service/pam: move pam execution to subprocess to allow killing it

Many pam modules can't be aborted well without this.

.clang-tidy

@@ -28,6 +28,7 @@ Checks: >
   -modernize-return-braced-init-list,
   -modernize-use-trailing-return-type,
   performance-*,
+  -performance-avoid-endl,
   portability-std-allocator-const,
   readability-*,
   -readability-function-cognitive-complexity,

src/services/pam/CMakeLists.txt

@@ -3,6 +3,8 @@
 qt_add_library(quickshell-service-pam STATIC
 	qml.cpp
 	conversation.cpp
+	ipc.cpp
+	subprocess.cpp
 )
 qt_add_qml_module(quickshell-service-pam
 	URI Quickshell.Services.Pam

src/services/pam/conversation.cpp

@@ -1,21 +1,22 @@
 #include "conversation.hpp"
-#include <utility>
 
 #include <qlogging.h>
 #include <qloggingcategory.h>
-#include <qmutex.h>
 #include <qobject.h>
+#include <qsocketnotifier.h>
 #include <qstring.h>
 #include <qtmetamacros.h>
-#include <security/_pam_types.h>
-#include <security/pam_appl.h>
+#include <sys/wait.h>
+
+#include "ipc.hpp"
 
 Q_LOGGING_CATEGORY(logPam, "quickshell.service.pam", QtWarningMsg);
 
 QString PamError::toString(PamError::Enum value) {
 	switch (value) {
-	case ConnectionFailed: return "Failed to connect to pam";
+	case StartFailed: return "Failed to start the PAM session";
 	case TryAuthFailed: return "Failed to try authenticating";
+	case InternalError: return "Internal error occurred";
 	default: return "Invalid error";
 	}
 }
@@ -26,160 +27,116 @@ QString PamResult::toString(PamResult::Enum value) {
 	case Failed: return "Failed";
 	case Error: return "Error occurred while authenticating";
 	case MaxTries: return "The authentication method has no more attempts available";
-	// case Expired: return "The account has expired";
-	// case PermissionDenied: return "Permission denied";
 	default: return "Invalid result";
 	}
 }
 
-void PamConversation::run() {
-	auto conv = pam_conv {
-	    .conv = &PamConversation::conversation,
-	    .appdata_ptr = this,
-	};
+PamConversation::~PamConversation() { this->abort(); }
 
-	pam_handle_t* handle = nullptr;
-
-	qCInfo(logPam) << this << "Starting pam session for user" << this->user << "with config"
-	               << this->config << "in configdir" << this->configDir;
-
-	auto result = pam_start_confdir(
-	    this->config.toStdString().c_str(),
-	    this->user.toStdString().c_str(),
-	    &conv,
-	    this->configDir.toStdString().c_str(),
-	    &handle
-	);
-
-	if (result != PAM_SUCCESS) {
-		qCCritical(logPam) << this << "Unable to start pam conversation with error"
-		                   << QString(pam_strerror(handle, result));
-		emit this->error(PamError::ConnectionFailed);
-		this->deleteLater();
+void PamConversation::start(const QString& configDir, const QString& config, const QString& user) {
+	this->childPid = PamConversation::createSubprocess(&this->pipes, configDir, config, user);
+	if (this->childPid == 0) {
+		qCCritical(logPam) << "Failed to create pam subprocess.";
+		emit this->error(PamError::InternalError);
 		return;
 	}
 
