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Merged
scheibelp merged 1 commit into from
May 20, 2026
Merged

execute: Improve handle handling #38

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157 changes: 116 additions & 41 deletions src/execute.cxx
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Original file line number Diff line number Diff line change
Expand Up @@ -83,9 +83,12 @@ void ExecuteCommand::SetupExecute() {
// This structure specifies the STDIN and STDOUT handles for redirection.
ZeroMemory(&si_start_info, sizeof(STARTUPINFOW));
si_start_info.cb = sizeof(STARTUPINFOW);
si_start_info.hStdError = this->ChildStdErr_Wd;
si_start_info.hStdOutput = this->ChildStdOut_Wd;
si_start_info.dwFlags |= STARTF_USESTDHANDLES;
// Do not attach the pipe handles here. We'll create inheritable
// duplicates of the write ends immediately before CreateProcess to
// minimize the inheritance window.
si_start_info.hStdError = INVALID_HANDLE_VALUE;
si_start_info.hStdOutput = INVALID_HANDLE_VALUE;
si_start_info.dwFlags = 0;
this->procInfo = pi_proc_info;
this->startInfo = si_start_info;
}
Expand All @@ -97,28 +100,25 @@ void ExecuteCommand::SetupExecute() {
int ExecuteCommand::CreateChildPipes() {
// Create stdout pipes
SECURITY_ATTRIBUTES sa_attr;
// Set the bInheritHandle flag so pipe handles are inherited.
// Create non-inheritable pipes. We'll duplicate the write ends to
// inheritable handles immediately before CreateProcess to reduce the
// window where other processes could inherit them.
sa_attr.nLength = sizeof(SECURITY_ATTRIBUTES);
sa_attr.bInheritHandle = TRUE;
sa_attr.bInheritHandle = FALSE;
sa_attr.lpSecurityDescriptor = nullptr;
this->saAttr = sa_attr;
if (!CreatePipe(&this->ChildStdOut_Rd, &this->ChildStdOut_Wd, &sa_attr, 0))
return 0;
if (!SetHandleInformation(this->ChildStdOut_Rd, HANDLE_FLAG_INHERIT, 0))
return 0;

// create stderr pipes
SECURITY_ATTRIBUTES sa_attr_err;
// Set the bInheritHandle flag so pipe handles are inherited.
sa_attr_err.nLength = sizeof(SECURITY_ATTRIBUTES);
sa_attr_err.bInheritHandle = TRUE;
sa_attr_err.bInheritHandle = FALSE;
sa_attr_err.lpSecurityDescriptor = nullptr;
this->saAttrErr = sa_attr_err;
if (!CreatePipe(&this->ChildStdErr_Rd, &this->ChildStdErr_Wd, &sa_attr_err,
0))
return 0;
if (!SetHandleInformation(this->ChildStdErr_Rd, HANDLE_FLAG_INHERIT, 0))
return 0;

return 1;
}
Expand All @@ -137,9 +137,38 @@ bool ExecuteCommand::ExecuteToolChainChild() {
std::cerr << e.what() << "\n";
return false;
}
wchar_t* nc_command_line = _wcsdup(c_command_line.c_str());
if (!CreateProcessW(nullptr, nc_command_line, nullptr, nullptr, TRUE, 0,
nullptr, nullptr, &this->startInfo, &this->procInfo)) {
// Duplicate command line into writable buffer expected by CreateProcessW
std::vector<wchar_t> cmdbuf(c_command_line.begin(), c_command_line.end());
cmdbuf.push_back(L'\0');
wchar_t* nc_command_line = cmdbuf.data();
// Duplicate our non-inheritable write handles into inheritable handles
// immediately before CreateProcess to minimize the inheritance window.
HANDLE inheritableOut = INVALID_HANDLE_VALUE;
HANDLE inheritableErr = INVALID_HANDLE_VALUE;
HANDLE const self = GetCurrentProcess();
if (this->ChildStdOut_Wd && this->ChildStdOut_Wd != INVALID_HANDLE_VALUE) {
if (!DuplicateHandle(self, this->ChildStdOut_Wd, self, &inheritableOut,
0, TRUE, DUPLICATE_SAME_ACCESS)) {
return false;
}
this->startInfo.hStdOutput = inheritableOut;
this->startInfo.dwFlags |= STARTF_USESTDHANDLES;
}
if (this->ChildStdErr_Wd && this->ChildStdErr_Wd != INVALID_HANDLE_VALUE) {
if (!DuplicateHandle(self, this->ChildStdErr_Wd, self, &inheritableErr,
0, TRUE, DUPLICATE_SAME_ACCESS)) {
// Clean up any previously duplicated handle
if (inheritableOut && inheritableOut != INVALID_HANDLE_VALUE)
CloseHandle(inheritableOut);
return false;
}
this->startInfo.hStdError = inheritableErr;
this->startInfo.dwFlags |= STARTF_USESTDHANDLES;
}

