Re: [PATCH security-next v2 19/26] LSM: Introduce CONFIG_LSM_ORDER

[Casey Schaufler]

On 9/20/2018 9:23 AM, Kees Cook wrote:
> This provides a way to declare LSM initialization order via Kconfig.
>
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
> ---
>  security/Kconfig    | 11 +++++++++++
>  security/security.c | 38 +++++++++++++++++++++++++++++++++++---
>  2 files changed, 46 insertions(+), 3 deletions(-)
>
> diff --git a/security/Kconfig b/security/Kconfig
> index 27d8b2688f75..de8202886c1d 100644
> --- a/security/Kconfig
> +++ b/security/Kconfig
> @@ -276,5 +276,16 @@ config DEFAULT_SECURITY
>  	default "apparmor" if DEFAULT_SECURITY_APPARMOR
>  	default "" if DEFAULT_SECURITY_DAC
>  
> +config LSM_ORDER
> +	string "Default initialization order of builtin LSMs"
> +	default "integrity"

I would like to see the default spelled out rather than
provided implicitly.

  +	  default "integrity,yama,loadpin,selinux,smack,apparmor,tomoyo"

> +	help
> +	  A comma-separated list of LSMs, in initialization order.
> +	  Any LSMs left off this list will be link-order initialized
> +	  after any listed LSMs. Any LSMs listed here but not built in
> +	  the kernel will be ignored.

This should also describe what will happen if you include multiple
major modules in the list.

> +
> +	  If unsure, leave this as the default.
> +
>  endmenu
>  
> diff --git a/security/security.c b/security/security.c
> index 2541a512a0f7..063ee2466e58 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -44,6 +44,8 @@ char *lsm_names;
>  /* Boot-time LSM user choice */
>  static __initdata const char *chosen_major_lsm;
>  
> +static __initconst const char * const builtin_lsm_order = CONFIG_LSM_ORDER;
> +
>  /* Ordered list of LSMs to initialize. */
>  static __initdata struct lsm_info **ordered_lsms;
>  
> @@ -108,14 +110,44 @@ static void __init append_ordered_lsm(struct lsm_info *lsm, const char *from)
>  		   (!lsm->enabled || *lsm->enabled) ? "en" : "dis");
>  }
>  
> -/* Populate ordered LSMs list from hard-coded list of LSMs. */
> +/* Populate ordered LSMs list from given string. */
> +static void __init parse_lsm_order(const char *order, const char *origin)
> +{
> +	struct lsm_info *lsm;
> +	char *sep, *name, *next;
> +
> +	sep = kstrdup(order, GFP_KERNEL);
> +	next = sep;
> +	/* Walk the list, looking for matching LSMs. */
> +	while ((name = strsep(&next, ",")) != NULL) {
> +		bool found = false;
> +
> +		for (lsm = __start_lsm_info; lsm < __end_lsm_info; lsm++) {
> +			if ((lsm->flags & LSM_FLAG_LEGACY_MAJOR) == 0 &&
> +			    strcmp(lsm->name, name) == 0) {
> +				append_ordered_lsm(lsm, origin);
> +				found = true;
> +			}
> +		}
> +
> +		if (!found)
> +			init_debug("%s ignored: %s\n", origin, name);
> +	}
> +	kfree(sep);
> +}
> +
> +/* Populate ordered LSMs list from builtin list of LSMs. */
>  static void __init prepare_lsm_order(void)
>  {
>  	struct lsm_info *lsm;
>  
> +	/* Parse order from builtin list. */
> +	parse_lsm_order(builtin_lsm_order, "builtin");
> +
> +	/* Add any missing LSMs, in link order. */
>  	for (lsm = __start_lsm_info; lsm < __end_lsm_info; lsm++) {
> -		if (strcmp(lsm->name, "integrity") == 0)
> -			append_ordered_lsm(lsm, "builtin");
> +		if ((lsm->flags & LSM_FLAG_LEGACY_MAJOR) == 0)
> +			append_ordered_lsm(lsm, "link-time");
>  	}
>  }
>