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, 107 insertions, 19 deletions

diff --git a/net/tipc/discover.c b/net/tipc/discover.c
index b4c4cd176b9b..e7655736abed 100644
--- a/net/tipc/discover.c
+++ b/net/tipc/discover.c
@@ -1,7 +1,7 @@
 /*
  * net/tipc/discover.c
  *
- * Copyright (c) 2003-2006, 2014-2015, Ericsson AB
+ * Copyright (c) 2003-2006, 2014-2018, Ericsson AB
  * Copyright (c) 2005-2006, 2010-2011, Wind River Systems
  * All rights reserved.
  *
@@ -78,34 +78,40 @@ struct tipc_discoverer {
  * @b: ptr to bearer issuing message
  */
 static void tipc_disc_init_msg(struct net *net, struct sk_buff *skb,
-			       u32 mtyp, struct tipc_bearer *b)
+			       u32 mtyp,  struct tipc_bearer *b)
 {
 	struct tipc_net *tn = tipc_net(net);
-	u32 self = tipc_own_addr(net);
 	u32 dest_domain = b->domain;
 	struct tipc_msg *hdr;
 
 	hdr = buf_msg(skb);
-	tipc_msg_init(self, hdr, LINK_CONFIG, mtyp,
+	tipc_msg_init(tn->trial_addr, hdr, LINK_CONFIG, mtyp,
 		      MAX_H_SIZE, dest_domain);
+	msg_set_size(hdr, MAX_H_SIZE + NODE_ID_LEN);
 	msg_set_non_seq(hdr, 1);
 	msg_set_node_sig(hdr, tn->random);
 	msg_set_node_capabilities(hdr, TIPC_NODE_CAPABILITIES);
 	msg_set_dest_domain(hdr, dest_domain);
 	msg_set_bc_netid(hdr, tn->net_id);
 	b->media->addr2msg(msg_media_addr(hdr), &b->addr);
+	msg_set_node_id(hdr, tipc_own_id(net));
 }
 
-static void tipc_disc_msg_xmit(struct net *net, u32 mtyp, u32 dst, u32 src,
+static void tipc_disc_msg_xmit(struct net *net, u32 mtyp, u32 dst,
+			       u32 src, u32 sugg_addr,
 			       struct tipc_media_addr *maddr,
 			       struct tipc_bearer *b)
 {
+	struct tipc_msg *hdr;
 	struct sk_buff *skb;
 
-	skb = tipc_buf_acquire(MAX_H_SIZE, GFP_ATOMIC);
+	skb = tipc_buf_acquire(MAX_H_SIZE + NODE_ID_LEN, GFP_ATOMIC);
 	if (!skb)
 		return;
+	hdr = buf_msg(skb);
 	tipc_disc_init_msg(net, skb, mtyp, b);
+	msg_set_sugg_node_addr(hdr, sugg_addr);
+	msg_set_dest_domain(hdr, dst);
 	tipc_bearer_xmit_skb(net, b->identity, skb, maddr);
 }
 
@@ -126,6 +132,52 @@ static void disc_dupl_alert(struct tipc_bearer *b, u32 node_addr,
 		media_addr_str, b->name);
 }
 
+/* tipc_disc_addr_trial(): - handle an address uniqueness trial from peer
+ */
+bool tipc_disc_addr_trial_msg(struct tipc_discoverer *d,
+			      struct tipc_media_addr *maddr,
+			      struct tipc_bearer *b,
+			      u32 dst, u32 src,
+			      u32 sugg_addr,
+			      u8 *peer_id,
+			      int mtyp)
+{
+	struct net *net = d->net;
+	struct tipc_net *tn = tipc_net(net);
+	bool trial = time_before(jiffies, tn->addr_trial_end);
+	u32 self = tipc_own_addr(net);
+
+	if (mtyp == DSC_TRIAL_FAIL_MSG) {
+		if (!trial)
+			return true;
+
+		/* Ignore if somebody else already gave new suggestion */
+		if (dst != tn->trial_addr)
+			return true;
+
+		/* Otherwise update trial address and restart trial period */
+		tn->trial_addr = sugg_addr;
+		msg_set_prevnode(buf_msg(d->skb), sugg_addr);
+		tn->addr_trial_end = jiffies + msecs_to_jiffies(1000);
+		return true;
+	}
+
+	/* Apply trial address if we just left trial period */
+	if (!trial && !self) {
+		tipc_net_finalize(net, tn->trial_addr);
+		msg_set_type(buf_msg(d->skb), DSC_REQ_MSG);
+	}
+
+	if (mtyp != DSC_TRIAL_MSG)
+		return false;
+
+	sugg_addr = tipc_node_try_addr(net, peer_id, src);
+	if (sugg_addr)
+		tipc_disc_msg_xmit(net, DSC_TRIAL_FAIL_MSG, src,
+				   self, sugg_addr, maddr, b);
+	return true;
+}
+
 /**
  * tipc_disc_rcv - handle incoming discovery message (request or response)
  * @net: applicable net namespace
@@ -139,17 +191,27 @@ void tipc_disc_rcv(struct net *net, struct sk_buff *skb,
 	struct tipc_msg *hdr = buf_msg(skb);
 	u16 caps = msg_node_capabilities(hdr);
 	bool legacy = tn->legacy_addr_format;
+	u32 sugg = msg_sugg_node_addr(hdr);
 	u32 signature = msg_node_sig(hdr);
+	u8 peer_id[NODE_ID_LEN] = {0,};
 	u32 dst = msg_dest_domain(hdr);
 	u32 net_id = msg_bc_netid(hdr);
-	u32 self = tipc_own_addr(net);
 	struct tipc_media_addr maddr;
 	u32 src = msg_prevnode(hdr);
 	u32 mtyp = msg_type(hdr);
 	bool dupl_addr = false;
 	bool respond = false;
+	u32 self;
 	int err;
 
