json_config: do not assume JSON contains 'params' field

Not all JSON methods require 'params' field to be supplied.
Verification of the JSON is done on server side in
parse_single_request().

We should not attempt to process garbage values on correct
JSON config file during app start.

Segfault can be observed if following valid JSON config is supplied:
{
	"method": "framework_wait_init"
}
Resulting in:
json_config.c:388:13: runtime error: applying non-zero offset 18446744073709551600 to null pointer
AddressSanitizer:DEADLYSIGNAL
=================================================================
==3386067==ERROR: AddressSanitizer: SEGV on unknown address (pc 0x0000007260ff bp 0x7ffe6ea06890 sp 0x7ffe6ea067e0 T0)
==3386067==The signal is caused by a READ memory access.
==3386067==Hint: this fault was caused by a dereference of a high value address (see register values below).  Dissassemble the provided pc to learn which register was used.
    #0 0x7260ff in app_json_config_load_subsystem_config_entry /home/tzawadzk/spdk/lib/event/json_config.c:391
    #1 0x7cbb13 in msg_queue_run_batch /home/tzawadzk/spdk/lib/thread/thread.c:505
    #2 0x7cd00a in thread_poll /home/tzawadzk/spdk/lib/thread/thread.c:581
    #3 0x7cfe18 in spdk_thread_poll /home/tzawadzk/spdk/lib/thread/thread.c:689
    #4 0x71d6ef in _reactor_run /home/tzawadzk/spdk/lib/event/reactor.c:326
    #5 0x71eb00 in reactor_run /home/tzawadzk/spdk/lib/event/reactor.c:382
    #6 0x71f911 in spdk_reactors_start /home/tzawadzk/spdk/lib/event/reactor.c:477
    #7 0x718237 in spdk_app_start /home/tzawadzk/spdk/lib/event/app.c:691
    #8 0x407e94 in main /home/tzawadzk/spdk/app/spdk_tgt/spdk_tgt.c:120
    #9 0x7f0f2eef2041 in __libc_start_main ../csu/libc-start.c:308
    #10 0x4079ad in _start (/home/tzawadzk/spdk/build/bin/spdk_tgt+0x4079ad)

Signed-off-by: Tomasz Zawadzki <[email protected]>
Change-Id: I7ef1a764467817ad788fdf5dbe17eaeb99dcc22e
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/3256
Community-CI: Mellanox Build Bot
Tested-by: SPDK CI Jenkins <[email protected]>
Reviewed-by: Jim Harris <[email protected]>
Reviewed-by: Shuhei Matsumoto <[email protected]>

lib/event/json_config.c

@@ -384,14 +384,17 @@ app_json_config_load_subsystem_config_entry(void *_ctx)
 		goto out;
 	}
 
-	/* Get _END by skipping params and going back by one element. */
-	params_end = cfg.params + spdk_json_val_len(cfg.params) - 1;
+	SPDK_DEBUG_APP_CFG("\tmethod: %s\n", cfg.method);
 
-	/* Need to add one character to include '}' */
-	params_len = params_end->start - cfg.params->start + 1;
+	if (cfg.params) {
+		/* Get _END by skipping params and going back by one element. */
+		params_end = cfg.params + spdk_json_val_len(cfg.params) - 1;
 
-	SPDK_DEBUG_APP_CFG("\tmethod: %s\n", cfg.method);
-	SPDK_DEBUG_APP_CFG("\tparams: %.*s\n", (int)params_len, (char *)cfg.params->start);
+		/* Need to add one character to include '}' */
+		params_len = params_end->start - cfg.params->start + 1;
+
+		SPDK_DEBUG_APP_CFG("\tparams: %.*s\n", (int)params_len, (char *)cfg.params->start);
+	}
 
 	rpc_request = spdk_jsonrpc_client_create_request();
 	if (!rpc_request) {
@@ -408,10 +411,13 @@ app_json_config_load_subsystem_config_entry(void *_ctx)
 
 	spdk_json_write_named_string(w, "method", cfg.method);
 
-	/* No need to parse "params". Just dump the whole content of "params"
-	 * directly into the request and let the remote side verify it. */
-	spdk_json_write_name(w, "params");
-	spdk_json_write_val_raw(w, cfg.params->start, params_len);
+	if (cfg.params) {
+		/* No need to parse "params". Just dump the whole content of "params"
+		 * directly into the request and let the remote side verify it. */
+		spdk_json_write_name(w, "params");
+		spdk_json_write_val_raw(w, cfg.params->start, params_len);
+	}
+
 	spdk_jsonrpc_end_request(rpc_request, w);
 
 	rc = client_send_request(ctx, rpc_request, app_json_config_load_subsystem_config_entry_next);