Catchable MemoryError for predictably oversized allocations

Zend/tests/bug40770.phpt

@@ -15,10 +15,9 @@ if ($zend_mm_enabled === "0") {
 --FILE--
 <?php
 ini_set('display_errors',true);
-$mb=148;
-$var = '';
-for ($i=0; $i<=$mb; $i++) {
-        $var.= str_repeat('a',1*1024*1024);
+$var = 'a';
+while (true) {
+        $var .= $var;
 }
 ?>
 --EXPECTF--

Zend/tests/bug55509.phpt

@@ -65,21 +65,24 @@ elseif (PHP_OS == 'FreeBSD') {
 memory_limit=2100M
 --FILE--
 <?php
-$a1 = str_repeat("1", 1024 * 1024 * 1024 * 0.5);
-echo "1\n";
-$a2 = str_repeat("2", 1024 * 1024 * 1024 * 0.5);
-echo "2\n";
-$a3 = str_repeat("3", 1024 * 1024 * 1024 * 0.5);
-echo "3\n";
-$a4 = str_repeat("4", 1024 * 1024 * 1024 * 0.5);
-echo "4\n";
-$a5 = str_repeat("5", 1024 * 1024 * 1024 * 0.5);
-echo "5\n";
+try {
+    $a1 = str_repeat("1", 1024 * 1024 * 1024 * 0.5);
+    echo "1\n";
+    $a2 = str_repeat("2", 1024 * 1024 * 1024 * 0.5);
+    echo "2\n";
+    $a3 = str_repeat("3", 1024 * 1024 * 1024 * 0.5);
+    echo "3\n";
+    $a4 = str_repeat("4", 1024 * 1024 * 1024 * 0.5);
+    echo "4\n";
+    $a5 = str_repeat("5", 1024 * 1024 * 1024 * 0.5);
+    echo "5\n";
+} catch (Throwable $t) {
+    echo $t::class . ': ' . $t->getMessage() . "\n";
+}
 ?>
---EXPECTF--
+--EXPECT--
 1
 2
 3
 4
-
-Fatal error: Allowed memory size of %d bytes exhausted%s(tried to allocate %d bytes) in %sbug55509.php on line %d
+MemoryError: The resulting string is too large to fit in the configured memory limit

Zend/tests/fibers/get-return-after-bailout.phpt

@@ -16,7 +16,10 @@ register_shutdown_function(static function (): void {
 });
 
 $fiber = new Fiber(static function (): void {
-    str_repeat('X', PHP_INT_MAX);
+    $x = 'X';
+    while (true) {
+        $x .= $x;
+    }
 });
 $fiber->start();
 

Zend/tests/fibers/out-of-memory-in-fiber.phpt

@@ -12,9 +12,9 @@ if (getenv("USE_ZEND_ALLOC") === "0") {
 <?php
 
 $fiber = new Fiber(function (): void {
-    $buffer = '';
+    $buffer = '.';
     while (true) {
-        $buffer .= str_repeat('.', 1 << 10);
+        $buffer .= $buffer;
     }
 });
 

Zend/tests/fibers/out-of-memory-in-nested-fiber.phpt

@@ -13,9 +13,9 @@ if (getenv("USE_ZEND_ALLOC") === "0") {
 
 $fiber = new Fiber(function (): void {
     $fiber = new Fiber(function (): void {
-        $buffer = '';
+        $buffer = '.';
         while (true) {
-            $buffer .= str_repeat('.', 1 << 10);
+            $buffer .= $buffer;
         }
     });
 

Zend/tests/memory_error_class.phpt

@@ -0,0 +1,22 @@
+--TEST--
+MemoryError is a catchable Error
+--FILE--
+<?php
+
+$e = new MemoryError('boom');
+var_dump($e instanceof Error);
+var_dump($e instanceof Throwable);
+var_dump($e->getMessage());
+
+try {
+    throw new MemoryError('caught as Error');
+} catch (Error $e) {
+    echo $e::class . ': ' . $e->getMessage() . "\n";
+}
+
+?>
+--EXPECT--
+bool(true)
+bool(true)
+string(4) "boom"
+MemoryError: caught as Error

