/*-
 * SPDX-License-Identifier: BSD-3-Clause
 *
 * Copyright (c) 1982, 1986, 1989, 1993
 *      The Regents of the University of California.  All rights reserved.
 * (c) UNIX System Laboratories, Inc.
 * All or some portions of this file are derived from material licensed
 * to the University of California by American Telephone and Telegraph
 * Co. or Unix System Laboratories, Inc. and are reproduced herein with
 * the permission of UNIX System Laboratories, Inc.
 *
 * 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 the University 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 THE REGENTS 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 REGENTS 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.
 */

#include <sys/cdefs.h>
#include "opt_capsicum.h"
#include "opt_ktrace.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/dirent.h>
#include <sys/kernel.h>
#include <sys/capsicum.h>
#include <sys/fcntl.h>
#include <sys/jail.h>
#include <sys/lock.h>
#include <sys/mutex.h>
#include <sys/namei.h>
#include <sys/vnode.h>
#include <sys/mount.h>
#include <sys/filedesc.h>
#include <sys/proc.h>
#include <sys/sdt.h>
#include <sys/syscallsubr.h>
#include <sys/sysctl.h>
#ifdef KTRACE
#include <sys/ktrace.h>
#endif
#ifdef INVARIANTS
#include <machine/_inttypes.h>
#endif

#include <security/audit/audit.h>
#include <security/mac/mac_framework.h>

#include <vm/uma.h>

#ifdef INVARIANTS
static void NDVALIDATE_impl(struct nameidata *, int);
#define NDVALIDATE(ndp) NDVALIDATE_impl(ndp, __LINE__)
#else
#define NDVALIDATE(ndp)
#endif

/*
 * Reset ndp to its original state.
 */
#define NDRESET(ndp) do {                                               \
        NDREINIT_DBG(ndp);                                              \
        ndp->ni_resflags = 0;                                           \
        ndp->ni_cnd.cn_flags &= ~NAMEI_INTERNAL_FLAGS;                  \
} while (0)
/*
 * Prepare namei() to restart. Reset components to its original state and set
 * ISRESTARTED flag which signals the underlying lookup code to change the root
 * from ABI root to actual root and prevents a further restarts.
 */
#define NDRESTART(ndp) do {                                             \
        NDRESET(ndp);                                           \
        ndp->ni_cnd.cn_flags |= ISRESTARTED;                            \
} while (0)

#ifdef KTRACE
#define NIKTRCAPFAIL(path)      ktrcapfail(CAPFAIL_NAMEI, (path))
#else
#define NIKTRCAPFAIL(path)
#endif

#define NI_CAP_VIOLATION(ndp, path)     do {                    \
        NIKTRCAPFAIL(path);                                     \
        (ndp)->ni_lcf &= ~NI_LCF_KTR_FLAGS;                     \
} while (0)

SDT_PROVIDER_DEFINE(vfs);
SDT_PROBE_DEFINE4(vfs, namei, lookup, entry, "struct vnode *", "char *",
    "unsigned long", "bool");
SDT_PROBE_DEFINE4(vfs, namei, lookup, return, "int", "struct vnode *", "bool",
    "struct nameidata");

/* Allocation zone for namei. */
uma_zone_t namei_zone;

/* Placeholder vnode for mp traversal. */
static struct vnode *vp_crossmp;

static int
crossmp_vop_islocked(struct vop_islocked_args *ap)
{

        return (LK_SHARED);
}

static int
crossmp_vop_lock1(struct vop_lock1_args *ap)
{
        struct vnode *vp;
        struct lock *lk __diagused;
        int flags;

        vp = ap->a_vp;
        lk = vp->v_vnlock;
        flags = ap->a_flags;

        KASSERT((flags & (LK_SHARED | LK_NOWAIT)) == (LK_SHARED | LK_NOWAIT),
            ("%s: invalid lock request 0x%x for crossmp", __func__, flags));

        if ((flags & LK_INTERLOCK) != 0)
                VI_UNLOCK(vp);
        LOCK_LOG_LOCK("SLOCK", &lk->lock_object, 0, 0, ap->a_file, ap->a_line);
        return (0);
}

static int
crossmp_vop_unlock(struct vop_unlock_args *ap)
{
        struct vnode *vp;
        struct lock *lk __diagused;

        vp = ap->a_vp;
        lk = vp->v_vnlock;

        LOCK_LOG_LOCK("SUNLOCK", &lk->lock_object, 0, 0, LOCK_FILE,
            LOCK_LINE);
        return (0);
}

static struct vop_vector crossmp_vnodeops = {
        .vop_default =          &default_vnodeops,
        .vop_islocked =         crossmp_vop_islocked,
        .vop_lock1 =            crossmp_vop_lock1,
        .vop_unlock =           crossmp_vop_unlock,
};
/*
 * VFS_VOP_VECTOR_REGISTER(crossmp_vnodeops) is not used here since the vnode
 * gets allocated early. See nameiinit for the direct call below.
 */

struct nameicap_tracker {
        TAILQ_ENTRY(nameicap_tracker) nm_link;
        struct mount *mp;
};

/* Zone for cap mode tracker elements used for dotdot capability checks. */
MALLOC_DEFINE(M_NAMEITRACKER, "namei_tracker", "namei tracking for dotdot");

static void
nameiinit(void *dummy __unused)
{

        namei_zone = uma_zcreate("NAMEI", MAXPATHLEN, NULL, NULL, NULL, NULL,
            UMA_ALIGN_PTR, 0);
        vfs_vector_op_register(&crossmp_vnodeops);
        getnewvnode("crossmp", NULL, &crossmp_vnodeops, &vp_crossmp);
        vp_crossmp->v_state = VSTATE_CONSTRUCTED;
        vp_crossmp->v_irflag |= VIRF_CROSSMP;
}
SYSINIT(vfs, SI_SUB_VFS, SI_ORDER_SECOND, nameiinit, NULL);

static int lookup_cap_dotdot = 1;
SYSCTL_INT(_vfs, OID_AUTO, lookup_cap_dotdot, CTLFLAG_RWTUN,
    &lookup_cap_dotdot, 0,
    "enables \"..\" components in path lookup in capability mode");
static int lookup_cap_dotdot_nonlocal = 1;
SYSCTL_INT(_vfs, OID_AUTO, lookup_cap_dotdot_nonlocal, CTLFLAG_RWTUN,
    &lookup_cap_dotdot_nonlocal, 0,
    "enables \"..\" components in path lookup in capability mode "
    "on non-local mount");

