avc_add_callback(3)

1avc_add_callback(3)        SELinux API documentation       avc_add_callback(3)
2
3
4

NAME

6       avc_add_callback  - additional event notification for SELinux userspace
7       object managers
8

SYNOPSIS

10       #include <selinux/selinux.h>
11       #include <selinux/avc.h>
12
13       int avc_add_callback(int (*callback)(uint32_t event,
14                                            security_id_t ssid,
15                                            security_id_t tsid,
16                                            security_class_t tclass,
17                                            access_vector_t perms,
18                                            access_vector_t *out_retained),
19                            uint32_t events, security_id_t ssid,
20                            security_id_t tsid, security_class_t tclass,
21                            access_vector_t perms);
22

DESCRIPTION

24       avc_add_callback() is used to register callback functions  on  security
25       events.  The purpose of this functionality is to allow userspace object
26       managers to take additional action when a policy change, usually a pol‐
27       icy reload, causes permissions to be granted or revoked.
28
29       events  is  the  bitwise-or of security events on which to register the
30       callback; see SECURITY EVENTS below.
31
32       ssid, tsid, tclass, and perms specify the source and target SID's, tar‐
33       get  class,  and specific permissions that the callback wishes to moni‐
34       tor.  The special symbol SECSID_WILD may be passed  as  the  source  or
35       target and will cause any SID to match.
36
37       callback is the callback function provided by the userspace object man‐
38       ager.  The event argument indicates the security event which  occurred;
39       the  remaining  arguments  are  interpreted  according  to the event as
40       described below.  The return value of the callback should  be  zero  on
41       success, -1 on error with errno set appropriately (but see RETURN VALUE
42       below).
43

SECURITY EVENTS

45       In all cases below, ssid and/or tsid may be set to  SECSID_WILD,  indi‐
46       cating  that  the  change  applies  to  all source and/or target SID's.
47       Unless otherwise indicated, the out_retained parameter is unused.
48
49       AVC_CALLBACK_GRANT
50              Previously denied permissions are now  granted  for  ssid,  tsid
51              with  respect  to  tclass.   perms  indicates the permissions to
52              grant.
53
54       AVC_CALLBACK_TRY_REVOKE
55              Previously granted permissions are now conditionally revoked for
56              ssid,  tsid with respect to tclass.  perms indicates the permis‐
57              sions to revoke.  The callback should set  out_retained  to  the
58              subset  of  perms  which  are  retained as migrated permissions.
59              Note that out_retained is ignored if the callback returns -1.
60
61       AVC_CALLBACK_REVOKE
62              Previously granted permissions are now  unconditionally  revoked
63              for ssid, tsid with respect to tclass.  perms indicates the per‐
64              missions to revoke.
65
66       AVC_CALLBACK_RESET
67              Indicates that the cache was flushed.  The SID, class, and  per‐
68              mission arguments are unused and are set to NULL.
69
70       AVC_CALLBACK_AUDITALLOW_ENABLE
71              The  permissions  given  by  perms  should  now  be audited when
72              granted for ssid, tsid with respect to tclass.
73
74       AVC_CALLBACK_AUDITALLOW_DISABLE
75              The permissions given by perms should no longer be audited  when
76              granted for ssid, tsid with respect to tclass.
77
78       AVC_CALLBACK_AUDITDENY_ENABLE
79              The permissions given by perms should now be audited when denied
80              for ssid, tsid with respect to tclass.
81
82       AVC_CALLBACK_AUDITDENY_DISABLE
83              The permissions given by perms should no longer be audited  when
84              denied for ssid, tsid with respect to tclass.
85

RETURN VALUE

87       On  success, avc_add_callback() returns zero.  On error, -1 is returned
88       and errno is set appropriately.
89
90       A return value of -1 from a callback is interpreted as a failed  policy
91       operation.   If such a return value is encountered, all remaining call‐
92       backs registered on the  event  are  called.   In  threaded  mode,  the
93       netlink  handler  thread may then terminate and cause the userspace AVC
94       to return EINVAL on all further permission checks until  avc_destroy(3)
95       is  called.   In  non-threaded  mode, the permission check on which the
96       error occurred will return -1 and the value of errno encountered to the
97       caller.  In both cases, a log message is produced and the kernel may be
98       notified of the error.
99

ERRORS

101       ENOMEM An attempt to allocate memory failed.
102

NOTES

104       If the userspace AVC is running in threaded mode, callbacks  registered
105       via  avc_add_callback()  may  be executed in the context of the netlink
106       handler thread.  This  will  likely  introduce  synchronization  issues
107       requiring the use of locks.  See avc_init(3).
108
109       Support for dynamic revocation and retained permissions is mostly unim‐
110       plemented in the SELinux kernel module.  The only security  event  that
111       currently gets exercised is AVC_CALLBACK_RESET.
112

AUTHOR

114       Eamon Walsh <ewalsh@tycho.nsa.gov>
115