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)