linux-kernel - Re: [RFC PATCH v1 0/6] proc: Add allowlist for procfs files

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Message-Id: <20230125153628.43c12cbe05423fef7d44f0dd@linux-foundation.org>
Date:   Wed, 25 Jan 2023 15:36:28 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Alexey Gladkov <legion@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, containers@...ts.linux.dev,
        linux-fsdevel@...r.kernel.org,
        Alexey Dobriyan <adobriyan@...il.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>,
        Val Cowan <vcowan@...hat.com>
Subject: Re: [RFC PATCH v1 0/6] proc: Add allowlist for procfs files

On Wed, 25 Jan 2023 16:28:47 +0100 Alexey Gladkov <legion@...nel.org> wrote:

> The patch expands subset= option. If the proc is mounted with the
> subset=allowlist option, the /proc/allowlist file will appear. This file
> contains the filenames and directories that are allowed for this
> mountpoint. By default, /proc/allowlist contains only its own name.
> Changing the allowlist is possible as long as it is present in the
> allowlist itself.
> 
> This allowlist is applied in lookup/readdir so files that will create
> modules after mounting will not be visible.
> 
> Compared to the previous patches [1][2], I switched to a special virtual
> file from listing filenames in the mount options.
> 

Changlog doesn't explain why you think Linux needs this feature.  The
[2/6] changelog hints that containers might be involved.  IOW, please
fully describe the requirement and use-case(s).

Also, please describe why /proc/allowlist is made available via a mount
option, rather than being permanently present.

And why add to subset=, instead of a separate mount option.

Does /proc/allowlist work in subdirectories?  Like, permit presence of
/proc/sys/vm/compact_memory?

I think the whole thing is misnamed, really.  "allowlist" implies
access permissions.  Some of the test here uses "visibility" and other
places use "presence", which are better.  "presentlist" and
/proc/presentlist might be better.  But why not simply /proc/contents?

Please run these patches through checkpatch and consider the result.