[src/trunk]: src/lib/libwrap Always return from expandm() with errno unaltere...

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

details:   https://anonhg.NetBSD.org/src/rev/bfc3ccc8fd13
branches:  trunk
changeset: 447482:bfc3ccc8fd13
user:      kre <kre%NetBSD.org@localhost>
date:      Sun Jan 13 06:10:34 2019 +0000

description:
Always return from expandm() with errno unaltered, so on the
off chance it failed, there's still the possibility that whatever
processes the result will be able to deal with the %m that would
(presumably) be left in the format string.

And as a frill, don't call strerror() until we know we are
going to use its result (still call it only once, no matter
how many %m's are in the format string).

diffstat:

 lib/libwrap/expandm.c |  11 ++++++++---
 1 files changed, 8 insertions(+), 3 deletions(-)

diffs (51 lines):

diff -r 94a350a336cb -r bfc3ccc8fd13 lib/libwrap/expandm.c
--- a/lib/libwrap/expandm.c     Sun Jan 13 04:45:35 2019 +0000
+++ b/lib/libwrap/expandm.c     Sun Jan 13 06:10:34 2019 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: expandm.c,v 1.6 2019/01/13 01:32:51 christos Exp $     */
+/*     $NetBSD: expandm.c,v 1.7 2019/01/13 06:10:34 kre Exp $  */
 
 /*-
  * Copyright (c) 2018 The NetBSD Foundation, Inc.
@@ -29,7 +29,7 @@
  * POSSIBILITY OF SUCH DAMAGE.
  */
 #include <sys/cdefs.h>
-__RCSID("$NetBSD: expandm.c,v 1.6 2019/01/13 01:32:51 christos Exp $");
+__RCSID("$NetBSD: expandm.c,v 1.7 2019/01/13 06:10:34 kre Exp $");
 
 #include <limits.h>
 #include <stdio.h>
@@ -48,7 +48,8 @@
 const char * __attribute__((__format_arg__(1)))
 expandm(const char *fmt, const char *sf, char **rbuf)
 {
-       const char *e = strerror(errno);
+       const int err = errno;
+       const char *e = NULL;
        char *buf, *m, *nbuf;
        const char *ptr;
 
@@ -74,6 +75,8 @@
                         buf = nbuf;
                 }
 
+               if (__predict_true(e == NULL && (cnt & 1) != 0))
+                       e = strerror(err);
                if (asprintf(&nbuf, "%s%.*s%s", buf ? buf : "",
                    (int)(m - ptr), ptr, (cnt & 1) ? e : "%m") == -1)
                        goto out;
@@ -87,11 +90,13 @@
        free(buf);
        if (rbuf)
                *rbuf = nbuf;
+       errno = err;
        return nbuf;
 out:
        free(buf);
        if (rbuf)
                *rbuf = NULL;
+       errno = err;
        return fmt;
 }