Method ueventProcessRead

src/Library/UMockdevDeviceManager.cpp:495–626

  }

  void UMockdevDeviceManager::ueventProcessRead()
  {
    std::string buffer(4096, 0);
    struct iovec iov[1];
    iov[0].iov_base = (void*)&buffer[0];
    iov[0].iov_len = buffer.capacity();
    struct sockaddr_nl peer_sockaddr = { };
    union {
      struct cmsghdr header;
      uint8_t ucred[CMSG_SPACE(sizeof(struct ucred))];
    } cmsg_un;
    cmsg_un.header.cmsg_len = CMSG_LEN(sizeof(struct ucred));
    cmsg_un.header.cmsg_level = SOL_SOCKET;
    cmsg_un.header.cmsg_type = SCM_CREDENTIALS;
    struct msghdr msg_header = { };
    msg_header.msg_control = cmsg_un.ucred;
    msg_header.msg_controllen = sizeof cmsg_un.ucred;
    msg_header.msg_iov = iov;
    msg_header.msg_iovlen = 1;
    msg_header.msg_name = &peer_sockaddr;
    msg_header.msg_namelen = sizeof peer_sockaddr;
    const int rc = recvmsg(_uevent_fd, &msg_header, MSG_DONTWAIT);

    if (rc <= 0) {
      const int saved_errno = errno;

      if (saved_errno == EAGAIN || saved_errno == EWOULDBLOCK) {
        USBGUARD_LOG(Warning) << "Read: "
          << "reading from uevent source would block thread execution";
        return;
      }
      else {
        USBGUARD_LOG(Error) << "ueventProcessRead: "
          << "failed to read pending uevent: "
          << "rc=" << rc << " errno=" << saved_errno;
        throw ErrnoException("UEvent device manager", "recvmsg", saved_errno);
      }
    }

    buffer.resize((size_t)rc);
    const struct cmsghdr* const cmsg_header = CMSG_FIRSTHDR(&msg_header);

    if (cmsg_header == nullptr) {
      /* ignore */
      USBGUARD_LOG(Warning) << "ueventProcessRead: "
        << "received uevent without required control message: ignoring.";
      return;
    }

    if (cmsg_header->cmsg_len != CMSG_LEN(sizeof(struct ucred))
      || cmsg_header->cmsg_level != SOL_SOCKET
      || cmsg_header->cmsg_type != SCM_CREDENTIALS) {
      /* unexpected control message -- ignore */
      USBGUARD_LOG(Warning) << "ueventProcessRead: "
        << "received uevent with an invalid control message: ignoring.";
      return;
    }