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Stability fixes in native code #226

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Stability fixes in native code #226

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42a9333
Stability fixes in native code
starix Jan 19, 2024
5118e53
Roll back some changes
starix Jan 24, 2024
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7 changes: 7 additions & 0 deletions krabs/krabs/etw.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -202,6 +202,9 @@ namespace krabs { namespace details {
PVOID trace_information,
ULONG information_length)
{
if (trace_.registrationHandle_ == INVALID_PROCESSTRACE_HANDLE)
return;

ULONG status = TraceSetInformation(
trace_.registrationHandle_,
information_class,
Expand Down Expand Up @@ -283,12 +286,16 @@ namespace krabs { namespace details {
template <typename T>
void trace_manager<T>::stop_trace()
{
if (trace_.registrationHandle_ == INVALID_PROCESSTRACE_HANDLE)
return;

trace_info info = fill_trace_info();
ULONG status = ControlTrace(
NULL,
trace_.name_.c_str(),
&info.properties,
EVENT_TRACE_CONTROL_STOP);
trace_.registrationHandle_ = INVALID_PROCESSTRACE_HANDLE;

if (status != ERROR_WMI_INSTANCE_NOT_FOUND) {
error_check_common_conditions(status);
Expand Down
32 changes: 31 additions & 1 deletion krabs/krabs/trace.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -282,6 +282,12 @@ namespace krabs {
*/
void set_default_event_callback(c_provider_callback callback);

template <typename U>
void set_default_event_callback(U& callback);

template <typename U>
void set_default_event_callback(const U& callback);

private:

/**
Expand Down Expand Up @@ -348,7 +354,8 @@ namespace krabs {
template <typename T>
trace<T>::~trace()
{
stop();
// Never throw in destructor
try { stop(); } catch (...) {}
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Did you see this throw? I'd need to look to see how trace_manager can throw.
Usually, we don't want to catch everything. There's also implications for SEH callbacks that might have been set up.

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Throwing an exception out of a destructor is dangerous. If another exception is already propagating the application will terminate.
ControlTrace(EVENT_TRACE_CONTROL_STOP) or CloseTrace() can return error inside stop(). Using SEH is to much.

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I'm aware that destructors shouldn't throw, however it's not a good pattern to just add "catch all" blocks in all the destructors. Catch what we expect.

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@starix starix Jan 24, 2024 •
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Ok. If we add error_callback to the trace object it may solve the user notification issue.

}

template <typename T>
Expand Down Expand Up @@ -440,7 +447,30 @@ namespace krabs {
template <typename T>
void trace<T>::set_default_event_callback(c_provider_callback callback)
{
// C function pointers don't interact well with std::ref, so we
// overload to take care of this scenario.
default_callback_ = callback;
}

template <typename T>
template <typename U>
void trace<T>::set_default_event_callback(U& callback)
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Do you have an example of what you're trying to solve here? I don't think you should need these at all.
If there is a good reason to have this, you should use a single function:

    template <typename T>
    template <typename U>
    void trace<T>::set_default_event_callback(U&& callback)

This can bind to all flavors of parameters correctly.

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@starix starix Jan 24, 2024 •
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Do you have an example of what you're trying to solve here?

auto fun = [&](const EVENT_RECORD& record) { ... };
krabs::user_trace trace;
trace.set_default_event_callback(fun);

The same approach is used in event_filter::add_on_error_callback or base_provider<T>::add_on_event_callback

{
// std::function copies its argument -- because our callbacks list
// is a list of std::function, this causes problems when a user
// intended for their particular instance to be called.
// std::ref lets us get around this and point to a specific instance
// that they handed us.
default_callback_ = std::ref(callback);
}

template <typename T>
template <typename U>
void trace<T>::set_default_event_callback(const U& callback)
{
// This is where temporaries bind to. Temporaries can't be wrapped in
// a std::ref because they'll go away very quickly. We are forced to
// actually copy these.
default_callback_ = callback;
}
}
19 changes: 11 additions & 8 deletions krabs/krabs/ut.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -164,7 +164,7 @@ namespace krabs { namespace details {
std::vector<BYTE> filterEventIdBuffer;
auto filterEventIdCount = settings.provider_filter_event_ids_.size();

if (filterEventIdCount > 0) {
if (filterEventIdCount > 0 && filterEventIdCount <= MAX_EVENT_FILTER_EVENT_ID_COUNT) {
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This should be an error condition that is bubbled up to the caller and then we can either:

  • Return an error condition (throw or return an error code)
  • Use the first MAX_EVENT_FILTER_EVENT_ID_COUNT items

I prefer throwing so it's obvious what went wrong.

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@starix starix Jan 24, 2024 •
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Both variants not ideal. We limit the user's use of krabs filtering. In my case we just "turn off" system pre-filtration. We will get all events (even unneeded) from provider but have a chance to filter them from in callback.

//event filters existing, set native filters using API
parameters.FilterDescCount = 1;
filterDesc.Type = EVENT_FILTER_TYPE_EVENT_ID;
Expand Down Expand Up @@ -237,15 +237,18 @@ namespace krabs { namespace details {

// for MOF providers, EventHeader.Provider is the *Message* GUID
// we need to ask TDH for event information in order to determine the
// correct provider to pass this event to
auto schema = get_event_schema_from_tdh(record);
auto eventInfo = reinterpret_cast<PTRACE_EVENT_INFO>(schema.get());
for (auto& provider : trace.providers_) {
if (eventInfo->ProviderGuid == provider.get().guid_) {
provider.get().on_event(record, trace.context_);
return;
// correct provider to pass this event to. Don't throw in callback.
try
{
auto eventInfo = trace.context_.schema_locator.get_event_schema(record);
for (auto& provider : trace.providers_) {
if (eventInfo->ProviderGuid == provider.get().guid_) {
provider.get().on_event(record, trace.context_);
return;
}
}
}
catch (krabs::could_not_find_schema&) {}
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This exception should not be caught. How else will a caller know why the callback is not working?
This layer needs to bubble up errors so that the calling application can know something went wrong.

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@starix starix Jan 24, 2024 •
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And trace session will close without any chance to resume. In my case we can still handle event in default callback. May be adding an error_callback to trace object is a good idea? We can call it from catch.


if (trace.default_callback_ != nullptr)
trace.default_callback_(record, trace.context_);
Expand Down