From 18e0d4f07812e7c1f52f1f78b613e057017019cf Mon Sep 17 00:00:00 2001
From: Florin Coras <fcoras@cisco.com>
Date: Wed, 2 Jan 2019 12:22:02 -0800
Subject: [PATCH] tcp: better randomize iss

Change-Id: I3638221e59024d6b7d82499d57e25b8e609f73cb
Signed-off-by: Florin Coras <fcoras@cisco.com>
---
 src/vnet/tcp/tcp.c | 36 ++++++++++++++++++++++++++++++++----
 src/vnet/tcp/tcp.h |  9 +++++++++
 2 files changed, 41 insertions(+), 4 deletions(-)

diff --git a/src/vnet/tcp/tcp.c b/src/vnet/tcp/tcp.c
index 8c3e8b10df0..51878b4069e 100644
--- a/src/vnet/tcp/tcp.c
+++ b/src/vnet/tcp/tcp.c
@@ -552,6 +552,26 @@ tcp_cc_algo_get (tcp_cc_algorithm_type_e type)
   return &tm->cc_algos[type];
 }
 
+/**
+ * Generate random iss as per rfc6528
+ */
+static u32
+tcp_generate_random_iss (tcp_connection_t * tc)
+{
+  tcp_main_t *tm = &tcp_main;
+  u64 tmp;
+
+  if (tc->c_is_ip4)
+    tmp = (u64) tc->c_lcl_ip.ip4.as_u32 << 32 | (u64) tc->c_rmt_ip.ip4.as_u32;
+  else
+    tmp = tc->c_lcl_ip.ip6.as_u64[0] ^ tc->c_lcl_ip.ip6.as_u64[1]
+      ^ tc->c_rmt_ip.ip6.as_u64[0] ^ tc->c_rmt_ip.ip6.as_u64[1];
+
+  tmp ^= tm->iss_seed.first | ((u64) tc->c_lcl_port << 16 | tc->c_rmt_port);
+  tmp ^= tm->iss_seed.second;
+  tmp = clib_xxhash (tmp) + clib_cpu_time_now ();
+  return ((tmp >> 32) ^ (tmp & 0xffffffff));
+}
 
 /**
  * Initialize connection send variables.
@@ -559,8 +579,6 @@ tcp_cc_algo_get (tcp_cc_algorithm_type_e type)
 void
 tcp_init_snd_vars (tcp_connection_t * tc)
 {
-  u32 time_now;
-
   /*
    * We use the time to randomize iss and for setting up the initial
    * timestamp. Make sure it's updated otherwise syn and ack in the
@@ -568,9 +586,8 @@ tcp_init_snd_vars (tcp_connection_t * tc)
    * direction for us.
    */
   tcp_set_time_now (tcp_get_worker (vlib_get_thread_index ()));
-  time_now = tcp_time_now ();
 
-  tc->iss = random_u32 (&time_now);
+  tc->iss = tcp_generate_random_iss (tc);
   tc->snd_una = tc->iss;
   tc->snd_nxt = tc->iss + 1;
   tc->snd_una_max = tc->snd_nxt;
@@ -1368,6 +1385,16 @@ tcp_initialize_timer_wheels (tcp_main_t * tm)
   /* *INDENT-ON* */
 }
 
+static void
+tcp_initialize_iss_seed (tcp_main_t * tm)
+{
+  u32 default_seed = random_default_seed ();
+  u64 time_now = clib_cpu_time_now ();
+
+  tm->iss_seed.first = (u64) random_u32 (&default_seed) << 32;
+  tm->iss_seed.second = random_u64 (&time_now);
+}
+
 static clib_error_t *
 tcp_main_enable (vlib_main_t * vm)
 {
@@ -1444,6 +1471,7 @@ tcp_main_enable (vlib_main_t * vm)
     }
 
   tcp_initialize_timer_wheels (tm);
+  tcp_initialize_iss_seed (tm);
 
   tm->bytes_per_buffer = VLIB_BUFFER_DATA_SIZE;
 
diff --git a/src/vnet/tcp/tcp.h b/src/vnet/tcp/tcp.h
index 3848f03f1dc..dca045128ed 100644
--- a/src/vnet/tcp/tcp.h
+++ b/src/vnet/tcp/tcp.h
@@ -437,6 +437,12 @@ typedef struct tcp_worker_ctx_
 
 } tcp_worker_ctx_t;
 
+typedef struct tcp_iss_seed_
+{
+  u64 first;
+  u64 second;
+} tcp_iss_seed_t;
+
 typedef struct _tcp_main
 {
   /* Per-worker thread tcp connection pools */
@@ -464,6 +470,9 @@ typedef struct _tcp_main
   /** vlib buffer size */
   u32 bytes_per_buffer;
 
+  /* Seed used to generate random iss */
+  tcp_iss_seed_t iss_seed;
+
   /*
    * Configuration
    */
-- 
2.16.6