From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-fsdevel-owner@vger.kernel.org>
Received: from mail-wr1-f65.google.com ([209.85.221.65]:37777 "EHLO
        mail-wr1-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1728565AbeLNPom (ORCPT
        <rfc822;linux-fsdevel@vger.kernel.org>);
        Fri, 14 Dec 2018 10:44:42 -0500
Date: Fri, 14 Dec 2018 18:44:36 +0300
From: Alexey Dobriyan <adobriyan@gmail.com>
To: =?utf-8?B?56iL5rSL?= <d17103513@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
        David Howells <dhowells@redhat.com>,
        "Peter Zijlstra (Intel)" <peterz@infradead.org>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Davidlohr Bueso <dbueso@suse.de>, linux-kernel@vger.kernel.org,
        linux-fsdevel@vger.kernel.org
Subject: Re: > [PATCH] Security: Handle hidepid option correctly
Message-ID: <20181214154436.GA16772@avx2>
References: <18d54cd3edbf4fd3a7c01962f41ead58@cnbox5.mioffice.cn>
 <CADd0cq1HHv4xXn0tEWb4SfQ2XvoH33O1d1rogojj=hBTm+Lwww@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <CADd0cq1HHv4xXn0tEWb4SfQ2XvoH33O1d1rogojj=hBTm+Lwww@mail.gmail.com>
Sender: linux-fsdevel-owner@vger.kernel.org
List-ID: <linux-fsdevel.vger.kernel.org>

On Wed, Dec 05, 2018 at 03:26:04PM +0800, 程洋 wrote:
> Anyone who can review my patch?
> 
> 程洋 <chengyang@xiaomi.com> 于2018年11月30日周五 上午10:34写道：
> >
> > Here is an article illustrates the details.
> > https://medium.com/@topjohnwu/from-anime-game-to-android-system-security-vulnerability-9b955a182f20
> >
> > And There is a similar fix on kernel-4.4:
> > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=99663be772c827b8f5f594fe87eb4807be1994e5
> >
> > Q: Other filesystems parse the options from fill_super().  Is proc special in some fashion?
> > A: According to my research, start_kernel will call proc_mount first, and initialize sb->s_root before any userspace process runs. If others want to mount it, all options will be ignored.
> >      AOSP change here: https://android-review.googlesource.com/c/platform/system/core/+/181345/4/init/init.cpp
> >      At first I though we should mount it with MS_REMOUNT flag. But kernel will crash if we did this.

This is not true: /proc is mounted by userspace (and it is easy to see
from the fact that proc_mount() is not called from kernel anywhere).

hidepid= in its current form is misdesigned, so might as well not bother
changing anything. IIRC there were(?) patches to make it per-mount.