Zend/tests/offsets/string_offset_write_memory_error.phpt

@@ -0,0 +1,33 @@
+--TEST--
+Writing to a string at an offset too large for the memory limit throws a catchable MemoryError
+--INI--
+memory_limit=64M
+opcache.enable_cli=0
+--FILE--
+<?php
+
+$s = 'abc';
+try {
+    $s[PHP_INT_MAX] = 'Z';
+} catch (MemoryError $e) {
+    echo $e->getMessage() . "\n";
+}
+var_dump($s);
+
+// The throw unwinds the whole assignment, so the outer target keeps its previous value.
+$r = 'untouched';
+try {
+    $r = ($s[PHP_INT_MAX] = 'Z');
+} catch (MemoryError $e) {
+    echo "caught\n";
+}
+var_dump($r);
+var_dump($s);
+
+?>
+--EXPECT--
+String offset assignment produces a string too large to fit in the configured memory limit
+string(3) "abc"
+caught
+string(9) "untouched"
+string(3) "abc"

Zend/zend_alloc.c

@@ -57,6 +57,7 @@
 #include "zend_operators.h"
 #include "zend_multiply.h"
 #include "zend_bitset.h"
+#include "zend_exceptions.h"
 #include "zend_mmap.h"
 #include "zend_portability.h"
 #include <signal.h>
@@ -2919,6 +2920,42 @@ ZEND_API zend_result zend_set_memory_limit(size_t memory_limit)
 	return SUCCESS;
 }
 
+ZEND_API size_t zend_memory_limit(void)
+{
+#if ZEND_MM_LIMIT
+	return AG(mm_heap)->limit;
+#else
+	return (size_t)Z_L(-1) >> 1;
+#endif
+}
+
+ZEND_API bool zend_memory_limit_is_unlimited(void)
+{
+	return zend_memory_limit() == ((size_t)Z_L(-1) >> 1);
+}
+
+ZEND_API bool zend_alloc_size_exceeds_memory(size_t nmemb, size_t size, size_t offset, const char *kind)
+{
+	bool overflow;
+	size_t needed = zend_safe_address(nmemb, size, offset, &overflow);
+
+	if (!overflow) {
+		if (zend_memory_limit_is_unlimited()) {
+			return false;
+		}
+		size_t limit = zend_memory_limit();
+		size_t usage = zend_memory_usage(false);
+		size_t available = (limit > usage) ? (limit - usage) : 0;
+		if (needed <= available) {
+			return false;
+		}
+	}
+
+	zend_throw_error(zend_ce_memory_error,
+		"The resulting %s is too large to fit in the configured memory limit", kind);
+	return true;
+}
+
 ZEND_API bool zend_alloc_in_memory_limit_error_reporting(void)
 {
 #if ZEND_MM_LIMIT

Zend/zend_alloc.h

@@ -215,8 +215,15 @@ ZEND_API ZEND_ATTRIBUTE_MALLOC char * __zend_strdup(const char *s);
 #define pestrdup_rel(s, persistent) ((persistent)?strdup(s):estrdup_rel(s))
 
 ZEND_API zend_result zend_set_memory_limit(size_t memory_limit);
+ZEND_API size_t zend_memory_limit(void);
+ZEND_API bool zend_memory_limit_is_unlimited(void);
 ZEND_API bool zend_alloc_in_memory_limit_error_reporting(void);
 
+/* Throws a catchable MemoryError and returns true when allocating "nmemb *
+ * size + offset" bytes would overflow or exceed the configured memory limit;
+ * returns false (without throwing) otherwise. */
+ZEND_API bool zend_alloc_size_exceeds_memory(size_t nmemb, size_t size, size_t offset, const char *kind);
+
 ZEND_API void start_memory_manager(void);
 ZEND_API void shutdown_memory_manager(bool silent, bool full_shutdown);
 ZEND_API void refresh_memory_manager(void);

