[PATCH] nisplus: Correct pwent parsing issue and resulting compilation error

["Maciej W. Rozycki" <macro@mips.com>]

Copy and null-terminate NIS+ password file UID and GID entries whose 
length is non-zero rather than zero, fixing a bug and a compilation 
issue causing an error with GCC 8:

nss_nisplus/nisplus-parser.c: In function '_nss_nisplus_parse_pwent':
nss_nisplus/nisplus-parser.c:90:7: error: 'strncpy' destination unchanged after copying no bytes [-Werror=stringop-truncation]
       strncpy (first_unused, numstr, len);
       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
nss_nisplus/nisplus-parser.c:106:7: error: 'strncpy' destination unchanged after copying no bytes [-Werror=stringop-truncation]
       strncpy (first_unused, numstr, len);
       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

introduced with commit ac05397075f6:

commit ac05397075f621cfdbe1db527c96167a58b6d18e
Author: Ulrich Drepper <drepper@redhat.com>
Date:   Sun Apr 30 07:01:26 2006 +0000

	* nis/nss_nisplus/nisplus-parser.c: Minor optimizations and
	cleanups.  Avoid copying data if it can be used in the old place.

(no mailing list reference available).  Obviously regardless of the 
recently added compiler diagnostics causing a build error this code has 
been long non-functional, so I guess NIS+ servers have been supplying 
strings that have already been null-terminated.  Which in turn made it 
unnecessary to make a null-terminated copy, masking this bug.

	* nis/nss_nisplus/nisplus-parser.c (_nss_nisplus_parse_pwent):
	Copy and null-terminate entries whose length is non-zero rather 
	than zero.
---
Hi,

 No issues seen in `mips-linux-gnu' o32 testing.  OK to apply?

 Also this may have to be backported and security implications evaluated.

  Maciej
---
 nis/nss_nisplus/nisplus-parser.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

glibc-nisplus-parse-pwent-len.diff
Index: glibc/nis/nss_nisplus/nisplus-parser.c
===================================================================
--- glibc.orig/nis/nss_nisplus/nisplus-parser.c	2018-02-14 14:57:00.000000000 +0000
+++ glibc/nis/nss_nisplus/nisplus-parser.c	2018-06-16 21:47:29.071633078 +0100
@@ -82,7 +82,7 @@ _nss_nisplus_parse_pwent (nis_result *re
 
   char *numstr = NISOBJVAL (2, obj);
   len = NISOBJLEN (2, obj);
-  if (len == 0 && numstr[len - 1] != '\0')
+  if (len != 0 && numstr[len - 1] != '\0')
     {
       if (len >= room_left)
 	goto no_more_room;
@@ -98,7 +98,7 @@ _nss_nisplus_parse_pwent (nis_result *re
 
   numstr = NISOBJVAL (3, obj);
   len = NISOBJLEN (3, obj);
-  if (len == 0 && numstr[len - 1] != '\0')
+  if (len != 0 && numstr[len - 1] != '\0')
     {
       if (len >= room_left)
 	goto no_more_room;