keys: Fix overwrite of key expiration on instantiation

The expiry time of a key is unconditionally overwritten during
instantiation, defaulting to turn it permanent. This causes a problem
for DNS resolution as the expiration set by user-space is overwritten to
TIME64_MAX, disabling further DNS updates. Fix this by restoring the
condition that key_set_expiry is only called when the pre-parser sets a
specific expiry.

Fixes: 39299bd ("keys, dns: Allow key types (eg. DNS) to be reclaimed immediately on expiry")
Signed-off-by: Silvio Gissi <sifonsec@amazon.com>
cc: David Howells <dhowells@redhat.com>
cc: Hazem Mohamed Abuelfotoh <abuehaze@amazon.com>
cc: linux-afs@lists.infradead.org
cc: linux-cifs@vger.kernel.org
cc: keyrings@vger.kernel.org
cc: netdev@vger.kernel.org
cc: stable@vger.kernel.org
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>

Author: Silvio Gissi

security/keys/key.c

@@ -465,7 +465,8 @@ static int __key_instantiate_and_link(struct key *key,
 			if (authkey)
 				key_invalidate(authkey);
 
-			key_set_expiry(key, prep->expiry);
+			if (prep->expiry != TIME64_MAX)
+				key_set_expiry(key, prep->expiry);
 		}
 	}