performance optimization for the DOS protection.

* half-open SAs per peer are tracked in a hash table
 * charon.dos_protection setting replaced with charon.cookie_threshold and charon.block_threshold
 * chunk_hash function added

src/charon/network/receiver.c

@@ -1,4 +1,5 @@
 /*
+ * Copyright (C) 2008 Tobias Brunner
  * Copyright (C) 2005-2006 Martin Willi
  * Copyright (C) 2005 Jan Hutter
  * Hochschule fuer Technik Rapperswil
@@ -34,10 +35,10 @@
 #define COOKIE_LIFETIME 10
 /** how many times to reuse the secret */
 #define COOKIE_REUSE 10000
-/** require cookies after half open IKE_SAs */
-#define COOKIE_TRESHOLD 10
-/** how many half open IKE_SAs per peer before blocking */
-#define BLOCK_TRESHOLD 5
+/** default value for private_receiver_t.cookie_threshold */
+#define COOKIE_THRESHOLD_DEFAULT 10
+/** default value for private_receiver_t.block_threshold */
+#define BLOCK_THRESHOLD_DEFAULT 5
 /** length of the secret to use for cookie calculation */
 #define SECRET_LENGTH 16
 
@@ -98,9 +99,14 @@ struct private_receiver_t {
  	hasher_t *hasher;
  	
  	/**
- 	 * use denial of service protection mechanisms (cookies)
+ 	 * require cookies after this many half open IKE_SAs
  	 */
- 	bool dos_protection;
+ 	u_int32_t cookie_threshold;
+ 	
+ 	/**
+ 	 * how many half open IKE_SAs per peer before blocking
+ 	 */
+ 	u_int32_t block_threshold;
 };
 
 /**
@@ -204,12 +210,12 @@ static bool cookie_required(private_receiver_t *this, message_t *message)
 	bool failed = FALSE;
 		
 	if (charon->ike_sa_manager->get_half_open_count(charon->ike_sa_manager,
-													NULL) >= COOKIE_TRESHOLD)
+												NULL) >= this->cookie_threshold)
 	{
 		/* check for a cookie. We don't use our parser here and do it
 		 * quick and dirty for performance reasons. 
-		 * we assume to cookie is the first payload (which is a MUST), and 
-		 * the cookies SPI length is zero. */
+		 * we assume the cookie is the first payload (which is a MUST), and 
+		 * the cookie's SPI length is zero. */
 		packet_t *packet = message->get_packet(message);
 		chunk_t data = packet->get_data(packet);
 		if (data.len < 
@@ -242,7 +248,7 @@ static bool cookie_required(private_receiver_t *this, message_t *message)
 static bool peer_to_aggressive(private_receiver_t *this, message_t *message)
 {
 	if (charon->ike_sa_manager->get_half_open_count(charon->ike_sa_manager,
-								message->get_source(message)) >= BLOCK_TRESHOLD)
+						message->get_source(message)) >= this->block_threshold)
 	{
 		return TRUE;
 	}
@@ -287,11 +293,10 @@ static job_requeue_t receive_packets(private_receiver_t *this)
 	}
 	
 	if (message->get_request(message) &&
-		message->get_exchange_type(message) == IKE_SA_INIT &&
-		this->dos_protection)
+		message->get_exchange_type(message) == IKE_SA_INIT)
 	{
 		/* check for cookies */
-		if (cookie_required(this, message))
+		if (this->cookie_threshold && cookie_required(this, message))
 		{
 			u_int32_t now = time(NULL);
 			chunk_t cookie = cookie_build(this, message, now - this->secret_offset,
@@ -319,7 +324,7 @@ static job_requeue_t receive_packets(private_receiver_t *this)
 		}
 		
