Two major changes:

- Added support for reading netgroups from NIS/YP in addition to the
local /etc/netgroups file. (Note that SunOS and many other systems only
support reading netgroups via NIS, which is a bit odd.)

- Fix Evil Null Pointer Dereferences From Hell (tm) that caused
parse_netgrp() to SEGV when expanding netgroups that include
references to other netgroups. Funny how nobody else noticed this.

This is the first step in implimenting +@netgroup substitution in
getpwent.c and any other places that could use it and don't already
support it (which is probably everywhere).

lib/libc/gen/getnetgrent.c

@@ -83,6 +83,11 @@ int getnetgrent(), innetgr();
 
 #define	LINSIZ	1024	/* Length of netgroup file line */
 
+#ifdef YP
+static int _netgr_yp_stepping;
+static int _netgr_yp_enabled;
+#endif
+
 /*
  * setnetgrent()
  * Parse the netgroup file looking for the netgroup and build the list
@@ -109,6 +114,9 @@ setnetgrent(group)
 		}
 	}
 	nextgrp = grouphead.gr;
+#ifdef YP
+	_netgr_yp_stepping = 0;
+#endif
 }
 
 /*
@@ -164,6 +172,9 @@ endnetgrent()
 		free((char *)ogp);
 	}
 	grouphead.gr = (struct netgrp *)0;
+#ifdef YP
+	_netgr_yp_stepping = 0;
+#endif
 }
 
 /*
@@ -217,7 +228,8 @@ parse_netgrp(group)
 	} else
 		lp->l_parsed = 1;
 	pos = lp->l_line;
-	while (*pos != '\0') {
+	/* Watch for null pointer dereferences, dammit! */
+	while (pos != NULL && *pos != '\0') {
 		if (*pos == '(') {
 			grp = (struct netgrp *)malloc(sizeof (struct netgrp));
 			bzero((char *)grp, sizeof (struct netgrp));
@@ -248,8 +260,10 @@ parse_netgrp(group)
 			if (parse_netgrp(spos))
 				return (1);
 		}
-		while (*pos == ' ' || *pos == ',' || *pos == '\t')
+		/* Watch for null pointer dereferences, dammit! */
-			pos++;
+		if (pos != NULL)
+			while (*pos == ' ' || *pos == ',' || *pos == '\t')
+				pos++;
 	}
 	return (0);
 errout:
@@ -271,9 +285,62 @@ read_for_group(group)
 	int cont;
 	struct linelist *lp;
 	char line[LINSIZ + 1];
+#ifdef YP
+	static char *_netgr_yp_domain;
+	static char *key, *lastkey;
+	static int keylen;
+	char *result;
+	int resultlen;
 
+	/* XXX   There's a small amount of magic at work here:
+	 * once the '+' has been found that tells us to use NIS,
+	 * we have to avoid checking the actual /etc/netgroups file
+	 * again until we're finished reading the netgroup map.
+	 * Therefore, we count on the second half of the test in
+	 * the while() loop not being executed so long as the first
+	 * part evaluates to true.
+	 */
+	while (_netgr_yp_enabled || fgets(line, LINSIZ, netf) != NULL) {
+		if (_netgr_yp_enabled) {
+			if(!_netgr_yp_domain)
+				if(yp_get_default_domain(&_netgr_yp_domain)) {
+					_netgr_yp_enabled = 0;
+					_netgr_yp_stepping = 0;
+					continue;
+				}
+			if (_netgr_yp_stepping) {
+				lastkey = key;
+				if(yp_next(_netgr_yp_domain, "netgroup", key,
+			     	keylen, &key, &keylen, &result, &resultlen)) {
+					_netgr_yp_enabled = 0;
+					_netgr_yp_stepping = 0;
+					free(lastkey);
+					continue;
+				}
+				free(lastkey);
+			} else {
+				if(key) free(key);
+				if (yp_first(_netgr_yp_domain, "netgroup",
+			      		&key, &keylen, &result, &resultlen)) {
+					_netgr_yp_enabled = 0;
+					_netgr_yp_stepping = 0;
+					continue;
+				}
+				_netgr_yp_stepping = 1;
+			}
+			sprintf(line, "%s %s", key, result);
+			free(result);
+		}
+#else
 	while (fgets(line, LINSIZ, netf) != NULL) {
-		pos = line;
+#endif
+		pos = (char *)&line;
+#ifdef YP
+		if (*pos == '+') {
+			_netgr_yp_enabled = 1;
+			continue;
+		}
+#endif
 		if (*pos == '#')
 			continue;
 		while (*pos == ' ' || *pos == '\t')