linux-kernel - Re: > [PATCH] Security: Handle hidepid option correctly

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Date:   Fri, 14 Dec 2018 18:44:36 +0300
From:   Alexey Dobriyan <adobriyan@...il.com>
To:     程洋 <d17103513@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        David Howells <dhowells@...hat.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Johannes Weiner <hannes@...xchg.org>,
        Davidlohr Bueso <dbueso@...e.de>, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: > [PATCH] Security: Handle hidepid option correctly

On Wed, Dec 05, 2018 at 03:26:04PM +0800, 程洋 wrote:
> Anyone who can review my patch?
> 
> 程洋 <chengyang@...omi.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.