Faking uinput: mount additional virtual devices without breaking container isolation

CMakeLists.txt

@@ -57,6 +57,7 @@ add_subdirectory(src/core)
 
 if (UNIX AND NOT APPLE)
     add_subdirectory(src/fake-udev)
+    add_subdirectory(src/fake-uinput)
 endif ()
 
 option(BUILD_MOONLIGHT "Build Moonlight server" ON)

src/fake-uinput/CMakeLists.txt

@@ -0,0 +1,18 @@
+option(BUILD_FAKE_UINPUT "Build fake-uinput library" ON)
+if (BUILD_FAKE_UINPUT)
+    message(STATUS "Building fake-uinput")
+
+    add_library(fake_uinput SHARED
+            fake-uinput.cpp)
+    add_library(fake-uinput::lib ALIAS fake_uinput)
+
+    target_compile_features(fake_uinput PRIVATE cxx_std_17)
+    option(FAKE_UINPUT_32BIT "Build fake-uinput 32-bit library" OFF)
+    if (FAKE_UINPUT_32BIT)
+        set_target_properties(fake_uinput PROPERTIES
+                # Force it to 32 bit
+                COMPILE_FLAGS "-m32" LINK_FLAGS "-m32"
+                # Change the name of the library to indicate it's 32-bit
+                OUTPUT_NAME "fake-uinput-32")
+    endif ()
+endif ()

src/fake-uinput/fake-uinput.cpp

@@ -0,0 +1,98 @@
+#include <cstdarg>
+#include <cstring>
+#include <dlfcn.h>
+#include <filesystem>
+#include <fstream>
+#include <iostream>
+#include <linux/uinput.h>
+#include <sys/ioctl.h>
+#include <sys/stat.h>
+#include <sys/sysmacros.h>
+
+/** https://github.com/whot/libevdev/blob/c3953e1bb8f813f3e248047d23fb0775b147da9f/libevdev/libevdev-uinput.c#L41 **/
+#define SYS_INPUT_DIR "/sys/devices/virtual/input/"
+
+#define LOG(Thing) std::cout << "[fake-uinput] " << Thing << std::endl;
+
+typedef int (*ioctl_t)(int, unsigned long, ...);
+static ioctl_t real_ioctl = nullptr;
+
+bool load_library() {
+  LOG("Loading ...")
+  // Load the real ioctl
+  real_ioctl = reinterpret_cast<ioctl_t>(dlsym(RTLD_NEXT, "ioctl"));
+  if (!real_ioctl) {
+    LOG("Error: " << dlerror());
+    return false;
+  }
+  return true;
+}
+
+void mount(const std::filesystem::path &sysfs_path, const std::string &filename) {
+  std::filesystem::path path(filename);
+  if (!std::filesystem::exists(path)) {
+    // Get the major and minor numbers of the device
+    // They are handily available in the sysfs directory
+    std::ifstream major_minor_file(sysfs_path / "dev");
+    unsigned int major, minor;
+    char sep;
+    major_minor_file >> major >> sep >> minor;
+
+    int rc = mknod(filename.c_str(), S_IFCHR | 0666, makedev(major, minor));
+    if (rc == -1) {
+      LOG("Error creating device node: " << strerror(errno));
+    } else {
+      LOG("Created device node: " << filename);
+    }
+  }
+}
+
+/**
+ * glibc, BSD
+ * TODO: musl uses int op instead of unsigned long
+ */
+extern "C" int ioctl(int fd, unsigned long request, ...) {
+  if (!real_ioctl) {
+    if (!load_library()) {
+      LOG("Error: real_ioctl is not initialized");
+      return -1;
+    }
+  }
+
+  // Call the real ioctl
+  va_list args;
+  va_start(args, request);
+  void *arg = va_arg(args, void *);
+  va_end(args);
+  int result = real_ioctl(fd, request, arg);
+
+  if (result >= 0 && request == UI_DEV_CREATE) { // Creating a new uinput device
+    LOG("Intercepted UI_DEV_CREATE ioctl call");
+
+    // Get the sysfs name of the created uinput device
+    char buf[sizeof(SYS_INPUT_DIR) + 64] = SYS_INPUT_DIR;
+    auto rc = real_ioctl(fd, UI_GET_SYSNAME(sizeof(buf) - strlen(SYS_INPUT_DIR)), &buf[strlen(SYS_INPUT_DIR)]);
+    if (rc != -1) {
+      // iterate over the files under /sys/devices/virtual/input/ and find "eventX" and "jsX" files
+      for (auto &p : std::filesystem::directory_iterator(buf)) {
+        if (p.is_directory()) {
+          auto path = p.path();
+          auto filename = path.filename().string();
+          if (filename.find("event") != std::string::npos) {
+            mount(path, "/dev/input/" + filename);
+          } else if (filename.find("js") != std::string::npos) {
+            mount(path, "/dev/input/" + filename);
+          }
+        }
+      }
+
+      // TODO: udev? using /sys/devices/virtual/input/{buf}/uevent ?
+
+    } else {
+      LOG("Error getting sysname: " << strerror(errno));
+    }
+  }
+
+  // return the original result
+  return result;
+}

src/moonlight-server/control/input_handler.cpp

@@ -497,21 +497,26 @@ void controller_multi(const CONTROLLER_MULTI_PACKET &pkt,
 
       // Remove the joypad, this will delete the last reference
       session.joypads->update([&](state::JoypadList joypads) { return joypads.erase(pkt.controller_number); });
+      return;
     }
   } else {
     // Old Moonlight doesn't support CONTROLLER_ARRIVAL, we create a default pad when it's first mentioned
     selected_pad = create_new_joypad(session, connected_clients, pkt.controller_number, XBOX, ANALOG_TRIGGERS | RUMBLE);
   }
-  std::visit(
-      [pkt](inputtino::Joypad &pad) {
-        std::uint16_t bf = pkt.button_flags;
-        std::uint32_t bf2 = pkt.buttonFlags2;
-        pad.set_pressed_buttons(bf | (bf2 << 16));
-        pad.set_stick(inputtino::Joypad::LS, pkt.left_stick_x, pkt.left_stick_y);
-        pad.set_stick(inputtino::Joypad::RS, pkt.right_stick_x, pkt.right_stick_y);
-        pad.set_triggers(pkt.left_trigger, pkt.right_trigger);
-      },
-      *selected_pad);
+
+  // Update the joypad state
+  if (selected_pad) {
+    std::visit(
+        [pkt](inputtino::Joypad &pad) {
+          std::uint16_t bf = pkt.button_flags;
+          std::uint32_t bf2 = pkt.buttonFlags2;
+          pad.set_pressed_buttons(bf | (bf2 << 16));
+          pad.set_stick(inputtino::Joypad::LS, pkt.left_stick_x, pkt.left_stick_y);
+          pad.set_stick(inputtino::Joypad::RS, pkt.right_stick_x, pkt.right_stick_y);
+          pad.set_triggers(pkt.left_trigger, pkt.right_trigger);
+        },
+        *selected_pad);
+  }
 }
 
 void controller_touch(const CONTROLLER_TOUCH_PACKET &pkt, state::StreamSession &session) {