/*-
 * SPDX-License-Identifier: BSD-3-Clause
 *
 * Copyright (c) 1999-2008 Apple Inc.
 * Copyright (c) 2006-2008, 2016, 2018 Robert N. M. Watson
 * All rights reserved.
 *
 * Portions of this software were developed by BAE Systems, the University of
 * Cambridge Computer Laboratory, and Memorial University under DARPA/AFRL
 * contract FA8650-15-C-7558 ("CADETS"), as part of the DARPA Transparent
 * Computing (TC) research program.
 *
 * 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.
 * 3.  Neither the name of Apple Inc. ("Apple") nor the names of
 *     its contributors may be used to endorse or promote products derived
 *     from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE AND ITS 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 APPLE OR ITS 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.
 */

#include <sys/param.h>
#include <sys/condvar.h>
#include <sys/conf.h>
#include <sys/file.h>
#include <sys/filedesc.h>
#include <sys/fcntl.h>
#include <sys/ipc.h>
#include <sys/kernel.h>
#include <sys/kthread.h>
#include <sys/malloc.h>
#include <sys/mount.h>
#include <sys/namei.h>
#include <sys/proc.h>
#include <sys/queue.h>
#include <sys/socket.h>
#include <sys/socketvar.h>
#include <sys/protosw.h>
#include <sys/domain.h>
#include <sys/stdarg.h>
#include <sys/sx.h>
#include <sys/sysproto.h>
#include <sys/sysent.h>
#include <sys/systm.h>
#include <sys/ucred.h>
#include <sys/uio.h>
#include <sys/un.h>
#include <sys/unistd.h>
#include <sys/vnode.h>

#include <bsm/audit.h>
#include <bsm/audit_internal.h>
#include <bsm/audit_kevents.h>

#include <netinet/in.h>
#include <netinet/in_pcb.h>

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

#include <vm/uma.h>

/*
 * Worker thread that will schedule disk I/O, etc.
 */
static struct proc              *audit_thread;

/*
 * audit_cred and audit_vp are the stored credential and vnode to use for
 * active audit trail.  They are protected by the audit worker lock, which
 * will be held across all I/O and all rotation to prevent them from being
 * replaced (rotated) while in use.  The audit_file_rotate_wait flag is set
 * when the kernel has delivered a trigger to auditd to rotate the trail, and
 * is cleared when the next rotation takes place.  It is also protected by
 * the audit worker lock.
 */
static int               audit_file_rotate_wait;
static struct ucred     *audit_cred;
static struct vnode     *audit_vp;
static off_t             audit_size;
static struct sx         audit_worker_lock;

#define AUDIT_WORKER_LOCK_INIT()        sx_init(&audit_worker_lock, \
                                            "audit_worker_lock");
#define AUDIT_WORKER_LOCK_ASSERT()      sx_assert(&audit_worker_lock, \
                                            SA_XLOCKED)
#define AUDIT_WORKER_LOCK()             sx_xlock(&audit_worker_lock)
#define AUDIT_WORKER_UNLOCK()           sx_xunlock(&audit_worker_lock)

static void
audit_worker_sync_vp(struct vnode *vp, struct mount *mp, const char *fmt, ...)
{
        struct mount *mp1;
        int error;
        va_list va;

        va_start(va, fmt);
        error = vn_start_write(vp, &mp1, 0);
        if (error == 0) {
                VOP_LOCK(vp, LK_EXCLUSIVE | LK_RETRY);
                (void)VOP_FSYNC(vp, MNT_WAIT, curthread);
                VOP_UNLOCK(vp);
                vn_finished_write(mp1);
        }
        vfs_unbusy(mp);
        vpanic(fmt, va);
        va_end(va);
}

/*
 * Write an audit record to a file, performed as the last stage after both
 * preselection and BSM conversion.  Both space management and write failures
 * are handled in this function.
 *
 * No attempt is made to deal with possible failure to deliver a trigger to
 * the audit daemon, since the message is asynchronous anyway.
 */
static void
audit_record_write(struct vnode *vp, struct ucred *cred, void *data,
    size_t len)
{
        static struct timeval last_lowspace_trigger;
        static struct timeval last_fail;
        static int cur_lowspace_trigger;
        struct statfs *mnt_stat;
        struct mount *mp;
        int error;
        static int cur_fail;
        long temp;

        AUDIT_WORKER_LOCK_ASSERT();

        if (vp == NULL)
                return;

        mp = vp->v_mount;
        if (mp == NULL) {
                error = EINVAL;
                goto fail;
        }
        error = vfs_busy(mp, 0);
        if (error != 0) {
                mp = NULL;
                goto fail;
        }
        mnt_stat = &mp->mnt_stat;

