Re: [PATCH v2 1/2] SELinux: reduce overhead of mls_level_isvalid() function call

[Stephen Smalley <sds@tycho.nsa.gov>]

On 06/05/2013 05:15 PM, Waiman Long wrote:
> diff --git a/security/selinux/ss/ebitmap.c b/security/selinux/ss/ebitmap.c
> index 30f119b..100b3e6 100644
> --- a/security/selinux/ss/ebitmap.c
> +++ b/security/selinux/ss/ebitmap.c
> @@ -213,7 +213,12 @@ netlbl_import_failure:
>   }
>   #endif /* CONFIG_NETLABEL */
>
> -int ebitmap_contains(struct ebitmap *e1, struct ebitmap *e2)
> +/*
> + * Check to see if all the bits set in e2 are also set in e1. Optionally,
> + * if last_e2bit is non-zero, the highest set bit in e2 cannot exceed
> + * last_e2bit.
> + */
> +int ebitmap_contains(struct ebitmap *e1, struct ebitmap *e2, u32 last_e2bit)
>   {
>   	struct ebitmap_node *n1, *n2;
>   	int i;
> @@ -223,6 +228,33 @@ int ebitmap_contains(struct ebitmap *e1, struct ebitmap *e2)
>
>   	n1 = e1->node;
>   	n2 = e2->node;
> +	if (last_e2bit) {
> +		while (n1 && n2 && (n1->startbit <= n2->startbit)) {
> +			int lastsetbit = -1;
> +
> +			if (n1->startbit < n2->startbit) {
> +				n1 = n1->next;
> +				continue;
> +			}
> +			for (i = EBITMAP_UNIT_NUMS - 1; i >= 0; i--) {
> +				if (!n2->maps[i])
> +					continue;
> +				if ((n1->maps[i] & n2->maps[i]) != n2->maps[i])
> +					return 0;
> +				if (lastsetbit < 0)
> +					lastsetbit = n2->startbit +
> +						     i * EBITMAP_UNIT_SIZE +
> +						     __fls(n2->maps[i]);
> +			}
> +			if ((lastsetbit >= 0) && (lastsetbit > last_e2bit))
> +				return 0;
> +
> +			n1 = n1->next;
> +			n2 = n2->next;
> +		}
> +		goto done;
> +	}
> +

Can't you unify this logic with the nearly identical logic below?

>   	while (n1 && n2 && (n1->startbit <= n2->startbit)) {
>   		if (n1->startbit < n2->startbit) {
>   			n1 = n1->next;
> @@ -237,6 +269,7 @@ int ebitmap_contains(struct ebitmap *e1, struct ebitmap *e2)
>   		n2 = n2->next;
>   	}
>
> +done:
>   	if (n2)
>   		return 0;
>