security/audit/audit_pipe.c

/*-
 * Copyright (c) 2006 Robert N. M. Watson
 * All rights reserved.
 *
 * This software was developed by Robert Watson for the TrustedBSD Project.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 * $FreeBSD: head/sys/security/audit/audit_pipe.c 155408 2006-02-06 22:50:39Z rwatson $
 */

#include <sys/param.h>
#include <sys/condvar.h>
#include <sys/conf.h>
#include <sys/eventhandler.h>
#include <sys/filio.h>
#include <sys/kernel.h>
#include <sys/lock.h>
#include <sys/malloc.h>
#include <sys/mutex.h>
#include <sys/poll.h>
#include <sys/proc.h>
#include <sys/queue.h>
#include <sys/selinfo.h>
#include <sys/sigio.h>
#include <sys/signal.h>
#include <sys/signalvar.h>
#include <sys/systm.h>
#include <sys/uio.h>

#include <security/audit/audit.h>
#include <security/audit/audit_private.h>

/*
 * Implementation of a clonable special device providing a live stream of BSM
 * audit data.  This is a "tee" of the data going to the file.  It provides
 * unreliable but timely access to audit events.  Consumers of this interface
 * should be very careful to avoid introducing event cycles.
 */

/*
 * Memory types.
 */
static MALLOC_DEFINE(M_AUDIT_PIPE, "audit_pipe", "Audit pipes");
static MALLOC_DEFINE(M_AUDIT_PIPE_ENTRY, "audit_pipeent",
    "Audit pipe entries and buffers");

/*
 * Audit pipe buffer parameters.
 */
#define	AUDIT_PIPE_QLIMIT_DEFAULT	(32)
#define	AUDIT_PIPE_QLIMIT_MAX		(1024)

/*
 * Description of an entry in an audit_pipe.
 */
struct audit_pipe_entry {
	void				*ape_record;
	u_int				 ape_record_len;
	TAILQ_ENTRY(audit_pipe_entry)	 ape_queue;
};

/*
 * Description of an individual audit_pipe.  Consists largely of a bounded
 * length queue.
 */
#define	AUDIT_PIPE_ASYNC	0x00000001
#define	AUDIT_PIPE_NBIO		0x00000002
struct audit_pipe {
	int				 ap_open;	/* Device open? */
	u_int				 ap_flags;

	struct selinfo			 ap_selinfo;
	struct sigio			*ap_sigio;

	u_int				 ap_qlen;
	u_int				 ap_qlimit;

	u_int64_t			 ap_inserts;	/* Records added. */
	u_int64_t			 ap_reads;	/* Records read. */
	u_int64_t			 ap_drops;	/* Records dropped. */
	u_int64_t			 ap_truncates;	/* Records too long. */

	TAILQ_HEAD(, audit_pipe_entry)	 ap_queue;

	TAILQ_ENTRY(audit_pipe)		 ap_list;
};

/*
 * Global list of audit pipes, mutex to protect it and the pipes.  Finder
 * grained locking may be desirable at some point.
 */
static TAILQ_HEAD(, audit_pipe)	 audit_pipe_list;
static struct mtx		 audit_pipe_mtx;

/*
 * This CV is used to wakeup on an audit record write.  Eventually, it should
 * probably be per-pipe.
 */
static struct cv		 audit_pipe_cv;

/*
 * Cloning related variables and constants.
 */
#define	AUDIT_PIPE_NAME		"auditpipe"
static eventhandler_tag		 audit_pipe_eh_tag;
static struct clonedevs		*audit_pipe_clones;

/*
 * Special device methods and definition.
 */
static d_open_t		audit_pipe_open;
static d_close_t	audit_pipe_close;
static d_read_t		audit_pipe_read;
static d_ioctl_t	audit_pipe_ioctl;
static d_poll_t		audit_pipe_poll;

static struct cdevsw	audit_pipe_cdevsw = {
	.d_version =	D_VERSION,
	.d_flags =	D_PSEUDO,
	.d_open =	audit_pipe_open,
	.d_close =	audit_pipe_close,
	.d_read =	audit_pipe_read,
	.d_ioctl =	audit_pipe_ioctl,
	.d_poll =	audit_pipe_poll,
	.d_name =	AUDIT_PIPE_NAME,
};