static int
nameicap_tracker_add(struct nameidata *ndp, struct vnode *dp)
{
        struct nameicap_tracker *nt;
        struct mount *mp;
        int error;

        if ((ndp->ni_lcf & NI_LCF_CAP_DOTDOT) == 0 || dp->v_type != VDIR)
                return (0);
        mp = NULL;
        error = VOP_GETWRITEMOUNT(dp, &mp);
        if (error != 0)
                return (error);
        nt = TAILQ_LAST(&ndp->ni_cap_tracker, nameicap_tracker_head);
        if (nt != NULL && nt->mp == mp) {
                vfs_rel(mp);
                return (0);
        }
        nt = malloc(sizeof(*nt), M_NAMEITRACKER, M_WAITOK);
        nt->mp = mp;
        error = lockmgr(&mp->mnt_renamelock, LK_SHARED | LK_NOWAIT, 0);
        if (error != 0) {
                MPASS(ndp->ni_nctrack_mnt == NULL);
                ndp->ni_nctrack_mnt = mp;
                free(nt, M_NAMEITRACKER);
                error = ERESTART;
        } else {
                TAILQ_INSERT_TAIL(&ndp->ni_cap_tracker, nt, nm_link);
        }
        return (error);
}

static void
nameicap_cleanup(struct nameidata *ndp, int error)
{
        struct nameicap_tracker *nt, *nt1;
        struct mount *mp;

        KASSERT((ndp->ni_nctrack_mnt == NULL &&
            TAILQ_EMPTY(&ndp->ni_cap_tracker)) ||
            (ndp->ni_lcf & NI_LCF_CAP_DOTDOT) != 0,
            ("tracker active and not strictrelative"));

        TAILQ_FOREACH_SAFE(nt, &ndp->ni_cap_tracker, nm_link, nt1) {
                mp = nt->mp;
                lockmgr(&mp->mnt_renamelock, LK_RELEASE, 0);
                vfs_rel(mp);
                TAILQ_REMOVE(&ndp->ni_cap_tracker, nt, nm_link);
                free(nt, M_NAMEITRACKER);
        }

        mp = ndp->ni_nctrack_mnt;
        if (mp != NULL) {
                if (error == ERESTART) {
                        lockmgr(&mp->mnt_renamelock, LK_EXCLUSIVE, 0);
                        lockmgr(&mp->mnt_renamelock, LK_RELEASE, 0);
                }
                vfs_rel(mp);
                ndp->ni_nctrack_mnt = NULL;
        }
}

/*
 * For dotdot lookups in capability mode, disallow walking over the
 * directory no_rbeneath_dpp that was used as the starting point of
 * the lookup.  Since we take the mnt_renamelocks of all mounts we
 * ever walked over during lookup, parallel renames are disabled.
 * This prevents the situation where we circumvent walk over
 * ni_rbeneath_dpp following dotdots.
 *
 * Also allow to force failure of dotdot lookups for non-local
 * filesystems, where external agents might assist local lookups to
 * escape the compartment.
 */
static int
nameicap_check_dotdot(struct nameidata *ndp, struct vnode *dp)
{
        struct mount *mp;

        if (dp == NULL || dp->v_type != VDIR || (ndp->ni_lcf &
            NI_LCF_STRICTREL) == 0)
                return (0);
        if (__predict_false((ndp->ni_lcf & (NI_LCF_STRICTREL_KTR |
            NI_LCF_CAP_DOTDOT_KTR)) == NI_LCF_STRICTREL_KTR))
                NI_CAP_VIOLATION(ndp, ndp->ni_cnd.cn_pnbuf);
        if ((ndp->ni_lcf & NI_LCF_CAP_DOTDOT) == 0)
                goto violation;
        if (dp == ndp->ni_rbeneath_dpp)
                goto violation;
        mp = dp->v_mount;
        if (lookup_cap_dotdot_nonlocal == 0 && mp != NULL &&
            (mp->mnt_flag & MNT_LOCAL) == 0)
                goto violation;
        return (0);

violation:
        if (__predict_false((ndp->ni_lcf & NI_LCF_STRICTREL_KTR) != 0))
                NI_CAP_VIOLATION(ndp, ndp->ni_cnd.cn_pnbuf);
        return (ENOTCAPABLE);
}

static void
namei_cleanup_cnp(struct componentname *cnp)
{

        uma_zfree(namei_zone, cnp->cn_pnbuf);
        cnp->cn_pnbuf = NULL;
        cnp->cn_nameptr = NULL;
}

static int
namei_handle_root(struct nameidata *ndp, struct vnode **dpp)
{
        struct componentname *cnp;

        cnp = &ndp->ni_cnd;
        if (__predict_false((ndp->ni_lcf & (NI_LCF_STRICTREL |
            NI_LCF_STRICTREL_KTR)) != 0)) {
                if ((ndp->ni_lcf & NI_LCF_STRICTREL_KTR) != 0)
                        NI_CAP_VIOLATION(ndp, cnp->cn_pnbuf);
                if ((ndp->ni_lcf & NI_LCF_STRICTREL) != 0)
                        return (ENOTCAPABLE);
        }
        while (*(cnp->cn_nameptr) == '/') {
                cnp->cn_nameptr++;
                ndp->ni_pathlen--;
        }
        *dpp = ndp->ni_rootdir;
        vrefact(*dpp);
        return (0);
}

static int
namei_setup(struct nameidata *ndp, struct vnode **dpp, struct pwd **pwdp)
{
        struct componentname *cnp;
        struct thread *td;
        struct pwd *pwd;
        int error;
        bool startdir_used;

        cnp = &ndp->ni_cnd;
        td = curthread;

        startdir_used = false;
        *pwdp = NULL;
        *dpp = NULL;

#ifdef CAPABILITY_MODE
        /*
         * In capability mode, lookups must be restricted to happen in
         * the subtree with the root specified by the file descriptor:
         * - The root must be real file descriptor, not the pseudo-descriptor
         *   AT_FDCWD.
         * - The passed path must be relative and not absolute.
         * - If lookup_cap_dotdot is disabled, path must not contain the
         *   '..' components.
         * - If lookup_cap_dotdot is enabled, we verify that all '..'
         *   components lookups result in the directories which were
         *   previously walked by us, which prevents an escape from
         *   the relative root.
         */
        if ((cnp->cn_flags & NOCAPCHECK) == 0) {
                if (CAP_TRACING(td)) {
                        ndp->ni_lcf |= NI_LCF_STRICTREL_KTR;
                        if (ndp->ni_dirfd == AT_FDCWD)
                                NI_CAP_VIOLATION(ndp, "AT_FDCWD");
                }
                if (IN_CAPABILITY_MODE(td)) {
                        ndp->ni_lcf |= NI_LCF_STRICTREL;
                        ndp->ni_resflags |= NIRES_STRICTREL;
                        if (ndp->ni_dirfd == AT_FDCWD)
                                return (ECAPMODE);
                }
        }
#endif
        error = 0;