 		/* check if peer has not too many IKE_SAs half open */
-		if (peer_to_aggressive(this, message))
+		if (this->block_threshold && peer_to_aggressive(this, message))
 		{
 			DBG1(DBG_NET, "ignoring IKE_SA setup from %H, "
 				 "peer too aggressive", message->get_source(message));
@@ -373,8 +378,10 @@ receiver_t *receiver_create()
 	this->secret_used = 0;
 	this->rng->get_bytes(this->rng, SECRET_LENGTH, this->secret);
 	memcpy(this->secret_old, this->secret, SECRET_LENGTH);
-	this->dos_protection = lib->settings->get_bool(lib->settings,
-												"charon.dos_protection", TRUE);
+	this->cookie_threshold = lib->settings->get_int(lib->settings,
+									"charon.cookie_threshold", COOKIE_THRESHOLD_DEFAULT);
+	this->block_threshold = lib->settings->get_int(lib->settings,
+									"charon.block_threshold", BLOCK_THRESHOLD_DEFAULT);
 
 	this->job = callback_job_create((callback_job_cb_t)receive_packets,
 									this, NULL, NULL);

src/charon/sa/ike_sa.c

@@ -1381,7 +1381,7 @@ static status_t process_message(private_ike_sa_t *this, message_t *message)
 			switch (status)
 			{
 				case NOT_SUPPORTED:
-					DBG1(DBG_IKE, "ciritcal unknown payloads found");
+					DBG1(DBG_IKE, "critical unknown payloads found");
 					if (is_request)
 					{
 						send_notify_response(this, message, UNSUPPORTED_CRITICAL_PAYLOAD);

src/charon/sa/ike_sa_manager.c

@@ -1,4 +1,5 @@
 /*
+ * Copyright (C) 2008 Tobias Brunner
  * Copyright (C) 2005-2006 Martin Willi
  * Copyright (C) 2005 Jan Hutter
  * Hochschule fuer Technik Rapperswil
@@ -88,6 +89,11 @@ struct entry_t {
 	 */
 	host_t *other;
 	
+	/**
+	 * As responder: Is this SA half-open?
+	 */
+	bool half_open;
+		
 	/**
 	 * own identity, required for duplicate checking
 	 */
@@ -138,6 +144,7 @@ static entry_t *entry_create(ike_sa_id_t *ike_sa_id)
 	this->message_id = -1;
 	this->init_hash = chunk_empty;
 	this->other = NULL;
+	this->half_open = FALSE;
 	this->my_id = NULL;
 	this->other_id = NULL;
 	
@@ -207,7 +214,43 @@ struct segment_t {
 	/* mutex to access a segment exclusively */
 	mutex_t *mutex;
 	
-	/* the number of items in this segment */
+	/* the number of entries in this segment */
+	u_int count;
+};
+
+typedef struct half_open_t half_open_t;
+
+/**
+ * Struct to manage half-open IKE_SAs per peer.
+ */
+struct half_open_t {
+	/* chunk of remote host address */
+	chunk_t other;
+	
+	/* the number of half-open IKE_SAs with that host */
+	u_int count;
+};
+
+/**
+ * Destroys a half_open_t object.
+ */
+static void half_open_destroy(half_open_t *this)
+{
+	chunk_free(&this->other);
+	free(this);
+}
+
+typedef struct half_open_segment_t half_open_segment_t;
+
+/**
+ * Struct to manage segments of the "half-open" hash table.
+ */
+struct half_open_segment_t {
+	/* rwlock to access a segment exclusively */
+	rwlock_t *lock;
+	
+	/* the number of half-open IKE_SAs in this segment (i.e. the sum of all
+	 * half_open_t.count in a segment) */
 	u_int count;
 };
 
@@ -252,6 +295,16 @@ struct private_ike_sa_manager_t {
 	  */
 	 u_int segment_mask;
 	 
+	 /**
+	  * Hash table with half_open_t objects.
+	  */
+	 linked_list_t **half_open_table;
+	 
+	 /**
+	  * Segments of the "half-open" hash table.
+	  */
+	 half_open_segment_t *half_open_segments;
+	 
 	 /**
 	  * RNG to get random SPIs for our side
 	  */
@@ -268,7 +321,6 @@ struct private_ike_sa_manager_t {
 	 bool reuse_ikesa;
 };
 
-
 /**
  * Acquire a lock to access the segment of the table row with the given index.
  * It also works with the segment index directly.
@@ -576,6 +628,88 @@ static bool wait_for_entry(private_ike_sa_manager_t *this, entry_t *entry,
 	return TRUE;
 }
 
