Re: [PATCH] json: Fix a memleak in parse_pair()

[Markus Armbruster]

Alex Chen <alex.chen@huawei.com> writes:

> In qobject_type(), NULL is returned when the 'QObject' returned from 
> parse_value() is not of QString type,
> and this 'QObject' memory will leaked.
> So we need to first check whether the 'QObject' returned from parse_value() 
> is of QString type,
> and if not, we free 'QObject' memory and return an error.
>
> The memleak stack is as follows:
> Direct leak of 32 byte(s) in 1 object(s) allocated from:
>     #0 0xfffe4b3c34fb in __interceptor_malloc (/lib64/libasan.so.4+0xd34fb)
>     #1 0xfffe4ae48aa3 in g_malloc (/lib64/libglib-2.0.so.0+0x58aa3)
>     #2 0xaaab3557d9f7 in qnum_from_int 
> /Images/source_org/qemu_master/qemu/qobject/qnum.c:25
>     #3 0xaaab35584d23 in parse_literal 
> /Images/source_org/qemu_master/qemu/qobject/json-parser.c:511
>     #4 0xaaab35584d23 in parse_value 
> /Images/source_org/qemu_master/qemu/qobject/json-parser.c:554
>     #5 0xaaab35583d77 in parse_pair 
> /Images/source_org/qemu_master/qemu/qobject/json-parser.c:270
>     #6 0xaaab355845db in parse_object 
> /Images/source_org/qemu_master/qemu/qobject/json-parser.c:327
>     #7 0xaaab355845db in parse_value 
> /Images/source_org/qemu_master/qemu/qobject/json-parser.c:546
>     #8 0xaaab35585b1b in json_parser_parse 
> /Images/source_org/qemu_master/qemu/qobject/json-parser.c:580
>     #9 0xaaab35583703 in json_message_process_token 
> /Images/source_org/qemu_master/qemu/qobject/json-streamer.c:92
>     #10 0xaaab355ddccf in json_lexer_feed_char 
> /Images/source_org/qemu_master/qemu/qobject/json-lexer.c:313
>     #11 0xaaab355de0eb in json_lexer_feed 
> /Images/source_org/qemu_master/qemu/qobject/json-lexer.c:350
>     #12 0xaaab354aff67 in tcp_chr_read 
> /Images/source_org/qemu_master/qemu/chardev/char-socket.c:525
>     #13 0xfffe4ae429db in g_main_context_dispatch 
> (/lib64/libglib-2.0.so.0+0x529db)
>     #14 0xfffe4ae42d8f  (/lib64/libglib-2.0.so.0+0x52d8f)
>     #15 0xfffe4ae430df in g_main_loop_run (/lib64/libglib-2.0.so.0+0x530df)
>     #16 0xaaab34d70bff in iothread_run 
> /Images/source_org/qemu_master/qemu/iothread.c:82
>     #17 0xaaab3559d71b in qemu_thread_start 
> /Images/source_org/qemu_master/qemu/util/qemu-thread-posix.c:519

Good catch, thanks!

> Fixes: 532fb5328473 ("qapi: Make more of qobject_to()")
> Reported-by: Euler Robot <euler.robot@huawei.com>
> Signed-off-by: Alex Chen <alex.chen@huawei.com>
> Signed-off-by: Chen Qun <kuhn.chenqun@huawei.com>
> ---
>  qobject/json-parser.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/qobject/json-parser.c b/qobject/json-parser.c
> index d083810d37..b37762a203 100644
> --- a/qobject/json-parser.c
> +++ b/qobject/json-parser.c
> @@ -267,10 +267,13 @@ static int parse_pair(JSONParserContext *ctxt, QDict 
> *dict)
>          goto out;
>      }
>  
> -    key = qobject_to(QString, parse_value(ctxt));
> -    if (!key) {
> -        parse_error(ctxt, peek, "key is not a string in object");
> +    value = parse_value(ctxt);
> +    if (!value || qobject_type(value) != QTYPE_QSTRING) {

The "is string" test becomes more cumbersome.  Also, we reuse @value for
another purpose.

> +        qobject_unref(value);
> +        parse_error(ctxt, peek, "value is not a string in object");

Changing error messages in a memory leak fix is inappropriate.
Accident?

>          goto out;
> +    } else {
> +        key = qobject_to(QString, value);
>      }
>  
>      token = parser_context_pop_token(ctxt);

Here's a simpler, straightforward fix, with a test case thrown in:

diff --git a/qobject/json-parser.c b/qobject/json-parser.c
index d083810d37..c0f521b56b 100644
--- a/qobject/json-parser.c
+++ b/qobject/json-parser.c
@@ -257,8 +257,9 @@ static JSONToken 
*parser_context_peek_token(JSONParserContext *ctxt)
  */
 static int parse_pair(JSONParserContext *ctxt, QDict *dict)
 {
+    QObject *key_obj = NULL;
+    QString *key;
     QObject *value;
-    QString *key = NULL;
     JSONToken *peek, *token;
 
     peek = parser_context_peek_token(ctxt);
@@ -267,7 +268,8 @@ static int parse_pair(JSONParserContext *ctxt, QDict *dict)
         goto out;
     }
 
-    key = qobject_to(QString, parse_value(ctxt));
+    key_obj = parse_value(ctxt);
+    key = qobject_to(QString, key_obj);
     if (!key) {
         parse_error(ctxt, peek, "key is not a string in object");
         goto out;
@@ -297,13 +299,11 @@ static int parse_pair(JSONParserContext *ctxt, QDict 
*dict)
 
     qdict_put_obj(dict, qstring_get_str(key), value);
 
-    qobject_unref(key);
-
+    qobject_unref(key_obj);
     return 0;
 
 out:
-    qobject_unref(key);
-
+    qobject_unref(key_obj);
     return -1;
 }
 
diff --git a/tests/check-qjson.c b/tests/check-qjson.c
index 07a773e653..9a02079099 100644
--- a/tests/check-qjson.c
+++ b/tests/check-qjson.c
@@ -1415,6 +1415,14 @@ static void invalid_dict_comma(void)
     g_assert(obj == NULL);
 }
 
+static void invalid_dict_key(void)
+{
+    Error *err = NULL;
+    QObject *obj = qobject_from_json("{32:'abc'}", &err);
+    error_free_or_abort(&err);
+    g_assert(obj == NULL);
+}
+
 static void unterminated_literal(void)
 {
     Error *err = NULL;
@@ -1500,6 +1508,7 @@ int main(int argc, char **argv)
     g_test_add_func("/errors/unterminated/dict_comma", 
unterminated_dict_comma);
     g_test_add_func("/errors/invalid_array_comma", invalid_array_comma);
     g_test_add_func("/errors/invalid_dict_comma", invalid_dict_comma);
+    g_test_add_func("/errors/invalid_dict_key", invalid_dict_key);
     g_test_add_func("/errors/unterminated/literal", unterminated_literal);
     g_test_add_func("/errors/limits/nesting", limits_nesting);
     g_test_add_func("/errors/multiple_values", multiple_values);