crash in QJsonDocument::fromJson

thamht4190

I have a file to store encrypted json binary data.

Here is the code:

    // compressedData is read from file, then decrypted
    QByteArray uncompressedData = qUncompress(compressedData);
    if (uncompressedData.size() == 0) {
        qWarning() << "[att_store] failed to uncompress, uuid:" << uuid;
        return ErrorCode::DB_ATT_PARSE_ERROR;
    }

    // parse json
    QJsonParseError err;
    QJsonDocument doc = QJsonDocument::fromJson(uncompressedData, &err); // <--- crash here
    if (err.error != QJsonParseError::NoError) {
        qWarning() << "[att_store] failed to parse json, err:"
                   << static_cast<int>(err.error) << "size:" << uncompressedData.size()
                   << "uuid:" << uuid;
        return ErrorCode::DB_ATT_PARSE_ERROR;
    }

When reading from file, sometimes, I get crash like this:

STACK_TEXT:  
000000ea`b39fa760 00007ffc`f6b7486d : 00000000`00000000 00007ffd`032a83d0 000001ee`eafe7633 001c35d7`00000000 : KERNELBASE!RaiseException+0x68
000000ea`b39fa840 000001ee`e99c1a0f : 000001ee`e9700000 000000ea`b39fa950 000000ea`b39fa9d0 00007ffc`ff7ea828 : VCRUNTIME140!CxxThrowException+0xad
000000ea`b39fa8b0 000001ee`e993dcf5 : 000000ea`b39fa950 000001ee`e973df78 00000000`001c35db 000000ea`b39faa58 : Qt5Core!__scrt_throw_std_bad_alloc+0x1f
000000ea`b39fa900 000001ee`e99362e8 : ffffffff`fffffffe 000000ea`b39fa9d0 000001ee`ea802758 00000000`00000000 : Qt5Core!QJsonPrivate::Parser::parse+0x45
000000ea`b39fa930 00007ff7`766c4d8c : 00000000`001c35db 000000ea`003fc14b 000001ee`ea802758 000001ee`eaff2040 : Qt5Core!QJsonDocument::fromJson+0x38
000000ea`b39fa990 00007ff7`7667ea82 : 000001ee`e9c92180 000000ea`b39fab18 000001ee`ea802758 000001ee`eaff2040 : CortexSync!Cortex::Storage::TrainingAttributesStore::get+0x33c

It happens on Windows.
Can anyone know why? The file still can be read, decrypted then decompressed and parsed to json normally several times before this crash happens.

VRonin

Looks like you are running out of memory. Either you have a memory leak somewhere or you are just storing too much data in RAM

thamht4190

@VRonin Thanks. I have another crash (seems the same root cause), when reading from that file:

STACK_TEXT:  
00000046`b70fac20 00007ff8`3b07486d : 000001f4`bc5af770 00007ff8`4476284a 00000000`00000008 00000000`00000008 : KERNELBASE!RaiseException+0x68
00000046`b70fad00 00007fff`fb141a0f : 00007fff`fae80000 00000046`b70fae60 00000000`0034ec46 00007fff`fafd6cdb : VCRUNTIME140!_CxxThrowException+0xad
00000046`b70fad70 00007fff`faebf74a : 00000046`b70fae60 000001f4`bd3cfb00 00000000`00000000 000001f4`00000000 : Qt5Core!__scrt_throw_std_bad_alloc+0x1f
00000046`b70fadc0 00007fff`fafa7bac : 000001f4`bd3cfb00 00000000`0034ec46 00000046`b70ff2f0 000001f4`bd32b0f8 : Qt5Core!QByteArray::resize+0xca
00000046`b70fadf0 00007ff7`74b44c7d : 00007fff`fb412180 00000046`b70fae88 000001f4`bd32b0f8 000001f4`bd4b2a20 : Qt5Core!QIODevice::readAll+0x1ac
00000046`b70fae60 00007ff7`74afea82 : 000001f4`00000008 00000046`b70fafe8 000001f4`bd32b0f8 00000000`00000001 : CortexSync!Cortex::Storage::TrainingAttributesStore::get+0x22d

Can you say more about this?

VRonin

@thamht4190 said in crash in QJsonDocument::fromJson:

__scrt_throw_std_bad_alloc

I don't think it's anything to do with Qt:

JKSH

@thamht4190 said in crash in QJsonDocument::fromJson:

Can you say more about this?

Like @VRonin already said: "Either you have a memory leak somewhere or you are just storing too much data in RAM"

Monitor your app's memory usage while it runs.

thamht4190

Thanks! I understand the problem now. I'll monitor my application memory usage.

thamht4190

I monitored my application's memory usage. Unfortunately I don't see any problems. My application's memory usage is <10Mb at minimum usage and < 100Mb at maximum usage and there is no memory leak.
Note that the crashes I received are reported automatically from my customers' machine. I've never seen this crash before among a lot of machines, only the machine of this customer.
Here is some info from this machine:

Windows 10 Version 17134 MP (4 procs) Free x64
Product: WinNt, suite: SingleUserTS Personal
17134.1.amd64fre.rs4_release.180410-1804

I know that it's NOT Qt problem. However, can you help give me some any suggestions/ideas to investigate more?

Christian Ehrlicher

How big is your uncompressed data?

thamht4190

How big is your uncompressed data?

@Christian-Ehrlicher we have more than 1 files. As I checked on this machine (from logs), there are 2 files, about 7 - 10Mb per each file.

aha_1980

@thamht4190 is it possible, that the JSON is corrupted/invalid so that some recursion within Qt's classes happens?

Christian Ehrlicher

The only way I see is to reduce the json until it does not crash anymore or use a debug build of Qt to see exactly where and why the parser crashes.

thamht4190

Thanks. I'll try to contact this customer to see if I can have his data to confirm the possibility that his data is corrupted/invalid.