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[PATCH] keys: allocate key serial numbers randomly 

Cause key_alloc_serial() to generate key serial numbers randomly rather than
in linear sequence.

Using an linear sequence permits a covert communication channel to be
established, in which one process can communicate with another by creating or
not creating new keys within a certain timeframe.  The second process can
probe for the expected next key serial number and judge its existence by the
error returned.

This is a problem as the serial number namespace is globally shared between
all tasks, regardless of their context.

For more information on this topic, this old TCSEC guide is recommended:

	http://www.radium.ncsc.mil/tpep/library/rainbow/NCSC-TG-030.html

Signed-off-by: Michael LeMay <mdlemay@epoch.ncsc.mil>
Signed-off-by: James Morris <jmorris@namei.org>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Michael LeMay 2006-06-26 00:24:54 -07:00 committed by Linus Torvalds
parent 5801649d8b
commit e51f6d3437
1 changed files with 14 additions and 14 deletions
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24
security/keys/key.c
View File

@ -15,11 +15,11 @@
#include <linux/slab.h> #include <linux/slab.h>
#include <linux/security.h> #include <linux/security.h>
#include <linux/workqueue.h> #include <linux/workqueue.h>
#include <linux/random.h>
#include <linux/err.h> #include <linux/err.h>
#include "internal.h" #include "internal.h"
static kmem_cache_t *key_jar; 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 */ struct rb_root key_serial_tree; /* tree of keys indexed by serial */
DEFINE_SPINLOCK(key_serial_lock); DEFINE_SPINLOCK(key_serial_lock);
@ -169,22 +169,23 @@ static void __init __key_insert_serial(struct key *key)
/*****************************************************************************/ /*****************************************************************************/
/* /*
* assign a key the next unique serial number * assign a key the next unique serial number
* - we work through all the serial numbers between 2 and 2^31-1 in turn and * - these are assigned randomly to avoid security issues through covert
* then wrap * channel problems
*/ */
static inline void key_alloc_serial(struct key *key) static inline void key_alloc_serial(struct key *key)
{ {
struct rb_node *parent, **p; struct rb_node *parent, **p;
struct key *xkey; struct key *xkey;
spin_lock(&key_serial_lock); /* propose a random serial number and look for a hole for it in the
/* propose a likely serial number and look for a hole for it in the
* serial number tree */ * serial number tree */
key->serial = key_serial_next; do {
if (key->serial < 3) get_random_bytes(&key->serial, sizeof(key->serial));
key->serial = 3;
key_serial_next = key->serial + 1; key->serial >>= 1; /* negative numbers are not permitted */
} while (key->serial < 3);
spin_lock(&key_serial_lock);
parent = NULL; parent = NULL;
p = &key_serial_tree.rb_node; p = &key_serial_tree.rb_node;
@ -206,10 +207,9 @@ static inline void key_alloc_serial(struct key *key)
* that point looking for the next unused serial number */ * that point looking for the next unused serial number */
serial_exists: serial_exists:
for (;;) { for (;;) {
key->serial = key_serial_next; key->serial++;
if (key->serial < 2) if (key->serial < 2)
key->serial = 2; key->serial = 2;
key_serial_next = key->serial + 1;
if (!rb_parent(parent)) if (!rb_parent(parent))
p = &key_serial_tree.rb_node; p = &key_serial_tree.rb_node;