if (!CreateProcessW(nullptr, nc_command_line, nullptr, nullptr, TRUE,
CREATE_UNICODE_ENVIRONMENT, nullptr, nullptr,
&this->startInfo, &this->procInfo)) {
// Handle errors coming from creation of child proc
FormatMessage(
FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM |
Expand All @@ -158,18 +187,37 @@ bool ExecuteCommand::ExecuteToolChainChild() {
}

std::cerr << "With error: ";
std::cerr << static_cast<char*>(lp_msg_buf) << "\n";
free(nc_command_line);
if (lp_msg_buf) {
std::cerr << static_cast<char*>(lp_msg_buf) << "\n";
LocalFree(lp_msg_buf);
} else {
std::cerr << reportLastError() << "\n";
}
this->cpw_initalization_failure = true;
return false;
}
// We've suceeded in kicking off the toolchain run
// Explicitly close write handle to child proc stdout
// as it is no longer needed and if we do not then cannot
// determine when child proc is done
free(nc_command_line);
CloseHandle(this->ChildStdOut_Wd);
CloseHandle(this->ChildStdErr_Wd);
// Parent no longer needs the inheritable duplicates; close them in the
// parent. The child has inherited its own copies.
if (this->startInfo.hStdOutput && this->startInfo.hStdOutput != INVALID_HANDLE_VALUE) {
CloseHandle(this->startInfo.hStdOutput);
this->startInfo.hStdOutput = INVALID_HANDLE_VALUE;
}
if (this->startInfo.hStdError && this->startInfo.hStdError != INVALID_HANDLE_VALUE) {
CloseHandle(this->startInfo.hStdError);
this->startInfo.hStdError = INVALID_HANDLE_VALUE;
}
// Also ensure our member copies of the write handles are closed in the
// parent; they reference the same kernel objects as the STARTUPINFO
// entries above.
if (this->ChildStdOut_Wd && this->ChildStdOut_Wd != INVALID_HANDLE_VALUE) {
SafeHandleCleanup(this->ChildStdOut_Wd);
this->ChildStdOut_Wd = INVALID_HANDLE_VALUE;
}
if (this->ChildStdErr_Wd && this->ChildStdErr_Wd != INVALID_HANDLE_VALUE) {
SafeHandleCleanup(this->ChildStdErr_Wd);
this->ChildStdErr_Wd = INVALID_HANDLE_VALUE;
}
return true;
}

Expand All @@ -182,7 +230,7 @@ int ExecuteCommand::PipeChildToStdStream(DWORD STD_HANDLE,
HANDLE reader_handle) {
DWORD dw_read;
DWORD dw_written;
CHAR ch_buf[BUFSIZE];
std::vector<char> ch_buf(BUFSIZE);
BOOL b_success = TRUE;
HANDLE h_parent_out;
if (this->write_to_file && this->fileout != INVALID_HANDLE_VALUE) {
Expand All @@ -192,30 +240,27 @@ int ExecuteCommand::PipeChildToStdStream(DWORD STD_HANDLE,
}

