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

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Date: Thu, 25 Apr 2024 17:25:53 -0400
From: Kent Overstreet <kent.overstreet@...ux.dev>
To: Suren Baghdasaryan <surenb@...gle.com>
Cc: Matthew Wilcox <willy@...radead.org>, 
	Kees Cook <keescook@...omium.org>, Andrew Morton <akpm@...ux-foundation.org>, 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 02:21:39PM -0700, Suren Baghdasaryan wrote:
> On Thu, Apr 25, 2024 at 2:04 PM Kent Overstreet
> <kent.overstreet@...ux.dev> wrote:
> >
> > On Thu, Apr 25, 2024 at 09:51:56PM +0100, Matthew Wilcox wrote:
> > > On Thu, Apr 25, 2024 at 04:45:51PM -0400, Kent Overstreet wrote:
> > > > On Thu, Apr 25, 2024 at 01:08:50PM -0700, Kees Cook wrote:
> > > > > The /proc/allocinfo file exposes a tremendous about of information about
> > > > > kernel build details, memory allocations (obviously), and potentially
> > > > > even image layout (due to ordering). As this is intended to be consumed
> > > > > by system owners (like /proc/slabinfo), use the same file permissions as
> > > > > there: 0400.
> > > >
> > > > Err...
> > > >
> > > > The side effect of locking down more and more reporting interfaces is
> > > > that programs that consume those interfaces now have to run as root.
> > >
> > > sudo cat /proc/allocinfo | analyse-that-fie
> >
> > Even that is still an annoyance, but I'm thinking more about a future
> > daemon to collect this every n seconds - that really shouldn't need to
> > be root.
> 
> Yeah, that would preclude some nice usecases. Could we maybe use
> CAP_SYS_ADMIN checks instead? That way we can still use it from a
> non-root process?

A sysctl would be more in line with what we do for perf. Capabilities
aren't very usable, and CAP_SYS_ADMIN is already way too much of an
everything bucket.