/*
 * Some global statistics on audit pipes.
 */
static int		audit_pipe_count;	/* Current number of pipes. */
static u_int64_t	audit_pipe_ever;	/* Pipes ever allocated. */
static u_int64_t	audit_pipe_records;	/* Records seen. */
static u_int64_t	audit_pipe_drops;	/* Global record drop count. */

/*
 * Free an audit pipe entry.
 */
static void
audit_pipe_entry_free(struct audit_pipe_entry *ape)
{

	free(ape->ape_record, M_AUDIT_PIPE_ENTRY);
	free(ape, M_AUDIT_PIPE_ENTRY);
}

/*
 * Apparent individual record to a queue -- allocate queue-local buffer, and
 * add to the queue.  We try to drop from the head of the queue so that more
 * recent events take precedence over older ones, but if allocation fails we
 * do drop the new event.
 */
static void
audit_pipe_append(struct audit_pipe *ap, void *record, u_int record_len)
{
	struct audit_pipe_entry *ape, *ape_remove;

	mtx_assert(&audit_pipe_mtx, MA_OWNED);

	ape = malloc(sizeof(*ape), M_AUDIT_PIPE_ENTRY, M_NOWAIT | M_ZERO);
	if (ape == NULL) {
		ap->ap_drops++;
		return;
	}

	ape->ape_record = malloc(record_len, M_AUDIT_PIPE_ENTRY, M_NOWAIT);
	if (ape->ape_record == NULL) {
		free(ape, M_AUDIT_PIPE_ENTRY);
		ap->ap_drops++;
		audit_pipe_drops++;
		return;
	}

	bcopy(record, ape->ape_record, record_len);
	ape->ape_record_len = record_len;

	if (ap->ap_qlen >= ap->ap_qlimit) {
		ape_remove = TAILQ_FIRST(&ap->ap_queue);
		TAILQ_REMOVE(&ap->ap_queue, ape_remove, ape_queue);
		audit_pipe_entry_free(ape_remove);
		ap->ap_drops++;
		audit_pipe_drops++;
	}

	TAILQ_INSERT_TAIL(&ap->ap_queue, ape, ape_queue);
	ap->ap_inserts++;
	ap->ap_qlen++;
	selwakeuppri(&ap->ap_selinfo, PSOCK);
	if (ap->ap_flags & AUDIT_PIPE_ASYNC)
		pgsigio(&ap->ap_sigio, SIGIO, 0);
}

/*
 * audit_pipe_submit(): audit_worker submits audit records via this
 * interface, which arranges for them to be delivered to pipe queues.
 */
void
audit_pipe_submit(void *record, u_int record_len)
{
	struct audit_pipe *ap;

	/*
	 * Lockless read to avoid mutex overhead if pipes are not in use.
	 */
	if (TAILQ_FIRST(&audit_pipe_list) == NULL)
		return;

	mtx_lock(&audit_pipe_mtx);
	TAILQ_FOREACH(ap, &audit_pipe_list, ap_list)
		audit_pipe_append(ap, record, record_len);
	audit_pipe_records++;
	mtx_unlock(&audit_pipe_mtx);
	cv_signal(&audit_pipe_cv);
}

/*
 * Read the next record off of an audit pipe.
 */
static struct audit_pipe_entry *
audit_pipe_pop(struct audit_pipe *ap)
{
	struct audit_pipe_entry *ape;

	mtx_assert(&audit_pipe_mtx, MA_OWNED);

	ape = TAILQ_FIRST(&ap->ap_queue);
	KASSERT((ape == NULL && ap->ap_qlen == 0) ||
	    (ape != NULL && ap->ap_qlen != 0), ("audit_pipe_pop: qlen"));
	if (ape == NULL)
		return (NULL);
	TAILQ_REMOVE(&ap->ap_queue, ape, ape_queue);
	ap->ap_qlen--;
	return (ape);
}

/*
 * Allocate a new audit pipe.  Connects the pipe, on success, to the global
 * list and updates statistics.
 */
static struct audit_pipe *
audit_pipe_alloc(void)
{
	struct audit_pipe *ap;

	mtx_assert(&audit_pipe_mtx, MA_OWNED);

	ap = malloc(sizeof(*ap), M_AUDIT_PIPE, M_NOWAIT | M_ZERO);
	if (ap == NULL)
		return (NULL);
	ap->ap_qlimit = AUDIT_PIPE_QLIMIT_DEFAULT;
	TAILQ_INIT(&ap->ap_queue);
	TAILQ_INSERT_HEAD(&audit_pipe_list, ap, ap_list);
	audit_pipe_count++;
	audit_pipe_ever++;
	return (ap);
}

