linux-kernel - Re: [RFC PATCH] rootfs: force mounting rootfs as tmpfs

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Date:   Thu, 1 Feb 2018 11:09:20 -0600
From:   Rob Landley <rob@...dley.net>
To:     Mimi Zohar <zohar@...ux.vnet.ibm.com>,
        Arvind Sankar <nivedita@...m.mit.edu>
Cc:     initramfs <initramfs@...r.kernel.org>,
        Taras Kondratiuk <takondra@...co.com>,
        Victor Kamensky <kamensky@...co.com>,
        linux-security-module <linux-security-module@...r.kernel.org>,
        Al Viro <viro@...IV.linux.org.uk>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] rootfs: force mounting rootfs as tmpfs

On 02/01/2018 09:55 AM, Mimi Zohar wrote:
> On Thu, 2018-02-01 at 09:20 -0600, Rob Landley wrote:
> 
>>> With your patch and specifying "root=tmpfs", dracut is complaining:
>>>
>>> dracut: FATAL: Don't know how to handle 'root=tmpfs'
>>> dracut: refusing to continue
>>
>> [googles]... I do not understand why this package exists.
>>
>> If you're switching to another root filesystem, using a tool that
>> wikipedia[citation needed] says has no purpose but to switch to another
>> root filesystem, (so let's reproduce the kernel infrastructure in
>> userspace while leaving it the kernel too)... why do you need initramfs
>> to be tmpfs? You're using it for half a second, then discarding it,
>> what's the point of it being tmpfs?
> 
> Unlike the kernel image which is signed by the distros, the initramfs
> doesn't come signed, because it is built on the target system.  Even
> if the initramfs did come signed, it is beneficial to measure and
> appraise the individual files in the initramfs.

You can still shoot yourself in the foot with tmpfs. People mount a /run
and a /tmp and then as a normal user you can go
https://twitter.com/landley/status/959103235305951233 and maybe the
default should be a little more clever there...

I'll throw it on the todo heap. :)

>> Sigh. If people are ok with having rootfs just be tmpfs whenever tmpfs
>> is configured in, even when you're then going to overmount it with
>> something else like you're doing, let's just _remove_ the test. If it
>> can be tmpfs, have it be tmpfs.
> 
> Very much appreciated!

Not yet tested, but something like the attached? (Sorry for the
half-finished doc changes in there, I'm at work and have a 5 minute
break. I can test properly this evening if you don't get to it...)

Rob

View attachment "initmpfs.patch" of type "text/x-patch" (6311 bytes)