tipc: add automatic session key exchange

With support from the master key option in the previous commit, it
becomes easy to make frequent updates/exchanges of session keys between
authenticated cluster nodes.
Basically, there are two situations where the key exchange will take in
place:

- When a new node joins the cluster (with the master key), it will need
  to get its peer's TX key, so that be able to decrypt further messages
  from that peer.

- When a new session key is generated (by either user manual setting or
  later automatic rekeying feature), the key will be distributed to all
  peer nodes in the cluster.

A key to be exchanged is encapsulated in the data part of a 'MSG_CRYPTO
/KEY_DISTR_MSG' TIPC v2 message, then xmit-ed as usual and encrypted by
using the master key before sending out. Upon receipt of the message it
will be decrypted in the same way as regular messages, then attached as
the sender's RX key in the receiver node.

In this way, the key exchange is reliable by the link layer, as well as
security, integrity and authenticity by the crypto layer.

Also, the forward security will be easily achieved by user changing the
master key actively but this should not be required very frequently.

The key exchange feature is independent on the presence of a master key
Note however that the master key still is needed for new nodes to be
able to join the cluster. It is also optional, and can be turned off/on
via the sysfs: 'net/tipc/key_exchange_enabled' [default 1: enabled].

Backward compatibility is guaranteed because for nodes that do not have
master key support, key exchange using master key ie. tx_key = 0 if any
will be shortly discarded at the message validation step. In other
words, the key exchange feature will be automatically disabled to those
nodes.

v2: fix the "implicit declaration of function 'tipc_crypto_key_flush'"
error in node.c. The function only exists when built with the TIPC
"CONFIG_TIPC_CRYPTO" option.

v3: use 'info->extack' for a message emitted due to netlink operations
instead (- David's comment).

Reported-by: kernel test robot <lkp@intel.com>
Acked-by: Jon Maloy <jmaloy@redhat.com>
Signed-off-by: Tuong Lien <tuong.t.lien@dektech.com.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 2 insertions, 0 deletions

diff --git a/net/tipc/node.h b/net/tipc/node.h
index 9f6f13f1604f..154a5bbb0d29 100644
--- a/net/tipc/node.h
+++ b/net/tipc/node.h
@@ -79,12 +79,14 @@ bool tipc_node_get_id(struct net *net, u32 addr, u8 *id);
 u32 tipc_node_get_addr(struct tipc_node *node);
 char *tipc_node_get_id_str(struct tipc_node *node);
 void tipc_node_put(struct tipc_node *node);
+void tipc_node_get(struct tipc_node *node);
 struct tipc_node *tipc_node_create(struct net *net, u32 addr, u8 *peer_id,
 				   u16 capabilities, u32 hash_mixes,
 				   bool preliminary);
 #ifdef CONFIG_TIPC_CRYPTO
 struct tipc_crypto *tipc_node_crypto_rx(struct tipc_node *__n);
 struct tipc_crypto *tipc_node_crypto_rx_by_list(struct list_head *pos);
+struct tipc_crypto *tipc_node_crypto_rx_by_addr(struct net *net, u32 addr);
 #endif
 u32 tipc_node_try_addr(struct net *net, u8 *id, u32 addr);
 void tipc_node_check_dest(struct net *net, u32 onode, u8 *peer_id128,