Re: [PATCH bpf-next v2 02/10] bpf: lsm: Add a skeleton and config options

From: Casey Schaufler <casey@schaufler-ca.com>
To: KP Singh <kpsingh@chromium.org>,
	Linux Security Module list 
	<linux-security-module@vger.kernel.org>,
	bpf@vger.kernel.org
Cc: Casey Schaufler <casey@schaufler-ca.com>
Subject: Re: [PATCH bpf-next v2 02/10] bpf: lsm: Add a skeleton and config options
Date: Wed, 15 Jan 2020 23:04:55 -0800	[thread overview]
Message-ID: <7b11f92b-259f-f2e1-924c-5c0518f49b3f@schaufler-ca.com> (raw)
In-Reply-To: <20200115171333.28811-3-kpsingh@chromium.org>

On 1/15/2020 9:13 AM, KP Singh wrote:
> From: KP Singh <kpsingh@google.com>
>
> The LSM can be enabled by CONFIG_SECURITY_BPF.
> Without CONFIG_SECURITY_BPF_ENFORCE, the LSM will run the
> attached eBPF programs but not enforce MAC policy based
> on the return value of the attached programs.
>
> Signed-off-by: KP Singh <kpsingh@google.com>
> ---
>  MAINTAINERS           |  7 +++++++
>  security/Kconfig      | 11 ++++++-----
>  security/Makefile     |  2 ++
>  security/bpf/Kconfig  | 22 ++++++++++++++++++++++
>  security/bpf/Makefile |  5 +++++
>  security/bpf/lsm.c    | 25 +++++++++++++++++++++++++
>  6 files changed, 67 insertions(+), 5 deletions(-)
>  create mode 100644 security/bpf/Kconfig
>  create mode 100644 security/bpf/Makefile
>  create mode 100644 security/bpf/lsm.c
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 66a2e5e07117..0941f478cfa5 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -3203,6 +3203,13 @@ S:	Supported
>  F:	arch/x86/net/
>  X:	arch/x86/net/bpf_jit_comp32.c
>  
> +BPF SECURITY MODULE
> +M:	KP Singh <kpsingh@chromium.org>
> +L:	linux-security-module@vger.kernel.org
> +L:	bpf@vger.kernel.org
> +S:	Maintained
> +F:	security/bpf/
> +
>  BROADCOM B44 10/100 ETHERNET DRIVER
>  M:	Michael Chan <michael.chan@broadcom.com>
>  L:	netdev@vger.kernel.org
> diff --git a/security/Kconfig b/security/Kconfig
> index 2a1a2d396228..6f1aab195e7d 100644
> --- a/security/Kconfig
> +++ b/security/Kconfig
> @@ -236,6 +236,7 @@ source "security/tomoyo/Kconfig"
>  source "security/apparmor/Kconfig"
>  source "security/loadpin/Kconfig"
>  source "security/yama/Kconfig"
> +source "security/bpf/Kconfig"
>  source "security/safesetid/Kconfig"
>  source "security/lockdown/Kconfig"
>  
> @@ -277,11 +278,11 @@ endchoice
>  
>  config LSM
>  	string "Ordered list of enabled LSMs"
> -	default "lockdown,yama,loadpin,safesetid,integrity,smack,selinux,tomoyo,apparmor" if DEFAULT_SECURITY_SMACK
> -	default "lockdown,yama,loadpin,safesetid,integrity,apparmor,selinux,smack,tomoyo" if DEFAULT_SECURITY_APPARMOR
> -	default "lockdown,yama,loadpin,safesetid,integrity,tomoyo" if DEFAULT_SECURITY_TOMOYO
> -	default "lockdown,yama,loadpin,safesetid,integrity" if DEFAULT_SECURITY_DAC
> -	default "lockdown,yama,loadpin,safesetid,integrity,selinux,smack,tomoyo,apparmor"
> +	default "lockdown,yama,loadpin,safesetid,integrity,smack,selinux,tomoyo,apparmor,bpf" if DEFAULT_SECURITY_SMACK
> +	default "lockdown,yama,loadpin,safesetid,integrity,apparmor,selinux,smack,tomoyo,bpf" if DEFAULT_SECURITY_APPARMOR
> +	default "lockdown,yama,loadpin,safesetid,integrity,tomoyo,bpf" if DEFAULT_SECURITY_TOMOYO
> +	default "lockdown,yama,loadpin,safesetid,integrity,bpf" if DEFAULT_SECURITY_DAC
> +	default "lockdown,yama,loadpin,safesetid,integrity,selinux,smack,tomoyo,apparmor,bpf"
>  	help
