[PATCH] keys: Discard duplicate keys from a keyring on link
Cause any links within a keyring to keys that match a key to be linked into
that keyring to be discarded as a link to the new key is added. The match is
contingent on the type and description strings being the same.
This permits requests, adds and searches to displace negative, expired,
revoked and dead keys easily. After some discussion it was concluded that
duplicate valid keys should probably be discarded also as they would otherwise
hide the new key.
Since request_key() is intended to be the primary method by which keys are
added to a keyring, duplicate valid keys wouldn't be an issue there as that
function would return an existing match in preference to creating a new key.
Signed-off-by: David Howells <dhowells@redhat.com>
Cc: Trond Myklebust <trond.myklebust@fys.uio.no>
Cc: Alexander Zangerl <az@bond.edu.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/security/keys/keyring.c b/security/keys/keyring.c
index 5d22c03..09d92d5 100644
--- a/security/keys/keyring.c
+++ b/security/keys/keyring.c
@@ -684,15 +684,31 @@
/*****************************************************************************/
/*
+ * dispose of a keyring list after the RCU grace period, freeing the unlinked
+ * key
+ */
+static void keyring_unlink_rcu_disposal(struct rcu_head *rcu)
+{
+ struct keyring_list *klist =
+ container_of(rcu, struct keyring_list, rcu);
+
+ key_put(klist->keys[klist->delkey]);
+ kfree(klist);
+
+} /* end keyring_unlink_rcu_disposal() */
+
+/*****************************************************************************/
+/*
* link a key into to a keyring
* - must be called with the keyring's semaphore write-locked
+ * - discard already extant link to matching key if there is one
*/
int __key_link(struct key *keyring, struct key *key)
{
struct keyring_list *klist, *nklist;
unsigned max;
size_t size;
- int ret;
+ int loop, ret;
ret = -EKEYREVOKED;
if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
@@ -714,6 +730,48 @@
goto error2;
}
+ /* see if there's a matching key we can displace */
+ klist = keyring->payload.subscriptions;
+
+ if (klist && klist->nkeys > 0) {
+ struct key_type *type = key->type;
+
+ for (loop = klist->nkeys - 1; loop >= 0; loop--) {
+ if (klist->keys[loop]->type == type &&
+ strcmp(klist->keys[loop]->description,
+ key->description) == 0
+ ) {
+ /* found a match - replace with new key */
+ size = sizeof(struct key *) * klist->maxkeys;
+ size += sizeof(*klist);
+ BUG_ON(size > PAGE_SIZE);
+
+ ret = -ENOMEM;
+ nklist = kmalloc(size, GFP_KERNEL);
+ if (!nklist)
+ goto error2;
+
+ memcpy(nklist, klist, size);
+
+ /* replace matched key */
+ atomic_inc(&key->usage);
+ nklist->keys[loop] = key;
+
+ rcu_assign_pointer(
+ keyring->payload.subscriptions,
+ nklist);
+
+ /* dispose of the old keyring list and the
+ * displaced key */
+ klist->delkey = loop;
+ call_rcu(&klist->rcu,
+ keyring_unlink_rcu_disposal);
+
+ goto done;
+ }
+ }
+ }
+
/* check that we aren't going to overrun the user's quota */
ret = key_payload_reserve(keyring,
keyring->datalen + KEYQUOTA_LINK_BYTES);
@@ -730,8 +788,6 @@
smp_wmb();
klist->nkeys++;
smp_wmb();
-
- ret = 0;
}
else {
/* grow the key list */
@@ -769,16 +825,16 @@
/* dispose of the old keyring list */
if (klist)
call_rcu(&klist->rcu, keyring_link_rcu_disposal);
-
- ret = 0;
}
- error2:
+done:
+ ret = 0;
+error2:
up_write(&keyring_serialise_link_sem);
- error:
+error:
return ret;
- error3:
+error3:
/* undo the quota changes */
key_payload_reserve(keyring,
keyring->datalen - KEYQUOTA_LINK_BYTES);
@@ -809,21 +865,6 @@
/*****************************************************************************/
/*
- * dispose of a keyring list after the RCU grace period, freeing the unlinked
- * key
- */
-static void keyring_unlink_rcu_disposal(struct rcu_head *rcu)
-{
- struct keyring_list *klist =
- container_of(rcu, struct keyring_list, rcu);
-
- key_put(klist->keys[klist->delkey]);
- kfree(klist);
-
-} /* end keyring_unlink_rcu_disposal() */
-
-/*****************************************************************************/
-/*
* unlink the first link to a key from a keyring
*/
int key_unlink(struct key *keyring, struct key *key)