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Fix a data race that could manifest as null pointer dereference in FutureBase::Release() #747

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Merged
dconeybe merged 7 commits into from
Nov 16, 2021
Merged

Fix a data race that could manifest as null pointer dereference in FutureBase::Release() #747

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7788946
Fix race condition in Future/FutureBase
dconeybe Nov 11, 2021
52c6da1
Add release notes entry skeleton
dconeybe Nov 12, 2021
18e0cc4
Add a link to the PR in the release notes
dconeybe Nov 12, 2021
17d6beb
future_impl.h: Fix a bug in FutureBase::operator=(FutureBase&&) where…
dconeybe Nov 15, 2021
ca4a566
future_impl.h: Remove code from the copy/move constructors that is du…
dconeybe Nov 15, 2021
4be3dd7
Swap out firebase::Mutex with std::mutex since future.h cannot includ…
dconeybe Nov 15, 2021
4aeb741
release_build_files/readme.md: tweak release notes entry
dconeybe Nov 15, 2021
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9 changes: 8 additions & 1 deletion app/src/include/firebase/future.h
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Original file line number Diff line number Diff line change
Expand Up @@ -20,6 +20,7 @@
#include <stddef.h>
#include <stdint.h>

#include <mutex>
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@jonsimantov jonsimantov Nov 15, 2021

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Can you use firebase::Mutex and firebase::MutexLock instead?
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@dconeybe dconeybe Nov 15, 2021

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As discussed, this change will be made in a follow-up PR. We want to get this merged to fix the flake in CI.
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@jonsimantov jonsimantov Nov 15, 2021

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After discussion, we're going to switch this to firebase::Mutex / firebase::MutexLock in a follow-up PR, as it also requires moving mutex.h to app/src/include/firebase/internal (and adding #ifndef DOXYGEN to avoid documenting the internal class).
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⚠️ Lint warning: <mutex> is an unapproved C++11 header.
#include <utility>

#include "firebase/internal/common.h"
Expand Down Expand Up @@ -309,6 +310,7 @@ class FutureBase {

/// Returns true if the two Futures reference the same result.
bool operator==(const FutureBase& rhs) const {
std::lock_guard<std::mutex> lock(mutex_);
return api_ == rhs.api_ && handle_ == rhs.handle_;
}

Expand All @@ -317,12 +319,17 @@ class FutureBase {

#if defined(INTERNAL_EXPERIMENTAL)
/// Returns the API-specific handle. Should only be called by the API.
const FutureHandle& GetHandle() const { return handle_; }
FutureHandle GetHandle() const {
std::lock_guard<std::mutex> lock(mutex_);
return handle_;
}
#endif // defined(INTERNAL_EXPERIMENTAL)

protected:
/// @cond FIREBASE_APP_INTERNAL

mutable std::mutex mutex_;

/// Backpointer to the issuing API class.
/// Set to nullptr when Future is invalidated.
detail::FutureApiInterface* api_;
Expand Down
55 changes: 43 additions & 12 deletions app/src/include/firebase/internal/future_impl.h
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Original file line number Diff line number Diff line change
Expand Up @@ -207,41 +207,63 @@ inline FutureBase::FutureBase(const FutureBase& rhs)
: api_(NULL) // NOLINT
{ // NOLINT
*this = rhs;
detail::RegisterForCleanup(api_, this);
}

inline FutureBase& FutureBase::operator=(const FutureBase& rhs) {
Release();
api_ = rhs.api_;
handle_ = rhs.handle_;
if (api_ != NULL) { // NOLINT
api_->ReferenceFuture(handle_);

detail::FutureApiInterface* new_api;
FutureHandle new_handle;
{
std::lock_guard<std::mutex> lock(rhs.mutex_);
new_api = rhs.api_;
new_handle = rhs.handle_;
}
detail::RegisterForCleanup(api_, this);

{
std::lock_guard<std::mutex> lock(mutex_);
api_ = new_api;
handle_ = new_handle;

if (api_ != NULL) { // NOLINT
api_->ReferenceFuture(handle_);
}
detail::RegisterForCleanup(api_, this);
}

return *this;
}

#if defined(FIREBASE_USE_MOVE_OPERATORS)
inline FutureBase::FutureBase(FutureBase&& rhs) noexcept
: api_(NULL) // NOLINT
{
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⚠️ Lint warning: { should almost always be at the end of the previous line
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@jonsimantov jonsimantov Nov 16, 2021

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Oh, could you fix the lint warning actually?
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@jonsimantov jonsimantov Nov 16, 2021