        /*
         * Get starting point for the translation.
         */
        pwd = pwd_hold(td);
        /*
         * The reference on ni_rootdir is acquired in the block below to avoid
         * back-to-back atomics for absolute lookups.
         */
        namei_setup_rootdir(ndp, cnp, pwd);
        ndp->ni_topdir = pwd->pwd_jdir;

        if (cnp->cn_pnbuf[0] == '/') {
                ndp->ni_resflags |= NIRES_ABS;
                error = namei_handle_root(ndp, dpp);
        } else {
                if (ndp->ni_startdir != NULL) {
                        *dpp = ndp->ni_startdir;
                        startdir_used = true;
                } else if (ndp->ni_dirfd == AT_FDCWD) {
                        *dpp = pwd->pwd_cdir;
                        vrefact(*dpp);
                } else {
                        if (cnp->cn_flags & AUDITVNODE1)
                                AUDIT_ARG_ATFD1(ndp->ni_dirfd);
                        if (cnp->cn_flags & AUDITVNODE2)
                                AUDIT_ARG_ATFD2(ndp->ni_dirfd);

                        error = fgetvp_lookup(ndp, dpp);
                }
                if (error == 0 && (*dpp)->v_type != VDIR &&
                    (cnp->cn_flags & OPENNAMED) == 0 &&
                    (cnp->cn_pnbuf[0] != '\0' ||
                    (cnp->cn_flags & EMPTYPATH) == 0))
                        error = ENOTDIR;
        }
        if (error == 0 && (cnp->cn_flags & RBENEATH) != 0) {
                if (cnp->cn_pnbuf[0] == '/') {
                        error = ENOTCAPABLE;
                } else if ((ndp->ni_lcf & NI_LCF_STRICTREL) == 0) {
                        ndp->ni_lcf |= NI_LCF_STRICTREL |
                            NI_LCF_CAP_DOTDOT;
                }
        }
        if (error == 0 && (ndp->ni_lcf & NI_LCF_STRICTREL) != 0)
                ndp->ni_rbeneath_dpp = *dpp;

        /*
         * If we are auditing the kernel pathname, save the user pathname.
         */
        if (AUDITING_TD(td)) {
                if (cnp->cn_flags & AUDITVNODE1)
                        AUDIT_ARG_UPATH1_VP(td, ndp->ni_rootdir, *dpp, cnp->cn_pnbuf);
                if (cnp->cn_flags & AUDITVNODE2)
                        AUDIT_ARG_UPATH2_VP(td, ndp->ni_rootdir, *dpp, cnp->cn_pnbuf);
        }
        if (ndp->ni_startdir != NULL && !startdir_used)
                vrele(ndp->ni_startdir);
        if (error != 0) {
                if (*dpp != NULL)
                        vrele(*dpp);
                pwd_drop(pwd);
                return (error);
        }
        if (lookup_cap_dotdot != 0) {
                if ((ndp->ni_lcf & NI_LCF_STRICTREL_KTR) != 0)
                        ndp->ni_lcf |= NI_LCF_CAP_DOTDOT_KTR;
                if ((ndp->ni_lcf & NI_LCF_STRICTREL) != 0)
                        ndp->ni_lcf |= NI_LCF_CAP_DOTDOT;
        }
        SDT_PROBE4(vfs, namei, lookup, entry, *dpp, cnp->cn_pnbuf,
            cnp->cn_flags, false);
        *pwdp = pwd;
        return (0);
}

static int
namei_getpath(struct nameidata *ndp)
{
        struct componentname *cnp;
        int error;

        cnp = &ndp->ni_cnd;

        /*
         * Get a buffer for the name to be translated, and copy the
         * name into the buffer.
         */
        cnp->cn_pnbuf = uma_zalloc(namei_zone, M_WAITOK);
        if (ndp->ni_segflg == UIO_SYSSPACE) {
                error = copystr(ndp->ni_dirp, cnp->cn_pnbuf, MAXPATHLEN,
                    &ndp->ni_pathlen);
        } else {
                error = copyinstr(ndp->ni_dirp, cnp->cn_pnbuf, MAXPATHLEN,
                    &ndp->ni_pathlen);
        }

        return (error);
}

static int
namei_emptypath(struct nameidata *ndp)
{
        struct componentname *cnp;
        struct pwd *pwd;
        struct vnode *dp;
        int error;

        cnp = &ndp->ni_cnd;
        MPASS(*cnp->cn_pnbuf == '\0');
        MPASS((cnp->cn_flags & EMPTYPATH) != 0);
        MPASS((cnp->cn_flags & (LOCKPARENT | WANTPARENT)) == 0);

        ndp->ni_resflags |= NIRES_EMPTYPATH;
        error = namei_setup(ndp, &dp, &pwd);
        if (error != 0) {
                goto errout;
        }

        /*
         * Usecount on dp already provided by namei_setup.
         */
        ndp->ni_vp = dp;
        pwd_drop(pwd);
        NDVALIDATE(ndp);
        if ((cnp->cn_flags & LOCKLEAF) != 0) {
                VOP_LOCK(dp, (cnp->cn_flags & LOCKSHARED) != 0 ?
                    LK_SHARED : LK_EXCLUSIVE);
                if (VN_IS_DOOMED(dp)) {
                        vput(dp);
                        error = ENOENT;
                        goto errout;
                }
        }
        SDT_PROBE4(vfs, namei, lookup, return, 0, ndp->ni_vp, false, ndp);
        return (0);

errout:
        SDT_PROBE4(vfs, namei, lookup, return, error, NULL, false, ndp);
        namei_cleanup_cnp(cnp);
        return (error);
}

static int __noinline
namei_follow_link(struct nameidata *ndp)
{
        char *cp;
        struct iovec aiov;
        struct uio auio;
        struct componentname *cnp;
        struct thread *td;
        int error, linklen;

        error = 0;
        cnp = &ndp->ni_cnd;
        td = curthread;

