avc_init(3) — Linux manual page


avc_init(3)             SELinux API documentation            avc_init(3)

NAME         top

       avc_init - legacy userspace SELinux AVC setup

SYNOPSIS         top

       #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);

DESCRIPTION         top

       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.

CALLBACKS         top

       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

       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

       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.


       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.


       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.

RETURN VALUE         top

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

NOTES         top

       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

       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         top

       Eamon Walsh <ewalsh@tycho.nsa.gov>

SEE ALSO         top

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

COLOPHON         top

       This page is part of the selinux (Security-Enhanced Linux user-
       space libraries and tools) project.  Information about the
       project can be found at 
       ⟨https://github.com/SELinuxProject/selinux/wiki⟩.  If you have a
       bug report for this manual page, see
       This page was obtained from the project's upstream Git repository
       ⟨https://github.com/SELinuxProject/selinux⟩ on 2023-12-22.  (At
       that time, the date of the most recent commit that was found in
       the repository was 2023-05-11.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
       is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to

                               27 May 2004                   avc_init(3)

Pages that refer to this page: avc_add_callback(3)avc_cache_stats(3)avc_compute_create(3)avc_context_to_sid(3)avc_has_perm(3)selinux_set_callback(3)