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[Bug 1540731] Re: SocketMessenger::update_session_creds() fails to get client PID


** Changed in: linux (Ubuntu)
   Importance: Undecided => High

** Tags added: kernel-key performing-bisect

** Changed in: linux (Ubuntu)
   Importance: High => Critical

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  SocketMessenger::update_session_creds() fails to get client PID

Status in GLibC:
Status in Mir:
Status in linux package in Ubuntu:

Bug description:
  Since updating to the 4.4.0-2 kernel recvmsg() fails SCM_CREDENTIALS
  request with EOPNOTSUPP.

  This manifests as a test failure in Mir:

      [ RUN      ] PromptSessionClientAPI.client_pid_is_associated_with_session
      unknown file: Failure

  Test case:

  #include <gtest/gtest.h>
  #include <gmock/gmock.h>
  #include <sys/socket.h>
  #include <sys/stat.h>

  TEST(IsItBroken, recvmsg)
      using namespace testing;

      enum { server, client, size };
      int socket_fd[size];
      int const opt = 1;

      ASSERT_THAT(socketpair(AF_LOCAL, SOCK_STREAM, 0, socket_fd),

      auto const msg = "A random message";
      send(socket_fd[client], msg, sizeof msg, MSG_DONTWAIT | MSG_NOSIGNAL);

      ASSERT_THAT(setsockopt(socket_fd[server], SOL_SOCKET, SO_PASSCRED,
  &opt, sizeof(opt)), Ne(-1));

      union {
          struct cmsghdr cmh;
          char   control[CMSG_SPACE(sizeof(ucred))];
      } control_un;

      control_un.cmh.cmsg_len = CMSG_LEN(sizeof(ucred));
      control_un.cmh.cmsg_level = SOL_SOCKET;
      control_un.cmh.cmsg_type = SCM_CREDENTIALS;

      msghdr msgh;
      msgh.msg_name = nullptr;
      msgh.msg_namelen = 0;
      msgh.msg_iov = nullptr;
      msgh.msg_iovlen = 0;
      msgh.msg_control = control_un.control;
      msgh.msg_controllen = sizeof(control_un.control);

      errno = 0;

      EXPECT_THAT(recvmsg(socket_fd[server], &msgh, MSG_PEEK), Ne(-1))
          << "Error: " << strerror(errno);

      for (auto socket : socket_fd) close(socket);

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