[src/trunk]: src/lib/libwrap And as long as we're attempting to achieve perfe...

[kre <kre%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/7341465ec640
branches:  trunk
changeset: 448156:7341465ec640
user:      kre <kre%NetBSD.org@localhost>
date:      Wed Jan 23 02:48:48 2019 +0000

description:
And as long as we're attempting to achieve perfection in code
that is never going to be executed, let's also check for possible
overflow in a sum that will never be computed...

diffstat:

 lib/libwrap/expandm.c |  18 +++++++++++++++---
 1 files changed, 15 insertions(+), 3 deletions(-)

diffs (39 lines):

diff -r 164a51c7a9fc -r 7341465ec640 lib/libwrap/expandm.c
--- a/lib/libwrap/expandm.c     Wed Jan 23 02:32:06 2019 +0000
+++ b/lib/libwrap/expandm.c     Wed Jan 23 02:48:48 2019 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: expandm.c,v 1.10 2019/01/23 02:32:06 kre Exp $ */
+/*     $NetBSD: expandm.c,v 1.11 2019/01/23 02:48:48 kre Exp $ */
 
 /*-
  * Copyright (c) 2019 The NetBSD Foundation, Inc.
@@ -29,7 +29,7 @@
  * POSSIBILITY OF SUCH DAMAGE.
  */
 #include <sys/cdefs.h>
-__RCSID("$NetBSD: expandm.c,v 1.10 2019/01/23 02:32:06 kre Exp $");
+__RCSID("$NetBSD: expandm.c,v 1.11 2019/01/23 02:48:48 kre Exp $");
 
 #include <limits.h>
 #include <stdio.h>
@@ -68,7 +68,19 @@
                 */
                if (__predict_false(nlen >= INT_MAX)) {
                        size_t blen = buf ? strlen(buf) : 0;
-                       size_t tlen = nlen + blen;
+                       size_t tlen;
+
+                       /*
+                        * if we would overflow a ptrdiff_t when computing
+                        * tlen, then don't bother.  The format string is
+                        * simply too large to be converted.
+                        */
+                       if (blen >= PTRDIFF_MAX ||
+                           nlen >= PTRDIFF_MAX - blen ||
+                           nlen >= SIZE_T_MAX - blen)
+                               goto out;
+
+                       tlen = nlen + blen;
 
                        /*
                         * We can't exceed PTRDIFF_MAX because we would