avc_init(3) SELinux API documentation avc_init(3)
NAME
avc_init - legacy userspace SELinux AVC setup
SYNOPSIS
#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
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 de-
fault is `uavc'. The remaining arguments, if non-NULL, specify call-
backs to be used by the userspace AVC.
CALLBACKS
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 argu-
ments 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 in-
terpretation 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 argu-
ment, 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 KERNEL STATUS PAGE
and NETLINK NOTIFICATION below.
Use an avc_lock_callback structure to specify functions to create, ob-
tain, 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 re-
lease lock. The func_free_lock callback should destroy lock, freeing
any resources associated with it. The default behavior is not to per-
form any locking. Note that undefined behavior may result if threading
is used without appropriate locking.
KERNEL STATUS PAGE
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 sta-
tus 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_call-
back(3) will still be honored.
avc_has_perm(3) and selinux_check_access(3) both check for status up-
dates 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 policy-
load events will result in a cache flush.
NETLINK NOTIFICATION
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 implementa-
tion, 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 immedi-
ately rather than at the time of the next permission query.
RETURN VALUE
Functions with a return value return zero on success. On error, -1 is
returned and errno is set appropriately.
NOTES
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.
AUTHOR
Eamon Walsh <ewalsh@tycho.nsa.gov>
SEE ALSO
avc_open(3), selinux_status_open(3), selinux_status_updated(3),
selinux_set_callback(3), selinux(8)
27 May 2004 avc_init(3)
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