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

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Message-ID: <2241c806-65c9-68f5-f822-9a245ecf7ba0@tycho.nsa.gov>
Date:   Fri, 27 Mar 2020 08:27:25 -0400
From:   Stephen Smalley <sds@...ho.nsa.gov>
To:     James Morris <jmorris@...ei.org>, KP Singh <kpsingh@...omium.org>
Cc:     linux-kernel@...r.kernel.org, bpf@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        Brendan Jackman <jackmanb@...gle.com>,
        Florent Revest <revest@...gle.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kees Cook <keescook@...omium.org>,
        Paul Turner <pjt@...gle.com>, Jann Horn <jannh@...gle.com>,
        Florent Revest <revest@...omium.org>,
        Brendan Jackman <jackmanb@...omium.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Paul Moore <paul@...l-moore.com>
Subject: Re: [PATCH bpf-next v7 4/8] bpf: lsm: Implement attach, detach and
 execution

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.