/*
 * Free an audit pipe.  Assumes mutex is held, audit_pipe is still on the
 * global list.  Frees any audit pipe entries in the queue.
 */
static void
audit_pipe_free(struct audit_pipe *ap)
{
	struct audit_pipe_entry *ape;

	mtx_assert(&audit_pipe_mtx, MA_OWNED);

	TAILQ_REMOVE(&audit_pipe_list, ap, ap_list);
	while ((ape = TAILQ_FIRST(&ap->ap_queue)) != NULL) {
		TAILQ_REMOVE(&ap->ap_queue, ape, ape_queue);
		audit_pipe_entry_free(ape);
		ap->ap_qlen--;
	}
	KASSERT(ap->ap_qlen == 0, ("audit_pipe_free: ap_qlen"));
	free(ap, M_AUDIT_PIPE);
	audit_pipe_count--;
}

/*
 * Audit pipe clone routine -- provide specific requested audit pipe, or a
 * fresh one if a specific one is not requested.
 */
static void
audit_pipe_clone(void *arg, struct ucred *cred, char *name, int namelen,
    struct cdev **dev)
{
	int i, u;

	if (*dev != NULL)
		return;

	if (strcmp(name, AUDIT_PIPE_NAME) == 0)
		u = -1;
	else if (dev_stdclone(name, NULL, AUDIT_PIPE_NAME, &u) != 1)
		return;

	i = clone_create(&audit_pipe_clones, &audit_pipe_cdevsw, &u, dev, 0);
	if (i) {
		*dev = make_dev(&audit_pipe_cdevsw, unit2minor(u), UID_ROOT,
		    GID_WHEEL, 0600, "%s%d", AUDIT_PIPE_NAME, u);
		if (*dev != NULL) {
			dev_ref(*dev);
			(*dev)->si_flags |= SI_CHEAPCLONE;
		}
	}
}

/*
 * Audit pipe open method.  Explicit suser check isn't used as this allows
 * file permissions on the special device to be used to grant audit review
 * access.
 */
static int
audit_pipe_open(struct cdev *dev, int oflags, int devtype, struct thread *td)
{
	struct audit_pipe *ap;

	mtx_lock(&audit_pipe_mtx);
	ap = dev->si_drv1;
	if (ap == NULL) {
		ap = audit_pipe_alloc();
		if (ap == NULL) {
			mtx_unlock(&audit_pipe_mtx);
			return (ENOMEM);
		}
		dev->si_drv1 = ap;
	} else {
		KASSERT(ap->ap_open, ("audit_pipe_open: ap && !ap_open"));
		mtx_unlock(&audit_pipe_mtx);
		return (EBUSY);
	}
	ap->ap_open = 1;
	mtx_unlock(&audit_pipe_mtx);
	fsetown(td->td_proc->p_pid, &ap->ap_sigio);
	return (0);
}

/*
 * Close audit pipe, tear down all records, etc.
 */
static int
audit_pipe_close(struct cdev *dev, int fflag, int devtype, struct thread *td)
{
	struct audit_pipe *ap;

	ap = dev->si_drv1;
	KASSERT(ap != NULL, ("audit_pipe_close: ap == NULL"));
	KASSERT(ap->ap_open, ("audit_pipe_close: !ap_open"));
	funsetown(&ap->ap_sigio);
	mtx_lock(&audit_pipe_mtx);
	ap->ap_open = 0;
	audit_pipe_free(ap);
	dev->si_drv1 = NULL;
	mtx_unlock(&audit_pipe_mtx);
	return (0);
}

/*
 * Audit pipe ioctl() routine.  Nothing for now, but eventually will allow
 * setting and retrieval of current queue depth, queue limit, flush, etc.
 *
 * Would be desirable to support filtering, although perhaps something simple
 * like an event mask, as opposed to something complicated like BPF.
 */
static int
audit_pipe_ioctl(struct cdev *dev, u_long cmd, caddr_t data, int flag,
    struct thread *td)
{
	struct audit_pipe *ap;
	int error;

	ap = dev->si_drv1;
	KASSERT(ap != NULL, ("audit_pipe_ioctl: ap == NULL"));
	switch (cmd) {
	case FIONBIO:
		mtx_lock(&audit_pipe_mtx);
		if (*(int *)data)
			ap->ap_flags |= AUDIT_PIPE_NBIO;
		else
			ap->ap_flags &= ~AUDIT_PIPE_NBIO;
		mtx_unlock(&audit_pipe_mtx);
		error = 0;
		break;