>  	  A comma-separated list of LSMs, in initialization order.
>  	  Any LSMs left off this list will be ignored. This can be
> diff --git a/security/Makefile b/security/Makefile
> index be1dd9d2cb2f..50e6821dd7b7 100644
> --- a/security/Makefile
> +++ b/security/Makefile
> @@ -12,6 +12,7 @@ subdir-$(CONFIG_SECURITY_YAMA)		+= yama
>  subdir-$(CONFIG_SECURITY_LOADPIN)	+= loadpin
>  subdir-$(CONFIG_SECURITY_SAFESETID)    += safesetid
>  subdir-$(CONFIG_SECURITY_LOCKDOWN_LSM)	+= lockdown
> +subdir-$(CONFIG_SECURITY_BPF)		+= bpf
>  
>  # always enable default capabilities
>  obj-y					+= commoncap.o
> @@ -29,6 +30,7 @@ obj-$(CONFIG_SECURITY_YAMA)		+= yama/
>  obj-$(CONFIG_SECURITY_LOADPIN)		+= loadpin/
>  obj-$(CONFIG_SECURITY_SAFESETID)       += safesetid/
>  obj-$(CONFIG_SECURITY_LOCKDOWN_LSM)	+= lockdown/
> +obj-$(CONFIG_SECURITY_BPF)		+= bpf/
>  obj-$(CONFIG_CGROUP_DEVICE)		+= device_cgroup.o
>  
>  # Object integrity file lists
> diff --git a/security/bpf/Kconfig b/security/bpf/Kconfig
> new file mode 100644
> index 000000000000..a5f6c67ae526
> --- /dev/null
> +++ b/security/bpf/Kconfig
> @@ -0,0 +1,22 @@
> +# SPDX-License-Identifier: GPL-2.0
> +#
> +# Copyright 2019 Google LLC.
> +
> +config SECURITY_BPF
> +	bool "BPF-based MAC and audit policy"
> +	depends on SECURITY
> +	depends on BPF_SYSCALL
> +	help
> +	  This enables instrumentation of the security hooks with
> +	  eBPF programs.
> +
> +	  If you are unsure how to answer this question, answer N.
> +
> +config SECURITY_BPF_ENFORCE
> +	bool "Deny operations based on the evaluation of the attached programs"
> +	depends on SECURITY_BPF
> +	help
> +	  eBPF programs attached to hooks can be used for both auditing and
> +	  enforcement. Enabling enforcement implies that the evaluation result
> +	  from the attached eBPF programs will allow or deny the operation
> +	  guarded by the security hook.
> diff --git a/security/bpf/Makefile b/security/bpf/Makefile
> new file mode 100644
> index 000000000000..26a0ab6f99b7
> --- /dev/null
> +++ b/security/bpf/Makefile
> @@ -0,0 +1,5 @@
> +# SPDX-License-Identifier: GPL-2.0
> +#
> +# Copyright 2019 Google LLC.
> +
> +obj-$(CONFIG_SECURITY_BPF) := lsm.o
> diff --git a/security/bpf/lsm.c b/security/bpf/lsm.c
> new file mode 100644
> index 000000000000..5c5c14f990ce
> --- /dev/null
> +++ b/security/bpf/lsm.c
> @@ -0,0 +1,25 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +/*
> + * Copyright 2019 Google LLC.
> + */
> +
> +#include <linux/lsm_hooks.h>
> +
> +/* This is only for internal hooks, always statically shipped as part of the
> + * BPF LSM. Statically defined hooks are appeneded to the security_hook_heads
> + * which is common for LSMs and R/O after init.
> + */
> +static struct security_hook_list lsm_hooks[] __lsm_ro_after_init = {};

s/lsm_hooks/bpf_hooks/

The lsm prefix is for the infrastructure. The way you have it is massively confusing.

> +
> +static int __init lsm_init(void)

s/lsm_init/bpf_init/

Same reason. When I'm looking at several security modules at once I
need to be able to tell them apart.

> +{
> +	security_add_hooks(lsm_hooks, ARRAY_SIZE(lsm_hooks), "bpf");
> +	pr_info("eBPF and LSM are friends now.\n");

Cute message, but not very informative if you haven't read the code.
"LSM support for eBPF active\n" is more likely to be comprehensible.

> +	return 0;
> +}
> +
> +DEFINE_LSM(bpf) = {
> +	.name = "bpf",
> +	.init = lsm_init,
> +};