tipc: handle collisions of 32-bit node address hash values

When a 32-bit node address is generated from a 128-bit identifier,
there is a risk of collisions which must be discovered and handled.

We do this as follows:
- We don't apply the generated address immediately to the node, but do
  instead initiate a 1 sec trial period to allow other cluster members
  to discover and handle such collisions.

- During the trial period the node periodically sends out a new type
  of message, DSC_TRIAL_MSG, using broadcast or emulated broadcast,
  to all the other nodes in the cluster.

- When a node is receiving such a message, it must check that the
  presented 32-bit identifier either is unused, or was used by the very
  same peer in a previous session. In both cases it accepts the request
  by not responding to it.

- If it finds that the same node has been up before using a different
  address, it responds with a DSC_TRIAL_FAIL_MSG containing that
  address.

- If it finds that the address has already been taken by some other
  node, it generates a new, unused address and returns it to the
  requester.

- During the trial period the requesting node must always be prepared
  to accept a failure message, i.e., a message where a peer suggests a
  different (or equal)  address to the one tried. In those cases it
  must apply the suggested value as trial address and restart the trial
  period.

This algorithm ensures that in the vast majority of cases a node will
have the same address before and after a reboot. If a legacy user
configures the address explicitly, there will be no trial period and
messages, so this protocol addition is completely backwards compatible.

Acked-by: Ying Xue <ying.xue@windriver.com>
Signed-off-by: Jon Maloy <jon.maloy@ericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 78 insertions, 7 deletions

diff --git a/net/tipc/node.c b/net/tipc/node.c
index 7b0c99347406..4a95c8c155c6 100644
--- a/net/tipc/node.c
+++ b/net/tipc/node.c
@@ -115,6 +115,7 @@ struct tipc_node {
 	u16 capabilities;
 	u32 signature;
 	u32 link_id;
+	u8 peer_id[16];
 	struct list_head publ_list;
 	struct list_head conn_sks;
 	unsigned long keepalive_intv;
@@ -156,6 +157,7 @@ static void tipc_node_delete(struct tipc_node *node);
 static void tipc_node_timeout(struct timer_list *t);
 static void tipc_node_fsm_evt(struct tipc_node *n, int evt);
 static struct tipc_node *tipc_node_find(struct net *net, u32 addr);
+static struct tipc_node *tipc_node_find_by_id(struct net *net, u8 *id);
 static void tipc_node_put(struct tipc_node *node);
 static bool node_is_up(struct tipc_node *n);
 
@@ -245,6 +247,30 @@ static struct tipc_node *tipc_node_find(struct net *net, u32 addr)
 	return node;
 }
 
+/* tipc_node_find_by_id - locate specified node object by its 128-bit id
+ * Note: this function is called only when a discovery request failed
+ * to find the node by its 32-bit id, and is not time critical
+ */
+static struct tipc_node *tipc_node_find_by_id(struct net *net, u8 *id)
+{
+	struct tipc_net *tn = tipc_net(net);
+	struct tipc_node *n;
+	bool found = false;
+
+	rcu_read_lock();
+	list_for_each_entry_rcu(n, &tn->node_list, list) {
+		read_lock_bh(&n->lock);
+		if (!memcmp(id, n->peer_id, 16) &&
+		    kref_get_unless_zero(&n->kref))
+			found = true;
+		read_unlock_bh(&n->lock);
+		if (found)
+			break;
+	}
+	rcu_read_unlock();
+	return found ? n : NULL;
+}
+
 static void tipc_node_read_lock(struct tipc_node *n)
 {
 	read_lock_bh(&n->lock);
@@ -307,7 +333,8 @@ static void tipc_node_write_unlock(struct tipc_node *n)
 	}
 }
 
