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 <ewalsh@tycho.nsa.gov>
SEE ALSO¶
avc_open(3),
selinux_set_callback(3),
selinux(8)
