linux-kernel - Re: [PATCH] LSM: Ignore "security=" when "lsm=" is specified

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Message-ID: <CAGXu5jJ86XosW71111EaaSKcVwzw+UYvi4j619KwoBn=DNwrNw@mail.gmail.com>
Date:   Mon, 11 Feb 2019 16:26:02 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     James Morris <jmorris@...ei.org>,
        linux-security-module <linux-security-module@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] LSM: Ignore "security=" when "lsm=" is specified

On Mon, Feb 11, 2019 at 4:21 PM Tetsuo Handa
<penguin-kernel@...ove.sakura.ne.jp> wrote:
>
> Kees Cook wrote:
> > To avoid potential confusion, explicitly ignore "security=" when "lsm=" is
> > used on the command line, and report that it is happening.
>
> To maintain the existing behavior of CONFIG_DEFAULT_SECURITY, I also suggest this change.
> This saves e.g. Ubuntu users who are using only AppArmor from explicitly specifying
> security=apparmor when they don't want to enable other LSM_FLAG_LEGACY_MAJOR modules.

No, this completely disables the purpose of lsm=

I don't understand the use-case you're concerned about?

-Kees

>
> ---
>  security/Kconfig    | 37 +++++++++++++++++++++++++++++++++++++
>  security/security.c |  5 ++++-
>  2 files changed, 41 insertions(+), 1 deletion(-)
>
> diff --git a/security/Kconfig b/security/Kconfig
> index 9555f49..6a40995 100644
> --- a/security/Kconfig
> +++ b/security/Kconfig
> @@ -250,5 +250,42 @@ config LSM
>
>           If unsure, leave this as the default.
>
> +choice
> +       prompt "Default exclusive security module"
> +       default DEFAULT_SECURITY_SELINUX if SECURITY_SELINUX
> +       default DEFAULT_SECURITY_SMACK if SECURITY_SMACK
> +       default DEFAULT_SECURITY_TOMOYO if SECURITY_TOMOYO
> +       default DEFAULT_SECURITY_APPARMOR if SECURITY_APPARMOR
> +       default DEFAULT_SECURITY_DAC
> +
> +       help
> +         The security module where only one of these modules should be enabled if
> +         neither the "security=" parameter nor the "lsm=" parameter is specified.
> +
> +       config DEFAULT_SECURITY_SELINUX
> +               bool "SELinux" if SECURITY_SELINUX=y
> +
> +       config DEFAULT_SECURITY_SMACK
> +               bool "Simplified Mandatory Access Control" if SECURITY_SMACK=y
> +
> +       config DEFAULT_SECURITY_TOMOYO
> +               bool "TOMOYO" if SECURITY_TOMOYO=y
> +
> +       config DEFAULT_SECURITY_APPARMOR
> +               bool "AppArmor" if SECURITY_APPARMOR=y
> +
> +       config DEFAULT_SECURITY_DAC
> +               bool "Unix Discretionary Access Controls"
> +
> +endchoice
> +
> +config DEFAULT_SECURITY
> +       string
> +       default "selinux" if DEFAULT_SECURITY_SELINUX
> +       default "smack" if DEFAULT_SECURITY_SMACK
> +       default "tomoyo" if DEFAULT_SECURITY_TOMOYO
> +       default "apparmor" if DEFAULT_SECURITY_APPARMOR
> +       default "" if DEFAULT_SECURITY_DAC
> +
>  endmenu
>
> diff --git a/security/security.c b/security/security.c
> index e6153ed..c44e3cd 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -294,8 +294,11 @@ static void __init ordered_lsm_init(void)
>                         chosen_major_lsm = NULL;
>                 }
>                 ordered_lsm_parse(chosen_lsm_order, "cmdline");
> -       } else
> +       } else {
> +               if (!chosen_major_lsm)
> +                       chosen_major_lsm = CONFIG_DEFAULT_SECURITY;
>                 ordered_lsm_parse(builtin_lsm_order, "builtin");
> +       }
>
>         for (lsm = ordered_lsms; *lsm; lsm++)
>                 prepare_lsm(*lsm);
> --
> 1.8.3.1
>


-- 
Kees Cook