Re: [PATCH v3 1/9] LSM: Identify modules by more than name

[Greg KH <gregkh@linuxfoundation.org>]

On Wed, Nov 23, 2022 at 12:15:44PM -0800, Casey Schaufler wrote:
> Create a struct lsm_id to contain identifying information
> about Linux Security Modules (LSMs). At inception this contains
> the name of the module and an identifier associated with the
> security module. Change the security_add_hooks() interface to
> use this structure. Change the individual modules to maintain
> their own struct lsm_id and pass it to security_add_hooks().
> 
> The values are for LSM identifiers are defined in a new UAPI
> header file linux/lsm.h. Each existing LSM has been updated to
> include it's LSMID in the lsm_id.
> 
> The LSM ID values are sequential, with the oldest module
> LSM_ID_CAPABILITY being the lowest value and the existing modules
> numbered in the order they were included in the main line kernel.
> This is an arbitrary convention for assigning the values, but
> none better presents itself. The value 0 is defined as being invalid.
> The values 1-99 are reserved for any special case uses which may
> arise in the future.

What would be a "special case" that deserves a lower number?

> diff --git a/security/bpf/hooks.c b/security/bpf/hooks.c
> index e5971fa74fd7..20983ae8d31f 100644
> --- a/security/bpf/hooks.c
> +++ b/security/bpf/hooks.c
> @@ -5,6 +5,7 @@
>   */
>  #include <linux/lsm_hooks.h>
>  #include <linux/bpf_lsm.h>
> +#include <uapi/linux/lsm.h>
>  
>  static struct security_hook_list bpf_lsm_hooks[] __lsm_ro_after_init = {
>  	#define LSM_HOOK(RET, DEFAULT, NAME, ...) \
> @@ -15,9 +16,19 @@ static struct security_hook_list bpf_lsm_hooks[] __lsm_ro_after_init = {
>  	LSM_HOOK_INIT(task_free, bpf_task_storage_free),
>  };
>  
> +/*
> + * slot has to be LSMBLOB_NEEDED because some of the hooks
> + * supplied by this module require a slot.
> + */
> +struct lsm_id bpf_lsmid __lsm_ro_after_init = {
> +	.lsm = "bpf",
> +	.id = LSM_ID_BPF,
> +};

I do not understand this comment, what is LSMBLOB_NEEDED and how does
that relate to the struct lsm_id?

thanks,

greg k-h