NAME

       avc_open, avc_destroy, avc_reset, avc_cleanup - userspace SELinux AVC setup and teardown

SYNOPSIS

       #include <selinux/selinux.h>
       #include <selinux/avc.h>

       int avc_open(struct selinux_opt *options, unsigned nopt);

       void avc_destroy(void);

       int avc_reset(void);

       void avc_cleanup(void);

DESCRIPTION

       avc_open() initializes the userspace AVC and must be called before any other AVC operation
       can be performed.

       avc_destroy() destroys the userspace AVC, freeing all internal memory  structures.   After
       this  call has been made, avc_open() must be called again before any AVC operations can be
       performed.  avc_destroy() also closes the SELinux  status  page,  which  might  have  been
       opened manually by selinux_status_open(3).

       avc_reset()  flushes  the userspace AVC, causing it to forget any cached access decisions.
       The userspace AVC normally calls this function  automatically  when  needed,  see  NETLINK
       NOTIFICATION below.

       avc_cleanup()  attempts to free unused memory within the userspace AVC, but does not flush
       any cached access decisions.  Under normal operation, calling this function should not  be
       necessary.

OPTIONS

       The  userspace  AVC  obeys  callbacks  set  via selinux_set_callback(3), in particular the
       logging and audit callbacks.

       The options which may be passed to avc_open() include the following:

       AVC_OPT_SETENFORCE
              This option forces the userspace AVC into enforcing mode if  the  option  value  is
              non-NULL; permissive mode otherwise.  The system enforcing mode will be ignored.

KERNEL STATUS PAGE

       Linux  kernel  version  2.6.37 supports the SELinux kernel status page, enabling userspace
       applications to mmap(2) SELinux status state in  read-only  mode  to  avoid  system  calls
       during the cache hit code path.

       avc_open() calls selinux_status_open(3) to initialize the selinux status state.

       avc_has_perm(3) and selinux_check_access(3) both check for status updates through calls to
       selinux_status_updated(3) at the start of each permission query and take  the  appropriate
       action.

       Two  status  types are currently implemented.  setenforce events will change the effective
       enforcing state used within the AVC, and policyload events will result in a cache flush.

NETLINK NOTIFICATION

       In the event that the kernel status page is  not  successfully  mmap(2)'ed  the  AVC  will
       default  to  the  netlink  fallback  mechanism, which opens a netlink socket for receiving
       status updates.  setenforce and policyload events will have the same results  as  for  the
       status page implementation, but all status update checks will now require a system call.

RETURN VALUE

       Functions  with a return value return zero on success.  On error, -1 is returned and errno
       is set appropriately.

AUTHOR

       Eamon Walsh <ewalsh@tycho.nsa.gov>

SEE ALSO

       selinux(8),     selinux_check_access(3),      avc_has_perm(3),      avc_context_to_sid(3),
       avc_cache_stats(3),              avc_add_callback(3),              selinux_status_open(3),
       selinux_status_updated(3), selinux_set_callback(3), security_compute_av(3)

                                           12 Jun 2008                                avc_open(3)