linux-hardening - Re: [PATCH] alloc_tag: Tighten file permissions on /proc/allocinfo

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Date: Thu, 25 Apr 2024 20:27:05 -0400
From: Kent Overstreet <kent.overstreet@...ux.dev>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Kees Cook <keescook@...omium.org>, 
	Matthew Wilcox <willy@...radead.org>, Suren Baghdasaryan <surenb@...gle.com>, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] alloc_tag: Tighten file permissions on /proc/allocinfo

On Thu, Apr 25, 2024 at 04:47:18PM -0700, Andrew Morton wrote:
> On Thu, 25 Apr 2024 15:42:30 -0700 Kees Cook <keescook@...omium.org> wrote:
> 
> > > The concern about leaking image layout could be addressed by sorting the
> > > output before returning to userspace.
> > 
> > It's trivial to change permissions from the default 0400 at boot time.
> > It can even have groups and ownership changed, etc. This is why we have
> > per-mount-namespace /proc instances:
> > 
> > # chgrp sysmonitor /proc/allocinfo
> > # chmod 0440 /proc/allocinfo
> > 
> > Poof, instant role-based access control. :)
> 
> Conversely, the paranoid could set it to 0400 at boot also.
> 
> > I'm just trying to make the _default_ safe.
> 
> Agree with this.
> 
> Semi-seriously, how about we set the permissions to 0000 and force
> distributors/users to make a decision.

I'm ok with 0400 for now since it's consistent with slabinfo, but I'd
really like to see a sysctl for debug info paranoia. We shouldn't be
leaving this to the distros; we're the ones with the expertise to say
what would be covered by that sysctl.