fs: Reorder inode_owner_or_capable() to avoid needless

Checking for capabilities should be the last operation when performing
access control tests so that PF_SUPERPRIV is set only when it was required
for success (implying that the capability was needed for the operation).

Reported-by: Solar Designer <solar@openwall.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Serge Hallyn <serge@hallyn.com>
Reviewed-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/inode.c

@@ -2023,7 +2023,7 @@ bool inode_owner_or_capable(const struct inode *inode)
 		return true;
 
 	ns = current_user_ns();
-	if (ns_capable(ns, CAP_FOWNER) && kuid_has_mapping(ns, inode->i_uid))
+	if (kuid_has_mapping(ns, inode->i_uid) && ns_capable(ns, CAP_FOWNER))
 		return true;
 	return false;
 }

fs/namei.c

@@ -1008,7 +1008,7 @@ static int may_linkat(struct path *link)
 	/* Source inode owner (or CAP_FOWNER) can hardlink all they like,
 	 * otherwise, it must be a safe source.
 	 */
-	if (inode_owner_or_capable(inode) || safe_hardlink_source(inode))
+	if (safe_hardlink_source(inode) || inode_owner_or_capable(inode))
 		return 0;
 
 	audit_log_link_denied("linkat", link);