-	result = pam_authenticate(handle, 0);
-
-	// Seems to require root and quickshell should not run as root.
-	// if (result == PAM_SUCCESS) {
-	//   result = pam_acct_mgmt(handle, 0);
-	// }
-
-	switch (result) {
-	case PAM_SUCCESS:
-		qCInfo(logPam) << this << "ended with successful authentication.";
-		emit this->completed(PamResult::Success);
-		break;
-	case PAM_AUTH_ERR:
-		qCInfo(logPam) << this << "ended with failed authentication.";
-		emit this->completed(PamResult::Failed);
-		break;
-	case PAM_MAXTRIES:
-		qCInfo(logPam) << this << "ended with failure: max tries.";
-		emit this->completed(PamResult::MaxTries);
-		break;
-	/*case PAM_ACCT_EXPIRED:
-		qCInfo(logPam) << this << "ended with failure: account expiration.";
-		emit this->completed(PamResult::Expired);
-		break;
-	case PAM_PERM_DENIED:
-		qCInfo(logPam) << this << "ended with failure: permission denied.";
-		emit this->completed(PamResult::PermissionDenied);
-		break;*/
-	default:
-		qCCritical(logPam) << this << "ended with error:" << QString(pam_strerror(handle, result));
-		emit this->error(PamError::TryAuthFailed);
-		break;
-	}
-
-	result = pam_end(handle, result);
-	if (result != PAM_SUCCESS) {
-		qCCritical(logPam) << this << "Failed to end pam conversation with error code"
-		                   << QString(pam_strerror(handle, result));
-	}
-
-	this->deleteLater();
+	QObject::connect(&this->notifier, &QSocketNotifier::activated, this, &PamConversation::onMessage);
+	this->notifier.setSocket(this->pipes.fdIn);
+	this->notifier.setEnabled(true);
 }
 
 void PamConversation::abort() {
-	qCDebug(logPam) << "Abort requested for" << this;
-	auto locker = QMutexLocker(&this->wakeMutex);
-	this->mAbort = true;
-	this->waker.wakeOne();
+	if (this->childPid != 0) {
+		qCDebug(logPam) << "Killing subprocess for" << this;
+		kill(this->childPid, SIGKILL); // NOLINT (include)
+		waitpid(this->childPid, nullptr, 0);
+		this->childPid = 0;
+	}
 }
 
-void PamConversation::respond(QString response) {
-	qCDebug(logPam) << "Set response for" << this;
-	auto locker = QMutexLocker(&this->wakeMutex);
-	this->response = std::move(response);
-	this->hasResponse = true;
-	this->waker.wakeOne();
+void PamConversation::internalError() {
+	if (this->childPid != 0) {
+		qCDebug(logPam) << "Killing subprocess for" << this;
+		kill(this->childPid, SIGKILL); // NOLINT (include)
+		waitpid(this->childPid, nullptr, 0);
+		this->childPid = 0;
+		emit this->error(PamError::InternalError);
+	}
 }
 
-int PamConversation::conversation(
-    int msgCount,
-    const pam_message** msgArray,
-    pam_response** responseArray,
-    void* appdata
-) {
-	auto* delegate = static_cast<PamConversation*>(appdata);
+void PamConversation::respond(const QString& response) {
+	qCDebug(logPam) << "Sending response for" << this;
+	if (!this->pipes.writeString(response.toStdString())) {
+		qCCritical(logPam) << "Failed to write response to subprocess.";
+		this->internalError();
+	}
+}
 
+void PamConversation::onMessage() {
 	{
-		auto locker = QMutexLocker(&delegate->wakeMutex);
-		if (delegate->mAbort) {
-			return PAM_ERROR_MSG;
-		}
-	}
+		qCDebug(logPam) << "Got message from subprocess.";
 
-	// freed by libc so must be alloc'd by it.
-	auto* responses = static_cast<pam_response*>(calloc(msgCount, sizeof(pam_response))); // NOLINT
+		auto type = PamIpcEvent::Exit;
 
-	for (auto i = 0; i < msgCount; i++) {
-		const auto* message = msgArray[i]; // NOLINT
-		auto& response = responses[i];     // NOLINT
+		auto ok = this->pipes.readBytes(
+		    reinterpret_cast<char*>(&type), // NOLINT
+		    sizeof(PamIpcEvent)
+		);
 
-		auto msgString = QString(message->msg);
-		auto messageChanged = true; // message->msg_style != PAM_PROMPT_ECHO_OFF;
-		auto isError = message->msg_style == PAM_ERROR_MSG;
-		auto responseRequired =
-		    message->msg_style == PAM_PROMPT_ECHO_OFF || message->msg_style == PAM_PROMPT_ECHO_ON;
+		if (!ok) goto fail;
 
