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Date:   Fri, 21 Feb 2020 20:26:04 -0800
From:   Kees Cook <keescook@chromium.org>
To:     KP Singh <kpsingh@chromium.org>
Cc:     linux-kernel@vger.kernel.org, bpf@vger.kernel.org,
        linux-security-module@vger.kernel.org,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
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        Thomas Garnier <thgarnie@chromium.org>,
        Michael Halcrow <mhalcrow@google.com>,
        Paul Turner <pjt@google.com>,
        Brendan Gregg <brendan.d.gregg@gmail.com>,
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        Matthew Garrett <mjg59@google.com>,
        Christian Brauner <christian@brauner.io>,
        Florent Revest <revest@chromium.org>,
        Brendan Jackman <jackmanb@chromium.org>,
        Martin KaFai Lau <kafai@fb.com>,
        Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
        "Serge E. Hallyn" <serge@hallyn.com>,
        "David S. Miller" <davem@davemloft.net>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Nicolas Ferre <nicolas.ferre@microchip.com>,
        Stanislav Fomichev <sdf@google.com>,
        Quentin Monnet <quentin.monnet@netronome.com>,
        Andrey Ignatov <rdna@fb.com>, Joe Stringer <joe@wand.net.nz>
Subject: Re: [PATCH bpf-next v4 4/8] bpf: lsm: Add support for
 enabling/disabling BPF hooks
Message-ID: <202002212023.1712A8AB@keescook>
References: <20200220175250.10795-1-kpsingh@chromium.org>
 <20200220175250.10795-5-kpsingh@chromium.org>
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On Thu, Feb 20, 2020 at 06:52:46PM +0100, KP Singh wrote:
> index aa111392a700..569cc07d5e34 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -804,6 +804,13 @@ int security_vm_enough_memory_mm(struct mm_struct *mm, long pages)
>  			break;
>  		}
>  	}
> +#ifdef CONFIG_BPF_LSM
> +	if (HAS_BPF_LSM_PROG(vm_enough_memory)) {
> +		rc = bpf_lsm_vm_enough_memory(mm, pages);
> +		if (rc <= 0)
> +			cap_sys_admin = 0;
> +	}
> +#endif

This pattern of using #ifdef in code is not considered best practice.
Using in-code IS_ENABLED(CONFIG_BPF_LSM) is preferred. But since this
pattern always uses HAS_BPF_LSM_PROG(), you could fold the
IS_ENABLED() into the definition of HAS_BPF_LSM_PROG itself -- or more
likely, have the macro defined as:

#ifdef CONFIG_BPF_LSM
# define HAS_BPF_LSM_PROG(x)    ....existing implementation....
#else
# define HAS_BPF_LSM_PROG(x)	false
#endif

Then none of these ifdefs are needed.

-- 
Kees Cook