linux-kernel - Re: [PATCH v7 02/11] LSM: Maintain a table of LSM attribute data

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Date:   Wed, 29 Mar 2023 21:10:30 -0400
From:   Paul Moore <paul@...l-moore.com>
To:     Casey Schaufler <casey@...aufler-ca.com>
Cc:     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 v7 02/11] LSM: Maintain a table of LSM attribute data

On Wed, Mar 15, 2023 at 6:47 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, 38 insertions(+), 8 deletions(-)

...

> diff --git a/security/security.c b/security/security.c
> index 58828a326024..aa84b1cf4253 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -513,6 +531,16 @@ 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. Landlock is one such case.
> +        */
> +       if (lsm_active_cnt == 0 || lsm_idlist[lsm_active_cnt - 1] != lsmid)
> +               lsm_idlist[lsm_active_cnt++] = lsmid;
> +
> +       if (lsm_active_cnt > LSM_COUNT)
> +               panic("%s Too many LSMs registered.\n", __func__);

In addition to the fixes needed to resolve the bug identified by the
kernel test robot, I think it might be wise to do the @lsm_active_cnt
check *before* potentially adding it to the @lsm_idlist array.

>         for (i = 0; i < count; i++) {
>                 hooks[i].lsmid = lsmid;
>                 hlist_add_tail_rcu(&hooks[i].list, hooks[i].head);
> --
> 2.39.2

--
paul-moore.com