Provided by: libselinux1-dev_3.5-2ubuntu2.1_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)