Re: [PATCH bpf-next v7 4/8] bpf: lsm: Implement attach, detach and execution

From: Stephen Smalley <sds@tycho.nsa.gov>
To: James Morris <jmorris@namei.org>, KP Singh <kpsingh@chromium.org>
Cc: linux-kernel@vger.kernel.org, bpf@vger.kernel.org,
	linux-security-module@vger.kernel.org,
	Brendan Jackman <jackmanb@google.com>,
	Florent Revest <revest@google.com>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Kees Cook <keescook@chromium.org>, Paul Turner <pjt@google.com>,
	Jann Horn <jannh@google.com>,
	Florent Revest <revest@chromium.org>,
	Brendan Jackman <jackmanb@chromium.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Paul Moore <paul@paul-moore.com>
Subject: Re: [PATCH bpf-next v7 4/8] bpf: lsm: Implement attach, detach and execution
Date: Fri, 27 Mar 2020 08:27:25 -0400	[thread overview]
Message-ID: <2241c806-65c9-68f5-f822-9a245ecf7ba0@tycho.nsa.gov> (raw)
In-Reply-To: <alpine.LRH.2.21.2003271119420.17089@namei.org>

On 3/26/20 8:24 PM, James Morris wrote:
> On Thu, 26 Mar 2020, KP Singh wrote:
> 
>> +int bpf_lsm_verify_prog(struct bpf_verifier_log *vlog,
>> +			const struct bpf_prog *prog)
>> +{
>> +	/* Only CAP_MAC_ADMIN users are allowed to make changes to LSM hooks
>> +	 */
>> +	if (!capable(CAP_MAC_ADMIN))
>> +		return -EPERM;
>> +
> 
> Stephen, can you confirm that your concerns around this are resolved
> (IIRC, by SELinux implementing a bpf_prog callback) ?

I guess the only residual concern I have is that CAP_MAC_ADMIN means 
something different to SELinux (ability to get/set file security 
contexts unknown to the currently loaded policy), so leaving the 
CAP_MAC_ADMIN check here (versus calling a new security hook here and 
checking CAP_MAC_ADMIN in the implementation of that hook for the 
modules that want that) conflates two very different things.  Prior to 
this patch, there are no users of CAP_MAC_ADMIN outside of individual 
security modules; it is only checked in module-specific logic within 
apparmor, safesetid, selinux, and smack, so the meaning was module-specific.