+/**
+ * Function that matches half_open_t objects by the given IP address chunk.
+ */
+static bool half_open_match(half_open_t *half_open, chunk_t *addr)
+{
+	return chunk_equals(*addr, half_open->other);
+}
+
+/**
+ * Put a half-open SA into the hash table.
+ */
+static void put_half_open(private_ike_sa_manager_t *this, entry_t *entry)
+{
+	half_open_t *half_open = NULL;
+	linked_list_t *list;
+	chunk_t addr = entry->other->get_address(entry->other);
+	u_int row = chunk_hash(addr) & this->table_mask;
+	u_int segment = row & this->segment_mask;
+	
+	rwlock_t *lock = this->half_open_segments[segment & this->segment_mask].lock;
+	lock->write_lock(lock);
+	if ((list = this->half_open_table[row]) == NULL)
+	{
+		list = this->half_open_table[row] = linked_list_create();
+	}
+	else
+	{
+		half_open_t *current;
+		if (list->find_first(list, (linked_list_match_t)half_open_match,
+							 (void**)&current, &addr) == SUCCESS)
+		{
+			half_open = current;
+			half_open->count++;
+			this->half_open_segments[segment].count++;
+		}
+	}
+	
+	if (!half_open)
+	{
+		half_open = malloc_thing(half_open_t);
+		half_open->other = chunk_clone(addr);
+		half_open->count = 1;
+		list->insert_last(list, half_open);
+		this->half_open_segments[segment].count++;
+	}
+	lock->unlock(lock);
+}
+
+/**
+ * Remove a half-open SA from the hash table.
+ */
+static void remove_half_open(private_ike_sa_manager_t *this, entry_t *entry)
+{
+	linked_list_t *list;
+	chunk_t addr = entry->other->get_address(entry->other);
+	u_int row = chunk_hash(addr) & this->table_mask;
+	u_int segment = row & this->segment_mask;
+	
+	rwlock_t *lock = this->half_open_segments[segment & this->segment_mask].lock;
+	lock->write_lock(lock);
+	if ((list = this->half_open_table[row]) != NULL)
+	{
+		half_open_t *current;
+		enumerator_t *enumerator = list->create_enumerator(list);
+		while (enumerator->enumerate(enumerator, &current))
+		{
+			if (half_open_match(current, &addr))
+			{
+				if (--current->count == 0)
+				{
+					list->remove_at(list, enumerator);
+					half_open_destroy(current);
+				}
+				this->half_open_segments[segment].count--;
+				break;
+			}
+		}
+		enumerator->destroy(enumerator);
+	}
+	lock->unlock(lock);
+}
+
 /**
  * Implementation of private_ike_sa_manager_t.get_next_spi.
  */
@@ -1050,12 +1184,30 @@ static status_t checkin(private_ike_sa_manager_t *this, ike_sa_t *ike_sa)
 		/* signal waiting threads */
 		entry->checked_out = FALSE;
 		entry->message_id = -1;
-		/* apply remote address for DoS detection */
+		/* check if this SA is half-open */
 		other = ike_sa->get_other_host(ike_sa);
-		if (!entry->other || !other->equals(other, entry->other))
+		if (entry->half_open && ike_sa->get_state(ike_sa) != IKE_CONNECTING)
 		{
+			/* not half open anymore */
+			entry->half_open = FALSE;
+			remove_half_open(this, entry);
+		}
+		else if (entry->half_open && !other->ip_equals(other, entry->other))
+		{
+			/* the other host's IP has changed, we must update the hash table */
+			remove_half_open(this, entry);
 			DESTROY_IF(entry->other);
 			entry->other = other->clone(other);
+			put_half_open(this, entry);
+		}
+		else if (!entry->half_open &&
+				 !entry->ike_sa_id->is_initiator(entry->ike_sa_id) &&
+				 ike_sa->get_state(ike_sa) == IKE_CONNECTING)
+		{
+			/* this is a new half-open SA */
+			entry->half_open = TRUE;
+			entry->other = other->clone(other);
+			put_half_open(this, entry);
 		}
 		/* apply identities for duplicate test */
 		my_id = ike_sa->get_my_id(ike_sa);
@@ -1122,6 +1274,11 @@ static status_t checkin_and_destroy(private_ike_sa_manager_t *this, ike_sa_t *ik
 			/* they will wake us again when their work is done */
 			entry->condvar->wait(entry->condvar, this->segments[segment].mutex);
 		}
+		
+		if (entry->half_open)
+		{
+			remove_half_open(this, entry);
+		}
 	
 		remove_entry(this, entry);
 		entry_destroy(entry);
@@ -1144,33 +1301,40 @@ static status_t checkin_and_destroy(private_ike_sa_manager_t *this, ike_sa_t *ik
  */
 static int get_half_open_count(private_ike_sa_manager_t *this, host_t *ip)
 {
-	enumerator_t *enumerator;
-	entry_t *entry;
-	u_int segment;
 	int count = 0;
 