for (;;) {
b_success = ReadFile(reader_handle, ch_buf, BUFSIZE, &dw_read, nullptr);
b_success = ReadFile(reader_handle, ch_buf.data(), BUFSIZE, &dw_read, nullptr);
if (!b_success || (dw_read == 0 && this->terminated))
break;
if (dw_read != 0) {
b_success =
WriteFile(h_parent_out, ch_buf, dw_read, &dw_written, nullptr);
WriteFile(h_parent_out, ch_buf.data(), dw_read, &dw_written, nullptr);
if (dw_written < dw_read && b_success) {
// incomplete write but not a failure
// since bSuccess is true
// So lets write until bSuccess is false or
// until all bytes are written
DWORD current_pos = dw_written;
while ((dw_written < dw_read) || dw_written == 0) {
dw_read = dw_read - dw_written;
CHAR* partial_buf = new CHAR[dw_read];
for (DWORD i = 0; i < dw_read; ++i) {
partial_buf[i] = ch_buf[current_pos + i];
}
b_success = WriteFile(h_parent_out, partial_buf, dw_read,
&dw_written, nullptr);
delete partial_buf;
DWORD remaining = dw_read - dw_written;
while (remaining > 0) {
DWORD to_write = remaining;
b_success = WriteFile(h_parent_out, ch_buf.data() + current_pos,
to_write, &dw_written, nullptr);
if (!b_success)
break;
current_pos += dw_written;
remaining -= dw_written;
}
}
if (!b_success) {
Expand All @@ -225,6 +270,20 @@ int ExecuteCommand::PipeChildToStdStream(DWORD STD_HANDLE,
if (!b_success)
break;
}
// Close the reader handle now that we're done reading from the pipe to
// release underlying kernel resources. This prevents leaking handles
// across many invocations which can cause pipes to never reach EOF and
// eventually exhaust kernel resources.
if (reader_handle && reader_handle != INVALID_HANDLE_VALUE) {
CloseHandle(reader_handle);
// Clear the member copy so CleanupHandles doesn't attempt to close the
// same handle again.
if (reader_handle == this->ChildStdOut_Rd) {
this->ChildStdOut_Rd = INVALID_HANDLE_VALUE;
} else if (reader_handle == this->ChildStdErr_Rd) {
this->ChildStdErr_Rd = INVALID_HANDLE_VALUE;
}
}
return static_cast<int>(static_cast<int>(b_success) == 0);
}

Expand Down Expand Up @@ -257,7 +316,9 @@ DWORD ExecuteCommand::ReportExitCode() {
break;
}
this->terminated = true;
CloseHandle(this->procInfo.hProcess);
// Use SafeHandleCleanup to close the process handle and mark it invalid
// so later cleanup paths do not attempt to close it again.
SafeHandleCleanup(this->procInfo.hProcess);
return exit_code;
}

Expand Down Expand Up @@ -288,21 +349,35 @@ bool ExecuteCommand::Execute(const std::string& filename) {
ConvertASCIIToWide(filename).c_str(), FILE_APPEND_DATA,
FILE_SHARE_WRITE | FILE_SHARE_READ, &this->saAttr, OPEN_ALWAYS,
FILE_ATTRIBUTE_NORMAL, nullptr);
if (this->fileout != INVALID_HANDLE_VALUE) {
// Ensure file handle is not inheritable by child processes
SetHandleInformation(this->fileout, HANDLE_FLAG_INHERIT, 0);
}
} catch (const std::overflow_error& e) {
std::cerr << e.what() << "\n";
return false;
}
}
// Start reader threads before spawning the child so they are ready to
// drain the pipe as soon as the child writes. This reduces a small race
// window where a very fast child can fill the pipe buffer before the
// parent starts reading.
this->child_out_future = std::async(
std::launch::async, &ExecuteCommand::PipeChildToStdStream, this,
STD_OUTPUT_HANDLE, this->ChildStdOut_Rd);
this->child_err_future = std::async(
std::launch::async, &ExecuteCommand::PipeChildToStdStream, this,
STD_ERROR_HANDLE, this->ChildStdErr_Rd);

bool const ret_code = this->ExecuteToolChainChild();
if (ret_code) {
this->child_out_future = std::async(
std::launch::async, &ExecuteCommand::PipeChildToStdStream, this,
STD_OUTPUT_HANDLE, this->ChildStdOut_Rd);
this->child_err_future = std::async(
std::launch::async, &ExecuteCommand::PipeChildToStdStream, this,
STD_ERROR_HANDLE, this->ChildStdErr_Rd);
// Start exit code watcher only after the process is created
this->exit_code_future = std::async(
std::launch::async, &ExecuteCommand::ReportExitCode, this);
} else {
// If we failed to spawn, ensure reader futures are cancelled/observed
// by setting terminated so readers can exit promptly.
this->terminated = true;
}
return ret_code;
}
Expand Down
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