        if (ndp->ni_loopcnt++ >= MAXSYMLINKS) {
                error = ELOOP;
                goto out;
        }
#ifdef MAC
        if ((cnp->cn_flags & NOMACCHECK) == 0) {
                error = mac_vnode_check_readlink(td->td_ucred, ndp->ni_vp);
                if (error != 0)
                        goto out;
        }
#endif
        if (ndp->ni_pathlen > 1)
                cp = uma_zalloc(namei_zone, M_WAITOK);
        else
                cp = cnp->cn_pnbuf;
        aiov.iov_base = cp;
        aiov.iov_len = MAXPATHLEN;
        auio.uio_iov = &aiov;
        auio.uio_iovcnt = 1;
        auio.uio_offset = 0;
        auio.uio_rw = UIO_READ;
        auio.uio_segflg = UIO_SYSSPACE;
        auio.uio_td = td;
        auio.uio_resid = MAXPATHLEN;
        error = VOP_READLINK(ndp->ni_vp, &auio, cnp->cn_cred);
        if (error != 0) {
                if (ndp->ni_pathlen > 1)
                        uma_zfree(namei_zone, cp);
                goto out;
        }
        linklen = MAXPATHLEN - auio.uio_resid;
        if (linklen == 0) {
                if (ndp->ni_pathlen > 1)
                        uma_zfree(namei_zone, cp);
                error = ENOENT;
                goto out;
        }
        if (linklen + ndp->ni_pathlen > MAXPATHLEN) {
                if (ndp->ni_pathlen > 1)
                        uma_zfree(namei_zone, cp);
                error = ENAMETOOLONG;
                goto out;
        }
        if (ndp->ni_pathlen > 1) {
                bcopy(ndp->ni_next, cp + linklen, ndp->ni_pathlen);
                uma_zfree(namei_zone, cnp->cn_pnbuf);
                cnp->cn_pnbuf = cp;
        } else
                cnp->cn_pnbuf[linklen] = '\0';
        ndp->ni_pathlen += linklen;
out:
        return (error);
}

/*
 * Convert a pathname into a pointer to a locked vnode.
 *
 * The FOLLOW flag is set when symbolic links are to be followed
 * when they occur at the end of the name translation process.
 * Symbolic links are always followed for all other pathname
 * components other than the last.
 *
 * The segflg defines whether the name is to be copied from user
 * space or kernel space.
 *
 * Overall outline of namei:
 *
 *      copy in name
 *      get starting directory
 *      while (!done && !error) {
 *              call lookup to search path.
 *              if symbolic link, massage name in buffer and continue
 *      }
 */
int
namei(struct nameidata *ndp)
{
        struct vnode *dp;       /* the directory we are searching */
        struct componentname *cnp;
        struct thread *td;
        struct pwd *pwd;
        int error;
        enum cache_fpl_status status;

        cnp = &ndp->ni_cnd;
        td = curthread;
#ifdef INVARIANTS
        KASSERT((ndp->ni_debugflags & NAMEI_DBG_CALLED) == 0,
            ("%s: repeated call to namei without NDREINIT", __func__));
        KASSERT(ndp->ni_debugflags == NAMEI_DBG_INITED,
            ("%s: bad debugflags %d", __func__, ndp->ni_debugflags));
        ndp->ni_debugflags |= NAMEI_DBG_CALLED;
        if (ndp->ni_startdir != NULL)
                ndp->ni_debugflags |= NAMEI_DBG_HADSTARTDIR;
        if (cnp->cn_flags & FAILIFEXISTS) {
                KASSERT(cnp->cn_nameiop == CREATE,
                    ("%s: FAILIFEXISTS passed for op %d", __func__, cnp->cn_nameiop));
                /*
                 * The limitation below is to restrict hairy corner cases.
                 */
                KASSERT((cnp->cn_flags & (LOCKPARENT | LOCKLEAF)) == LOCKPARENT,
                    ("%s: FAILIFEXISTS must be passed with LOCKPARENT and without LOCKLEAF",
                    __func__));
        }
#endif
        ndp->ni_cnd.cn_cred = td->td_ucred;
        KASSERT(ndp->ni_resflags == 0, ("%s: garbage in ni_resflags: %x",
            __func__, ndp->ni_resflags));
        KASSERT(cnp->cn_cred && td->td_proc, ("namei: bad cred/proc"));
        KASSERT((cnp->cn_flags & NAMEI_INTERNAL_FLAGS) == 0,
            ("namei: unexpected flags: %#jx",
            (uintmax_t)(cnp->cn_flags & NAMEI_INTERNAL_FLAGS)));
        if (cnp->cn_flags & NOCACHE)
                KASSERT(cnp->cn_nameiop != LOOKUP,
                    ("%s: NOCACHE passed with LOOKUP", __func__));
        MPASS(ndp->ni_startdir == NULL || ndp->ni_startdir->v_type == VDIR ||
            ndp->ni_startdir->v_type == VBAD);

restart:
        ndp->ni_lcf = 0;
        ndp->ni_loopcnt = 0;
        ndp->ni_vp = NULL;

        error = namei_getpath(ndp);
        if (__predict_false(error != 0)) {
                namei_cleanup_cnp(cnp);
                nameicap_cleanup(ndp, error);
                SDT_PROBE4(vfs, namei, lookup, return, error, NULL,
                    false, ndp);
                return (error);
        }

        cnp->cn_nameptr = cnp->cn_pnbuf;

#ifdef KTRACE
        if (KTRPOINT(td, KTR_NAMEI)) {
                ktrnamei(cnp->cn_pnbuf);
        }
#endif
        TSNAMEI(curthread->td_proc->p_pid, cnp->cn_pnbuf);