	case FIONREAD:
		mtx_lock(&audit_pipe_mtx);
		if (TAILQ_FIRST(&ap->ap_queue) != NULL)
			*(int *)data =
			    TAILQ_FIRST(&ap->ap_queue)->ape_record_len;
		else
			*(int *)data = 0;
		mtx_unlock(&audit_pipe_mtx);
		error = 0;
		break;

	case FIOASYNC:
		mtx_lock(&audit_pipe_mtx);
		if (*(int *)data)
			ap->ap_flags |= AUDIT_PIPE_ASYNC;
		else
			ap->ap_flags &= ~AUDIT_PIPE_ASYNC;
		mtx_unlock(&audit_pipe_mtx);
		error = 0;
		break;

	case FIOSETOWN:
		error = fsetown(*(int *)data, &ap->ap_sigio);
		break;

	case FIOGETOWN:
		*(int *)data = fgetown(&ap->ap_sigio);
		error = 0;

	default:
		error = ENOTTY;
	}
	return (error);
}

/*
 * Audit pipe read.  Pull one record off the queue and copy to user space.
 * On error, the record is dropped.
 */
static int
audit_pipe_read(struct cdev *dev, struct uio *uio, int flag)
{
	struct audit_pipe_entry *ape;
	struct audit_pipe *ap;
	int error;

	ap = dev->si_drv1;
	KASSERT(ap != NULL, ("audit_pipe_read: ap == NULL"));
	mtx_lock(&audit_pipe_mtx);
	do {
		/*
		 * Wait for a record that fits into the read buffer, dropping
		 * records that would be truncated if actually passed to the
		 * process.  This helps maintain the discreet record read
		 * interface.
		 */
		while ((ape = audit_pipe_pop(ap)) == NULL) {
			if (ap->ap_flags & AUDIT_PIPE_NBIO) {
				mtx_unlock(&audit_pipe_mtx);
				return (EAGAIN);
			}
			error = cv_wait_sig(&audit_pipe_cv, &audit_pipe_mtx);
			if (error) {
				mtx_unlock(&audit_pipe_mtx);
				return (error);
			}
		}
		if (ape->ape_record_len <= uio->uio_resid)
			break;
		audit_pipe_entry_free(ape);
		ap->ap_truncates++;
	} while (1);
	mtx_unlock(&audit_pipe_mtx);

	/*
	 * Now read record to user space memory.  Even if the read is short,
	 * we abandon the remainder of the record, supporting only discreet
	 * record reads.
	 */
	error = uiomove(ape->ape_record, ape->ape_record_len, uio);
	audit_pipe_entry_free(ape);
	return (error);
}

/*
 * Audit pipe poll.
 */
static int
audit_pipe_poll(struct cdev *dev, int events, struct thread *td)
{
	struct audit_pipe *ap;
	int revents;

	revents = 0;
	ap = dev->si_drv1;
	KASSERT(ap != NULL, ("audit_pipe_poll: ap == NULL"));
	if (events & (POLLIN | POLLRDNORM)) {
		mtx_lock(&audit_pipe_mtx);
		if (TAILQ_FIRST(&ap->ap_queue) != NULL)
			revents |= events & (POLLIN | POLLRDNORM);
		else
			selrecord(td, &ap->ap_selinfo);
		mtx_unlock(&audit_pipe_mtx);
	}
	return (revents);
}

/*
 * Initialize the audit pipe system.
 */
static void
audit_pipe_init(void *unused)
{

	TAILQ_INIT(&audit_pipe_list);
	mtx_init(&audit_pipe_mtx, "audit_pipe_mtx", NULL, MTX_DEF);
	cv_init(&audit_pipe_cv, "audit_pipe_cv");

	clone_setup(&audit_pipe_clones);
	audit_pipe_eh_tag = EVENTHANDLER_REGISTER(dev_clone,
	    audit_pipe_clone, 0, 1000);
	if (audit_pipe_eh_tag == NULL)
		panic("audit_pipe_init: EVENTHANDLER_REGISTER");
}

SYSINIT(audit_pipe_init, SI_SUB_DRIVERS, SI_ORDER_MIDDLE, audit_pipe_init,
    NULL);