        /*
         * First, gather statistics on the audit log file and file system so
         * that we know how we're doing on space.  Consider failure of these
         * operations to indicate a future inability to write to the file.
         */
        error = VFS_STATFS(mp, mnt_stat);
        if (error != 0)
                goto fail;

        /*
         * We handle four different space-related limits:
         *
         * - A fixed (hard) limit on the minimum free blocks we require on
         *   the file system, and results in record loss, a trigger, and
         *   possible fail stop due to violating invariants.
         *
         * - An administrative (soft) limit, which when fallen below, results
         *   in the kernel notifying the audit daemon of low space.
         *
         * - An audit trail size limit, which when gone above, results in the
         *   kernel notifying the audit daemon that rotation is desired.
         *
         * - The total depth of the kernel audit record exceeding free space,
         *   which can lead to possible fail stop (with drain), in order to
         *   prevent violating invariants.  Failure here doesn't halt
         *   immediately, but prevents new records from being generated.
         *
         * Possibly, the last of these should be handled differently, always
         * allowing a full queue to be lost, rather than trying to prevent
         * loss.
         *
         * First, handle the hard limit, which generates a trigger and may
         * fail stop.  This is handled in the same manner as ENOSPC from
         * VOP_WRITE, and results in record loss.
         */
        if (mnt_stat->f_bfree < AUDIT_HARD_LIMIT_FREE_BLOCKS) {
                error = ENOSPC;
                goto fail_enospc;
        }

        /*
         * Second, handle falling below the soft limit, if defined; we send
         * the daemon a trigger and continue processing the record.  Triggers
         * are limited to 1/sec.
         */
        if (audit_qctrl.aq_minfree != 0) {
                temp = mnt_stat->f_blocks / (100 / audit_qctrl.aq_minfree);
                if (mnt_stat->f_bfree < temp) {
                        if (ppsratecheck(&last_lowspace_trigger,
                            &cur_lowspace_trigger, 1)) {
                                (void)audit_send_trigger(
                                    AUDIT_TRIGGER_LOW_SPACE);
                                printf("Warning: disk space low (< %d%% free) "
                                    "on audit log file-system\n",
                                    audit_qctrl.aq_minfree);
                        }
                }
        }

        /*
         * If the current file is getting full, generate a rotation trigger
         * to the daemon.  This is only approximate, which is fine as more
         * records may be generated before the daemon rotates the file.
         */
        if (audit_fstat.af_filesz != 0 &&
            audit_size >= audit_fstat.af_filesz * (audit_file_rotate_wait + 1)) {
                AUDIT_WORKER_LOCK_ASSERT();

                audit_file_rotate_wait++;
                (void)audit_send_trigger(AUDIT_TRIGGER_ROTATE_KERNEL);
        }

        /*
         * If the estimated amount of audit data in the audit event queue
         * (plus records allocated but not yet queued) has reached the amount
         * of free space on the disk, then we need to go into an audit fail
         * stop state, in which we do not permit the allocation/committing of
         * any new audit records.  We continue to process records but don't
         * allow any activities that might generate new records.  In the
         * future, we might want to detect when space is available again and
         * allow operation to continue, but this behavior is sufficient to
         * meet fail stop requirements in CAPP.
         */
        if (audit_fail_stop) {
                if ((unsigned long)((audit_q_len + audit_pre_q_len + 1) *
                    MAX_AUDIT_RECORD_SIZE) / mnt_stat->f_bsize >=
                    (unsigned long)(mnt_stat->f_bfree)) {
                        if (ppsratecheck(&last_fail, &cur_fail, 1))
                                printf("audit_record_write: free space "
                                    "below size of audit queue, failing "
                                    "stop\n");
                        audit_in_failure = 1;
                } else if (audit_in_failure) {
                        /*
                         * Note: if we want to handle recovery, this is the
                         * spot to do it: unset audit_in_failure, and issue a
                         * wakeup on the cv.
                         */
                }
        }

        error = vn_rdwr(UIO_WRITE, vp, data, len, (off_t)0, UIO_SYSSPACE,
            IO_APPEND|IO_UNIT, cred, NULL, NULL, curthread);
        if (error == ENOSPC)
                goto fail_enospc;
        else if (error)
                goto fail;
        AUDIT_WORKER_LOCK_ASSERT();
        audit_size += len;