        /*
         * First try looking up the target without locking any vnodes.
         *
         * We may need to start from scratch or pick up where it left off.
         */
        error = cache_fplookup(ndp, &status, &pwd);
        switch (status) {
        case CACHE_FPL_STATUS_UNSET:
                __assert_unreachable();
                break;
        case CACHE_FPL_STATUS_HANDLED:
                if (error == 0)
                        NDVALIDATE(ndp);
                else if (__predict_false(pwd->pwd_adir != pwd->pwd_rdir &&
                    (cnp->cn_flags & ISRESTARTED) == 0)) {
                        namei_cleanup_cnp(cnp);
                        nameicap_cleanup(ndp, ERESTART);
                        NDRESTART(ndp);
                        goto restart;
                }
                return (error);
        case CACHE_FPL_STATUS_PARTIAL:
                dp = ndp->ni_startdir;
                break;
        case CACHE_FPL_STATUS_DESTROYED:
                ndp->ni_loopcnt = 0;
                error = namei_getpath(ndp);
                if (__predict_false(error != 0)) {
                        namei_cleanup_cnp(cnp);
                        nameicap_cleanup(ndp, error);
                        return (error);
                }
                cnp->cn_nameptr = cnp->cn_pnbuf;
                /* FALLTHROUGH */
        case CACHE_FPL_STATUS_ABORTED:
                MPASS(ndp->ni_lcf == 0);
                if (*cnp->cn_pnbuf == '\0') {
                        if ((cnp->cn_flags & EMPTYPATH) != 0) {
                                error = namei_emptypath(ndp);
                                nameicap_cleanup(ndp, error);
                                return (error);
                        }
                        namei_cleanup_cnp(cnp);
                        nameicap_cleanup(ndp, ENOENT);
                        SDT_PROBE4(vfs, namei, lookup, return, ENOENT, NULL,
                            false, ndp);
                        return (ENOENT);
                }
                error = namei_setup(ndp, &dp, &pwd);
                if (error != 0) {
                        namei_cleanup_cnp(cnp);
                        nameicap_cleanup(ndp, error);
                        return (error);
                }
                break;
        }

        /*
         * Locked lookup.
         */
        for (;;) {
                ndp->ni_startdir = dp;
                error = vfs_lookup(ndp);
                if (error != 0) {
                        uint64_t was_restarted;
                        bool abi_restart;

                        was_restarted = ndp->ni_cnd.cn_flags &
                            ISRESTARTED;
                        abi_restart = pwd->pwd_adir != pwd->pwd_rdir &&
                            error == ENOENT && was_restarted == 0;
                        if (error != ERESTART && !abi_restart)
                                goto out;
                        nameicap_cleanup(ndp, error);
                        pwd_drop(pwd);
                        namei_cleanup_cnp(cnp);
                        NDRESET(ndp);
                        if (abi_restart)
                                was_restarted = ISRESTARTED;
                        ndp->ni_cnd.cn_flags |= was_restarted;
                        goto restart;
                }

                /*
                 * If not a symbolic link, we're done.
                 */
                if ((cnp->cn_flags & ISSYMLINK) == 0) {
                        SDT_PROBE4(vfs, namei, lookup, return, error,
                            ndp->ni_vp, false, ndp);
                        nameicap_cleanup(ndp, 0);
                        pwd_drop(pwd);
                        NDVALIDATE(ndp);
                        return (0);
                }
                error = namei_follow_link(ndp);
                if (error != 0)
                        break;
                vput(ndp->ni_vp);
                dp = ndp->ni_dvp;
                /*
                 * Check if root directory should replace current directory.
                 */
                cnp->cn_nameptr = cnp->cn_pnbuf;
                if (*(cnp->cn_nameptr) == '/') {
                        /*
                         * Reset the lookup to start from the real root without
                         * origin path name reloading.
                         */
                        if (__predict_false(ndp->ni_rootdir != pwd->pwd_rdir)) {
                                cnp->cn_flags |= ISRESTARTED;
                                ndp->ni_rootdir = pwd->pwd_rdir;
                        }
                        vrele(dp);
                        error = namei_handle_root(ndp, &dp);
                        if (error != 0)
                                goto out;
                }
        }
        vput(ndp->ni_vp);
        ndp->ni_vp = NULL;
        vrele(ndp->ni_dvp);
out:
        MPASS(error != 0 && error != ERESTART);
        SDT_PROBE4(vfs, namei, lookup, return, error, NULL, false, ndp);
        namei_cleanup_cnp(cnp);
        nameicap_cleanup(ndp, error);
        pwd_drop(pwd);
        return (error);
}

static int
enforce_lkflags(struct mount *mp, int lkflags)
{

        if (mp == NULL || ((lkflags & LK_SHARED) &&
            !(mp->mnt_kern_flag & MNTK_LOOKUP_SHARED))) {
                lkflags &= ~LK_SHARED;
                lkflags |= LK_EXCLUSIVE;
        }
        lkflags |= LK_NODDLKTREAT;
        return (lkflags);
}

static __inline int
needs_exclusive_leaf(struct mount *mp, int flags)
{

        /*
         * Intermediate nodes can use shared locks, we only need to
         * force an exclusive lock for leaf nodes.
         */
        if ((flags & (ISLASTCN | LOCKLEAF)) != (ISLASTCN | LOCKLEAF))
                return (0);

        /* Always use exclusive locks if LOCKSHARED isn't set. */
        if (!(flags & LOCKSHARED))
                return (1);

        /*
         * For lookups during open(), if the mount point supports
         * extended shared operations, then use a shared lock for the
         * leaf node, otherwise use an exclusive lock.
         */
        if ((flags & ISOPEN) != 0)
                return (!MNT_EXTENDED_SHARED(mp));

        /*
         * Lookup requests outside of open() that specify LOCKSHARED
         * only need a shared lock on the leaf vnode.
         */
        return (0);
}

/*
 * Various filesystems expect to be able to copy a name component with length
 * bounded by NAME_MAX into a directory entry buffer of size MAXNAMLEN.  Make
 * sure that these are the same size.
 */
_Static_assert(MAXNAMLEN == NAME_MAX,
    "MAXNAMLEN and NAME_MAX have different values");

static int __noinline
vfs_lookup_degenerate(struct nameidata *ndp, struct vnode *dp, int wantparent)
{
        struct componentname *cnp;
        struct mount *mp;
        int error;

        cnp = &ndp->ni_cnd;

        cnp->cn_flags |= ISLASTCN;

        mp = atomic_load_ptr(&dp->v_mount);
        if (needs_exclusive_leaf(mp, cnp->cn_flags)) {
                cnp->cn_lkflags &= ~LK_SHARED;
                cnp->cn_lkflags |= LK_EXCLUSIVE;
        }

        vn_lock(dp, enforce_lkflags(mp, cnp->cn_lkflags | LK_RETRY));

        if (dp->v_type != VDIR) {
                error = ENOTDIR;
                goto bad;
        }
        if (cnp->cn_nameiop != LOOKUP) {
                error = EISDIR;
                goto bad;
        }
        if (wantparent) {
                ndp->ni_dvp = dp;
                vref(dp);
        }
        ndp->ni_vp = dp;
        cnp->cn_namelen = 0;

        if (cnp->cn_flags & AUDITVNODE1)
                AUDIT_ARG_VNODE1(dp);
        else if (cnp->cn_flags & AUDITVNODE2)
                AUDIT_ARG_VNODE2(dp);

        if (!(cnp->cn_flags & (LOCKPARENT | LOCKLEAF)))
                VOP_UNLOCK(dp);
        return (0);
bad:
        VOP_UNLOCK(dp);
        return (error);
}

struct nameidata *
vfs_lookup_nameidata(struct componentname *cnp)
{
        if ((cnp->cn_flags & NAMEILOOKUP) == 0)
                return (NULL);
        return (__containerof(cnp, struct nameidata, ni_cnd));
}

