Re: libselinux: add selinux_status_* interfaces for /selinux/status

[KaiGai Kohei <kaigai@ak.jp.nec.com>]

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I updated my patch to reference /selinux/status entry.

The interface of selinux_status_open() and selinux_status_updated() was
revised to eliminate an argument of 'last_seqlock' that holds a sequence
value when we call this function last time.
At first, I tried to give this storage externally for thread-safing, but
fallback routine was not thread-safe anyway, so it became nonsense.

The attached status.c is an example program to call these APIs.

Any comments please. Thanks,

(2011/01/22 22:42), Kohei KaiGai wrote:
> The attached patch adds several interfaces to reference /selinux/status
> according to sequential-lock logic.
> 
> selinux_status_open() open the kernel status page and mmap it with
> read-only mode, or open netlink socket as a fallback in older kernels.
> 
> Then, we can obtain status information from the mmap'ed page using
> selinux_status_updated(), selinux_status_getenfoce(),
> selinux_status_policyload() or selinux_status_deny_unknown().
> 
> It enables to help to implement userspace avc with heavy access control
> decision; that we cannot ignore the cost to communicate with kernel for
> validation of userspace caches.
> 
> Thanks,
-- 
KaiGai Kohei <kaigai@ak.jp.nec.com>

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#include <stdio.h>
#include <selinux/avc.h>

int main(int argc, char *argv[])
{
	int	fallback = 1;
	int	rc;

	if (argc > 1)
		fallback = atoi(argv[1]);

	rc = selinux_status_open(1);
	if (rc < 0)
		return 1;

	printf("-- selinux kernel status page %s--\n"
	       "policyload = %d, enforcing = %d, deny_unknown = %d\n",
	       !rc ? "" : "(netlink fallback)",
	       selinux_status_policyload(),
	       selinux_status_getenforce(),
	       selinux_status_deny_unknown());

	while (1)
	{
		usleep(100000);

		if (!selinux_status_updated())
			continue;

		printf("policyload = %d, enforcing = %d, deny_unknown = %d\n",
		       selinux_status_policyload(),
		       selinux_status_getenforce(),
		       selinux_status_deny_unknown());
	}
	return 0;
}