Re: [PATCH v3 2/5] LSM: security_lsmblob_to_secctx module selection

[Fan Wu]

On Wed, Mar 19, 2025 at 7:50 PM Casey Schaufler <casey@xxxxxxxxxxxxxxxx> wrote:
>
> Add a parameter lsmid to security_lsmblob_to_secctx() to identify which
> of the security modules that may be active should provide the security
> context. If the value of lsmid is LSM_ID_UNDEF the first LSM providing
> a hook is used. security_secid_to_secctx() is unchanged, and will
> always report the first LSM providing a hook.
>
> Signed-off-by: Casey Schaufler <casey@xxxxxxxxxxxxxxxx>
...
> diff --git a/security/security.c b/security/security.c
> index 143561ebc3e8..55f9c7ad3f89 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -4312,6 +4312,7 @@ EXPORT_SYMBOL(security_ismaclabel);
>   * security_secid_to_secctx() - Convert a secid to a secctx
>   * @secid: secid
>   * @cp: the LSM context
> + * @lsmid: which security module to report
>   *
>   * Convert secid to security context.  If @cp is NULL the length of the
>   * result will be returned, but no data will be returned.  This
> @@ -4338,9 +4339,17 @@ EXPORT_SYMBOL(security_secid_to_secctx);
>   *
>   * Return: Return length of data on success, error on failure.
>   */
> -int security_lsmprop_to_secctx(struct lsm_prop *prop, struct lsm_context *cp)
> +int security_lsmprop_to_secctx(struct lsm_prop *prop, struct lsm_context *cp,
> +                              int lsmid)
>  {
> -       return call_int_hook(lsmprop_to_secctx, prop, cp);
> +       struct lsm_static_call *scall;
> +
> +       lsm_for_each_hook(scall, lsmprop_to_secctx) {
> +               if (lsmid != 0 && lsmid != scall->hl->lsmid->id)

It took me some time to figure out why if LSM_ID_UNDEF is passed the
first LSM providing a hook is used, might be better to change it to:

               if (lsmid != LSM_ID_UNDEF && lsmid != scall->hl->lsmid->id)

Otherwise, it works as described. I'm working on adding a new IPE
property based on SELinux file labels, and this just came up as I
needed it. Thank you.

Tested-by: Fan Wu <wufan@xxxxxxxxxx>

> +                       continue;
> +               return scall->hl->hook.lsmprop_to_secctx(prop, cp);
> +       }
> +       return LSM_RET_DEFAULT(lsmprop_to_secctx);
>  }
>  EXPORT_SYMBOL(security_lsmprop_to_secctx);
>
> --
> 2.47.0
>
>