-		qCDebug(logPam) << delegate << "got new message message:" << msgString
-		                << "messageChanged:" << messageChanged << "isError:" << isError
-		                << "responseRequired" << responseRequired;
+		if (type == PamIpcEvent::Exit) {
+			auto code = PamIpcExitCode::OtherError;
 
-		delegate->hasResponse = false;
-		emit delegate->message(msgString, messageChanged, isError, responseRequired);
+			ok = this->pipes.readBytes(
+			    reinterpret_cast<char*>(&code), // NOLINT
+			    sizeof(PamIpcExitCode)
+			);
 
-		{
-			auto locker = QMutexLocker(&delegate->wakeMutex);
+			if (!ok) goto fail;
 
-			if (delegate->mAbort) {
-				free(responses); // NOLINT
-				return PAM_ERROR_MSG;
+			qCDebug(logPam) << "Subprocess exited with code" << static_cast<int>(code);
+
+			switch (code) {
+			case PamIpcExitCode::Success: emit this->completed(PamResult::Success); break;
+			case PamIpcExitCode::AuthFailed: emit this->completed(PamResult::Failed); break;
+			case PamIpcExitCode::StartFailed: emit this->error(PamError::StartFailed); break;
+			case PamIpcExitCode::MaxTries: emit this->completed(PamResult::MaxTries); break;
+			case PamIpcExitCode::PamError: emit this->error(PamError::TryAuthFailed); break;
+			case PamIpcExitCode::OtherError: emit this->error(PamError::InternalError); break;
 			}
 
-			if (responseRequired) {
-				if (!delegate->hasResponse) {
-					delegate->waker.wait(locker.mutex());
+			waitpid(this->childPid, nullptr, 0);
+			this->childPid = 0;
+		} else if (type == PamIpcEvent::Request) {
+			PamIpcRequestFlags flags {};
 
-					if (delegate->mAbort) {
-						free(responses); // NOLINT
-						return PAM_ERROR_MSG;
-					}
-				}
+			ok = this->pipes.readBytes(
+			    reinterpret_cast<char*>(&flags), // NOLINT
+			    sizeof(PamIpcRequestFlags)
+			);
 
-				if (!delegate->hasResponse) {
-					qCCritical(logPam
-					) << "Pam conversation requires response and does not have one. This should not happen.";
-				}
+			if (!ok) goto fail;
 
-				response.resp = strdup(delegate->response.toStdString().c_str()); // NOLINT (include error)
-			}
+			auto message = this->pipes.readString(&ok);
+
+			if (!ok) goto fail;
+
+			this->message(
+			    QString::fromUtf8(message),
+			    /*flags.echo*/ true,
+			    flags.error,
+			    flags.responseRequired
+			);
+		} else {
+			qCCritical(logPam) << "Unexpected message from subprocess.";
+			goto fail;
 		}
 	}
+	return;
 
-	*responseArray = responses;
-	return PAM_SUCCESS;
+fail:
+	qCCritical(logPam) << "Failed to read subprocess request.";
+	this->internalError();
 }

src/services/pam/conversation.hpp

@@ -2,13 +2,16 @@
 
 #include <utility>
 
-#include <qmutex.h>
+#include <qloggingcategory.h>
 #include <qobject.h>
 #include <qqmlintegration.h>
-#include <qthread.h>
+#include <qsocketnotifier.h>
+#include <qtclasshelpermacros.h>
 #include <qtmetamacros.h>
-#include <qwaitcondition.h>
-#include <security/pam_appl.h>
+
+#include "ipc.hpp"
+
+Q_DECLARE_LOGGING_CATEGORY(logPam);
 
 /// The result of an authentication.
 class PamResult: public QObject {
@@ -26,10 +29,6 @@ public:
 		Error = 2,
 		/// The authentication method ran out of tries and should not be used again.
 		MaxTries = 3,
-		// The account has expired.
-		// Expired  4,
-		// Permission denied.
-		// PermissionDenied  5,
 	};
 	Q_ENUM(Enum);
 
