orig_zv, element);
element->child = new;
bool added_new;
added = phpdbg_add_bucket_watch_element((Bucket *) orig_zv, element, &added_new);
if (!added_new) {
*element_ptr = added;
return PHPDBG_WATCH_DUPLICATE;
}
element = added;

new = ecalloc(1, sizeof(phpdbg_watch_element));
new->flags = PHPDBG_WATCH_SIMPLE;
new->str = zend_string_copy(str);
new->parent = element;
phpdbg_add_ht_watch_element(zv, new);
added = phpdbg_add_ht_watch_element(zv, new, &added_new);
if (added != NULL && !added_new) {
phpdbg_clean_watch_element(element);
phpdbg_free_watch_element(element);
*element_ptr = added;
return PHPDBG_WATCH_DUPLICATE;
}
element->child = new;
*element_ptr = element;
return SUCCESS;
}

static int phpdbg_create_recursive_watchpoint(zval *zv, phpdbg_watch_element *element) {
element->flags = PHPDBG_WATCH_RECURSIVE | PHPDBG_WATCH_RECURSIVE_ROOT;
element->child = NULL;
phpdbg_add_bucket_watch_element((Bucket *) zv, element);
static int phpdbg_create_recursive_watchpoint(zval *zv, phpdbg_watch_element **element) {
phpdbg_watch_element *added;
(*element)->flags = PHPDBG_WATCH_RECURSIVE | PHPDBG_WATCH_RECURSIVE_ROOT;
(*element)->child = NULL;
bool added_new;
added = phpdbg_add_bucket_watch_element((Bucket *) zv, *element, &added_new);
if (!added_new) {
*element = added;
return PHPDBG_WATCH_DUPLICATE;
}
return SUCCESS;
}

typedef struct { int (*callback)(zval *zv, phpdbg_watch_element *); zend_string *str; } phpdbg_watch_parse_struct;
typedef struct { int (*callback)(zval *zv, phpdbg_watch_element **); zend_string *str; } phpdbg_watch_parse_struct;

static int phpdbg_watchpoint_parse_wrapper(char *name, size_t namelen, char *key, size_t keylen, HashTable *parent, zval *zv, phpdbg_watch_parse_struct *info) {
int ret;
Expand All @@ -1298,13 +1386,25 @@ static int phpdbg_watchpoint_parse_wrapper(char *name, size_t namelen, char *key
element->parent = PHPDBG_G(watch_tmp);
element->child = NULL;

ret = info->callback(zv, element);
ret = info->callback(zv, &element);

efree(name);
efree(key);

if (ret != SUCCESS) {
if (ret == FAILURE) {
phpdbg_remove_watch_element(element);
} else if (ret == PHPDBG_WATCH_DUPLICATE) {
phpdbg_notice("%.*s is already being watched", (int) ZSTR_LEN(element->str), ZSTR_VAL(element->str));
while (PHPDBG_G(watch_tmp) && PHPDBG_G(watch_tmp)->child == NULL) {
phpdbg_watch_element *parent = PHPDBG_G(watch_tmp)->parent;
phpdbg_clean_watch_element(PHPDBG_G(watch_tmp));
phpdbg_free_watch_element(PHPDBG_G(watch_tmp));
if (parent) {
parent->child = NULL;
}
PHPDBG_G(watch_tmp) = parent;
}
ret = SUCCESS;
} else {
if (PHPDBG_G(watch_tmp)) {
PHPDBG_G(watch_tmp)->child = element;
Expand Down Expand Up @@ -1346,7 +1446,7 @@ static int phpdbg_watchpoint_parse_step(char *name, size_t namelen, char *key, s
element->name_in_parent = zend_string_init(key, keylen, 0);
element->parent_container = parent;
element->parent = PHPDBG_G(watch_tmp);
element = phpdbg_add_bucket_watch_element((Bucket *) zv, element);
element = phpdbg_add_bucket_watch_element((Bucket *) zv, element, NULL);

efree(name);
efree(key);
Expand All @@ -1359,7 +1459,7 @@ static int phpdbg_watchpoint_parse_step(char *name, size_t namelen, char *key, s
return SUCCESS;
}

static int phpdbg_watchpoint_parse_symtables(char *input, size_t len, int (*callback)(zval *, phpdbg_watch_element *)) {
static int phpdbg_watchpoint_parse_symtables(char *input, size_t len, int (*callback)(zval *, phpdbg_watch_element **)) {
zend_class_entry *scope = zend_get_executed_scope();
phpdbg_watch_parse_struct info;
int ret;
Expand Down
34 changes: 34 additions & 0 deletions sapi/phpdbg/tests/gh22480.phpt
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Original file line number Diff line number Diff line change
@@ -0,0 +1,34 @@
--TEST--
GH-22480 (Use-after-free when re-watching an already-watched variable)
--PHPDBG--
b 6
r
w a $a
w a $a
c

q
--EXPECTF--
[Successful compilation of %s]
prompt> [Breakpoint #0 added at %s:6]
prompt> [Breakpoint #0 at %s:6, hits: 1]
>00006: $a[0] = 2;
00007:
00008: $a = [0 => 3, 1 => 4];
prompt> [Added watchpoint #0 for $a[]]
prompt> [$a[] is already being watched]
prompt> [Breaking on watchpoint $a[]]
1 elements were added to the array
>00009:
prompt> [$a[] has been removed, removing watchpoint]
[Script ended normally]
prompt>
--FILE--
<?php

$a = [];

$a[0] = 1;
$a[0] = 2;

$a = [0 => 3, 1 => 4];
30 changes: 30 additions & 0 deletions sapi/phpdbg/tests/gh22480_2.phpt
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Original file line number Diff line number Diff line change
@@ -0,0 +1,30 @@
--TEST--
GH-22480 (Use-after-free re-watching a sub-path of a recursive watchpoint)
--INI--
opcache.optimization_level=0
--PHPDBG--
b 5
r
w r $a
w $a[x]
c
q
--EXPECTF--
[Successful compilation of %s]
prompt> [Breakpoint #0 added at %s:5]
prompt> [Breakpoint #0 at %s:5, hits: 1]
>00005: $a['x'] = 2;
00006:
prompt> [Added watchpoint #0 for $a[]]
prompt> [$a[x] is already being watched]
prompt> [Breaking on watchpoint $a]
Old value%s
New value: Array ([x] => 2)
>00006:
prompt> [$a has been removed, removing watchpoint recursively]
--FILE--
<?php

$a = ['x' => 1];

$a['x'] = 2;
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