Fix an infinite loop in setnetgrent(3) with NIS netgroups.

Handle an empty result from yp_match() by returning NULL, which is
consistent with the handling of an empty netgroup in /etc/netgroup.
setnetgrent(3) has no return value, so there is no particular need to
distinguish this case from an error.

PR:		26486
MFC after:	2 weeks

1 files changed, 4 insertions, 0 deletions

diff --git a/lib/libc/gen/getnetgrent.c b/lib/libc/gen/getnetgrent.c
index 71a36e2..ab3a46f 100644
--- a/lib/libc/gen/getnetgrent.c
+++ b/lib/libc/gen/getnetgrent.c
@@ -558,6 +558,10 @@ read_for_group(const char *group)
 					continue;
 				}
 			}
+			if (strlen(result) == 0) {
+				free(result);
+				return (NULL);
+			}
 			snprintf(line, LINSIZ, "%s %s", group, result);
 			free(result);
 		}