Import reallocarray() from OpenBSD

Wrapper for realloc() that checks for overflow when multiplying
arguments together, so we don't have to add overflow checks to
every single call.  For documentation on usage, see:
http://www.openbsd.org/cgi-bin/man.cgi/OpenBSD-current/man3/calloc.3

Signed-off-by: Alan Coopersmith <alan.coopersmith@oracle.com>
Acked-by: Matt Turner <mattst88@gmail.com>

configure.ac

@@ -219,7 +219,7 @@ dnl Checks for library functions.
 AC_CHECK_FUNCS([backtrace ffs geteuid getuid issetugid getresuid \
 	getdtablesize getifaddrs getpeereid getpeerucred getprogname getzoneid \
 	mmap seteuid shmctl64 strncasecmp vasprintf vsnprintf walkcontext])
-AC_REPLACE_FUNCS([strcasecmp strcasestr strlcat strlcpy strndup])
+AC_REPLACE_FUNCS([reallocarray strcasecmp strcasestr strlcat strlcpy strndup])
 
 AC_CHECK_DECLS([program_invocation_short_name], [], [], [[#include <errno.h>]])
 

include/dix-config.h.in

@@ -149,6 +149,9 @@
 /* Define to 1 if you have the <ndir.h> header file, and it defines `DIR'. */
 #undef HAVE_NDIR_H
 
+/* Define to 1 if you have the `reallocarray' function. */
+#undef HAVE_REALLOCARRAY
+
 /* Define to 1 if you have the <rpcsvc/dbm.h> header file. */
 #undef HAVE_RPCSVC_DBM_H
 

include/os.h

@@ -517,7 +517,14 @@ ddxGiveUp(enum ExitCode error);
 extern _X_EXPORT int
 TimeSinceLastInputEvent(void);
 
-/* strcasecmp.c */
+/* Function fallbacks provided by AC_REPLACE_FUNCS in configure.ac */
+
+#ifndef HAVE_REALLOCARRAY
+#define reallocarray xreallocarray
+extern _X_EXPORT void *
+reallocarray(void *optr, size_t nmemb, size_t size);
+#endif
+
 #ifndef HAVE_STRCASECMP
 #define strcasecmp xstrcasecmp
 extern _X_EXPORT int

include/xorg-server.h.in

@@ -47,6 +47,9 @@
 /* Define to 1 if you have the `ffs' function. */
 #undef HAVE_FFS
 
+/* Define to 1 if you have the `reallocarray' function. */
+#undef HAVE_REALLOCARRAY
+
 /* Define to 1 if you have the `strcasecmp' function. */
 #undef HAVE_STRCASECMP
 

os/reallocarray.c

@@ -0,0 +1,43 @@
+/*	$OpenBSD: reallocarray.c,v 1.2 2014/12/08 03:45:00 bcook Exp $	*/
+/*
+ * Copyright (c) 2008 Otto Moerbeek <otto@drijf.net>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#ifdef HAVE_DIX_CONFIG_H
+#include <dix-config.h>
+#endif
+
+#include <sys/types.h>
+#include <errno.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include "os.h"
+
+/*
+ * This is sqrt(SIZE_MAX+1), as s1*s2 <= SIZE_MAX
+ * if both s1 < MUL_NO_OVERFLOW and s2 < MUL_NO_OVERFLOW
+ */
+#define MUL_NO_OVERFLOW	((size_t)1 << (sizeof(size_t) * 4))
+
+void *
+reallocarray(void *optr, size_t nmemb, size_t size)
+{
+	if ((nmemb >= MUL_NO_OVERFLOW || size >= MUL_NO_OVERFLOW) &&
+	    nmemb > 0 && SIZE_MAX / nmemb < size) {
+		errno = ENOMEM;
+		return NULL;
+	}
+	return realloc(optr, size * nmemb);
+}