nat: fix nat44-ed port range with multiple workers

The number of available dynamic ports is set to (0xffff - 1024) =
64511, which is not divisable by the pow2 number of workers - the
only integer divisors are 31 and 2081.
So, total dynamic port range of all workers will be less than it:
    1 wrk: n = (port_per_thread = 64511/1)*1 = 64511 + 1025 = 65536
    2 wrk: n = (port_per_thread = 64511/2)*2 = 64510 + 1025 = 65535
    4 wrk: n = (port_per_thread = 64511/4)*4 = 64508 + 1025 = 65533
    8 wrk: n = (port_per_thread = 64511/8)*8 = 64504 + 1025 = 65529
    ...
As seen, with multiple workers there are unused trailing ports for every
nat pool address and that is the reason of out-of-bound index in the
worker array on out2in path due (port - 1024) / port_per_thread math.
This was fixed in 5c9f9968de63fa627b4a72b344df36cdc686d18a, so packets
to unused ports will go to existing worker and dropped there.

Per RFC 6335 https://www.rfc-editor.org/rfc/rfc6335#section-6:
6.  Port Number Ranges
   o  the System Ports, also known as the Well Known Ports, from 0-1023
      (assigned by IANA)
   o  the User Ports, also known as the Registered Ports, from 1024-
      49151 (assigned by IANA)
   o  the Dynamic Ports, also known as the Private or Ephemeral Ports,
      from 49152-65535 (never assigned)

According that let's allocate dynamic ports from 1024 and have full port
range with a wide range of the workers number - 64 integer divisors in
total, including pow2 ones:
    1 wrk: n = (port_per_thread = 64512/1)*1 = 64512 + 1024 = 65536
    2 wrk: n = (port_per_thread = 64512/2)*2 = 64512 + 1024 = 65536
    3 wrk: n = (port_per_thread = 64512/3)*3 = 64512 + 1024 = 65536
    4 wrk: n = (port_per_thread = 64512/4)*4 = 64512 + 1024 = 65536
    5 wrk: n = (port_per_thread = 64512/5)*5 = 64510 + 1024 = 65534
    6 wrk: n = (port_per_thread = 64512/6)*6 = 64512 + 1024 = 65536
    7 wrk: n = (port_per_thread = 64512/7)*7 = 64512 + 1024 = 65536
    8 wrk: n = (port_per_thread = 64512/8)*8 = 64512 + 1024 = 65536
    ...
Modulo from 5c9f9968de63fa627b4a72b344df36cdc686d18a is still required
when the numbers of workers is not the integer divisor of 64512.

Type: fix
Fixes: 5c9f9968de63fa627b4a72b344df36cdc686d18a
Change-Id: I9edaea07e58ff4888812b0d86cbf41a3784b189e
Signed-off-by: Vladislav Grishenko <themiron@yandex-team.ru>

4 files changed, 15 insertions, 8 deletions

diff --git a/src/plugins/nat/nat44-ed/nat44_ed.c b/src/plugins/nat/nat44-ed/nat44_ed.c
index 27c1870ccef..2e4c791ef80 100644
--- a/src/plugins/nat/nat44-ed/nat44_ed.c
+++ b/src/plugins/nat/nat44-ed/nat44_ed.c
@@ -762,8 +762,8 @@ get_thread_idx_by_port (u16 e_port)
   if (sm->num_workers > 1)
     {
       thread_idx = sm->first_worker_index +
-		   sm->workers[(e_port - 1024) / sm->port_per_thread %
-			       _vec_len (sm->workers)];
+		   sm->workers[(e_port - ED_USER_PORT_OFFSET) /
+			       sm->port_per_thread % _vec_len (sm->workers)];
     }
   return thread_idx;
 }
@@ -2133,7 +2133,7 @@ snat_set_workers (uword * bitmap)
       j++;
     }
 