-struct tipc_node *tipc_node_create(struct net *net, u32 addr, u16 capabilities)
+struct tipc_node *tipc_node_create(struct net *net, u32 addr,
+				   u8 *peer_id, u16 capabilities)
 {
 	struct tipc_net *tn = net_generic(net, tipc_net_id);
 	struct tipc_node *n, *temp_node;
@@ -326,6 +353,7 @@ struct tipc_node *tipc_node_create(struct net *net, u32 addr, u16 capabilities)
 		goto exit;
 	}
 	n->addr = addr;
+	memcpy(&n->peer_id, peer_id, 16);
 	n->net = net;
 	n->capabilities = capabilities;
 	kref_init(&n->kref);
@@ -344,8 +372,8 @@ struct tipc_node *tipc_node_create(struct net *net, u32 addr, u16 capabilities)
 	n->signature = INVALID_NODE_SIG;
 	n->active_links[0] = INVALID_BEARER_ID;
 	n->active_links[1] = INVALID_BEARER_ID;
-	if (!tipc_link_bc_create(net, tipc_own_addr(net), n->addr,
-				 U16_MAX,
+	if (!tipc_link_bc_create(net, tipc_own_addr(net),
+				 addr, U16_MAX,
 				 tipc_link_window(tipc_bc_sndlink(net)),
 				 n->capabilities,
 				 &n->bc_entry.inputq1,
@@ -735,8 +763,51 @@ bool tipc_node_is_up(struct net *net, u32 addr)
 	return retval;
 }
 
-void tipc_node_check_dest(struct net *net, u32 onode,
-			  struct tipc_bearer *b,
+static u32 tipc_node_suggest_addr(struct net *net, u32 addr)
+{
+	struct tipc_node *n;
+
+	addr ^= tipc_net(net)->random;
+	while ((n = tipc_node_find(net, addr))) {
+		tipc_node_put(n);
+		addr++;
+	}
+	return addr;
+}
+
+/* tipc_node_try_addr(): Check if addr can be used by peer, suggest other if not
+ */
+u32 tipc_node_try_addr(struct net *net, u8 *id, u32 addr)
+{
+	struct tipc_net *tn = tipc_net(net);
+	struct tipc_node *n;
+
+	/* Suggest new address if some other peer is using this one */
+	n = tipc_node_find(net, addr);
+	if (n) {
+		if (!memcmp(n->peer_id, id, NODE_ID_LEN))
+			addr = 0;
+		tipc_node_put(n);
+		if (!addr)
+			return 0;
+		return tipc_node_suggest_addr(net, addr);
+	}
+
+	/* Suggest previously used address if peer is known */
+	n = tipc_node_find_by_id(net, id);
+	if (n) {
+		addr = n->addr;
+		tipc_node_put(n);
+	}
+	/* Even this node may be in trial phase */
+	if (tn->trial_addr == addr)
+		return tipc_node_suggest_addr(net, addr);
+
+	return addr;
+}
+
+void tipc_node_check_dest(struct net *net, u32 addr,
+			  u8 *peer_id, struct tipc_bearer *b,
 			  u16 capabilities, u32 signature,
 			  struct tipc_media_addr *maddr,
 			  bool *respond, bool *dupl_addr)
@@ -755,7 +826,7 @@ void tipc_node_check_dest(struct net *net, u32 onode,
 	*dupl_addr = false;
 	*respond = false;
 
-	n = tipc_node_create(net, onode, capabilities);
+	n = tipc_node_create(net, addr, peer_id, capabilities);
 	if (!n)
 		return;
 
@@ -840,7 +911,7 @@ void tipc_node_check_dest(struct net *net, u32 onode,
 		if (!tipc_link_create(net, if_name, b->identity, b->tolerance,
 				      b->net_plane, b->mtu, b->priority,
 				      b->window, mod(tipc_net(net)->random),
-				      tipc_own_addr(net), onode,
+				      tipc_own_addr(net), addr, peer_id,
 				      n->capabilities,
 				      tipc_bc_sndlink(n->net), n->bc_entry.link,
 				      &le->inputq,