Zend/zend_exceptions.c

@@ -47,6 +47,7 @@ ZEND_API zend_class_entry *zend_ce_argument_count_error;
 ZEND_API zend_class_entry *zend_ce_value_error;
 ZEND_API zend_class_entry *zend_ce_arithmetic_error;
 ZEND_API zend_class_entry *zend_ce_division_by_zero_error;
+ZEND_API zend_class_entry *zend_ce_memory_error;
 ZEND_API zend_class_entry *zend_ce_unhandled_match_error;
 ZEND_API zend_class_entry *zend_ce_request_parse_body_exception;
 
@@ -854,6 +855,9 @@ void zend_register_default_exception(void) /* {{{ */
 	zend_ce_division_by_zero_error = register_class_DivisionByZeroError(zend_ce_arithmetic_error);
 	zend_init_exception_class_entry(zend_ce_division_by_zero_error);
 
+	zend_ce_memory_error = register_class_MemoryError(zend_ce_error);
+	zend_init_exception_class_entry(zend_ce_memory_error);
+
 	zend_ce_unhandled_match_error = register_class_UnhandledMatchError(zend_ce_error);
 	zend_init_exception_class_entry(zend_ce_unhandled_match_error);
 

Zend/zend_exceptions.h

@@ -36,6 +36,7 @@ extern ZEND_API zend_class_entry *zend_ce_argument_count_error;
 extern ZEND_API zend_class_entry *zend_ce_value_error;
 extern ZEND_API zend_class_entry *zend_ce_arithmetic_error;
 extern ZEND_API zend_class_entry *zend_ce_division_by_zero_error;
+extern ZEND_API zend_class_entry *zend_ce_memory_error;
 extern ZEND_API zend_class_entry *zend_ce_unhandled_match_error;
 extern ZEND_API zend_class_entry *zend_ce_request_parse_body_exception;
 

Zend/zend_exceptions.stub.php

@@ -167,6 +167,10 @@ class DivisionByZeroError extends ArithmeticError
 {
 }
 
+class MemoryError extends Error
+{
+}
+
 class UnhandledMatchError extends Error
 {
 }

Zend/zend_execute.c

@@ -2037,6 +2037,17 @@ ZEND_API ZEND_COLD void ZEND_FASTCALL zend_false_to_array_deprecated(void)
 	zend_error(E_DEPRECATED, "Automatic conversion of false to array is deprecated");
 }
 
+static zend_always_inline bool zend_string_offset_extend_exceeds_memory(size_t new_len)
+{
+	if (zend_memory_limit_is_unlimited()) {
+		return false;
+	}
+	size_t limit = zend_memory_limit();
+	size_t usage = zend_memory_usage(false);
+	size_t available = (limit > usage) ? (limit - usage) : 0;
+	return new_len > available;
+}
+
 static zend_never_inline void zend_assign_to_string_offset(zval *str, zval *dim, zval *value OPLINE_DC EXECUTE_DATA_DC)
 {
 	zend_uchar c;
@@ -2161,6 +2172,14 @@ static zend_never_inline void zend_assign_to_string_offset(zval *str, zval *dim,
 	if ((size_t)offset >= ZSTR_LEN(s)) {
 		/* Extend string if needed */
 		zend_long old_len = ZSTR_LEN(s);
+		if (UNEXPECTED(zend_string_offset_extend_exceeds_memory((size_t)offset + 1))) {
+			zend_throw_error(zend_ce_memory_error,
+				"String offset assignment produces a string too large to fit in the configured memory limit");
+			if (UNEXPECTED(RETURN_VALUE_USED(opline))) {
+				ZVAL_UNDEF(EX_VAR(opline->result.var));
+			}
+			return;
+		}
 		ZVAL_NEW_STR(str, zend_string_extend(s, (size_t)offset + 1, 0));
 		memset(Z_STRVAL_P(str) + old_len, ' ', offset - old_len);
 		Z_STRVAL_P(str)[offset+1] = 0;

Zend/zend_hash.c

@@ -391,6 +391,12 @@ ZEND_API void ZEND_FASTCALL zend_hash_to_packed(HashTable *ht)
 	pefree(old_data, GC_FLAGS(ht) & IS_ARRAY_PERSISTENT);
 }
 