/*
 * Would a dotdot lookup relative to dvp cause this lookup to cross a jail or
 * chroot boundary?
 */
bool
vfs_lookup_isroot(struct nameidata *ndp, struct vnode *dvp)
{
        for (struct prison *pr = ndp->ni_cnd.cn_cred->cr_prison; pr != NULL;
            pr = pr->pr_parent) {
                if (dvp == pr->pr_root)
                        return (true);
        }
        return (dvp == ndp->ni_rootdir || dvp == ndp->ni_topdir ||
            dvp == rootvnode);
}

/*
 * FAILIFEXISTS handling.
 *
 * XXX namei called with LOCKPARENT but not LOCKLEAF has the strange
 * behaviour of leaving the vnode unlocked if the target is the same
 * vnode as the parent.
 */
static int __noinline
vfs_lookup_failifexists(struct nameidata *ndp)
{
        struct componentname *cnp __diagused;

        cnp = &ndp->ni_cnd;

        MPASS((cnp->cn_flags & ISSYMLINK) == 0);
        if (ndp->ni_vp == ndp->ni_dvp)
                vrele(ndp->ni_dvp);
        else
                vput(ndp->ni_dvp);
        vrele(ndp->ni_vp);
        ndp->ni_dvp = NULL;
        ndp->ni_vp = NULL;
        NDFREE_PNBUF(ndp);
        return (EEXIST);
}

static int __noinline
vfs_lookup_cross_mount(struct nameidata *ndp)
{
        struct componentname *cnp;
        struct mount *mp;
        struct vnode *dp, *tdp;
        int error, crosslkflags;
        bool crosslock;

        cnp = &ndp->ni_cnd;
        dp = ndp->ni_vp;

        /*
         * The vnode has been mounted on, find the root of the mounted
         * filesystem.
         */
        do {
                mp = dp->v_mountedhere;
                ASSERT_VOP_LOCKED(dp, __func__);
                VNPASS((vn_irflag_read(dp) & VIRF_MOUNTPOINT) != 0 && mp != NULL, dp);

                crosslock = (dp->v_vflag & VV_CROSSLOCK) != 0;
                crosslkflags = enforce_lkflags(mp, cnp->cn_lkflags);
                if (__predict_false(crosslock)) {
                        /*
                         * We are going to be holding the vnode lock, which
                         * in this case is shared by the root vnode of the
                         * filesystem mounted at mp, across the call to
                         * VFS_ROOT().  Make the situation clear to the
                         * filesystem by passing LK_CANRECURSE if the
                         * lock is held exclusive, or by clearinng
                         * LK_NODDLKTREAT to allow recursion on the shared
                         * lock in the presence of an exclusive waiter.
                         */
                        if (VOP_ISLOCKED(dp) == LK_EXCLUSIVE) {
                                crosslkflags &= ~LK_SHARED;
                                crosslkflags |= LK_EXCLUSIVE | LK_CANRECURSE;
                        } else if ((crosslkflags & LK_EXCLUSIVE) != 0) {
                                error = vn_lock(dp, LK_UPGRADE);
                                if (error != 0) {
                                        MPASS(error == ENOENT);
                                        vrele(dp);
                                        if (dp != ndp->ni_dvp)
                                                vput(ndp->ni_dvp);
                                        else
                                                vrele(ndp->ni_dvp);
                                        break;
                                }
                                if (dp->v_mountedhere != mp) {
                                        /*
                                         * Note that we rely on the
                                         * VIRF_MOUNTPOINT loop condition to
                                         * ensure we stop iterating if dp is
                                         * no longer a mountpoint at all.
                                         */
                                        continue;
                                }
                        } else
                                crosslkflags &= ~LK_NODDLKTREAT;
                }
                if (vfs_busy(mp, 0) != 0)
                        continue;
                if (__predict_true(!crosslock))
                        vput(dp);
                if (dp != ndp->ni_dvp)
                        vput(ndp->ni_dvp);
                else
                        vrele(ndp->ni_dvp);
                vrefact(vp_crossmp);
                ndp->ni_dvp = vp_crossmp;
                error = VFS_ROOT(mp, crosslkflags, &tdp);
                vfs_unbusy(mp);
                if (__predict_false(crosslock))
                        vput(dp);
                if (vn_lock(vp_crossmp, LK_SHARED | LK_NOWAIT))
                        panic("vp_crossmp exclusively locked or reclaimed");
                if (error != 0)
                        break;
                ndp->ni_vp = dp = tdp;
        } while ((vn_irflag_read(dp) & VIRF_MOUNTPOINT) != 0);

