From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <SRS0=vN1y=BQ=vger.kernel.org=linux-kernel-owner@kernel.org>
X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on
	aws-us-west-2-korg-lkml-1.web.codeaurora.org
X-Spam-Level: 
X-Spam-Status: No, score=-4.0 required=3.0 tests=BAYES_00,
	HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,
	URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0
Received: from mail.kernel.org (mail.kernel.org [198.145.29.99])
	by smtp.lore.kernel.org (Postfix) with ESMTP id 607D7C433E0
	for <linux-kernel@archiver.kernel.org>; Thu,  6 Aug 2020 17:25:00 +0000 (UTC)
Received: from vger.kernel.org (vger.kernel.org [23.128.96.18])
	by mail.kernel.org (Postfix) with ESMTP id C2F3B23119
	for <linux-kernel@archiver.kernel.org>; Thu,  6 Aug 2020 17:25:00 +0000 (UTC)
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1729840AbgHFRY5 (ORCPT
        <rfc822;linux-kernel@archiver.kernel.org>);
        Thu, 6 Aug 2020 13:24:57 -0400
Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44978 "EHLO
        lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1729842AbgHFRDY (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Thu, 6 Aug 2020 13:03:24 -0400
Received: from ZenIV.linux.org.uk (zeniv.linux.org.uk [IPv6:2002:c35c:fd02::1])
        by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4D2D8C061A19;
        Thu,  6 Aug 2020 05:09:12 -0700 (PDT)
Received: from viro by ZenIV.linux.org.uk with local (Exim 4.92.3 #3 (Red Hat Linux))
        id 1k3ehe-00ATwx-OM; Thu, 06 Aug 2020 12:08:58 +0000
Date:   Thu, 6 Aug 2020 13:08:58 +0100
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     linmiaohe <linmiaohe@huawei.com>
Cc:     davem@davemloft.net, kuba@kernel.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 3/5] net: Set fput_needed iff FDPUT_FPUT is set
Message-ID: <20200806120858.GA2497432@ZenIV.linux.org.uk>
References: <1596714796-25298-1-git-send-email-linmiaohe@huawei.com>
 <20200806115915.GO1236603@ZenIV.linux.org.uk>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20200806115915.GO1236603@ZenIV.linux.org.uk>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Thu, Aug 06, 2020 at 12:59:16PM +0100, Al Viro wrote:
> On Thu, Aug 06, 2020 at 07:53:16PM +0800, linmiaohe wrote:
> > From: Miaohe Lin <linmiaohe@huawei.com>
> > 
> > We should fput() file iff FDPUT_FPUT is set. So we should set fput_needed
> > accordingly.
> > 
> > Fixes: 00e188ef6a7e ("sockfd_lookup_light(): switch to fdget^W^Waway from fget_light")
> 
> Explain, please.  We are getting it from fdget(); what else can we get in flags there?

FWIW, struct fd ->flags may have two bits set: FDPUT_FPUT and FDPUT_POS_UNLOCK.
The latter is set only by __fdget_pos() and its callers, and that only for
regular files and directories.

Nevermind that sockfd_lookup_light() does *not* use ..._pos() family of
primitives, even if it started to use e.g. fdget_pos() it *still* would
not end up with anything other than FDPUT_FPUT to deal with on that
path - it checks that what it got is a socket.  Anything else is dropped
right there, without leaving fput() to caller.

So could you explain what exactly the bug is - if you are seeing some
breakage and this patch fixes it, something odd is definitely going on
and it would be nice to figure out what that something is.