-  sm->port_per_thread = (0xffff - 1024) / _vec_len (sm->workers);
+  sm->port_per_thread = (65536 - ED_USER_PORT_OFFSET) / _vec_len (sm->workers);
 
   return 0;
 }
@@ -2384,7 +2384,7 @@ nat_init (vlib_main_t * vm)
 	}
     }
   num_threads = tm->n_vlib_mains - 1;
-  sm->port_per_thread = 0xffff - 1024;
+  sm->port_per_thread = 65536 - ED_USER_PORT_OFFSET;
   vec_validate (sm->per_thread_data, num_threads);
 
   /* Use all available workers by default */
diff --git a/src/plugins/nat/nat44-ed/nat44_ed.h b/src/plugins/nat/nat44-ed/nat44_ed.h
index 5b5b2ec8cfd..6c64c754073 100644
--- a/src/plugins/nat/nat44-ed/nat44_ed.h
+++ b/src/plugins/nat/nat44-ed/nat44_ed.h
@@ -41,6 +41,11 @@
  * as if there were no free ports available to conserve resources */
 #define ED_PORT_ALLOC_ATTEMPTS (10)
 
+/* system ports range is 0-1023, first user port is 1024 per
+ * https://www.rfc-editor.org/rfc/rfc6335#section-6
+ */
+#define ED_USER_PORT_OFFSET 1024
+
 /* NAT buffer flags */
 #define SNAT_FLAG_HAIRPINNING (1 << 0)
 
diff --git a/src/plugins/nat/nat44-ed/nat44_ed_in2out.c b/src/plugins/nat/nat44-ed/nat44_ed_in2out.c
index 2d8d96a0f5a..61ce70f357f 100644
--- a/src/plugins/nat/nat44-ed/nat44_ed_in2out.c
+++ b/src/plugins/nat/nat44-ed/nat44_ed_in2out.c
@@ -102,14 +102,15 @@ nat_ed_alloc_addr_and_port_with_snat_address (
   u16 port_per_thread, u32 snat_thread_index, snat_session_t *s,
   ip4_address_t *outside_addr, u16 *outside_port)
 {
-  const u16 port_thread_offset = (port_per_thread * snat_thread_index) + 1024;
+  const u16 port_thread_offset =
+    (port_per_thread * snat_thread_index) + ED_USER_PORT_OFFSET;
 
   s->o2i.match.daddr = a->addr;
   /* first try port suggested by caller */
   u16 port = clib_net_to_host_u16 (*outside_port);
   u16 port_offset = port - port_thread_offset;
-  if (port <= port_thread_offset ||
-      port > port_thread_offset + port_per_thread)
+  if (port < port_thread_offset ||
+      port >= port_thread_offset + port_per_thread)
     {
       /* need to pick a different port, suggested port doesn't fit in
        * this thread's port range */
diff --git a/src/plugins/nat/nat44-ed/nat44_ed_out2in.c b/src/plugins/nat/nat44-ed/nat44_ed_out2in.c
index 33449122e43..dfe4a15752b 100644
--- a/src/plugins/nat/nat44-ed/nat44_ed_out2in.c
+++ b/src/plugins/nat/nat44-ed/nat44_ed_out2in.c
@@ -279,7 +279,8 @@ nat44_ed_alloc_i2o_port (snat_main_t *sm, snat_address_t *a, snat_session_t *s,
   for (int i = 0; i < ED_PORT_ALLOC_ATTEMPTS; ++i)
     {
       portnum = (sm->port_per_thread * snat_thread_index) +
-		snat_random_port (0, sm->port_per_thread - 1) + 1024;
+		snat_random_port (0, sm->port_per_thread - 1) +
+		ED_USER_PORT_OFFSET;
       portnum = clib_host_to_net_u16 (portnum);
       nat_6t_i2o_flow_init (sm, thread_index, s, i2o_addr, i2o_port, a->addr,
 			    portnum, i2o_fib_index, proto);