Don't edit permissions of pre-existing directories during extract.

This closes a security hole.  Otherwise, libarchive will happily
extract into directories to which it lacks write permissions by
resetting the permissions during the extract.

Thanks to: Kris Kennaway

lib/libarchive/archive_read_extract.c

@@ -479,7 +479,7 @@ extract_dir(struct archive *a, struct archive_entry *entry, int flags)
 	if (extract->pst != NULL) {
 		extract->pst = &extract->st;
 		if (S_ISDIR(extract->pst->st_mode))
-			goto success;
+			return (ARCHIVE_OK);
 		/* It exists but isn't a dir. */
 		if ((flags & ARCHIVE_EXTRACT_UNLINK))
 			unlink(path);