Add reallocarray implementation.

In a similar model as _safe_*alloc api but for the `userland` it guards
against overflow before (re)allocation, usage concealed in fpm for now.
Modern Linux and most of BSD already have it.
Closes #8871.

configure.ac

@@ -689,7 +689,7 @@ if test "$ac_cv_func_getaddrinfo" = yes; then
   AC_DEFINE(HAVE_GETADDRINFO,1,[Define if you have the getaddrinfo function])
 fi
 
-AC_REPLACE_FUNCS(strlcat strlcpy explicit_bzero getopt)
+AC_REPLACE_FUNCS(strlcat strlcpy explicit_bzero getopt reallocarray)
 AC_FUNC_ALLOCA
 PHP_TIME_R_TYPE
 PHP_CHECK_IN_ADDR_T
@@ -1616,7 +1616,7 @@ PHP_ADD_SOURCES(main, main.c snprintf.c spprintf.c \
        php_ini_builder.c \
        php_ini.c SAPI.c rfc1867.c php_content_types.c strlcpy.c \
        strlcat.c explicit_bzero.c reentrancy.c php_variables.c php_ticks.c \
-       network.c php_open_temporary_file.c php_odbc_utils.c safe_bcmp.c \
+       network.c php_open_temporary_file.c php_odbc_utils.c safe_bcmp.c reallocarray.c \
        output.c getopt.c php_syslog.c, -DZEND_ENABLE_STATIC_TSRMLS_CACHE=1)
 
 PHP_ADD_SOURCES_X(main, fastcgi.c, -DZEND_ENABLE_STATIC_TSRMLS_CACHE=1, PHP_FASTCGI_OBJS, no)

main/php.h

@@ -179,6 +179,14 @@ END_EXTERN_C()
 #define explicit_bzero php_explicit_bzero
 #endif
 
+#ifndef HAVE_REALLOCARRAY
+BEGIN_EXTERN_C()
+PHPAPI void* php_reallocarray(void *p, size_t nmb, size_t siz);
+END_EXTERN_C()
+#undef reallocarray
+#define reallocarray php_reallocarray
+#endif
+
 BEGIN_EXTERN_C()
 PHPAPI int php_safe_bcmp(const zend_string *a, const zend_string *b);
 END_EXTERN_C()

main/reallocarray.c

@@ -0,0 +1,41 @@
+/*
+  +----------------------------------------------------------------------+
+  | Copyright (c) The PHP Group                                          |
+  +----------------------------------------------------------------------+
+  | This source file is subject to version 3.01 of the PHP license,      |
+  | that is bundled with this package in the file LICENSE, and is        |
+  | available through the world-wide-web at the following url:           |
+  | https://www.php.net/license/3_01.txt                                 |
+  | If you did not receive a copy of the PHP license and are unable to   |
+  | obtain it through the world-wide-web, please send a note to          |
+  | license@php.net so we can mail you a copy immediately.               |
+  +----------------------------------------------------------------------+
+  | Author: David Carlier <devnexen@gmail.com>                           |
+  +----------------------------------------------------------------------+
+*/
+
+#include "php.h"
+
+#ifndef HAVE_REALLOCARRAY
+
+#include <string.h>
+
+PHPAPI void* php_reallocarray(void *p, size_t nmb, size_t siz)
+{
+	size_t r;
+#ifndef _WIN32
+	if (__builtin_mul_overflow(nmb, siz, &r)) {
+#else
+	
+	r = siz * nmb;
+	if (siz != 0 && r / siz != nmb) {
+#endif
+		// EOVERFLOW may have been, arguably, more appropriate
+		// but this is what other implementations set
+		errno = ENOMEM;
+		return NULL;
+	}
+
+	return realloc(p, r);
+}
+#endif

sapi/fpm/fpm/fpm_arrays.h

@@ -6,6 +6,8 @@
 #include <stdlib.h>
 #include <string.h>
 
+#include "php.h"
+
 struct fpm_array_s {
 	void *data;
 	size_t sz;
@@ -84,7 +86,7 @@ static inline void *fpm_array_push(struct fpm_array_s *a) /* {{{ */
 
 	if (a->used == a->allocated) {
 		size_t new_allocated = a->allocated ? a->allocated * 2 : 20;
-		void *new_ptr = realloc(a->data, a->sz * new_allocated);
+		void *new_ptr = reallocarray(a->data, a->sz, new_allocated);
 
 		if (!new_ptr) {
 			return 0;