Check for illegal character '=' in environment variable names.

Make sure the string passed as variable name does not contain a '='
character. This not only prevents the common error or typing
"setenv foo=bar" instead of "setenv foo bar", but (more importantly)
also closes a backdoor which allowed to delete write-protected
environment variables, for example by using "setenv ethaddr=".

common/cmd_nvedit.c

@@ -167,6 +167,11 @@ int _do_setenv (int flag, int argc, char *argv[])
 
 	name = argv[1];
 
+	if (strchr(name, '=')) {
+		printf ("## Error: illegal character '=' in variable name \"%s\"\n", name);
+		return 1;
+	}
+
 	/*
 	 * search if variable with this name already exists
 	 */