        /*
         * Catch completion of a queue drain here; if we're draining and the
         * queue is now empty, fail stop.  That audit_fail_stop is implicitly
         * true, since audit_in_failure can only be set of audit_fail_stop is
         * set.
         *
         * Note: if we handle recovery from audit_in_failure, then we need to
         * make panic here conditional.
         */
        if (audit_in_failure) {
                if (audit_q_len == 0 && audit_pre_q_len == 0) {
                        audit_worker_sync_vp(vp, mp,
                            "Audit store overflow; record queue drained.");
                }
        }

        vfs_unbusy(mp);
        return;

fail_enospc:
        /*
         * ENOSPC is considered a special case with respect to failures, as
         * this can reflect either our preemptive detection of insufficient
         * space, or ENOSPC returned by the vnode write call.
         */
        if (audit_fail_stop) {
                audit_worker_sync_vp(vp, mp,
                    "Audit log space exhausted and fail-stop set.");
        }
        (void)audit_send_trigger(AUDIT_TRIGGER_NO_SPACE);
        audit_trail_suspended = 1;
        audit_syscalls_enabled_update();

        /* FALLTHROUGH */
fail:
        /*
         * We have failed to write to the file, so the current record is
         * lost, which may require an immediate system halt.
         */
        if (audit_panic_on_write_fail) {
                audit_worker_sync_vp(vp, mp,
                    "audit_worker: write error %d\n", error);
        } else if (ppsratecheck(&last_fail, &cur_fail, 1))
                printf("audit_worker: write error %d\n", error);
        if (mp != NULL)
                vfs_unbusy(mp);
}

/*
 * Given a kernel audit record, process as required.  Kernel audit records
 * are converted to one, or possibly two, BSM records, depending on whether
 * there is a user audit record present also.  Kernel records need be
 * converted to BSM before they can be written out.  Both types will be
 * written to disk, and audit pipes.
 */
static void
audit_worker_process_record(struct kaudit_record *ar)
{
        struct au_record *bsm;
        au_class_t class;
        au_event_t event;
        au_id_t auid;
        int error, sorf;
        int locked;

        /*
         * We hold the audit worker lock over both writes, if there are two,
         * so that the two records won't be split across a rotation and end
         * up in two different trail files.
         */
        if (((ar->k_ar_commit & AR_COMMIT_USER) &&
            (ar->k_ar_commit & AR_PRESELECT_USER_TRAIL)) ||
            (ar->k_ar_commit & AR_PRESELECT_TRAIL)) {
                AUDIT_WORKER_LOCK();
                locked = 1;
        } else
                locked = 0;

        /*
         * First, handle the user record, if any: commit to the system trail
         * and audit pipes as selected.
         */
        if ((ar->k_ar_commit & AR_COMMIT_USER) &&
            (ar->k_ar_commit & AR_PRESELECT_USER_TRAIL)) {
                AUDIT_WORKER_LOCK_ASSERT();
                audit_record_write(audit_vp, audit_cred, ar->k_udata,
                    ar->k_ulen);
        }

        if ((ar->k_ar_commit & AR_COMMIT_USER) &&
            (ar->k_ar_commit & AR_PRESELECT_USER_PIPE))
                audit_pipe_submit_user(ar->k_udata, ar->k_ulen);

        if (!(ar->k_ar_commit & AR_COMMIT_KERNEL) ||
            ((ar->k_ar_commit & AR_PRESELECT_PIPE) == 0 &&
            (ar->k_ar_commit & AR_PRESELECT_TRAIL) == 0 &&
            (ar->k_ar_commit & AR_PRESELECT_DTRACE) == 0))
                goto out;

        auid = ar->k_ar.ar_subj_auid;
        event = ar->k_ar.ar_event;
        class = au_event_class(event);
        if (ar->k_ar.ar_errno == 0)
                sorf = AU_PRS_SUCCESS;
        else
                sorf = AU_PRS_FAILURE;

        error = kaudit_to_bsm(ar, &bsm);
        switch (error) {
        case BSM_NOAUDIT:
                goto out;

        case BSM_FAILURE:
                printf("audit_worker_process_record: BSM_FAILURE\n");
                goto out;

        case BSM_SUCCESS:
                break;

        default:
                panic("kaudit_to_bsm returned %d", error);
        }

        if (ar->k_ar_commit & AR_PRESELECT_TRAIL) {
                AUDIT_WORKER_LOCK_ASSERT();
                audit_record_write(audit_vp, audit_cred, bsm->data, bsm->len);
        }

        if (ar->k_ar_commit & AR_PRESELECT_PIPE)
                audit_pipe_submit(auid, event, class, sorf,
                    ar->k_ar_commit & AR_PRESELECT_TRAIL, bsm->data,
                    bsm->len);

