linux-kernel - Re: [PATCH 3/3] capabilities: add cap userns sysctl mask

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Date: Mon, 20 May 2024 15:13:23 -0600
From: Tycho Andersen <tycho@...ho.pizza>
To: Jonathan Calmels <jcalmels@...0.net>
Cc: brauner@...nel.org, ebiederm@...ssion.com,
	Luis Chamberlain <mcgrof@...nel.org>,
	Kees Cook <keescook@...omium.org>,
	Joel Granados <j.granados@...sung.com>,
	Serge Hallyn <serge@...lyn.com>, Paul Moore <paul@...l-moore.com>,
	James Morris <jmorris@...ei.org>,
	David Howells <dhowells@...hat.com>,
	Jarkko Sakkinen <jarkko@...nel.org>, containers@...ts.linux.dev,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-security-module@...r.kernel.org, keyrings@...r.kernel.org
Subject: Re: [PATCH 3/3] capabilities: add cap userns sysctl mask

On Mon, May 20, 2024 at 12:25:27PM -0700, Jonathan Calmels wrote:
> On Mon, May 20, 2024 at 07:30:14AM GMT, Tycho Andersen wrote:
> > there is an ongoing effort (started at [0]) to constify the first arg
> > here, since you're not supposed to write to it. Your usage looks
> > correct to me, so I think all it needs is a literal "const" here.
> 
> Will do, along with the suggestions from Jarkko
> 
> > > +	struct ctl_table t;
> > > +	unsigned long mask_array[2];
> > > +	kernel_cap_t new_mask, *mask;
> > > +	int err;
> > > +
> > > +	if (write && (!capable(CAP_SETPCAP) ||
> > > +		      !capable(CAP_SYS_ADMIN)))
> > > +		return -EPERM;
> > 
> > ...why CAP_SYS_ADMIN? You mention it in the changelog, but don't
> > explain why.
> 
> No reason really, I was hoping we could decide what we want here.
> UMH uses CAP_SYS_MODULE, Serge mentioned adding a new cap maybe.

I don't have a strong preference between SETPCAP and a new capability,
but I do think it should be just one. SYS_ADMIN is already god mode
enough, IMO.

Tycho