[PATCH for-4.21 1/6] tools/{lib,}xl: fix usage of error return from json_tokener_parse_verbose()

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

It's possible for json_tokener_parse_verbose() to return NULL and leave the
error parameter unset.  Initialize the error token to success, and only
print it if the function has actually set it to a value different than
success.

Reported by XenServer internal Coverity instance.

Fixes: 7e95dab9eb63 ("libxl: Convert libxl__json_parse() to use json-c")
Fixes: f6c6f2679d49 ("libxl: Convert libxl__object_to_json() to json-c")
Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
 tools/libs/light/libxl_json.c | 6 ++++--
 tools/xl/xl_info.c            | 5 +++--
 2 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/tools/libs/light/libxl_json.c b/tools/libs/light/libxl_json.c
index c76ae9f64a9d..a9e06b06932d 100644
--- a/tools/libs/light/libxl_json.c
+++ b/tools/libs/light/libxl_json.c
@@ -1366,11 +1366,13 @@ libxl__json_object *libxl__json_parse(libxl__gc *gc, 
const char *s)
     libxl__json_object *o = NULL;
 #ifdef USE_LIBJSONC_PARSER
     json_object *jso;
-    enum json_tokener_error error;
+    enum json_tokener_error error = json_tokener_success;
 
     jso = json_tokener_parse_verbose(s, &error);
     if (!jso) {
-        LOG(ERROR, "json-c parse error: %s", json_tokener_error_desc(error));
+        LOG(ERROR, "json-c parse error: %s",
+            error != json_tokener_success ? json_tokener_error_desc(error)
+                                          : "unspecified error");
         goto out;
     }
 #endif
diff --git a/tools/xl/xl_info.c b/tools/xl/xl_info.c
index 80a3b25aac81..777ff2c64294 100644
--- a/tools/xl/xl_info.c
+++ b/tools/xl/xl_info.c
@@ -67,7 +67,7 @@ static int printf_info_one_json(json_object **jso_r, int 
domid,
 {
     json_object *jso = NULL;
     json_object *jso_config = NULL;
-    enum json_tokener_error error;
+    enum json_tokener_error error = json_tokener_success;
     char *s = NULL;
     int r = EXIT_FAILURE;
 
@@ -75,7 +75,8 @@ static int printf_info_one_json(json_object **jso_r, int 
domid,
     jso_config = json_tokener_parse_verbose(s, &error);
     if (!jso_config) {
         fprintf(stderr, "fail to parse JSON from 
libxl_domain_config_to_json(): %s\n",
-                json_tokener_error_desc(error));
+                error != json_tokener_success ? json_tokener_error_desc(error)
+                                              : "unspecified error");
         goto out;
     }
 
-- 
2.51.0