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Fix GH-24319: opcache hash entries can be seen before they are initialised #24320

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Fix GH-24319: opcache hash entries can be seen before they are initialised #24320

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13 changes: 13 additions & 0 deletions ext/opcache/zend_accelerator_hash.c
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Original file line number Diff line number Diff line change
Expand Up @@ -97,6 +97,10 @@ zend_accel_hash_entry* zend_accel_hash_update(zend_accel_hash *accel_hash, zend_
if (entry->hash_value == hash_value
&& zend_string_equals(entry->key, key)) {

/* Lookups are lock-free: order the initialization of whatever the new
* data points to before the pointer update (writer side only; readers
* rely on the address dependency when following data). */
ZEND_ATOMIC_FENCE_RELEASE();
if (entry->indirect) {
if (indirect_bucket) {
entry->data = indirect_bucket;
Expand Down Expand Up @@ -134,6 +138,10 @@ zend_accel_hash_entry* zend_accel_hash_update(zend_accel_hash *accel_hash, zend_
entry->hash_value = hash_value;
entry->key = key;
entry->next = accel_hash->hash_table[index];
/* Lookups are lock-free: the entry must be fully initialized before it
* becomes reachable from the bucket, otherwise a concurrent reader can see
* a matching hash_value with a NULL key (weakly ordered CPUs, e.g. aarch64). */
ZEND_ATOMIC_FENCE_RELEASE();
accel_hash->hash_table[index] = entry;
return entry;
}
Expand All @@ -151,6 +159,11 @@ static zend_always_inline void* zend_accel_hash_find_ex(zend_accel_hash *accel_h
index = hash_value % accel_hash->max_num_entries;

entry = accel_hash->hash_table[index];
if (entry) {
/* Order the bucket read before the entry field reads; pairs with the
* release fence before the bucket store in zend_accel_hash_update(). */
ZEND_ATOMIC_FENCE_ACQUIRE();
}
while (entry) {
if (entry->hash_value == hash_value
&& zend_string_equals(entry->key, key)) {
Expand Down
7 changes: 6 additions & 1 deletion ext/opcache/zend_accelerator_module.c
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Original file line number Diff line number Diff line change
Expand Up @@ -611,7 +611,12 @@ static int accelerator_get_scripts(zval *return_value)

array_init(return_value);
for (i = 0; i<ZCSG(hash).max_num_entries; i++) {
for (cache_entry = ZCSG(hash).hash_table[i]; cache_entry; cache_entry = cache_entry->next) {
cache_entry = ZCSG(hash).hash_table[i];
if (cache_entry) {
/* Lock-free reader, see zend_accel_hash_find_ex(). */
ZEND_ATOMIC_FENCE_ACQUIRE();
}
for (; cache_entry; cache_entry = cache_entry->next) {
zend_persistent_script *script;
char *str;
size_t len;
Expand Down
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