[PATCH] keys: allocate key serial numbers randomly

#include <linux/slab.h>

#include <linux/security.h>

#include <linux/workqueue.h>

#include <linux/random.h>

#include <linux/err.h>

#include "internal.h"

static kmem_cache_t	*key_jar;

static key_serial_t	key_serial_next = 3;

struct rb_root		key_serial_tree; /* tree of keys indexed by serial */

DEFINE_SPINLOCK(key_serial_lock);

/*****************************************************************************/

/*

 * assign a key the next unique serial number

 * - we work through all the serial numbers between 2 and 2^31-1 in turn and

 *   then wrap

 * - these are assigned randomly to avoid security issues through covert

 *   channel problems

 */

static inline void key_alloc_serial(struct key *key)

{

	struct rb_node *parent, **p;

	struct key *xkey;

	spin_lock(&key_serial_lock);

	/* propose a likely serial number and look for a hole for it in the

	/* propose a random serial number and look for a hole for it in the

	 * serial number tree */

	key->serial = key_serial_next;

	if (key->serial < 3)

		key->serial = 3;

	key_serial_next = key->serial + 1;

	do {

		get_random_bytes(&key->serial, sizeof(key->serial));

		key->serial >>= 1; /* negative numbers are not permitted */

	} while (key->serial < 3);

	spin_lock(&key_serial_lock);

	parent = NULL;

	p = &key_serial_tree.rb_node;

	 * that point looking for the next unused serial number */

serial_exists:

	for (;;) {

		key->serial = key_serial_next;

		key->serial++;

		if (key->serial < 2)

			key->serial = 2;

		key_serial_next = key->serial + 1;

		if (!rb_parent(parent))

			p = &key_serial_tree.rb_node;