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Date: Mon, 1 Oct 2018 14:46:54 -0700
From: John Johansen <john.johansen@...onical.com>
To: Kees Cook <keescook@...omium.org>, James Morris <jmorris@...ei.org>
Cc: Casey Schaufler <casey@...aufler-ca.com>,
Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
Paul Moore <paul@...l-moore.com>,
Stephen Smalley <sds@...ho.nsa.gov>,
"Schaufler, Casey" <casey.schaufler@...el.com>,
LSM <linux-security-module@...r.kernel.org>,
Jonathan Corbet <corbet@....net>, linux-doc@...r.kernel.org,
linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH security-next v3 18/29] LSM: Introduce lsm.enable= and
lsm.disable=
On 09/24/2018 05:18 PM, Kees Cook wrote:
> This introduces the "lsm.enable=..." and "lsm.disable=..." boot parameters
> which each can contain a comma-separated list of LSMs to enable or
> disable, respectively. The string "all" matches all LSMs.
>
> This has very similar functionality to the existing per-LSM enable
> handling ("apparmor.enabled=...", etc), but provides a centralized
> place to perform the changes. These parameters take precedent over any
> LSM-specific boot parameters.
>
> Disabling an LSM means it will not be considered when performing
> initializations. Enabling an LSM means either undoing a previous
> LSM-specific boot parameter disabling or a undoing a default-disabled
> CONFIG setting.
>
> For example: "lsm.disable=apparmor apparmor.enabled=1" will result in
> AppArmor being disabled. "selinux.enabled=0 lsm.enable=selinux" will
> result in SELinux being enabled.
>
> Signed-off-by: Kees Cook <keescook@...omium.org>
I don't like this. It brings about conflicting kernel params that are
bound to confuse users. Its pretty easy for a user to understand that
when they specify a parameter manually at boot, that it overrides the
build time default. But conflicting kernel parameters are a lot harder
to deal with.
I prefer a plain enabled= list being an override of the default build
time value. Where conflicts with LSM-specific configs always result in
the LSM being disabled with a complaint about the conflict.
Though I have yet to be convinced its worth the cost, I do recognize
it is sometimes convenient to disable a single LSM, instead of typing
in a whole list of what to enable. If we have to have conflicting
kernel parameters I would prefer that the conflict throw up a warning
and leaving the LSM with the conflicting config disabled.
> ---
> .../admin-guide/kernel-parameters.txt | 12 ++++++++++
> security/Kconfig | 4 +++-
> security/security.c | 22 +++++++++++++++++++
> 3 files changed, 37 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 32d323ee9218..67c90985d2b8 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -2276,6 +2276,18 @@
>
> lsm.debug [SECURITY] Enable LSM initialization debugging output.
>
> + lsm.disable=lsm1,...,lsmN
> + [SECURITY] Comma-separated list of LSMs to disable
> + at boot time. This overrides "lsm.enable=",
> + CONFIG_LSM_ENABLE, and any per-LSM CONFIGs and boot
> + parameters.
> +
> + lsm.enable=lsm1,...,lsmN
> + [SECURITY] Comma-separated list of LSMs to enable
> + at boot time. This overrides any omissions from
> + CONFIG_LSM_ENABLE, and any per-LSM CONFIGs and
> + boot parameters.
> +
> machvec= [IA-64] Force the use of a particular machine-vector
> (machvec) in a generic kernel.
> Example: machvec=hpzx1_swiotlb
> diff --git a/security/Kconfig b/security/Kconfig
> index 71306b046270..1a82a006cc62 100644
> --- a/security/Kconfig
> +++ b/security/Kconfig
> @@ -282,7 +282,9 @@ config LSM_ENABLE
> help
> A comma-separate list of LSMs to enable by default at boot. The
> default is "all", to enable all LSM modules at boot. Any LSMs
> - not listed here will be disabled by default.
> + not listed here will be disabled by default. This can be
> + changed with the "lsm.enable=" and "lsm.disable=" boot
> + parameters.
>
> endmenu
>
> diff --git a/security/security.c b/security/security.c
> index 7ecb9879a863..456a3f73bc36 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -44,6 +44,8 @@ char *lsm_names;
> /* Boot-time LSM user choice */
> static __initdata char chosen_lsm[SECURITY_NAME_MAX + 1] =
> CONFIG_DEFAULT_SECURITY;
> +static __initdata const char *chosen_lsm_enable;
> +static __initdata const char *chosen_lsm_disable;
>
> static __initconst const char * const builtin_lsm_enable = CONFIG_LSM_ENABLE;
>
> @@ -185,6 +187,10 @@ static void __init prepare_lsm_enable(void)
> {
> /* Prepare defaults. */
> parse_lsm_enable(builtin_lsm_enable, default_enabled, true);
> +
> + /* Process "lsm.enable=" and "lsm.disable=", if given. */
> + parse_lsm_enable(chosen_lsm_enable, set_enabled, true);
> + parse_lsm_enable(chosen_lsm_disable, set_enabled, false);
> }
>
> /**
> @@ -240,6 +246,22 @@ static int __init enable_debug(char *str)
> }
> __setup("lsm.debug", enable_debug);
>
> +/* Explicitly enable a list of LSMs. */
> +static int __init enable_lsm(char *str)
> +{
> + chosen_lsm_enable = str;
> + return 1;
> +}
> +__setup("lsm.enable=", enable_lsm);
> +
> +/* Explicitly disable a list of LSMs. */
> +static int __init disable_lsm(char *str)
> +{
> + chosen_lsm_disable = str;
> + return 1;
> +}
> +__setup("lsm.disable=", disable_lsm);
> +
> static bool match_last_lsm(const char *list, const char *lsm)
> {
> const char *last;
>
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