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Fix alignment in zend_string_safe_alloc()/zend_string_safe_realloc() #23869

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Fix alignment in zend_string_safe_alloc()/zend_string_safe_realloc() #23869

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0f7af60
Fix alignment in `zend_string_safe_alloc()`/`zend_string_safe_realloc()`
realFlowControl Sep 23, 2026
e48596b
Update chunk_split 32bit test for new overflow offset
realFlowControl Sep 24, 2026
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10 changes: 8 additions & 2 deletions Zend/zend_string.h
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Original file line number Diff line number Diff line change
Expand Up @@ -127,6 +127,12 @@ static zend_always_inline zend_string *ZSTR_KNOWN(size_t idx) {

#define _ZSTR_STRUCT_SIZE(len) (_ZSTR_HEADER_SIZE + len + 1)

/* ALIGN(n * m + header + l + 1). The "+ ALIGNMENT - 1" of the rounding is
* done inside the overflow check, so the final "& MASK" can only shrink
* the value and can not wrap. */
#define _ZSTR_SAFE_STRUCT_SIZE(n, m, l) \
(zend_safe_address_guarded(n, m, _ZSTR_STRUCT_SIZE(l) + ZEND_MM_ALIGNMENT - 1) & ZEND_MM_ALIGNMENT_MASK)

#define ZSTR_MAX_OVERHEAD (ZEND_MM_ALIGNED_SIZE(_ZSTR_HEADER_SIZE + 1))
#define ZSTR_MAX_LEN (SIZE_MAX - ZSTR_MAX_OVERHEAD)

Expand Down Expand Up @@ -198,7 +204,7 @@ static zend_always_inline zend_string *zend_string_alloc(size_t len, bool persis

static zend_always_inline zend_string *zend_string_safe_alloc(size_t n, size_t m, size_t l, bool persistent)
{
zend_string *ret = (zend_string *)safe_pemalloc(n, m, ZEND_MM_ALIGNED_SIZE(_ZSTR_STRUCT_SIZE(l)), persistent);
zend_string *ret = (zend_string *)pemalloc(_ZSTR_SAFE_STRUCT_SIZE(n, m, l), persistent);

GC_SET_REFCOUNT(ret, 1);
GC_TYPE_INFO(ret) = GC_STRING | ((persistent ? IS_STR_PERSISTENT : 0) << GC_FLAGS_SHIFT);
Expand Down Expand Up @@ -325,7 +331,7 @@ static zend_always_inline zend_string *zend_string_safe_realloc(zend_string *s,

if (!ZSTR_IS_INTERNED(s)) {
if (GC_REFCOUNT(s) == 1) {
ret = (zend_string *)safe_perealloc(s, n, m, ZEND_MM_ALIGNED_SIZE(_ZSTR_STRUCT_SIZE(l)), persistent);
ret = (zend_string *)perealloc(s, _ZSTR_SAFE_STRUCT_SIZE(n, m, l), persistent);
ZSTR_LEN(ret) = (n * m) + l;
zend_string_forget_hash_val(ret);
return ret;
Expand Down
2 changes: 1 addition & 1 deletion ext/standard/tests/strings/chunk_split_variation2_32bit.phpt
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Expand Up @@ -16,4 +16,4 @@ var_dump(chunk_split($a,$b,$c));
--EXPECTF--
*** Testing chunk_split() : unexpected large 'end' string argument variation 2 ***

Fatal error: Possible integer overflow in memory allocation (65537 * 65537 + %r65556|65560%r) in %s on line %d
Fatal error: Possible integer overflow in memory allocation (65537 * 65537 + %r65557|65561%r) in %s on line %d
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