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>

1 files changed, 2 insertions, 1 deletions

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);