-	enumerator = create_table_enumerator(this);
-	while (enumerator->enumerate(enumerator, &entry, &segment))
+	if (ip)
 	{
-		/* we check if we have a responder CONNECTING IKE_SA without checkout */
-		if (!entry->ike_sa_id->is_initiator(entry->ike_sa_id) &&
-			entry->ike_sa->get_state(entry->ike_sa) == IKE_CONNECTING)
+		linked_list_t *list;
+		chunk_t addr = ip->get_address(ip);
+		u_int row = chunk_hash(addr) & this->table_mask;
+		u_int segment = row & this->segment_mask;
+		
+		rwlock_t *lock = this->half_open_segments[segment & this->segment_mask].lock;
+		lock->read_lock(lock);
+		if ((list = this->half_open_table[row]) != NULL)
 		{
-			/* if we have a host, count only matching IKE_SAs */
-			if (ip)
+			half_open_t *current;
+			if (list->find_first(list, (linked_list_match_t)half_open_match,
+								 (void**)&current, &addr) == SUCCESS)
 			{
-				if (entry->other && ip->ip_equals(ip, entry->other))
-				{
-					count++;
-				}
-			}
-			else
-			{
-				count++;
+				count = current->count;
 			}
 		}
+		lock->unlock(lock);
+	}
+	else
+	{
+		u_int segment;
+		for (segment = 0; segment < this->segment_count; ++segment)
+		{
+			rwlock_t *lock;
+			lock = this->half_open_segments[segment & this->segment_mask].lock;
+			lock->read_lock(lock);
+			count += this->half_open_segments[segment].count;
+			lock->unlock(lock);
+		}
 	}
-	enumerator->destroy(enumerator);
 	
 	return count;
 }
@@ -1227,6 +1391,10 @@ static void flush(private_ike_sa_manager_t *this)
 	while (enumerator->enumerate(enumerator, &entry, &segment))
 	{
 		charon->bus->set_sa(charon->bus, entry->ike_sa);
+		if (entry->half_open)
+		{
+			remove_half_open(this, entry);
+		}
 		remove_entry_at((private_enumerator_t*)enumerator);
 		entry_destroy(entry);
 	}
@@ -1250,13 +1418,21 @@ static void destroy(private_ike_sa_manager_t *this)
 		{
 			list->destroy(list);
 		}
+		if ((list = this->half_open_table[i]) != NULL)
+		{
+			list->destroy(list);
+		}
 	}
 	free(this->ike_sa_table);
+	free(this->half_open_table);
 	for (i = 0; i < this->segment_count; ++i)
 	{
 		this->segments[i].mutex->destroy(this->segments[i].mutex);
+		this->half_open_segments[i].lock->destroy(this->half_open_segments[i].lock);
 	}
 	free(this->segments);
+	free(this->half_open_segments);
+	
 	this->rng->destroy(this->rng);
 	this->hasher->destroy(this->hasher);
 	free(this);
@@ -1341,6 +1517,17 @@ ike_sa_manager_t *ike_sa_manager_create()
 		this->segments[i].count = 0;
 	}
 	
