avc_init - legacy userspace SELinux AVC setup

       Eamon Walsh <ewalsh@tycho.nsa.gov>

       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 arguments 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  argument,  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 KERNELSTATUSPAGE and NETLINKNOTIFICATION 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 perform any locking.  Note that undefined behavior may result if threading
       is used without appropriate locking.

avc_init()  is  deprecated; please use avc_open(3) in conjunction with selinux_set_callback(3) in all new
       code.

       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  callbacks  to  be  used  by  the
       userspace AVC.

       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_init()  calls  selinux_status_open(3)  to  initialize  the  selinux  status  state.  If  successfully
       initialized, the userspace AVC will default to single-threaded mode and ignore the func_create_thread and
       func_stop_thread callbacks. All callbacks set via selinux_set_callback(3) will still be honored.

       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.

       avc_init - legacy userspace SELinux AVC setup

       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.

       By  default, avc_open(3) does not set threading or locking callbacks. In the fallback case, 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(), a dedicated thread will be started to listen on the netlink socket.
       This may increase performance in the absence of the status page and will ensure  that  log  messages  are
       generated immediately rather than at the time of the next permission query.

       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.

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

avc_open(3), selinux_status_open(3), selinux_status_updated(3), selinux_set_callback(3), selinux(8)

                                                   27 May 2004                                       avc_init(3)

#include<selinux/selinux.h>#include<selinux/avc.h>intavc_init(constchar*msgprefix,conststructavc_memory_callback*mem_callbacks,conststructavc_log_callback*log_callbacks,conststructavc_thread_callback*thread_callbacks,conststructavc_lock_callback*lock_callbacks);