NAT: TCP MSS clamping

[vpp.git] / src / plugins / nat / nat_inlines.h

diff --git a/src/plugins/nat/nat_inlines.h b/src/plugins/nat/nat_inlines.h
index adfb1d5..8922c05 100644 (file)
--- a/src/plugins/nat/nat_inlines.h
+++ b/src/plugins/nat/nat_inlines.h
@@ -328,6 +328,54 @@ make_sm_kv (clib_bihash_kv_8_8_t * kv, ip4_address_t * addr, u8 proto,
   kv->value = ~0ULL;
 }
 
+always_inline void
+mss_clamping (snat_main_t * sm, tcp_header_t * tcp, ip_csum_t * sum)
+{
+  u8 *data;
+  u8 opt_len, opts_len, kind;
+  u16 mss;
+
+  if (!(sm->mss_clamping && tcp_syn (tcp)))
+    return;
+
+  opts_len = (tcp_doff (tcp) << 2) - sizeof (tcp_header_t);
+  data = (u8 *) (tcp + 1);
+  for (; opts_len > 0; opts_len -= opt_len, data += opt_len)
+    {
+      kind = data[0];
+
+      if (kind == TCP_OPTION_EOL)
+       break;
+      else if (kind == TCP_OPTION_NOOP)
+       {
+         opt_len = 1;
+         continue;
+       }
+      else
+       {
+         if (opts_len < 2)
+           return;
+         opt_len = data[1];
+
+         if (opt_len < 2 || opt_len > opts_len)
+           return;
+       }
+
+      if (kind == TCP_OPTION_MSS)
+       {
+         mss = *(u16 *) (data + 2);
+         if (clib_net_to_host_u16 (mss) > sm->mss_clamping)
+           {
+             *sum =
+               ip_csum_update (*sum, mss, sm->mss_value_net, ip4_header_t,
+                               length);
+             clib_memcpy (data + 2, &sm->mss_value_net, 2);
+           }
+         return;
+       }
+    }
+}
+
 #endif /* __included_nat_inlines_h__ */
 
 /*