Return NULL for wildcard values in getnetgrent from nscd (BZ #16759)

getnetgrent is supposed to return NULL for values that are wildcards
in the (host, user, domain) triplet.  This works correctly with nscd
disabled, but with it enabled, it returns a blank ("") instead of a
NULL.  This is easily seen with the output of `getent netgroup foonet`
for a netgroup foonet defined as follows in /etc/netgroup:

    foonet (,foo,)

The output with nscd disabled is:

    foonet ( ,foo,)

while with nscd enabled, it is:

    foonet (,foo,)

The extra space with nscd disabled is due to the fact that `getent
netgroup` adds it if the return value from getnetgrent is NULL for
either host or user.

3 files changed, 17 insertions, 4 deletions

diff --git a/ChangeLog b/ChangeLog
index 7cf7bd1..796978d 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,9 @@
 2014-03-27  Siddhesh Poyarekar  <siddhesh@redhat.com>
 
+	[BZ #16759]
+	* inet/getnetgrent_r.c (get_nonempty_val): New function.
+	(nscd_getnetgrent): Use it.
+
 	[BZ #16760]
 	* nscd/netgroupcache.c (addgetnetgrentX): Use memmove instead
 	of stpcpy.
diff --git a/NEWS b/NEWS
index 6286681..afe4021 100644
--- a/NEWS
+++ b/NEWS
@@ -12,7 +12,8 @@ Version 2.20
   15347, 15804, 15894, 16002, 16198, 16284, 16357, 16447, 16532, 16545,
   16574, 16599, 16600, 16609, 16610, 16611, 16613, 16623, 16632, 16634,
   16639, 16642, 16649, 16670, 16674, 16677, 16680, 16683, 16689, 16695,
-  16701, 16706, 16707, 16712, 16713, 16714, 16731, 16743, 16758, 16760.
+  16701, 16706, 16707, 16712, 16713, 16714, 16731, 16743, 16758, 16759,
+  16760.
 
 * Running the testsuite no longer terminates as soon as a test fails.
   Instead, a file tests.sum (xtests.sum from "make xcheck") is generated,
diff --git a/inet/getnetgrent_r.c b/inet/getnetgrent_r.c
index 62cdfda..f6d064d 100644
--- a/inet/getnetgrent_r.c
+++ b/inet/getnetgrent_r.c
@@ -235,6 +235,14 @@ endnetgrent (void)
 }
 
 #ifdef USE_NSCD
+static const char *
+get_nonempty_val (const char *in)
+{
+  if (*in == '\0')
+    return NULL;
+  return in;
+}
+
 static enum nss_status
 nscd_getnetgrent (struct __netgrent *datap, char *buffer, size_t buflen,
 		  int *errnop)
@@ -243,11 +251,11 @@ nscd_getnetgrent (struct __netgrent *datap, char *buffer, size_t buflen,
     return NSS_STATUS_UNAVAIL;
 
   datap->type = triple_val;
-  datap->val.triple.host = datap->cursor;
+  datap->val.triple.host = get_nonempty_val (datap->cursor);
   datap->cursor = (char *) __rawmemchr (datap->cursor, '\0') + 1;
-  datap->val.triple.user = datap->cursor;
+  datap->val.triple.user = get_nonempty_val (datap->cursor);
   datap->cursor = (char *) __rawmemchr (datap->cursor, '\0') + 1;
-  datap->val.triple.domain = datap->cursor;
+  datap->val.triple.domain = get_nonempty_val (datap->cursor);
   datap->cursor = (char *) __rawmemchr (datap->cursor, '\0') + 1;
 
   return NSS_STATUS_SUCCESS;