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avc_init


Section: SELinux API documentation (3)
Updated: 27 May 2004
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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 default is `uavc’. The remaining arguments, if non-NULL, specify callbacks 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 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
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

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
NETLINK NOTIFICATION

below.


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.


 

NETLINK NOTIFICATION

Beginning with version 2.6.4, the Linux kernel supports SELinux status change notification via netlink. Two message types are currently implemented, indicating changes to the enforcing mode and to the loaded policy in the kernel, respectively. The userspace AVC listens for these messages and takes the appropriate action, modifying the behavior of
avc_has_perm(3)

to reflect the current enforcing mode and flushing the cache on receipt of a policy load notification. Audit messages are produced when netlink notifications are processed.


In the default single-threaded mode, 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

however, a dedicated thread will be started to listen on the netlink socket. This may increase performance and will ensure that log messages are generated immediately 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 <[email protected]>


 

SEE ALSO

avc_open(3),

selinux_set_callback(3),

selinux(8)




 

Index



NAME

SYNOPSIS

DESCRIPTION

CALLBACKS

NETLINK NOTIFICATION

RETURN VALUE

NOTES

AUTHOR

SEE ALSO



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