@@ -44,52 +43,56 @@ class PamError: public QObject {
 
 public:
 	enum Enum {
-		/// Failed to initiate the pam connection.
-		ConnectionFailed = 1,
+		/// Failed to start the pam session.
+		StartFailed = 1,
 		/// Failed to try to authenticate the user.
 		/// This is not the same as the user failing to authenticate.
 		TryAuthFailed = 2,
+		/// An error occurred inside quickshell's pam interface.
+		InternalError = 3,
 	};
 	Q_ENUM(Enum);
 
 	Q_INVOKABLE static QString toString(PamError::Enum value);
 };
 
-class PamConversation: public QThread {
+// PAM has no way to abort a running module except when it sends a message,
+// meaning aborts for things like fingerprint scanners
+// and hardware keys don't actually work without aborting the process...
+// so we have a subprocess.
+class PamConversation: public QObject {
 	Q_OBJECT;
 
 public:
-	explicit PamConversation(QString config, QString configDir, QString user)
-	    : config(std::move(config))
-	    , configDir(std::move(configDir))
-	    , user(std::move(user)) {}
+	explicit PamConversation(QObject* parent): QObject(parent) {}
+	~PamConversation() override;
+	Q_DISABLE_COPY_MOVE(PamConversation);
 
 public:
-	void run() override;
+	void start(const QString& configDir, const QString& config, const QString& user);
 
 	void abort();
-	void respond(QString response);
+	void respond(const QString& response);
 
 signals:
 	void completed(PamResult::Enum result);
 	void error(PamError::Enum error);
 	void message(QString message, bool messageChanged, bool isError, bool responseRequired);
 
+private slots:
+	void onMessage();
+
 private:
-	static int conversation(
-	    int msgCount,
-	    const pam_message** msgArray,
-	    pam_response** responseArray,
-	    void* appdata
+	static pid_t createSubprocess(
+	    PamIpcPipes* pipes,
+	    const QString& configDir,
+	    const QString& config,
+	    const QString& user
 	);
 
-	QString config;
-	QString configDir;
-	QString user;
+	void internalError();
 
-	QMutex wakeMutex;
-	QWaitCondition waker;
-	bool mAbort = false;
-	bool hasResponse = false;
-	QString response;
+	pid_t childPid = 0;
+	PamIpcPipes pipes;
+	QSocketNotifier notifier {QSocketNotifier::Read};
 };

src/services/pam/ipc.cpp

@@ -0,0 +1,69 @@
+#include "ipc.hpp"
+#include <cstddef>
+#include <cstdint>
+#include <string>
+
+#include <unistd.h>
+
+PamIpcPipes::~PamIpcPipes() {
+	if (this->fdIn != 0) close(this->fdIn);
+	if (this->fdOut != 0) close(this->fdOut);
+}
+
+bool PamIpcPipes::readBytes(char* buffer, size_t length) const {
+	size_t i = 0;
+
+	while (i < length) {
+		auto count = read(this->fdIn, buffer + i, length - i); // NOLINT
+
+		if (count == -1 || count == 0) {
+			return false;
+		}
+
+		i += count;
+	}
+
+	return true;
+}
+
+bool PamIpcPipes::writeBytes(const char* buffer, size_t length) const {
+	size_t i = 0;
+	while (i < length) {
+		auto count = write(this->fdOut, buffer + i, length - i); // NOLINT
+
+		if (count == -1 || count == 0) {
+			return false;
+		}
+
+		i += count;
+	}
+
+	return true;
+}
+
+std::string PamIpcPipes::readString(bool* ok) const {
+	if (ok != nullptr) *ok = false;
+
+	uint32_t length = 0;
+	if (!this->readBytes(reinterpret_cast<char*>(&length), sizeof(length))) { // NOLINT
+		return "";
+	}
+
+	char data[length]; // NOLINT
+	if (!this->readBytes(data, length)) {
+		return "";
+	}
+
+	if (ok != nullptr) *ok = true;
+
+	return std::string(data, length);
+}
+
+bool PamIpcPipes::writeString(const std::string& string) const {
+	uint32_t length = string.length();
+	if (!this->writeBytes(reinterpret_cast<char*>(&length), sizeof(length))) { // NOLINT
+		return false;
+	}
+
+	return this->writeBytes(string.data(), string.length());
+}