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Oh wait just noticed it's not in your code - never mind.
detail::UnregisterForCleanup(rhs.api_, &rhs);
*this = std::move(rhs);
detail::RegisterForCleanup(api_, this);
}

inline FutureBase& FutureBase::operator=(FutureBase&& rhs) noexcept {
Release();
detail::UnregisterForCleanup(rhs.api_, &rhs);
api_ = rhs.api_;
handle_ = rhs.handle_;
rhs.api_ = NULL; // NOLINT

detail::FutureApiInterface* new_api;
FutureHandle new_handle;
{
std::lock_guard<std::mutex> lock(rhs.mutex_);
detail::UnregisterForCleanup(rhs.api_, &rhs);
new_api = rhs.api_;
new_handle = rhs.handle_;
rhs.api_ = NULL; // NOLINT
}

std::lock_guard<std::mutex> lock(mutex_);
api_ = new_api;
handle_ = new_handle;
detail::RegisterForCleanup(api_, this);
return *this;
}
#endif // defined(FIREBASE_USE_MOVE_OPERATORS)

inline void FutureBase::Release() {
std::lock_guard<std::mutex> lock(mutex_);
if (api_ != NULL) { // NOLINT
detail::UnregisterForCleanup(api_, this);
api_->ReleaseFuture(handle_);
Expand All @@ -250,25 +272,30 @@ inline void FutureBase::Release() {
}

inline FutureStatus FutureBase::status() const {
std::lock_guard<std::mutex> lock(mutex_);
return api_ == NULL ? // NOLINT
kFutureStatusInvalid
: api_->GetFutureStatus(handle_);
}

inline int FutureBase::error() const {
std::lock_guard<std::mutex> lock(mutex_);
return api_ == NULL ? -1 : api_->GetFutureError(handle_); // NOLINT
}

inline const char* FutureBase::error_message() const {
std::lock_guard<std::mutex> lock(mutex_);
return api_ == NULL ? NULL : api_->GetFutureErrorMessage(handle_); // NOLINT
}

inline const void* FutureBase::result_void() const {
std::lock_guard<std::mutex> lock(mutex_);
return api_ == NULL ? NULL : api_->GetFutureResult(handle_); // NOLINT
}

inline void FutureBase::OnCompletion(CompletionCallback callback,
void* user_data) const {
std::lock_guard<std::mutex> lock(mutex_);
if (api_ != NULL) { // NOLINT
api_->AddCompletionCallback(handle_, callback, user_data, nullptr,
/*clear_existing_callbacks=*/true);
Expand All @@ -278,6 +305,7 @@ inline void FutureBase::OnCompletion(CompletionCallback callback,
#if defined(INTERNAL_EXPERIMENTAL)
inline FutureBase::CompletionCallbackHandle FutureBase::AddOnCompletion(
CompletionCallback callback, void* user_data) const {
std::lock_guard<std::mutex> lock(mutex_);
if (api_ != NULL) { // NOLINT
return api_->AddCompletionCallback(handle_, callback, user_data, nullptr,
/*clear_existing_callbacks=*/false);
Expand All @@ -287,6 +315,7 @@ inline FutureBase::CompletionCallbackHandle FutureBase::AddOnCompletion(

inline void FutureBase::RemoveOnCompletion(
CompletionCallbackHandle completion_handle) const {
std::lock_guard<std::mutex> lock(mutex_);
if (api_ != NULL) { // NOLINT
api_->RemoveCompletionCallback(handle_, completion_handle);
}
Expand All @@ -296,6 +325,7 @@ inline void FutureBase::RemoveOnCompletion(
#if defined(FIREBASE_USE_STD_FUNCTION)
inline void FutureBase::OnCompletion(
std::function<void(const FutureBase&)> callback) const {
std::lock_guard<std::mutex> lock(mutex_);
if (api_ != NULL) { // NOLINT
api_->AddCompletionCallbackLambda(handle_, callback,
/*clear_existing_callbacks=*/true);
Expand All @@ -305,6 +335,7 @@ inline void FutureBase::OnCompletion(
#if defined(INTERNAL_EXPERIMENTAL)
inline FutureBase::CompletionCallbackHandle FutureBase::AddOnCompletion(
std::function<void(const FutureBase&)> callback) const {
std::lock_guard<std::mutex> lock(mutex_);
if (api_ != NULL) { // NOLINT
return api_->AddCompletionCallbackLambda(
handle_, callback,
Expand Down
3 changes: 3 additions & 0 deletions release_build_files/readme.md
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Expand Up @@ -569,6 +569,9 @@ code.
## Release Notes
### Next Release
- Changes
- General (Android): Fixed a data race that could manifest as null pointer
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@jonsimantov jonsimantov Nov 16, 2021

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One last note (it can wait for the followup) - this isn't Android only, right? We can remove the "(Android)" tag.
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@dconeybe dconeybe Nov 16, 2021

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Ahh right. I've opened #749 to fix the release notes entry.
dereference in `FutureBase::Release()`.
([#747](https://github.com/firebase/firebase-cpp-sdk/pull/747))
- Auth (Desktop): Fixed a crash in `error_code()` when a request
is cancelled or times out.
([#737](https://github.com/firebase/firebase-cpp-sdk/issues/737))
Expand Down