Re: [PATCH v5 5/8] LSM: Create lsm_module_list system call

[Paul Moore]

On Mon, Jan 9, 2023 at 1:09 PM Casey Schaufler <casey@xxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxx>
> ---
>  Documentation/userspace-api/lsm.rst |  3 +++
>  include/linux/syscalls.h            |  1 +
>  kernel/sys_ni.c                     |  1 +
>  security/lsm_syscalls.c             | 41 +++++++++++++++++++++++++++++
>  4 files changed, 46 insertions(+)

...

> diff --git a/security/lsm_syscalls.c b/security/lsm_syscalls.c
> index 55e8bf61ac8a..92af1fcaa654 100644
> --- a/security/lsm_syscalls.c
> +++ b/security/lsm_syscalls.c
> @@ -180,3 +180,44 @@ SYSCALL_DEFINE3(lsm_get_self_attr,
>         kfree(final);
>         return rc;
>  }
> +
> +/**
> + * sys_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.
> + */
> +SYSCALL_DEFINE3(lsm_module_list,
> +               u32 __user *, ids,
> +               size_t __user *, size,
> +               u64, flags)
> +{
> +       size_t total_size = lsm_active_cnt * sizeof(*ids);
> +       size_t usize;
> +       int i;
> +
> +       if (flags)
> +               return -EINVAL;
> +
> +       if (get_user(usize, size))
> +               return -EFAULT;
> +
> +       if (put_user(total_size, size) != 0)
> +               return -EFAULT;
> +
> +       if (usize < total_size)
> +               return -E2BIG;
> +
> +       for (i = 0; i < lsm_active_cnt; i++)
> +               if (put_user(lsm_idlist[i]->id, ids++))
> +                       return -EFAULT;
> +
> +       return lsm_active_cnt;
> +}

Similar to my comments in 4/8, I would probably create a new LSM hook
for this syscall so that the lsm_ctx is passed through the LSM layer
directly to the target LSM:

  int security_sys_setselfattr(u64 attr, struct lsm_ctx __user *ctx,
size_t len);

--
paul-moore.com