        return (error);
}

/*
 * Search a pathname.
 * This is a very central and rather complicated routine.
 *
 * The pathname is pointed to by cn_nameptr and is of length ni_pathlen.
 * The starting directory is taken from ni_startdir. The pathname is
 * descended until done, or a symbolic link is encountered. The cn_flags
 * has ISLASTCN or'ed if the path is completed or ISSYMLINK or'ed if a
 * symbolic link needing interpretation is encountered.
 *
 * The cn_nameiop is LOOKUP, CREATE, RENAME, or DELETE depending on
 * whether the name is to be looked up, created, renamed, or deleted.
 * When CREATE, RENAME, or DELETE is specified, information usable in
 * creating, renaming, or deleting a directory entry may be calculated.
 * If cn_flags has LOCKPARENT or'ed into it, the parent directory is returned
 * locked. If it has WANTPARENT or'ed into it, the parent directory is
 * returned unlocked. Otherwise the parent directory is not returned. If
 * the target of the pathname exists and LOCKLEAF is or'ed into the cn_flags
 * the target is returned locked, otherwise it is returned unlocked.
 *
 * Overall outline of lookup:
 *
 *      handle degenerate case where name is null string
 *
 * dirloop:
 *      identify next component of name at ndp->ni_cnd.cn_nameptr
 *      handle .. special cases related to capabilities, chroot, jail
 *      if .. and crossing mount points and on mounted filesys, find parent
 *      call VOP_LOOKUP routine for next component name
 *          directory vnode returned in ni_dvp, unlocked unless LOCKPARENT set
 *          component vnode returned in ni_vp (if it exists), locked.
 *      if result vnode is mounted on and crossing mount points,
 *          find mounted on vnode
 *      if more components of name, do next level at dirloop
 *      if VOP_LOOKUP returns ERELOOKUP, repeat the same level at dirloop
 *      return the answer in ni_vp, locked if LOCKLEAF set
 *          if LOCKPARENT set, return locked parent in ni_dvp
 *          if WANTPARENT set, return unlocked parent in ni_dvp
 */
int
vfs_lookup(struct nameidata *ndp)
{
        char *cp;                       /* pointer into pathname argument */
        char *prev_ni_next;             /* saved ndp->ni_next */
        char *nulchar;                  /* location of '\0' in cn_pnbuf */
        char *lastchar;                 /* location of the last character */
        struct vnode *dp = NULL;        /* the directory we are searching */
        struct vnode *tdp;              /* saved dp */
        size_t prev_ni_pathlen;         /* saved ndp->ni_pathlen */
        int docache;                    /* == 0 do not cache last component */
        int wantparent;                 /* 1 => wantparent or lockparent flag */
        int rdonly;                     /* lookup read-only flag bit */
        int error = 0;
        int relookup = 0;               /* do not consume the path component */
        struct componentname *cnp = &ndp->ni_cnd;
        int lkflags_save;
        int ni_dvp_unlocked;

        /*
         * Setup: break out flag bits into variables.
         */
        ni_dvp_unlocked = 0;
        wantparent = cnp->cn_flags & (LOCKPARENT | WANTPARENT);
        KASSERT(cnp->cn_nameiop == LOOKUP || wantparent,
            ("CREATE, DELETE, RENAME require LOCKPARENT or WANTPARENT."));
        /*
         * When set to zero, docache causes the last component of the
         * pathname to be deleted from the cache and the full lookup
         * of the name to be done (via VOP_CACHEDLOOKUP()). Often
         * filesystems need some pre-computed values that are made
         * during the full lookup, for instance UFS sets dp->i_offset.
         *
         * The docache variable is set to zero when requested by the
         * NOCACHE flag and for all modifying operations except CREATE.
         */
        docache = (cnp->cn_flags & NOCACHE) ^ NOCACHE;
        if (cnp->cn_nameiop == DELETE ||
            (wantparent && cnp->cn_nameiop != CREATE &&
             cnp->cn_nameiop != LOOKUP))
                docache = 0;
        rdonly = cnp->cn_flags & RDONLY;
        cnp->cn_flags &= ~ISSYMLINK;
        ndp->ni_dvp = NULL;

        cnp->cn_lkflags = LK_SHARED;
        dp = ndp->ni_startdir;
        ndp->ni_startdir = NULL;

        /*
         * Leading slashes, if any, are supposed to be skipped by the caller.
         */
        MPASS(cnp->cn_nameptr[0] != '/');

        /*
         * Check for degenerate name (e.g. / or "") which is a way of talking
         * about a directory, e.g. like "/." or ".".
         */
        if (__predict_false(cnp->cn_nameptr[0] == '\0')) {
                error = vfs_lookup_degenerate(ndp, dp, wantparent);
                if (error == 0)
                        goto success_right_lock;
                goto bad_unlocked;
        }

        /*
         * Nul-out trailing slashes (e.g., "foo///" -> "foo").
         *
         * This must be done before VOP_LOOKUP() because some fs's don't know
         * about trailing slashes.  Remember if there were trailing slashes to
         * handle symlinks, existing non-directories and non-existing files
         * that won't be directories specially later.
         */
        MPASS(ndp->ni_pathlen >= 2);
        lastchar = &cnp->cn_nameptr[ndp->ni_pathlen - 2];
        if (*lastchar == '/') {
                while (lastchar >= cnp->cn_pnbuf) {
                        *lastchar = '\0';
                        lastchar--;
                        ndp->ni_pathlen--;
                        if (*lastchar != '/') {
                                break;
                        }
                }
                cnp->cn_flags |= TRAILINGSLASH;
        }

        /*
         * We use shared locks until we hit the parent of the last cn then
         * we adjust based on the requesting flags.
         */
        vn_lock(dp,
            enforce_lkflags(dp->v_mount, cnp->cn_lkflags | LK_RETRY));

dirloop:
        /*
         * Search a new directory.
         *
         * The last component of the filename is left accessible via
         * cnp->cn_nameptr. It has to be freed with a call to NDFREE*.
         *
         * Store / as a temporary sentinel so that we only have one character
         * to test for. Pathnames tend to be short so this should not be
         * resulting in cache misses.
         */
        nulchar = &cnp->cn_nameptr[ndp->ni_pathlen - 1];
        KASSERT(*nulchar == '\0',
            ("%s: expected nul at %p; string [%s]\n", __func__, nulchar,
            cnp->cn_pnbuf));
        *nulchar = '/';
        for (cp = cnp->cn_nameptr; *cp != '/'; cp++) {
                KASSERT(*cp != '\0',
                    ("%s: encountered unexpected nul; string [%s]\n", __func__,
                    cnp->cn_nameptr));
                continue;
        }
        *nulchar = '\0';
        cnp->cn_namelen = cp - cnp->cn_nameptr;
        if (__predict_false(cnp->cn_namelen > NAME_MAX)) {
                error = ENAMETOOLONG;
                goto bad;
        }
        prev_ni_pathlen = ndp->ni_pathlen;
        ndp->ni_pathlen -= cnp->cn_namelen;
        KASSERT(ndp->ni_pathlen <= PATH_MAX,
            ("%s: ni_pathlen underflow to %zd\n", __func__, ndp->ni_pathlen));
        prev_ni_next = ndp->ni_next;
        ndp->ni_next = cp;