+ZEND_API bool zend_array_alloc_size_exceeds_memory(size_t nelems, bool packed)
+{
+	size_t elem_size = packed ? sizeof(zval) : sizeof(Bucket) + sizeof(uint32_t);
+	return zend_alloc_size_exceeds_memory(nelems, elem_size, 0, "array");
+}
+
 ZEND_API void ZEND_FASTCALL zend_hash_extend(HashTable *ht, uint32_t nSize, bool packed)
 {
 	HT_ASSERT_RC1(ht);

Zend/zend_hash.h

@@ -119,6 +119,11 @@ ZEND_API void ZEND_FASTCALL zend_hash_extend(HashTable *ht, uint32_t nSize, bool
 ZEND_API void ZEND_FASTCALL zend_hash_discard(HashTable *ht, uint32_t nNumUsed);
 ZEND_API void ZEND_FASTCALL zend_hash_packed_grow(HashTable *ht);
 
+/* Throws a catchable MemoryError and returns true when a table of "nelems"
+ * elements cannot fit in the configured memory limit; returns false (without
+ * throwing) otherwise. */
+ZEND_API bool zend_array_alloc_size_exceeds_memory(size_t nelems, bool packed);
+
 /* additions/updates/changes */
 ZEND_API zval* ZEND_FASTCALL zend_hash_add_or_update(HashTable *ht, zend_string *key, zval *pData, uint32_t flag);
 ZEND_API zval* ZEND_FASTCALL zend_hash_update(HashTable *ht, zend_string *key,zval *pData);

Zend/zend_string.c

@@ -528,6 +528,11 @@ ZEND_API zend_string *zend_string_concat3(
 	return res;
 }
 
+ZEND_API bool zend_string_alloc_size_exceeds_memory(size_t nmemb, size_t size, size_t offset)
+{
+	return zend_alloc_size_exceeds_memory(nmemb, size, offset, "string");
+}
+
 /* strlcpy and strlcat are not always intercepted by msan, so we need to do it
  * ourselves. Apply a simple heuristic to determine the platforms that need it.
  * See https://github.com/php/php-src/issues/20002. */

Zend/zend_string.h

@@ -54,6 +54,11 @@ ZEND_API zend_string *zend_string_concat3(
 	const char *str2, size_t str2_len,
 	const char *str3, size_t str3_len);
 
+/* Throws a catchable MemoryError and returns true when allocating a string of
+ * "nmemb * size + offset" bytes would overflow or exceed the configured memory
+ * limit; returns false (without throwing) otherwise. */
+ZEND_API bool zend_string_alloc_size_exceeds_memory(size_t nmemb, size_t size, size_t offset);
+
 ZEND_API void zend_interned_strings_init(void);
 ZEND_API void zend_interned_strings_dtor(void);
 ZEND_API void zend_interned_strings_activate(void);

ext/gmp/gmp.c

@@ -672,6 +672,11 @@ static void gmp_strval(zval *result, mpz_t gmpnum, int base) /* {{{ */
 		num_len++;
 	}
 
+	if (UNEXPECTED(zend_string_alloc_size_exceeds_memory(num_len, 1, 0))) {
+		ZVAL_EMPTY_STRING(result);
+		return;
+	}
+
 	str = zend_string_alloc(num_len, 0);
 	mpz_get_str(ZSTR_VAL(str), base, gmpnum);
 
@@ -841,6 +846,10 @@ ZEND_FUNCTION(gmp_export)
 		size_t bits_per_word = (size_t) size * 8;
 		size_t count = (size_in_base_2 + bits_per_word - 1) / bits_per_word;
 
+		if (UNEXPECTED(zend_string_alloc_size_exceeds_memory(count, size, 0))) {
+			RETURN_THROWS();
+		}
+
 		zend_string *out_string = zend_string_safe_alloc(count, size, 0, 0);
 		mpz_export(ZSTR_VAL(out_string), NULL, order, size, endian, 0, gmpnumber);
 		ZSTR_VAL(out_string)[ZSTR_LEN(out_string)] = '\0';