src/services/pam/ipc.hpp

@@ -0,0 +1,43 @@
+#pragma once
+
+#include <cstddef>
+#include <cstdint>
+#include <string>
+
+#include <qtclasshelpermacros.h>
+
+enum class PamIpcEvent : uint8_t {
+	Request,
+	Exit,
+};
+
+enum class PamIpcExitCode : uint8_t {
+	Success,
+	StartFailed,
+	AuthFailed,
+	MaxTries,
+	PamError,
+	OtherError,
+};
+
+struct PamIpcRequestFlags {
+	bool echo;
+	bool error;
+	bool responseRequired;
+};
+
+class PamIpcPipes {
+public:
+	explicit PamIpcPipes() = default;
+	explicit PamIpcPipes(int fdIn, int fdOut): fdIn(fdIn), fdOut(fdOut) {}
+	~PamIpcPipes();
+	Q_DISABLE_COPY_MOVE(PamIpcPipes);
+
+	[[nodiscard]] bool readBytes(char* buffer, size_t length) const;
+	[[nodiscard]] bool writeBytes(const char* buffer, size_t length) const;
+	[[nodiscard]] std::string readString(bool* ok) const;
+	[[nodiscard]] bool writeString(const std::string& string) const;
+
+	int fdIn = 0;
+	int fdOut = 0;
+};

src/services/pam/qml.cpp

@@ -13,12 +13,6 @@
 
 #include "conversation.hpp"
 
-PamContext::~PamContext() {
-	if (this->conversation != nullptr && this->conversation->isRunning()) {
-		this->conversation->abort();
-	}
-}
-
 void PamContext::componentComplete() {
 	this->postInit = true;
 
@@ -91,12 +85,12 @@ void PamContext::startConversation() {
 		}
 	}
 
-	this->conversation = new PamConversation(this->mConfig, this->mConfigDirectory, user);
+	this->conversation = new PamConversation(this);
 	QObject::connect(this->conversation, &PamConversation::completed, this, &PamContext::onCompleted);
 	QObject::connect(this->conversation, &PamConversation::error, this, &PamContext::onError);
 	QObject::connect(this->conversation, &PamConversation::message, this, &PamContext::onMessage);
 	emit this->activeChanged();
-	this->conversation->start();
+	this->conversation->start(this->mConfigDirectory, this->mConfig, user);
 }
 
 void PamContext::abortConversation() {
@@ -104,7 +98,7 @@ void PamContext::abortConversation() {
 	this->mTargetActive = false;
 
 	QObject::disconnect(this->conversation, nullptr, this, nullptr);
-	if (this->conversation->isRunning()) this->conversation->abort();
+	this->conversation->deleteLater();
 	this->conversation = nullptr;
 	emit this->activeChanged();
 
@@ -124,9 +118,9 @@ void PamContext::abortConversation() {
 	}
 }
 
-void PamContext::respond(QString response) {
+void PamContext::respond(const QString& response) {
 	if (this->isActive() && this->mIsResponseRequired) {
-		this->conversation->respond(std::move(response));
+		this->conversation->respond(response);
 	} else {
 		qWarning() << "PamContext response was ignored as this context does not require one.";
 	}

src/services/pam/qml.hpp

@@ -51,8 +51,6 @@ class PamContext
 
 public:
 	explicit PamContext(QObject* parent = nullptr): QObject(parent) {}
-	~PamContext() override;
-	Q_DISABLE_COPY_MOVE(PamContext);
 
 	void classBegin() override {}
 	void componentComplete() override;
@@ -69,7 +67,7 @@ public:
 	/// Respond to pam.
 	///
 	/// May not be called unless `responseRequired` is true.
-	Q_INVOKABLE void respond(QString response);
+	Q_INVOKABLE void respond(const QString& response);
 