+	/* we use the same parameters as above for the hash table to track half-open SAs */
+	this->half_open_table = (linked_list_t**)calloc(this->table_size, sizeof(linked_list_t*));
+	memset(this->half_open_table, 0, this->table_size * sizeof(linked_list_t*));
+	
+	this->half_open_segments = (half_open_segment_t*)calloc(this->segment_count, sizeof(half_open_segment_t));
+	for (i = 0; i < this->segment_count; ++i)
+	{
+		this->half_open_segments[i].lock = rwlock_create(RWLOCK_DEFAULT);
+		this->half_open_segments[i].count = 0;
+	}
+	
 	this->reuse_ikesa = lib->settings->get_bool(lib->settings,
 												"charon.reuse_ikesa", TRUE);
 	return &this->public;

src/libstrongswan/chunk.c

@@ -1,4 +1,5 @@
 /*
+ * Copyright (C) 2008 Tobias Brunner
  * Copyright (C) 2005-2006 Martin Willi
  * Copyright (C) 2005 Jan Hutter
  * Hochschule fuer Technik Rapperswil
@@ -26,6 +27,16 @@
 #include <debug.h>
 #include <printf_hook.h>
 
+/* required for chunk_hash */
+#undef get16bits
+#if (defined(__GNUC__) && defined(__i386__))
+#define get16bits(d) (*((const u_int16_t*)(d)))
+#endif
+#if !defined (get16bits)
+#define get16bits(d) ((((u_int32_t)(((const u_int8_t*)(d))[1])) << 8)\
+                      + (u_int32_t)(((const u_int8_t*)(d))[0]) )
+#endif
+
 /**
  * Empty chunk.
  */
@@ -251,7 +262,7 @@ static char hexdig_lower[] = "0123456789abcdef";
  */
 chunk_t chunk_to_hex(chunk_t chunk, char *buf, bool uppercase)
 {
-	int i, len;;
+	int i, len;
 	char *hexdig = hexdig_lower;
 	
 	if (uppercase)
@@ -482,6 +493,75 @@ bool chunk_equals(chunk_t a, chunk_t b)
 			a.len == b.len && memeq(a.ptr, b.ptr, a.len);
 }
 
+/**
+ * Described in header.
+ * 
+ * The implementation is based on Paul Hsieh's SuperFastHash:
+ * 	 http://www.azillionmonkeys.com/qed/hash.html
+ */
+u_int32_t chunk_hash(chunk_t chunk)
+{
+	u_char *data = chunk.ptr;
+	size_t len = chunk.len;
+	u_int32_t hash = len, tmp;
+	int rem;
+	
+	if (!len || data == NULL)
+	{
+		return 0;
+	}
+	
+	rem = len & 3;
+	len >>= 2;
+	
+	/* Main loop */
+	for (; len > 0; --len)
+	{
+		hash += get16bits(data);
+		tmp   = (get16bits(data + 2) << 11) ^ hash;
+		hash  = (hash << 16) ^ tmp;
+		data += 2 * sizeof(u_int16_t);
+		hash += hash >> 11;
+	}
+	
+	/* Handle end cases */
+	switch (rem)
+	{
+		case 3:
+		{
+			hash += get16bits(data);
+			hash ^= hash << 16;
+			hash ^= data[sizeof(u_int16_t)] << 18;
+			hash += hash >> 11;
+			break;
+		}
+		case 2:
+		{
+			hash += get16bits(data);
+			hash ^= hash << 11;
+			hash += hash >> 17;
+			break;
+		}
+		case 1:
+		{
+			hash += *data;
+			hash ^= hash << 10;
+			hash += hash >> 1;
+			break;
+		}
+	}
+	
+	/* Force "avalanching" of final 127 bits */
+	hash ^= hash << 3;
+	hash += hash >> 5;
+	hash ^= hash << 4;
+	hash += hash >> 17;
+	hash ^= hash << 25;
+	hash += hash >> 6;
+	
+	return hash;
+}
+
 /**
  * output handler in printf() for chunks
  */

src/libstrongswan/chunk.h

@@ -1,4 +1,5 @@
 /*
+ * Copyright (C) 2008 Tobias Brunner
  * Copyright (C) 2005-2008 Martin Willi
  * Copyright (C) 2005 Jan Hutter
  * Hochschule fuer Technik Rapperswil
@@ -199,6 +200,12 @@ int chunk_compare(chunk_t a, chunk_t b);
  */
 bool chunk_equals(chunk_t a, chunk_t b);
 
+/**
+ * Computes a 32 bit hash of the given chunk.
+ * Note: This hash is only intended for hash tables not for cryptographic purposes.
+ */
+u_int32_t chunk_hash(chunk_t chunk);
+
 /**
  * Get printf hooks for a chunk.
  *