Re: [PATCH v2 3/6] LSM: security_lsmblob_to_secctx module selection

[Paul Moore <paul@paul-moore.com>]

On Mar  7, 2025 Casey Schaufler <casey@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@schaufler-ca.com>
> ---
>  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
> @@ -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)

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.

--
paul-moore.com