keys, dns: Allow key types (eg. DNS) to be reclaimed immediately on expiry

If a key has an expiration time, then when that time passes, the key is
left around for a certain amount of time before being collected (5 mins by
default) so that EKEYEXPIRED can be returned instead of ENOKEY.  This is a
problem for DNS keys because we want to redo the DNS lookup immediately at
that point.

Fix this by allowing key types to be marked such that keys of that type
don't have this extra period, but are reclaimed as soon as they expire and
turn this on for dns_resolver-type keys.  To make this easier to handle,
key->expiry is changed to be permanent if TIME64_MAX rather than 0.

Furthermore, give such new-style negative DNS results a 1s default expiry
if no other expiry time is set rather than allowing it to stick around
indefinitely.  This shouldn't be zero as ls will follow a failing stat call
immediately with a second with AT_SYMLINK_NOFOLLOW added.

Fixes: 1a4240f4764a ("DNS: Separate out CIFS DNS Resolver code")
Signed-off-by: David Howells <dhowells@redhat.com>
Tested-by: Markus Suvanto <markus.suvanto@gmail.com>
cc: Wang Lei <wang840925@gmail.com>
cc: Jeff Layton <jlayton@redhat.com>
cc: Steve French <smfrench@gmail.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: Jarkko Sakkinen <jarkko@kernel.org>
cc: "David S. Miller" <davem@davemloft.net>
cc: Eric Dumazet <edumazet@google.com>
cc: Jakub Kicinski <kuba@kernel.org>
cc: Paolo Abeni <pabeni@redhat.com>
cc: linux-afs@lists.infradead.org
cc: linux-cifs@vger.kernel.org
cc: linux-nfs@vger.kernel.org
cc: ceph-devel@vger.kernel.org
cc: keyrings@vger.kernel.org
cc: netdev@vger.kernel.org

1 files changed, 5 insertions, 10 deletions

diff --git a/security/keys/key.c b/security/keys/key.c
index 0260a1902922..5b10641debd5 100644
--- a/security/keys/key.c
+++ b/security/keys/key.c
@@ -294,6 +294,7 @@ struct key *key_alloc(struct key_type *type, const char *desc,
 	key->uid = uid;
 	key->gid = gid;
 	key->perm = perm;
+	key->expiry = TIME64_MAX;
 	key->restrict_link = restrict_link;
 	key->last_used_at = ktime_get_real_seconds();
 
@@ -463,10 +464,7 @@ static int __key_instantiate_and_link(struct key *key,
 			if (authkey)
 				key_invalidate(authkey);
 
-			if (prep->expiry != TIME64_MAX) {
-				key->expiry = prep->expiry;
-				key_schedule_gc(prep->expiry + key_gc_delay);
-			}
+			key_set_expiry(key, prep->expiry);
 		}
 	}
 
@@ -606,8 +604,7 @@ int key_reject_and_link(struct key *key,
 		atomic_inc(&key->user->nikeys);
 		mark_key_instantiated(key, -error);
 		notify_key(key, NOTIFY_KEY_INSTANTIATED, -error);
-		key->expiry = ktime_get_real_seconds() + timeout;
-		key_schedule_gc(key->expiry + key_gc_delay);
+		key_set_expiry(key, ktime_get_real_seconds() + timeout);
 
 		if (test_and_clear_bit(KEY_FLAG_USER_CONSTRUCT, &key->flags))
 			awaken = 1;
@@ -723,16 +720,14 @@ found_kernel_type:
 
 void key_set_timeout(struct key *key, unsigned timeout)
 {
-	time64_t expiry = 0;
+	time64_t expiry = TIME64_MAX;
 
 	/* make the changes with the locks held to prevent races */
 	down_write(&key->sem);
 
 	if (timeout > 0)
 		expiry = ktime_get_real_seconds() + timeout;
-
-	key->expiry = expiry;
-	key_schedule_gc(key->expiry + key_gc_delay);
+	key_set_expiry(key, expiry);
 
 	up_write(&key->sem);
 }