Re: [PATCH v13 02/11] LSM: Maintain a table of LSM attribute data

["Mickaël Salaün" <mic@digikod.net>]

On Wed, Aug 02, 2023 at 10:44:25AM -0700, Casey Schaufler wrote:
> As LSMs are registered add their lsm_id pointers to a table.
> This will be used later for attribute reporting.
> 
> Determine the number of possible security modules based on
> their respective CONFIG options. This allows the number to be
> known at build time. This allows data structures and tables
> to use the constant.
> 
> Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
> Reviewed-by: Kees Cook <keescook@chromium.org>
> Reviewed-by: Serge Hallyn <serge@hallyn.com>
> ---
>  include/linux/security.h |  2 ++
>  security/security.c      | 37 +++++++++++++++++++++++++++++++++++++
>  2 files changed, 39 insertions(+)
> 
> diff --git a/include/linux/security.h b/include/linux/security.h
> index 32828502f09e..a20a4ceda6d9 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -138,6 +138,8 @@ enum lockdown_reason {
>  };
>  
>  extern const char *const lockdown_reasons[LOCKDOWN_CONFIDENTIALITY_MAX+1];
> +extern u32 lsm_active_cnt;
> +extern const struct lsm_id *lsm_idlist[];
>  
>  /* These functions are in security/commoncap.c */
>  extern int cap_capable(const struct cred *cred, struct user_namespace *ns,
> diff --git a/security/security.c b/security/security.c
> index feaae09581dc..87b70a55a028 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -36,6 +36,25 @@
>  /* How many LSMs were built into the kernel? */
>  #define LSM_COUNT (__end_lsm_info - __start_lsm_info)
>  
> +/*
> + * How many LSMs are built into the kernel as determined at
> + * build time. Used to determine fixed array sizes.
> + * The capability module is accounted for by CONFIG_SECURITY
> + */
> +#define LSM_CONFIG_COUNT ( \
> +	(IS_ENABLED(CONFIG_SECURITY) ? 1 : 0) + \
> +	(IS_ENABLED(CONFIG_SECURITY_SELINUX) ? 1 : 0) + \
> +	(IS_ENABLED(CONFIG_SECURITY_SMACK) ? 1 : 0) + \
> +	(IS_ENABLED(CONFIG_SECURITY_TOMOYO) ? 1 : 0) + \
> +	(IS_ENABLED(CONFIG_IMA) ? 1 : 0) + \
> +	(IS_ENABLED(CONFIG_SECURITY_APPARMOR) ? 1 : 0) + \
> +	(IS_ENABLED(CONFIG_SECURITY_YAMA) ? 1 : 0) + \
> +	(IS_ENABLED(CONFIG_SECURITY_LOADPIN) ? 1 : 0) + \
> +	(IS_ENABLED(CONFIG_SECURITY_SAFESETID) ? 1 : 0) + \
> +	(IS_ENABLED(CONFIG_SECURITY_LOCKDOWN_LSM) ? 1 : 0) + \
> +	(IS_ENABLED(CONFIG_BPF_LSM) ? 1 : 0) + \
> +	(IS_ENABLED(CONFIG_SECURITY_LANDLOCK) ? 1 : 0))
> +
>  /*
>   * These are descriptions of the reasons that can be passed to the
>   * security_locked_down() LSM hook. Placing this array here allows
> @@ -245,6 +264,12 @@ static void __init initialize_lsm(struct lsm_info *lsm)
>  	}
>  }
>  
> +/*
> + * Current index to use while initializing the lsm id list.
> + */
> +u32 lsm_active_cnt __ro_after_init;
> +const struct lsm_id *lsm_idlist[LSM_CONFIG_COUNT] __ro_after_init;

I guess __ro_after_init is superfluous here.

Reviewed-by: Mickaël Salaün <mic@digikod.net>


> +
>  /* Populate ordered LSMs list from comma-separated LSM name list. */
>  static void __init ordered_lsm_parse(const char *order, const char *origin)
>  {
> @@ -521,6 +546,18 @@ void __init security_add_hooks(struct security_hook_list *hooks, int count,
>  {
>  	int i;
>  
> +	/*
> +	 * A security module may call security_add_hooks() more
> +	 * than once during initialization, and LSM initialization
> +	 * is serialized. Landlock is one such case.
> +	 * Look at the previous entry, if there is one, for duplication.
> +	 */
> +	if (lsm_active_cnt == 0 || lsm_idlist[lsm_active_cnt - 1] != lsmid) {
> +		if (lsm_active_cnt >= LSM_CONFIG_COUNT)
> +			panic("%s Too many LSMs registered.\n", __func__);
> +		lsm_idlist[lsm_active_cnt++] = lsmid;
> +	}
> +
>  	for (i = 0; i < count; i++) {
>  		hooks[i].lsmid = lsmid;
>  		hlist_add_tail_rcu(&hooks[i].list, hooks[i].head);
> -- 
> 2.41.0
>