Fix bounds check in zio_crypt_do_objset_hmacs

The current bounds check in zio_crypt_do_objset_hmacs() does not
properly handle the possible sizes of the objset_phys_t and
can therefore read outside the buffer's memory. If that memory
happened to match what the check was actually looking for, the
objset would fail to be owned, complaining that the MAC was
invalid.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Tom Caputi <tcaputi@datto.com>
Closes #7210

module/zfs/zio_crypt.c

@@ -1196,13 +1196,17 @@ zio_crypt_do_objset_hmacs(zio_crypt_key_t *key, void *data, uint_t datalen,
 	bcopy(raw_portable_mac, portable_mac, ZIO_OBJSET_MAC_LEN);
 
 	/*
-	 * The local MAC protects the user and group accounting. If these
-	 * objects are not present, the local MAC is zeroed out.
+	 * The local MAC protects the user, group and project accounting.
+	 * If these objects are not present, the local MAC is zeroed out.
 	 */
-	if (datalen >= OBJSET_PHYS_SIZE_V2 &&
+	if ((datalen >= OBJSET_PHYS_SIZE_V3 &&
 	    osp->os_userused_dnode.dn_type == DMU_OT_NONE &&
 	    osp->os_groupused_dnode.dn_type == DMU_OT_NONE &&
-	    osp->os_projectused_dnode.dn_type == DMU_OT_NONE) {
+	    osp->os_projectused_dnode.dn_type == DMU_OT_NONE) ||
+	    (datalen >= OBJSET_PHYS_SIZE_V2 &&
+	    osp->os_userused_dnode.dn_type == DMU_OT_NONE &&
+	    osp->os_groupused_dnode.dn_type == DMU_OT_NONE) ||
+	    (datalen <= OBJSET_PHYS_SIZE_V1)) {
 		bzero(local_mac, ZIO_OBJSET_MAC_LEN);
 		return (0);
 	}