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

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Message-ID: <lrxro6vscss37qje4guawymibqcpao4ar4oitc4wjnpkfgkhdi@pmfn3gi2wvxn>
Date: Fri, 26 Apr 2024 04:46:43 -0400
From: Kent Overstreet <kent.overstreet@...ux.dev>
To: Pavel Machek <pavel@....cz>
Cc: Suren Baghdasaryan <surenb@...gle.com>, 
	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 Fri, Apr 26, 2024 at 10:32:27AM +0200, Pavel Machek wrote:
> Hi!
> 
> > > > > > 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?
> 
> CAP_SYS_ADMIN is really not suitable, as it can do changes to the
> system. On working system, allocinfo is really not dangerous, it just
> may make exploits harder. CAP_KERNEL_OBSERVER or something...

There's _really_ no reason to use capabilities at all for something that
has file ownership - just use a group.