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

[Paul Moore]

On Mar 19, 2025 Casey Schaufler <casey at schaufler-ca.com> 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 at schaufler-ca.com>
> Tested-by: Fan Wu <wufan at kernel.org>
> ---
>  include/linux/security.h     |  6 ++++--
>  kernel/audit.c               |  4 ++--
>  kernel/auditsc.c             |  8 +++++---
>  net/netlabel/netlabel_user.c |  3 ++-
>  security/security.c          | 13 +++++++++++--
>  5 files changed, 24 insertions(+), 10 deletions(-)

...

> 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)
> +			continue;

As mentioned in the v2 review:

 "Let's use LSM_ID_UNDEF instead of 0 here to add some clarity on
  how an undefined ID is handled.  The function header comment
  should also explain the special handling when LSM_ID_UNDEF is
  specified."

https://lore.kernel.org/audit/5838489ecd5186900315f8f6c6e02f22@paul-moore.com/

> +		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

--
paul-moore.com