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avc_init(3)		   SELinux API documentation		   avc_init(3)

NAME
       avc_init,  avc_destroy,	avc_reset, avc_cleanup - userspace SELinux AVC
       setup and teardown.

SYNOPSIS
       #include <selinux/selinux.h>

       #include <selinux/avc.h>

       int avc_init(const char *msgprefix,
		    const struct avc_memory_callback *mem_callbacks,

		    const struct avc_log_callback *log_callbacks,

		    const struct avc_thread_callback *thread_callbacks,

		    const struct avc_lock_callback *lock_callbacks);

       void avc_destroy(void);

       int avc_reset(void);

       void avc_cleanup(void);

DESCRIPTION
       avc_init initializes the userspace AVC and must be  called  before  any
       other  AVC  operation  can  be performed.  A non-NULL msgprefix will be
       prepended to all audit messages produced by  the	 userspace  AVC.   The
       default is `uavc'.  The remaining arguments, if non-NULL, specify call‐
       backs to be used by the userspace AVC.  See CALLBACKS below.

       avc_destroy destroys the userspace AVC,	freeing	 all  internal	memory
       structures.   After  this  call	has been made, avc_init must be called
       again before any AVC operations can be performed.

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

       avc_cleanup forces the userspace AVC to search for and free all	unused
       SID's  and  any	access decision entries that refer to them.  Normally,
       the userspace AVC lazily reclaims unused SID's.

CALLBACKS
       The userspace AVC can be directed how  to  perform  memory  allocation,
       logging,	 thread creation, and locking via callback functions passed to
       avc_init.  The purpose of this functionality is to allow the  userspace
       AVC to be smoothly integrated into existing userspace object managers.

       Use an avc_memory_callback structure to specify alternate functions for
       dynamic memory allocation.

	      struct avc_memory_callback {
		  void	*(*func_malloc)(size_t size);
		  void	(*func_free)(void *ptr);
	      };

       The two fields of the structure should be pointers to  functions	 which
       behave as malloc(3) and free(3), which are used by default.

       Use  an	avc_log_callback  structure to specify alternate functions for
       logging.

	      struct avc_log_callback {
		  void	(*func_log)(const char *fmt, ...);
		  void	(*func_audit)(void *auditdata,
				      security_class_t class,
				      char *msgbuf, size_t msgbufsize);
	      };

       The func_log callback should accept a printf(3) style format and	 argu‐
       ments and log them as desired.  The default behavior prints the message
       on the standard error.  The func_audit callback	should	interpret  the
       auditdata  parameter  for  the  given  class, printing a human-readable
       interpretation to msgbuf using no more than msgbufsize characters.  The
       default behavior is to ignore auditdata.

       Use  an avc_thread_callback structure to specify functions for starting
       and manipulating threads.

	      struct avc_thread_callback {
		  void	*(*func_create_thread)(void (*run)(void));
		  void	(*func_stop_thread)(void *thread);
	      };

       The func_create_thread callback should create a new thread and return a
       pointer	which  references it.  The thread should execute the run argu‐
       ment,  which  does   not	  return   under   normal   conditions.	   The
       func_stop_thread	 callback  should cancel the running thread referenced
       by thread.  By default, threading is not used; see NETLINK NOTIFICATION
       below.

       Use  an	avc_lock_callback  structure  to  specify functions to create,
       obtain, and release locks for use by threads.

	      struct avc_lock_callback {
		  void	*(*func_alloc_lock)(void);
		  void	(*func_get_lock)(void *lock);
		  void	(*func_release_lock)(void *lock);
		  void	(*func_free_lock)(void *lock);
	      };

       The func_alloc_lock callback should create  a  new  lock,  returning  a
       pointer	which references it.  The func_get_lock callback should obtain
       lock, blocking if necessary.   The  func_release_lock  callback	should
       release lock.  The func_free_lock callback should destroy lock, freeing
       any resources associated with it.  The default behavior is not to  per‐
       form any locking.  Note that undefined behavior may result if threading
       is used without appropriate locking.

NETLINK NOTIFICATION
       Beginning with version 2.6.4, the Linux kernel supports SELinux	status
       change  notification  via  netlink.   Two  message  types are currently
       implemented, indicating changes to the enforcing mode and to the loaded
       policy  in  the	kernel,	 respectively.	 The userspace AVC listens for
       these messages and takes the appropriate action, modifying the behavior
       of  avc_has_perm(3)  to reflect the current enforcing mode and flushing
       the cache on receipt of a policy load notification.  Audit messages are
       produced when netlink notifications are processed.

       In  the	default single-threaded mode, the userspace AVC checks for new
       netlink messages at the start of each permission query.	 If  threading
       and  locking  callbacks	are  passed  to	 avc_init however, a dedicated
       thread will be started to listen	 on  the  netlink  socket.   This  may
       increase	 performance  and  will ensure that log messages are generated
       immediately rather than at the time of the next permission query.

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

NOTES
       The  msgprefix  argument to avc_init currently has a length limit of 15
       characters and will be truncated if necessary.

       If a provided func_malloc callback does not set errno appropriately  on
       error, userspace AVC calls may exhibit the same behavior.

       If  a netlink thread has been created and an error occurs on the socket
       (such as an access error), the  thread  may  terminate  and  cause  the
       userspace  AVC  to return EINVAL on all further permission checks until
       avc_destroy is called.

AUTHOR
       Eamon Walsh <ewalsh@tycho.nsa.gov>

SEE ALSO
       avc_has_perm(3),	      avc_context_to_sid(3),	   avc_cache_stats(3),
       avc_add_callback(3), security_compute_av(3) selinux(8)

				  27 May 2004			   avc_init(3)
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