NAME
avc_add_callback - additional event notification for SELinux userspace
object managers.
SYNOPSIS
#include <selinux/selinux.h>
#include <selinux/avc.h>
int avc_add_callback(int (*callback)(uint32_t event,
security_id_t ssid,
security_id_t tsid,
security_class_t tclass,
access_vector_t perms,
access_vector_t *out_retained),
uint32_t events, security_id_t ssid,
security_id_t tsid, security_class_t tclass,
access_vector_t perms);
DESCRIPTION
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.
events is the bitwise-or of security events on which to register the
callback; see SECURITY EVENTS below.
ssid, tsid, tclass, and perms specify the source and target SID’s,
target class, and specific permissions that the callback wishes to
monitor. The special symbol SECSID_WILD may be passed as the source or
target and will cause any SID to match.
callback is the callback function provided by the userspace object
manager. The 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 RETURN VALUE
below).
SECURITY EVENTS
In all cases below, ssid and/or tsid may be set to SECSID_WILD,
indicating that the change applies to all source and/or target SID’s.
Unless otherwise indicated, the out_retained parameter is unused.
AVC_CALLBACK_GRANT
Previously denied permissions are now granted for ssid, tsid
with respect to tclass. perms indicates the permissions to
grant.
AVC_CALLBACK_TRY_REVOKE
Previously granted permissions are now conditionally revoked for
ssid, tsid with respect to tclass. perms indicates the
permissions to revoke. The callback should set out_retained to
the subset of perms which are retained as migrated permissions.
Note that out_retained is ignored if the callback returns -1.
AVC_CALLBACK_REVOKE
Previously granted permissions are now unconditionally revoked
for ssid, tsid with respect to tclass. perms indicates the
permissions to revoke.
AVC_CALLBACK_RESET
Indicates that the cache was flushed. The SID, class, and
permission arguments are unused and are set to NULL.
AVC_CALLBACK_AUDITALLOW_ENABLE
The permissions given by perms should now be audited when
granted for ssid, tsid with respect to tclass.
AVC_CALLBACK_AUDITALLOW_DISABLE
The permissions given by perms should no longer be audited when
granted for ssid, tsid with respect to tclass.
AVC_CALLBACK_AUDITDENY_ENABLE
The permissions given by perms should now be audited when denied
for ssid, tsid with respect to tclass.
AVC_CALLBACK_AUDITDENY_DISABLE
The permissions given by perms should no longer be audited when
denied for ssid, tsid with respect to tclass.
RETURN VALUE
On success, avc_add_callback returns zero. On error, -1 is returned
and 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 EINVAL on all further permission checks until avc_destroy(3)
is called. In non-threaded mode, the permission check on which the
error occurred will return -1 and the value of errno encountered to the
caller. In both cases, a log message is produced and the kernel may be
notified of the error.
ERRORS
ENOMEM An attempt to allocate memory failed.
NOTES
If the userspace AVC is running in threaded mode, callbacks registered
via 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 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 AVC_CALLBACK_RESET.
AUTHOR
Eamon Walsh <ewalsh@tycho.nsa.gov>
SEE ALSO
avc_init(3), avc_has_perm(3), avc_context_to_sid(3),
avc_cache_stats(3), security_compute_av(3) selinux(8)
9 June 2004 avc_add_callback(3)