+	skb_linearize(skb);
+	hdr = buf_msg(skb);
+
+	if (caps & TIPC_NODE_ID128)
+		memcpy(peer_id, msg_node_id(hdr), NODE_ID_LEN);
+	else
+		sprintf(peer_id, "%x", src);
+
 	err = b->media->msg2addr(b, &maddr, msg_media_addr(hdr));
 	kfree_skb(skb);
 	if (err || maddr.broadcast) {
@@ -161,6 +223,12 @@ void tipc_disc_rcv(struct net *net, struct sk_buff *skb,
 		return;
 	if (net_id != tn->net_id)
 		return;
+	if (tipc_disc_addr_trial_msg(b->disc, &maddr, b, dst,
+				     src, sugg, peer_id, mtyp))
+		return;
+	self = tipc_own_addr(net);
+
+	/* Message from somebody using this node's address */
 	if (in_own_node(net, src)) {
 		disc_dupl_alert(b, self, &maddr);
 		return;
@@ -169,8 +237,7 @@ void tipc_disc_rcv(struct net *net, struct sk_buff *skb,
 		return;
 	if (!tipc_in_scope(legacy, b->domain, src))
 		return;
-
-	tipc_node_check_dest(net, src, b, caps, signature,
+	tipc_node_check_dest(net, src, peer_id, b, caps, signature,
 			     &maddr, &respond, &dupl_addr);
 	if (dupl_addr)
 		disc_dupl_alert(b, src, &maddr);
@@ -178,7 +245,7 @@ void tipc_disc_rcv(struct net *net, struct sk_buff *skb,
 		return;
 	if (mtyp != DSC_REQ_MSG)
 		return;
-	tipc_disc_msg_xmit(net, DSC_RESP_MSG, src, self, &maddr, b);
+	tipc_disc_msg_xmit(net, DSC_RESP_MSG, src, self, 0, &maddr, b);
 }
 
 /* tipc_disc_add_dest - increment set of discovered nodes
@@ -216,9 +283,11 @@ void tipc_disc_remove_dest(struct tipc_discoverer *d)
 static void tipc_disc_timeout(struct timer_list *t)
 {
 	struct tipc_discoverer *d = from_timer(d, t, timer);
+	struct tipc_net *tn = tipc_net(d->net);
+	u32 self = tipc_own_addr(d->net);
 	struct tipc_media_addr maddr;
 	struct sk_buff *skb = NULL;
-	struct net *net;
+	struct net *net = d->net;
 	u32 bearer_id;
 
 	spin_lock_bh(&d->lock);
@@ -228,16 +297,29 @@ static void tipc_disc_timeout(struct timer_list *t)
 		d->timer_intv = TIPC_DISC_INACTIVE;
 		goto exit;
 	}
+
+	/* Did we just leave the address trial period ? */
+	if (!self && !time_before(jiffies, tn->addr_trial_end)) {
+		self = tn->trial_addr;
+		tipc_net_finalize(net, self);
+		msg_set_prevnode(buf_msg(d->skb), self);
+		msg_set_type(buf_msg(d->skb), DSC_REQ_MSG);
+	}
+
 	/* Adjust timeout interval according to discovery phase */
-	d->timer_intv *= 2;
-	if (d->num_nodes && d->timer_intv > TIPC_DISC_SLOW)
-		d->timer_intv = TIPC_DISC_SLOW;
-	else if (!d->num_nodes && d->timer_intv > TIPC_DISC_FAST)
-		d->timer_intv = TIPC_DISC_FAST;
+	if (time_before(jiffies, tn->addr_trial_end)) {
+		d->timer_intv = TIPC_DISC_INIT;
+	} else {
+		d->timer_intv *= 2;
+		if (d->num_nodes && d->timer_intv > TIPC_DISC_SLOW)
+			d->timer_intv = TIPC_DISC_SLOW;
+		else if (!d->num_nodes && d->timer_intv > TIPC_DISC_FAST)
+			d->timer_intv = TIPC_DISC_FAST;
+	}
+
 	mod_timer(&d->timer, jiffies + d->timer_intv);
 	memcpy(&maddr, &d->dest, sizeof(maddr));
 	skb = skb_clone(d->skb, GFP_ATOMIC);
-	net = d->net;
 	bearer_id = d->bearer_id;
 exit:
 	spin_unlock_bh(&d->lock);
@@ -257,18 +339,24 @@ exit:
 int tipc_disc_create(struct net *net, struct tipc_bearer *b,
 		     struct tipc_media_addr *dest, struct sk_buff **skb)
 {
+	struct tipc_net *tn = tipc_net(net);
 	struct tipc_discoverer *d;
 
 	d = kmalloc(sizeof(*d), GFP_ATOMIC);
 	if (!d)
 		return -ENOMEM;
-	d->skb = tipc_buf_acquire(MAX_H_SIZE, GFP_ATOMIC);
+	d->skb = tipc_buf_acquire(MAX_H_SIZE + NODE_ID_LEN, GFP_ATOMIC);
 	if (!d->skb) {
 		kfree(d);
 		return -ENOMEM;
 	}
-
 	tipc_disc_init_msg(net, d->skb, DSC_REQ_MSG, b);
+
+	/* Do we need an address trial period first ? */
+	if (!tipc_own_addr(net)) {
+		tn->addr_trial_end = jiffies + msecs_to_jiffies(1000);
+		msg_set_type(buf_msg(d->skb), DSC_TRIAL_MSG);
+	}
 	memcpy(&d->dest, dest, sizeof(*dest));
 	d->net = net;
 	d->bearer_id = b->identity;