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References: <20230315224704.2672-1-casey@schaufler-ca.com> <20230315224704.2672-6-casey@schaufler-ca.com>
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From:   Paul Moore <paul@paul-moore.com>
Date:   Wed, 29 Mar 2023 21:12:51 -0400
Message-ID: <CAHC9VhR8WycNQ_mxeB9icN6ddQKtNCkkzTPtdJJKDW-qQXL3ug@mail.gmail.com>
Subject: Re: [PATCH v7 05/11] LSM: Create lsm_list_modules system call
To:     Casey Schaufler <casey@schaufler-ca.com>
Cc:     linux-security-module@vger.kernel.org, jmorris@namei.org,
        keescook@chromium.org, john.johansen@canonical.com,
        penguin-kernel@i-love.sakura.ne.jp, stephen.smalley.work@gmail.com,
        linux-kernel@vger.kernel.org, linux-api@vger.kernel.org,
        mic@digikod.net
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On Wed, Mar 15, 2023 at 6:48=E2=80=AFPM Casey Schaufler <casey@schaufler-ca=
.com> wrote:
>
> Create a system call to report the list of Linux Security Modules
> that are active on the system. The list is provided as an array
> of LSM ID numbers.
>
> The calling application can use this list determine what LSM
> specific actions it might take. That might include chosing an
> output format, determining required privilege or bypassing
> security module specific behavior.
>
> Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
> ---
>  Documentation/userspace-api/lsm.rst |  3 +++
>  include/linux/syscalls.h            |  1 +
>  kernel/sys_ni.c                     |  1 +
>  security/lsm_syscalls.c             | 39 +++++++++++++++++++++++++++++
>  4 files changed, 44 insertions(+)

...

> diff --git a/security/lsm_syscalls.c b/security/lsm_syscalls.c
> index feee31600219..6efbe244d304 100644
> --- a/security/lsm_syscalls.c
> +++ b/security/lsm_syscalls.c
> @@ -53,3 +53,42 @@ SYSCALL_DEFINE4(lsm_get_self_attr, unsigned int, attr,=
 struct lsm_ctx __user *,
>  {
>         return security_getselfattr(attr, ctx, size, flags);
>  }
> +
> +/**
> + * sys_lsm_list_modules - Return a list of the active security modules
> + * @ids: the LSM module ids
> + * @size: size of @ids, updated on return
> + * @flags: reserved for future use, must be zero
> + *
> + * Returns a list of the active LSM ids. On success this function
> + * returns the number of @ids array elements. This value may be zero
> + * if there are no LSMs active. If @size is insufficient to contain
> + * the return data -E2BIG is returned and @size is set to the minimum
> + * required size. In all other cases a negative value indicating the
> + * error is returned.
> + */
> +SYSCALL_DEFINE3(lsm_list_modules, u64 __user *, ids, size_t __user *, si=
ze,
> +               u32, flags)
> +{
> +       size_t total_size =3D lsm_active_cnt * sizeof(*ids);
> +       size_t usize;
> +       int i;
> +
> +       if (flags)
> +               return -EINVAL;

In other patches in this patchset you use 'if (flags !=3D 0)'; I don't
care too much which approach you take, but please be consistent.

Actually, I guess you might as well just go with 'if (flags)' since
I'm pretty sure someone later down the line will end up wasting
reviewer time by changing '(flags !=3D 0)' into '(flags)' ...


> +       if (get_user(usize, size))
> +               return -EFAULT;
> +
> +       if (put_user(total_size, size) !=3D 0)
> +               return -EFAULT;
> +
> +       if (usize < total_size)
> +               return -E2BIG;
> +
> +       for (i =3D 0; i < lsm_active_cnt; i++)
> +               if (put_user(lsm_idlist[i]->id, ids++))
> +                       return -EFAULT;
> +
> +       return lsm_active_cnt;
> +}
> --
> 2.39.2

--
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