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Fix potential spin in interop message relay #41319

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Feng Wang (chemwolf6922) wants to merge 5 commits into
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Fix potential spin in interop message relay #41319

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e95d16a
handle success && bytes read == 0
chemwolf6922 Aug 12, 2026
8c6bfb4
handle partial reads
chemwolf6922 Aug 12, 2026
c887310
refactor with MultiHandleWait
chemwolf6922 Aug 13, 2026
4414fd4
trigger pipeline
chemwolf6922 Aug 13, 2026
7f8d0f3
trigger pipeline
chemwolf6922 Aug 13, 2026
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111 changes: 52 additions & 59 deletions src/windows/common/interop.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -14,6 +14,7 @@ Module Name:

#include "precomp.h"
#include "interop.hpp"
#include "HandleIO.h"
#include "helpers.hpp"
#include "socket.hpp"
#include "hvsocket.hpp"
Expand Down Expand Up @@ -408,78 +409,70 @@ std::string FormatCommandLine(gsl::span<gsl::byte> CommandLineData, USHORT Comma
DWORD
ProcessInteropMessages(_In_ HANDLE MessageHandle, _Inout_ CreateProcessResult* Result)
{
OVERLAPPED Overlapped = {0};
const wil::unique_event OverlappedEvent(wil::EventOptions::ManualReset);
Overlapped.hEvent = OverlappedEvent.get();
const HANDLE WaitHandles[] = {Overlapped.hEvent, Result->Process.get()};
namespace io = wsl::windows::common::io;

// Read messages from the message handle. Break out of the loop if the pipe
// is connection is closed or the process exits.
//
// N.B. ReadFile will automatically reset the event in the overlapped
// structure.
DWORD ExitCode = 1;
for (;;)
{
DWORD BytesRead;
LX_INIT_WINDOW_SIZE_CHANGED WindowSizeMessage;
bool Success = ReadFile(MessageHandle, &WindowSizeMessage, sizeof(WindowSizeMessage), &BytesRead, &Overlapped);
if (!Success)
{
const auto LastError = GetLastError();
if ((LastError == ERROR_BROKEN_PIPE) || (LastError == ERROR_HANDLE_EOF))
{
if (WI_IsFlagClear(Result->Flags, LX_INIT_CREATE_PROCESS_RESULT_FLAG_GUI_APPLICATION))
{
THROW_IF_WIN32_BOOL_FALSE(TerminateProcess(Result->Process.get(), 1));
}
DWORD exitCode = 1;
size_t pendingSize = 0;
LX_INIT_WINDOW_SIZE_CHANGED pendingMessage{};

break;
}
auto processExit = [&] {
THROW_IF_WIN32_BOOL_FALSE(GetExitCodeProcess(Result->Process.get(), &exitCode));

THROW_LAST_ERROR_IF(LastError != ERROR_IO_PENDING);

auto CancelIo = wil::scope_exit_log(WI_DIAGNOSTICS_INFO, [&] {
CancelIoEx(MessageHandle, &Overlapped);
GetOverlappedResult(MessageHandle, &Overlapped, &BytesRead, TRUE);
});
// Close the pseudoconsole, this causes all pending data to be flushed.
Result->PseudoConsole.reset();
};

const DWORD WaitStatus = WaitForMultipleObjects(RTL_NUMBER_OF(WaitHandles), WaitHandles, FALSE, INFINITE);
if (WaitStatus == WAIT_OBJECT_0)
{
Success = GetOverlappedResult(MessageHandle, &Overlapped, &BytesRead, FALSE);
CancelIo.release();
if ((!Success) || (BytesRead == 0))
io::MultiHandleWait wait;
wait.AddHandle(
std::make_unique<io::ReadHandle>(
io::HandleWrapper{MessageHandle},
[&](const gsl::span<char>& input) {
if (input.empty())
{
if (WI_IsFlagClear(Result->Flags, LX_INIT_CREATE_PROCESS_RESULT_FLAG_GUI_APPLICATION))
const DWORD waitStatus = WaitForSingleObject(Result->Process.get(), 0);
if (waitStatus == WAIT_OBJECT_0)
{
processExit();
}
else
{
THROW_IF_WIN32_BOOL_FALSE(TerminateProcess(Result->Process.get(), 1));
THROW_HR_IF(E_UNEXPECTED, waitStatus != WAIT_TIMEOUT);
if (WI_IsFlagClear(Result->Flags, LX_INIT_CREATE_PROCESS_RESULT_FLAG_GUI_APPLICATION))
{
THROW_IF_WIN32_BOOL_FALSE(TerminateProcess(Result->Process.get(), 1));
}
}

break;
return;
}

WI_ASSERT((BytesRead == sizeof(WindowSizeMessage)) && (WindowSizeMessage.Header.MessageType == LxInitMessageWindowSizeChanged));
auto remaining = input;

@OneBlue Blue (OneBlue) Aug 14, 2026

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remaining should be stored outside of this lambda, since it's possible for a read to be partial, and if that happens, we want the bytes to be stored until the next call.

In an ideal world, we'd reuse ReadSocketMessageHandle, but it currently only supports sockets. Maybe we can add a flag to add support for non-socket handles, but that's outside the scope of this change

while (!remaining.empty())
{
const size_t bytesToCopy = (std::min)(remaining.size(), sizeof(pendingMessage) - pendingSize);
std::copy_n(remaining.data(), bytesToCopy, reinterpret_cast<char*>(&pendingMessage) + pendingSize);

@OneBlue Blue (OneBlue) Aug 14, 2026

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I think we can skip the copy into pendingMessage here. If we have enough bytes for a full message, we could just access it via:

const auto& message = gslhelper::get_struct<LX_INIT_WINDOW_SIZE_CHANGED>(remaining);

pendingSize += bytesToCopy;
remaining = remaining.subspan(bytesToCopy);

const COORD Size{static_cast<SHORT>(WindowSizeMessage.Columns), static_cast<SHORT>(WindowSizeMessage.Rows)};
THROW_IF_FAILED(ResizePseudoConsole(Result->PseudoConsole.get(), Size));
}
else if (WaitStatus == (WAIT_OBJECT_0 + 1))
{
THROW_IF_WIN32_BOOL_FALSE(GetExitCodeProcess(Result->Process.get(), &ExitCode));
if (pendingSize == sizeof(pendingMessage))
{
THROW_HR_IF(
E_UNEXPECTED,
(pendingMessage.Header.MessageType != LxInitMessageWindowSizeChanged) ||
(pendingMessage.Header.MessageSize != sizeof(pendingMessage)));

const COORD size{static_cast<SHORT>(pendingMessage.Columns), static_cast<SHORT>(pendingMessage.Rows)};
THROW_IF_FAILED(ResizePseudoConsole(Result->PseudoConsole.get(), size));
pendingSize = 0;
}
}
}),
io::MultiHandleWait::CancelOnCompleted);

// Close the pseudoconsole, this causes all pending data to be flushed.
Result->PseudoConsole.reset();
break;
}
else
{
THROW_HR(E_UNEXPECTED);
}
}
}
wait.AddHandle(std::make_unique<io::EventHandle>(io::HandleWrapper{Result->Process.get()}, processExit), io::MultiHandleWait::CancelOnCompleted);

return ExitCode;
wait.Run(std::nullopt);
return exitCode;
}

} // namespace
Expand Down