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

[Alex Chen]

On 2020/11/12 14:37, Markus Armbruster wrote:
> 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);
> 

Thanks for your review，your patch is better than mine.
I will send the patch v2.

Thanks,
Alex