linux-kernel - Re: [PATCH v5 2/8] LSM: Maintain a table of LSM attribute data

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Message-ID: <CAHC9VhTaySsuvkj0U9Jbp405+WoRfhtq+ib5ynO-a9BeM+a5Ew@mail.gmail.com>
Date:   Wed, 11 Jan 2023 16:01:02 -0500
From:   Paul Moore <paul@...l-moore.com>
To:     Casey Schaufler <casey@...aufler-ca.com>
Cc:     casey.schaufler@...el.com, linux-security-module@...r.kernel.org,
        jmorris@...ei.org, keescook@...omium.org,
        john.johansen@...onical.com, penguin-kernel@...ove.sakura.ne.jp,
        stephen.smalley.work@...il.com, linux-kernel@...r.kernel.org,
        linux-api@...r.kernel.org, mic@...ikod.net
Subject: Re: [PATCH v5 2/8] LSM: Maintain a table of LSM attribute data

On Mon, Jan 9, 2023 at 1:07 PM Casey Schaufler <casey@...aufler-ca.com> 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@...aufler-ca.com>
> ---
>  include/linux/security.h |  2 ++
>  security/security.c      | 44 +++++++++++++++++++++++++++++++++-------
>  2 files changed, 39 insertions(+), 7 deletions(-)
>
> diff --git a/include/linux/security.h b/include/linux/security.h
> index 5b67f208f7de..33ed1860b96f 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 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 07a8fe7f92bf..a590fa98ddd6 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -28,12 +28,29 @@
>  #include <linux/backing-dev.h>
>  #include <linux/string.h>
>  #include <linux/msg.h>
> +#include <uapi/linux/lsm.h>
>  #include <net/flow.h>
>
>  #define MAX_LSM_EVM_XATTR      2
>
> -/* 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_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_SECURITY_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
> @@ -90,7 +107,7 @@ static __initdata const char *chosen_major_lsm;
>  static __initconst const char * const builtin_lsm_order = CONFIG_LSM;
>
>  /* Ordered list of LSMs to initialize. */
> -static __initdata struct lsm_info **ordered_lsms;
> +static __initdata struct lsm_info *ordered_lsms[LSM_COUNT + 1];

I'm guessing this 'LSM_COUNT + 1' logic is basically just copied from
ordered_lsm_init() - which is okay - but can you remind me why it is
'LSM_COUNT + 1' and not just 'LSM_COUNT'?  Based on the LSM_COUNT
macro above it seems like LSM_COUNT should be enough, no?

>  static __initdata struct lsm_info *exclusive;
>
>  static __initdata bool debug;
> @@ -341,13 +358,16 @@ static void __init report_lsm_order(void)
>         pr_cont("\n");
>  }
>
> +/*
> + * Current index to use while initializing the lsm id list.
> + */
> +u32 lsm_active_cnt __lsm_ro_after_init;
> +struct lsm_id *lsm_idlist[LSM_COUNT] __lsm_ro_after_init;
> +
>  static void __init ordered_lsm_init(void)
>  {
>         struct lsm_info **lsm;
>
> -       ordered_lsms = kcalloc(LSM_COUNT + 1, sizeof(*ordered_lsms),
> -                               GFP_KERNEL);
> -
>         if (chosen_lsm_order) {
>                 if (chosen_major_lsm) {
>                         pr_warn("security=%s is ignored because it is superseded by lsm=%s\n",
> @@ -388,7 +408,7 @@ static void __init ordered_lsm_init(void)
>         for (lsm = ordered_lsms; *lsm; lsm++)
>                 initialize_lsm(*lsm);
>
> -       kfree(ordered_lsms);
> +       init_debug("lsm count            = %d\n", lsm_active_cnt);
>  }

Given 86ef3c735ec8 ("LSM: Better reporting of actual LSMs at boot"),
is this needed?

--
paul-moore.com