misc: binary api fuzz test fixes

Add a hook to src/vlibapi/api_shared.c to fuzz (screw up) binary API
messages, e.g. by xoring random data into them before processing. We
specifically exempt client connection messages, and inband debug CLI
messages. We step over msg_id, client index, client context, and
sw_if_index. Otherwise, "make test" vectors fail too rapidly to learn
anything.

The goal is to reduce the number of crashes caused to zero. We're
fairly close with this patch.

Add vl_msg_api_max_length(void *mp), which returns the maximum
plausible length for a binary API message.

Use it to hardern vl_api_from_api_to_new_vec(...) which takes an
additional argument - message pointer - so it can verify that
astr->length is sane. If it's not sane, return a u8 *vector of the
form "insane astr->length nnnn\0".

Verify array lengths in vl_api_dhcp6_send_client_message_t_handler(...)
and vl_api_dhcp6_pd_send_client_message_t_handler(...).

Add a fairly effective binary API fuzz hook to the unittest plugin,
and modify the "make test" framework.py to pass "api-fuzz { on|off }"
to enable API fuzzing: "make API_FUZZ=on TEST=xxx test-debug" or similar

Type: improvement

Signed-off-by: Dave Barach <dave@barachs.net>
Change-Id: I0157267652a163c01553d5267620f719cc6c3bde

3 files changed, 28 insertions, 2 deletions

diff --git a/src/vlibapi/api.h b/src/vlibapi/api.h
index 3d5c8698f73..431155c5e09 100644
--- a/src/vlibapi/api.h
+++ b/src/vlibapi/api.h
@@ -109,6 +109,7 @@ void vl_msg_api_handler_with_vm_node (api_main_t * am, svm_region_t * vlib_rp,
 				      void *the_msg, vlib_main_t * vm,
 				      vlib_node_runtime_t * node,
 				      u8 is_private);
+u32 vl_msg_api_max_length (void *mp);
 vl_api_trace_t *vl_msg_api_trace_get (api_main_t * am,
 				      vl_api_trace_which_t which);
 void vl_msg_api_add_msg_name_crc (api_main_t * am, const char *string,
diff --git a/src/vlibapi/api_shared.c b/src/vlibapi/api_shared.c
index 28e9f481650..fbaa9c9e013 100644
--- a/src/vlibapi/api_shared.c
+++ b/src/vlibapi/api_shared.c
@@ -533,6 +533,8 @@ msg_handler_internal (api_main_t * am,
     }
 }
 
+void (*vl_msg_api_fuzz_hook) (u16, void *);
+
 /* This is only to be called from a vlib/vnet app */
 void
 vl_msg_api_handler_with_vm_node (api_main_t * am, svm_region_t * vlib_rp,
@@ -600,6 +602,10 @@ vl_msg_api_handler_with_vm_node (api_main_t * am, svm_region_t * vlib_rp,
 	  am->vlib_rp = vlib_rp;
 	  am->shmem_hdr = (void *) vlib_rp->user_ctx;
 	}
+
+      if (PREDICT_FALSE (vl_msg_api_fuzz_hook != 0))
+	(*vl_msg_api_fuzz_hook) (id, the_msg);
+
       (*handler) (the_msg, vm, node);
       if (is_private)
 	{
@@ -870,6 +876,21 @@ vl_msg_api_queue_handler (svm_queue_t * q)
     vl_msg_api_handler ((void *) msg);
 }
 
+u32
+vl_msg_api_max_length (void *mp)
+{
+  msgbuf_t *mb;
+  u32 data_len = ~0;
+
+  /* Work out the maximum sane message length, and return it */
+  if (PREDICT_TRUE (mp != 0))
+    {
+      mb = (msgbuf_t *) (((u8 *) mp) - offsetof (msgbuf_t, data));
+      data_len = clib_net_to_host_u32 (mb->data_len);
+    }
+  return data_len;
+}
+
 vl_api_trace_t *
 vl_msg_api_trace_get (api_main_t * am, vl_api_trace_which_t which)
 {
@@ -1132,9 +1153,13 @@ vl_api_format_string (u8 * s, va_list * args)
  * NOT nul terminated.
  */
 u8 *
-vl_api_from_api_to_new_vec (vl_api_string_t * astr)
+vl_api_from_api_to_new_vec (void *mp, vl_api_string_t * astr)
 {
   u8 *v = 0;
+
+  if (vl_msg_api_max_length (mp) < clib_net_to_host_u32 (astr->length))
+    return format (0, "insane astr->length %u%c",
+		   clib_net_to_host_u32 (astr->length), 0);
   vec_add (v, astr->buf, clib_net_to_host_u32 (astr->length));
   return v;
 }
diff --git a/src/vlibapi/api_types.h b/src/vlibapi/api_types.h
index 21fcde53b0e..07c7aaba0c5 100644
--- a/src/vlibapi/api_types.h
+++ b/src/vlibapi/api_types.h
@@ -46,7 +46,7 @@ extern int vl_api_vec_to_api_string (const u8 *vec, vl_api_string_t * str);
 extern u32 vl_api_string_len (vl_api_string_t * astr);
 
 /* Returns new vector. NON nul terminated */
-extern u8 * vl_api_from_api_to_new_vec (vl_api_string_t *astr);
+extern u8 * vl_api_from_api_to_new_vec (void *mp, vl_api_string_t *astr);
 /* Returns new vector. Nul terminated */
 extern char * vl_api_from_api_to_new_c_string (vl_api_string_t *astr);