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

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,