 	[[nodiscard]] bool isActive() const;
 	void setActive(bool active);

src/services/pam/subprocess.cpp

@@ -0,0 +1,209 @@
+#include "subprocess.hpp"
+#include <array>
+#include <ostream>
+#include <string>
+
+#include <qlogging.h>
+#include <qloggingcategory.h>
+#include <qstring.h>
+#include <sched.h>
+#include <security/_pam_types.h>
+#include <security/pam_appl.h>
+#include <unistd.h>
+
+#include "conversation.hpp"
+#include "ipc.hpp"
+
+pid_t PamConversation::createSubprocess(
+    PamIpcPipes* pipes,
+    const QString& configDir,
+    const QString& config,
+    const QString& user
+) {
+	auto toSubprocess = std::array<int, 2>();
+	auto fromSubprocess = std::array<int, 2>();
+
+	if (pipe(toSubprocess.data()) == -1 || pipe(fromSubprocess.data()) == -1) {
+		qCDebug(logPam) << "Failed to create pipes for subprocess.";
+		return 0;
+	}
+
+	auto* configDirF = strdup(configDir.toStdString().c_str()); // NOLINT (include)
+	auto* configF = strdup(config.toStdString().c_str());       // NOLINT (include)
+	auto* userF = strdup(user.toStdString().c_str());           // NOLINT (include)
+	auto log = logPam().isDebugEnabled();
+
+	auto pid = fork();
+
+	if (pid < 0) {
+		qCDebug(logPam) << "Failed to fork for subprocess.";
+	} else if (pid == 0) {
+		close(toSubprocess[1]);   // close w
+		close(fromSubprocess[0]); // close r
+
+		{
+			auto subprocess = PamSubprocess(log, toSubprocess[0], fromSubprocess[1]);
+			auto code = subprocess.exec(configDirF, configF, userF);
+			subprocess.sendCode(code);
+		}
+
+		free(configDirF); // NOLINT
+		free(configF);    // NOLINT
+		free(userF);      // NOLINT
+
+		// do not do cleanup that may affect the parent
+		_exit(0);
+	} else {
+		close(toSubprocess[0]);   // close r
+		close(fromSubprocess[1]); // close w
+
+		pipes->fdIn = fromSubprocess[0];
+		pipes->fdOut = toSubprocess[1];
+
+		free(configDirF); // NOLINT
+		free(configF);    // NOLINT
+		free(userF);      // NOLINT
+
+		return pid;
+	}
+
+	return -1; // should never happen but lint
+}
+
+PamIpcExitCode PamSubprocess::exec(const char* configDir, const char* config, const char* user) {
+	logIf(this->log) << "Waiting for parent confirmation..." << std::endl;
+
+	auto conv = pam_conv {
+	    .conv = &PamSubprocess::conversation,
+	    .appdata_ptr = this,
+	};
+
+	pam_handle_t* handle = nullptr;
+
+	logIf(this->log) << "Starting pam session for user \"" << user << "\" with config \"" << config
+	                 << "\" in dir \"" << configDir << "\"" << std::endl;
+
+	auto result = pam_start_confdir(config, user, &conv, configDir, &handle);
+
+	if (result != PAM_SUCCESS) {
+		logIf(true) << "Unable to start pam conversation with error \"" << pam_strerror(handle, result)
+		            << "\" (code " << result << ")" << std::endl;
+		return PamIpcExitCode::StartFailed;
+	}
+
+	result = pam_authenticate(handle, 0);
+	PamIpcExitCode code = PamIpcExitCode::OtherError;
+
+	switch (result) {
+	case PAM_SUCCESS:
+		logIf(this->log) << "Authenticated successfully." << std::endl;
+		code = PamIpcExitCode::Success;
+		break;
+	case PAM_AUTH_ERR:
+		logIf(this->log) << "Failed to authenticate." << std::endl;
+		code = PamIpcExitCode::AuthFailed;
+		break;
+	case PAM_MAXTRIES:
+		logIf(this->log) << "Failed to authenticate due to hitting max tries." << std::endl;
+		code = PamIpcExitCode::MaxTries;
+		break;
+	default:
+		logIf(true) << "Error while authenticating: \"" << pam_strerror(handle, result) << "\" (code "
