mcstransd does not work after enabling hidepid on RHEL 7

Issue

• How to configure mcstrans to work with hidepid mount options for /proc on Red Hat Enterprise Linux 7.

• The mcstransd service reports the following errors in the system message logs:

  mcstransd[xxxx]: Failed to get context of client process (pid=xx)
  mcstransd[xxxx]: Servicing of request failed for fd (x)
  

• The mcstransd service does not translate SELinux contexts even when it is running:

  # ls -Zd /tmp
  drwxrwxrwt. root root system_u:object_r:tmp_t:SystemLow    /tmp
  # mount -o remount,hidepid=2,gid=10 /proc
  # ls -Zd /tmp
  drwxrwxrwt. root root system_u:object_r:tmp_t:s0    /tmp
  

• The mcstransd service has no effect even if the client user is in the hidepid / gid group.