.\" Hey Emacs! This file is -*- nroff -*- source.
.\"
.\" Author: Eamon Walsh (ewalsh@epoch.ncsc.mil) 2004
.TH "avc_add_callback" "3" "9 June 2004" "" "SE Linux API documentation"
.SH "NAME"
avc_add_callback \- additional event notification for userspace object managers.
.SH "SYNOPSIS"
.B #include <selinux/selinux.h>
.br
.B #include <selinux/avc.h>
.sp
.BI "int avc_add_callback(int (*" callback ")(u_int32_t " event , 
.in +\w'int avc_add_callback(int (*callback)('u
.BI "security_id_t " ssid ,
.br
.BI "security_id_t " tsid ,
.br
.BI "security_class_t " tclass ,
.br
.BI "access_vector_t " perms ,
.br
.BI "access_vector_t *" out_retained "),"
.in
.in +\w'int avc_add_callback('u
.BI "u_int32_t " events ", security_id_t " ssid , 
.br
.BI "security_id_t " tsid ", security_class_t " tclass ,
.br
.BI "access_vector_t " perms ");"
.in
.SH "DESCRIPTION"
.B avc_add_callback
is used to register callback functions on security events.  The purpose of this functionality is to allow userspace object managers to take additional action when a policy change, usually a policy reload, causes permissions to be granted or revoked.

.I events
is the
.RI bitwise- or
of security events on which to register the callback; see
.B SECURITY EVENTS
below.

.IR ssid ,
.IR tsid ,
.IR tclass ,
and
.I perms
specify the source and target SID's, target class, and specific permissions that the callback wishes to monitor.  The special symbol
.B SECSID_WILD
may be passed as the
.I source
or
.I target
and will cause any SID to match.

.I callback
is the callback function provided by the userspace object manager.  The
.I event
argument indicates the security event which occured; the remaining arguments are interpreted according to the event as described below.  The return value of the callback should be zero on success, \-1 on error with errno set appropriately (but see
.B RETURN VALUE
below).

.SH "SECURITY EVENTS"
In all cases below,
.I ssid
and/or
.I tsid
may be set to
.BR SECSID_WILD ,
indicating that the change applies to all source and/or target SID's.  Unless otherwise indicated, the
.I out_retained
parameter is unused.

.TP
.B AVC_CALLBACK_GRANT
Previously denied permissions are now granted for
.IR ssid ,
.I tsid
with respect to
.IR tclass .
.I perms
indicates the permissions to grant.
.TP
.B AVC_CALLBACK_TRY_REVOKE
Previously granted permissions are now conditionally revoked for
.IR ssid ,
.I tsid
with respect to
.IR tclass .
.I perms
indicates the permissions to revoke.  The callback should set
.I out_retained
to the subset of
.I perms
which are retained as migrated permissions.  Note that
.I out_retained
is ignored if the callback returns \-1.
.TP
.B AVC_CALLBACK_REVOKE
Previously granted permissions are now unconditionally revoked for
.IR ssid ,
.I tsid
with respect to
.IR tclass .
.I perms
indicates the permissions to revoke.
.TP
.B AVC_CALLBACK_RESET
Indicates that the cache was flushed.  The SID, class, and permission arguments are unused and are set to NULL.
.TP
.B AVC_CALLBACK_AUDITALLOW_ENABLE
The permissions given by
.I perms
should now be audited when granted for
.IR ssid ,
.I tsid
with respect to
.IR tclass .
.TP
.B AVC_CALLBACK_AUDITALLOW_DISABLE
The permissions given by
.I perms
should no longer be audited when granted for
.IR ssid ,
.I tsid
with respect to
.IR tclass .
.TP
.B AVC_CALLBACK_AUDITDENY_ENABLE
The permissions given by
.I perms
should now be audited when denied for
.IR ssid ,
.I tsid
with respect to
.IR tclass .
.TP
.B AVC_CALLBACK_AUDITDENY_DISABLE
The permissions given by
.I perms
should no longer be audited when denied for
.IR ssid ,
.I tsid
with respect to
.IR tclass .

.SH "RETURN VALUE"
On success,
.B avc_add_callback
returns zero.  On error, \-1 is returned and
.I errno
is set appropriately.

A return value of \-1 from a callback is interpreted as a failed policy operation.  If such a return value is encountered, all remaining callbacks registered on the event are called.  In threaded mode, the netlink handler thread may then terminate and cause the userspace AVC to return
.B EINVAL
on all further permission checks until
.BR avc_destroy (3)
is called.  In non-threaded mode, the permission check on which the error occurred will return \-1 and the value of 
.I errno
encountered to the caller.  In both cases, a log message is produced and the kernel may be notified of the error.

.SH "ERRORS"
.TP
.B ENOMEM
An attempt to allocate memory failed.

.SH "NOTES"
If the userspace AVC is running in threaded mode, callbacks registered via
.B avc_add_callback
may be executed in the context of the netlink handler thread.  This will likely introduce synchronization issues requiring the use of locks.  See
.BR avc_init (3).

Support for dynamic revocation and retained permissions is mostly unimplemented in the SELinux kernel module.  The only security event that currently gets excercised is
.BR AVC_CALLBACK_RESET .

.SH "AUTHOR"
Eamon Walsh <ewalsh@epoch.ncsc.mil>

.SH "SEE ALSO"
.BR avc_init (3),
.BR avc_has_perm (3),
.BR avc_context_to_sid (3),
.BR avc_cache_stats (3),
.BR security_compute_av (3)