lib/port.c: getportent(): Make sure there are at least 2 ':' in the line

Otherwise, the line is invalidly formatted, and we ignore it.

Closes: <https://github.com/shadow-maint/shadow/issues/1036>
Signed-off-by: Alejandro Colomar <alx@kernel.org>

lib/port.c

@@ -147,17 +147,15 @@ next:
 	 * TTY devices.
 	 */
 
+	if (strchr(buf, ':') == NULL)
+		goto next;
+
 	port.pt_names = ttys;
 	for (cp = buf, j = 0; j < PORT_TTY; j++) {
 		port.pt_names[j] = cp;
 		cp = strpbrk(cp, ":,");
-		if (cp == NULL)
-			goto next;	/* line format error */
-
-		if (':' == *cp) {	/* end of tty name list */
+		if (':' == *cp)		/* end of tty name list */
 			break;
-		}
-
 		if (',' == *cp)		/* end of current tty name */
 			stpcpy(cp++, "");
 	}
@@ -171,6 +169,9 @@ next:
 	 * The last entry in the list is a NULL pointer.
 	 */
 
+	if (strchr(cp, ':') == NULL)
+		goto next;
+
 	if (':' != *cp) {
 		port.pt_users = users;
 		port.pt_users[0] = cp;