#ifdef KDTRACE_HOOKS
        /*
         * Version of the dtaudit commit hook that accepts BSM.
         */
        if (ar->k_ar_commit & AR_PRESELECT_DTRACE) {
                if (dtaudit_hook_bsm != NULL)
                        dtaudit_hook_bsm(ar, auid, event, class, sorf,
                            bsm->data, bsm->len);
        }
#endif

        kau_free(bsm);
out:
        if (locked)
                AUDIT_WORKER_UNLOCK();
}

/*
 * The audit_worker thread is responsible for watching the event queue,
 * dequeueing records, converting them to BSM format, and committing them to
 * disk.  In order to minimize lock thrashing, records are dequeued in sets
 * to a thread-local work queue.
 *
 * Note: this means that the effect bound on the size of the pending record
 * queue is 2x the length of the global queue.
 */
static void
audit_worker(void *arg)
{
        struct kaudit_queue ar_worklist;
        struct kaudit_record *ar;
        int lowater_signal;

        TAILQ_INIT(&ar_worklist);
        mtx_lock(&audit_mtx);
        while (1) {
                mtx_assert(&audit_mtx, MA_OWNED);

                /*
                 * Wait for a record.
                 */
                while (TAILQ_EMPTY(&audit_q))
                        cv_wait(&audit_worker_cv, &audit_mtx);

                /*
                 * If there are records in the global audit record queue,
                 * transfer them to a thread-local queue and process them
                 * one by one.  If we cross the low watermark threshold,
                 * signal any waiting processes that they may wake up and
                 * continue generating records.
                 */
                lowater_signal = 0;
                while ((ar = TAILQ_FIRST(&audit_q))) {
                        TAILQ_REMOVE(&audit_q, ar, k_q);
                        audit_q_len--;
                        if (audit_q_len == audit_qctrl.aq_lowater)
                                lowater_signal++;
                        TAILQ_INSERT_TAIL(&ar_worklist, ar, k_q);
                }
                if (lowater_signal)
                        cv_broadcast(&audit_watermark_cv);

                mtx_unlock(&audit_mtx);
                while ((ar = TAILQ_FIRST(&ar_worklist))) {
                        TAILQ_REMOVE(&ar_worklist, ar, k_q);
                        audit_worker_process_record(ar);
                        audit_free(ar);
                }
                mtx_lock(&audit_mtx);
        }
}

/*
 * audit_rotate_vnode() is called by a user or kernel thread to configure or
 * de-configure auditing on a vnode.  The arguments are the replacement
 * credential (referenced) and vnode (referenced and opened) to substitute
 * for the current credential and vnode, if any.  If either is set to NULL,
 * both should be NULL, and this is used to indicate that audit is being
 * disabled.  Any previous cred/vnode will be closed and freed.  We re-enable
 * generating rotation requests to auditd.
 */
void
audit_rotate_vnode(struct ucred *cred, struct vnode *vp)
{
        struct ucred *old_audit_cred;
        struct vnode *old_audit_vp;
        struct vattr vattr;

        KASSERT((cred != NULL && vp != NULL) || (cred == NULL && vp == NULL),
            ("audit_rotate_vnode: cred %p vp %p", cred, vp));

        if (vp != NULL) {
                vn_lock(vp, LK_SHARED | LK_RETRY);
                if (VOP_GETATTR(vp, &vattr, cred) != 0)
                        vattr.va_size = 0;
                VOP_UNLOCK(vp);
        } else {
                vattr.va_size = 0;
        }

        /*
         * Rotate the vnode/cred, and clear the rotate flag so that we will
         * send a rotate trigger if the new file fills.
         */
        AUDIT_WORKER_LOCK();
        old_audit_cred = audit_cred;
        old_audit_vp = audit_vp;
        audit_cred = cred;
        audit_vp = vp;
        audit_size = vattr.va_size;
        audit_file_rotate_wait = 0;
        audit_trail_enabled = (audit_vp != NULL);
        audit_syscalls_enabled_update();
        AUDIT_WORKER_UNLOCK();

        /*
         * If there was an old vnode/credential, close and free.
         */
        if (old_audit_vp != NULL) {
                vn_close(old_audit_vp, AUDIT_CLOSE_FLAGS, old_audit_cred,
                    curthread);
                crfree(old_audit_cred);
        }
}

void
audit_worker_init(void)
{
        int error;

        AUDIT_WORKER_LOCK_INIT();
        error = kproc_create(audit_worker, NULL, &audit_thread, RFHIGHPID,
            0, "audit");
        if (error)
                panic("audit_worker_init: kproc_create returned %d", error);
}