Provided by: libselinux1-dev_3.5-1_amd64 
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 KERNEL STATUS PAGE and
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.
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 status 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_callback(3) will still be honored.
avc_has_perm(3) and selinux_check_access(3) both check for status updates 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 policyload 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 implementation, 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 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 <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)