Don't ignore unknown characters. The previous code treated a line like:

hosts:!!!!!!!!@@@@@$%^&*()()*$(files{}{}|||++!)(dns

exactly the same as:

hosts: files dns

Recover from parse errors by looking for the end of a line; this
allows entries without errors to still be parsed even if there is
an erroneous entry earlier in the file.

lib/libc/net/nslexer.l

@@ -94,9 +94,7 @@ STRING		[a-zA-Z][a-zA-Z0-9_]*
 			return STRING;
 		}
 
-[:=\[\]]	return yytext[0];
-
-.		;	/* ignore all else */
+.		return yytext[0];
 
 %%
 

lib/libc/net/nsparser.y

@@ -87,6 +87,10 @@ Entry
 		{
 			_nsdbtput(&curdbt);
 		}
+	| error NL
+		{
+			yyerrok;
+		}
 	;
 
 Database