In a nutshell, pam_selinux sets up the default security context for the next execed shell.

When an application opens a session using pam_selinux, the shell that gets executed will be run in the default security context, or if the user chooses and the pam file allows the selected security context. Also the controlling tty will have it's security context modified to match the users.

Adding pam_selinux into a pam file could cause other pam modules to change their behavior if the exec another application. The close and open option help mitigate this problem. close option will only cause the close portion of the pam_selinux to execute, and open will only cause the open portion to run. You can add pam_selinux to the config file twice. Add the pam_selinux close as the executes the open pass through the modules, pam_selinux open_session will happen last. When PAM executes the close pass through the modules pam_selinux close_session will happen first.

Only the session service is supported.

auth     required  pam_unix.so
session  required  pam_permit.so    
session  optional  pam_selinux.so
    

pam_selinux was written by Dan Walsh <dwalsh@redhat.com>.