KEYS: Add missing smp_rmb() primitives to the keyring search code

Add missing smp_rmb() primitives to the keyring search code.

When keyring payloads are appended to without replacement (thus using up spare
slots in the key pointer array), an smp_wmb() is issued between the pointer
assignment and the increment of the key count (nkeys).

There should be corresponding read barriers between the read of nkeys and
dereferences of keys[n] when n is dependent on the value of nkeys.

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: James Morris <jmorris@namei.org>

1 files changed, 3 insertions, 1 deletions

diff --git a/security/keys/gc.c b/security/keys/gc.c
index bf4d8da5a79..a42b45531aa 100644
--- a/security/keys/gc.c
+++ b/security/keys/gc.c
@@ -145,7 +145,9 @@ static void key_gc_keyring(struct key *keyring, time_t limit)
         if (!klist)
                 goto unlock_dont_gc;
 
-        for (loop = klist->nkeys - 1; loop >= 0; loop--) {
+        loop = klist->nkeys;
+        smp_rmb();
+        for (loop--; loop >= 0; loop--) {
                 key = klist->keys[loop];
                 if (test_bit(KEY_FLAG_DEAD, &key->flags) ||
                     (key->expiry > 0 && key->expiry <= limit))