linux-kernel - Re: [PATCH v1 7/8] LSM: Create lsm_module

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Message-ID: <CAHC9VhQ5Jrt3Ns+m7DFZ+_pP81AWqSx588HMZR+7MUuMfSZoig@mail.gmail.com>
Date:   Wed, 9 Nov 2022 18:35:22 -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 v1 7/8] LSM: Create lsm_module_list system call

On Tue, Oct 25, 2022 at 2:48 PM Casey Schaufler <casey@...aufler-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@...aufler-ca.com>
> ---
>  include/linux/syscalls.h |  1 +
>  kernel/sys_ni.c          |  1 +
>  security/lsm_syscalls.c  | 38 ++++++++++++++++++++++++++++++++++++++
>  3 files changed, 40 insertions(+)

...

> diff --git a/security/lsm_syscalls.c b/security/lsm_syscalls.c
> index da0fab7065e2..cd5db370b974 100644
> --- a/security/lsm_syscalls.c
> +++ b/security/lsm_syscalls.c
> @@ -154,3 +154,41 @@ SYSCALL_DEFINE3(lsm_self_attr,
>         kfree(final);
>         return rc;
>  }
> +
> +/**
> + * lsm_module_list - 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.
> + */

Let's make a promise that for this syscall we will order the LSM IDs
in the array in the same order as which they are configured/executed.
I'm doubtful that only a *very* small number of applications will care
about this (if any), but this is something we can do so let's do it
now while we can.

> +SYSCALL_DEFINE3(lsm_module_list,
> +               unsigned int __user *, ids,
> +               size_t __user *, size,
> +               unsigned int, flags)

--
paul-moore.com