+		            << result << ")" << std::endl;
+		code = PamIpcExitCode::PamError;
+		break;
+	}
+
+	result = pam_end(handle, result);
+	if (result != PAM_SUCCESS) {
+		logIf(true) << "Error in pam_end: \"" << pam_strerror(handle, result) << "\" (code " << result
+		            << ")" << std::endl;
+	}
+
+	return code;
+}
+
+void PamSubprocess::sendCode(PamIpcExitCode code) {
+	{
+		auto eventType = PamIpcEvent::Exit;
+		auto ok = this->pipes.writeBytes(
+		    reinterpret_cast<char*>(&eventType), // NOLINT
+		    sizeof(PamIpcEvent)
+		);
+
+		if (!ok) goto fail;
+
+		ok = this->pipes.writeBytes(
+		    reinterpret_cast<char*>(&code), // NOLINT
+		    sizeof(PamIpcExitCode)
+		);
+
+		if (!ok) goto fail;
+
+		return;
+	}
+
+fail:
+	_exit(1);
+}
+
+int PamSubprocess::conversation(
+    int msgCount,
+    const pam_message** msgArray,
+    pam_response** responseArray,
+    void* appdata
+) {
+	auto* delegate = static_cast<PamSubprocess*>(appdata);
+
+	// freed by libc so must be alloc'd by it.
+	auto* responses = static_cast<pam_response*>(calloc(msgCount, sizeof(pam_response))); // NOLINT
+
+	for (auto i = 0; i < msgCount; i++) {
+		const auto* message = msgArray[i]; // NOLINT
+		auto& response = responses[i];     // NOLINT
+
+		auto msgString = std::string(message->msg);
+		auto req = PamIpcRequestFlags {
+		    .echo = message->msg_style != PAM_PROMPT_ECHO_OFF,
+		    .error = message->msg_style == PAM_ERROR_MSG,
+		    .responseRequired =
+		        message->msg_style == PAM_PROMPT_ECHO_OFF || message->msg_style == PAM_PROMPT_ECHO_ON,
+		};
+
+		logIf(delegate->log) << "Relaying pam message: \"" << msgString << "\" echo: " << req.echo
+		                     << " error: " << req.error << " responseRequired: " << req.responseRequired
+		                     << std::endl;
+
+		auto eventType = PamIpcEvent::Request;
+		auto ok = delegate->pipes.writeBytes(
+		    reinterpret_cast<char*>(&eventType), // NOLINT
+		    sizeof(PamIpcEvent)
+		);
+
+		if (!ok) goto fail;
+
+		ok = delegate->pipes.writeBytes(
+		    reinterpret_cast<const char*>(&req), // NOLINT
+		    sizeof(PamIpcRequestFlags)
+		);
+
+		if (!ok) goto fail;
+		if (!delegate->pipes.writeString(msgString)) goto fail;
+
+		if (req.responseRequired) {
+			auto ok = false;
+			auto resp = delegate->pipes.readString(&ok);
+			if (!ok) _exit(static_cast<int>(PamIpcExitCode::OtherError));
+			logIf(delegate->log) << "Got response for request.";
+
+			response.resp = strdup(resp.c_str()); // NOLINT (include)
+		}
+	}
+
+	*responseArray = responses;
+	return PAM_SUCCESS;
+
+fail:
+	free(responseArray); // NOLINT
+	_exit(1);
+}

src/services/pam/subprocess.hpp

@@ -0,0 +1,31 @@
+#pragma once
+
+#include <iostream>
+
+#include <security/pam_appl.h>
+
+#include "ipc.hpp"
+
+// endls are intentional as it makes debugging much easier when the buffer actually flushes.
+// NOLINTBEGIN
+#define logIf(log)                                                                                 \
+	if (log) std::cout << "quickshell.service.pam.subprocess: "
+// NOLINTEND
+
+class PamSubprocess {
+public:
+	explicit PamSubprocess(bool log, int fdIn, int fdOut): log(log), pipes(fdIn, fdOut) {}
+	PamIpcExitCode exec(const char* configDir, const char* config, const char* user);
+	void sendCode(PamIpcExitCode code);
+
+private:
+	static int conversation(
+	    int msgCount,
+	    const pam_message** msgArray,
+	    pam_response** responseArray,
+	    void* appdata
+	);
+
+	bool log;
+	PamIpcPipes pipes;
+};