nat: fix EI hairpinning thread safety

Avoid doing inter-thread reads without locks by doing a handoff before
destination address rewrite. Destination address is read from a session
which is possibly owned by a different thread. By splitting the work in
two parts with a handoff in the middle, we can do both in a thread safe
way.

Type: improvement
Signed-off-by: Klement Sekera <ksekera@cisco.com>
Change-Id: I1c50d188393a610f5564fa230c75771a8065f273

1 files changed, 92 insertions, 0 deletions

diff --git a/src/plugins/nat/nat44_hairpinning.h b/src/plugins/nat/nat44_hairpinning.h
new file mode 100644
index 00000000000..2a8b73db6ab
--- /dev/null
+++ b/src/plugins/nat/nat44_hairpinning.h
@@ -0,0 +1,92 @@
+#ifndef __included_nat44_hairpinning_h__
+#define __included_nat44_hairpinning_h__
+
+#include <nat/nat.h>
+
+#define foreach_nat44_hairpinning_handoff_error                               \
+  _ (CONGESTION_DROP, "congestion drop")
+
+typedef enum
+{
+#define _(sym, str) NAT44_HAIRPINNING_HANDOFF_ERROR_##sym,
+  foreach_nat44_hairpinning_handoff_error
+#undef _
+    NAT44_HAIRPINNING_HANDOFF_N_ERROR,
+} nat44_hairpinning_handoff_error_t;
+
+static char *nat44_hairpinning_handoff_error_strings[] = {
+#define _(sym, string) string,
+  foreach_nat44_hairpinning_handoff_error
+#undef _
+};
+
+typedef struct
+{
+  u32 next_worker_index;
+} nat44_hairpinning_handoff_trace_t;
+
+static u8 *
+format_nat44_hairpinning_handoff_trace (u8 *s, va_list *args)
+{
+  CLIB_UNUSED (vlib_main_t * vm) = va_arg (*args, vlib_main_t *);
+  CLIB_UNUSED (vlib_node_t * node) = va_arg (*args, vlib_node_t *);
+  nat44_hairpinning_handoff_trace_t *t =
+    va_arg (*args, nat44_hairpinning_handoff_trace_t *);
+
+  s = format (s, "nat-hairpinning-handoff: next-worker %d",
+	      t->next_worker_index);
+
+  return s;
+}
+
+always_inline uword
+nat44_hairpinning_handoff_fn_inline (vlib_main_t *vm,
+				     vlib_node_runtime_t *node,
+				     vlib_frame_t *frame, u32 fq_index)
+{
+  vlib_buffer_t *bufs[VLIB_FRAME_SIZE], **b;
+  u32 n_enq, n_left_from, *from;
+  u16 thread_indices[VLIB_FRAME_SIZE], *ti;
+
+  from = vlib_frame_vector_args (frame);
+  n_left_from = frame->n_vectors;
+  vlib_get_buffers (vm, from, bufs, n_left_from);
+
+  b = bufs;
+  ti = thread_indices;
+
+  while (n_left_from > 0)
+    {
+      ti[0] = vnet_buffer (b[0])->snat.required_thread_index;
+
+      if (PREDICT_FALSE ((node->flags & VLIB_NODE_FLAG_TRACE) &&
+			 (b[0]->flags & VLIB_BUFFER_IS_TRACED)))
+	{
+	  nat44_hairpinning_handoff_trace_t *t =
+	    vlib_add_trace (vm, node, b[0], sizeof (*t));
+	  t->next_worker_index = ti[0];
+	}
+
+      n_left_from -= 1;
+      ti += 1;
+      b += 1;
+    }
+  n_enq = vlib_buffer_enqueue_to_thread (vm, fq_index, from, thread_indices,
+					 frame->n_vectors, 1);
+
+  if (n_enq < frame->n_vectors)
+    vlib_node_increment_counter (
+      vm, node->node_index, NAT44_HAIRPINNING_HANDOFF_ERROR_CONGESTION_DROP,
+      frame->n_vectors - n_enq);
+  return frame->n_vectors;
+}
+
+#endif // __included_nat44_hairpinning_h__
+
+/*
+ * fd.io coding-style-patch-verification: ON
+ *
+ * Local Variables:
+ * eval: (c-set-style "gnu")
+ * End:
+ */