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

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

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());
+}