        /*
         * Something else should be clearing this.
         */
        cnp->cn_flags &= ~(ISDOTDOT|ISLASTCN);

        cnp->cn_flags |= MAKEENTRY;
        if (*cp == '\0' && docache == 0)
                cnp->cn_flags &= ~MAKEENTRY;
        if (cnp->cn_namelen == 2 &&
            cnp->cn_nameptr[1] == '.' && cnp->cn_nameptr[0] == '.')
                cnp->cn_flags |= ISDOTDOT;
        if (*ndp->ni_next == 0) {
                cnp->cn_flags |= ISLASTCN;

                if (__predict_false(cnp->cn_namelen == 1 && cnp->cn_nameptr[0] == '.' &&
                    (cnp->cn_nameiop == DELETE || cnp->cn_nameiop == RENAME))) {
                        error = EINVAL;
                        goto bad;
                }
        }

        error = nameicap_tracker_add(ndp, dp);
        if (error != 0)
                goto bad;

        /*
         * Make sure degenerate names don't get here, their handling was
         * previously found in this spot.
         */
        MPASS(cnp->cn_nameptr[0] != '\0');

        /*
         * Handle "..": five special cases.
         * 0. If doing a capability lookup and lookup_cap_dotdot is
         *    disabled, return ENOTCAPABLE.
         * 1. Return an error if this is the last component of
         *    the name and the operation is DELETE or RENAME.
         * 2. If at root directory (e.g. after chroot)
         *    or at absolute root directory
         *    then ignore it so can't get out.
         * 3. If this vnode is the root of a mounted
         *    filesystem, then replace it with the
         *    vnode which was mounted on so we take the
         *    .. in the other filesystem.
         * 4. If the vnode is the top directory of
         *    the jail or chroot, don't let them out.
         * 5. If doing a capability lookup and lookup_cap_dotdot is
         *    enabled, return ENOTCAPABLE if the lookup would escape
         *    from the initial file descriptor directory.
         */
        if (cnp->cn_flags & ISDOTDOT) {
                if (__predict_false((ndp->ni_lcf & (NI_LCF_STRICTREL_KTR |
                    NI_LCF_CAP_DOTDOT_KTR)) == NI_LCF_STRICTREL_KTR))
                        NI_CAP_VIOLATION(ndp, cnp->cn_pnbuf);
                if (__predict_false((ndp->ni_lcf & (NI_LCF_STRICTREL |
                    NI_LCF_CAP_DOTDOT)) == NI_LCF_STRICTREL)) {
                        error = ENOTCAPABLE;
                        goto bad;
                }
                if ((cnp->cn_flags & ISLASTCN) != 0 &&
                    (cnp->cn_nameiop == DELETE || cnp->cn_nameiop == RENAME)) {
                        error = EINVAL;
                        goto bad;
                }
                for (;;) {
                        bool isroot;

                        isroot = vfs_lookup_isroot(ndp, dp);
                        if (__predict_false(isroot && (ndp->ni_lcf &
                            (NI_LCF_STRICTREL | NI_LCF_STRICTREL_KTR)) != 0)) {
                                if ((ndp->ni_lcf & NI_LCF_STRICTREL_KTR) != 0)
                                        NI_CAP_VIOLATION(ndp, cnp->cn_pnbuf);
                                if ((ndp->ni_lcf & NI_LCF_STRICTREL) != 0) {
                                        error = ENOTCAPABLE;
                                        goto bad;
                                }
                        }
                        if (isroot || ((dp->v_vflag & VV_ROOT) != 0 &&
                            (cnp->cn_flags & NOCROSSMOUNT) != 0)) {
                                ndp->ni_dvp = dp;
                                ndp->ni_vp = dp;
                                vref(dp);
                                goto nextname;
                        }
                        if ((dp->v_vflag & VV_ROOT) == 0)
                                break;
                        if (VN_IS_DOOMED(dp)) { /* forced unmount */
                                error = ENOENT;
                                goto bad;
                        }
                        tdp = dp;
                        dp = dp->v_mount->mnt_vnodecovered;
                        vref(dp);
                        vput(tdp);
                        vn_lock(dp,
                            enforce_lkflags(dp->v_mount, cnp->cn_lkflags |
                            LK_RETRY));
                }
        }

        /*
         * We now have a segment name to search for, and a directory to search.
         */
unionlookup:
#ifdef MAC
        error = mac_vnode_check_lookup(cnp->cn_cred, dp, cnp);
        if (__predict_false(error))
                goto bad;
#endif
        ndp->ni_dvp = dp;
        ndp->ni_vp = NULL;
        ASSERT_VOP_LOCKED(dp, "lookup");
        /*
         * If we have a shared lock we may need to upgrade the lock for the
         * last operation.
         */
        if ((cnp->cn_flags & LOCKPARENT) && (cnp->cn_flags & ISLASTCN) &&
            dp != vp_crossmp && VOP_ISLOCKED(dp) == LK_SHARED)
                vn_lock(dp, LK_UPGRADE|LK_RETRY);
        if (VN_IS_DOOMED(dp)) {
                error = ENOENT;
                goto bad;
        }
        /*
         * If we're looking up the last component and we need an exclusive
         * lock, adjust our lkflags.
         */
        if (needs_exclusive_leaf(dp->v_mount, cnp->cn_flags))
                cnp->cn_lkflags = LK_EXCLUSIVE;
        lkflags_save = cnp->cn_lkflags;
        cnp->cn_lkflags = enforce_lkflags(dp->v_mount, cnp->cn_lkflags);
        error = VOP_LOOKUP(dp, &ndp->ni_vp, cnp);
        cnp->cn_lkflags = lkflags_save;
        if (error != 0) {
                KASSERT(ndp->ni_vp == NULL, ("leaf should be empty"));
                if ((error == ENOENT) &&
                    (dp->v_vflag & VV_ROOT) && (dp->v_mount != NULL) &&
                    (dp->v_mount->mnt_flag & MNT_UNION)) {
                        tdp = dp;
                        dp = dp->v_mount->mnt_vnodecovered;
                        vref(dp);
                        vput(tdp);
                        vn_lock(dp,
                            enforce_lkflags(dp->v_mount, cnp->cn_lkflags |
                            LK_RETRY));
                        error = nameicap_tracker_add(ndp, dp);
                        if (error != 0)
                                goto bad;
                        goto unionlookup;
                }

                if (error == ERELOOKUP) {
                        vref(dp);
                        ndp->ni_vp = dp;
                        error = 0;
                        relookup = 1;
                        goto good;
                }

                if (error != EJUSTRETURN)
                        goto bad;
                /*
                 * At this point, we know we're at the end of the
                 * pathname.  If creating / renaming, we can consider
                 * allowing the file or directory to be created / renamed,
                 * provided we're not on a read-only filesystem.
                 */
                if (rdonly) {
                        error = EROFS;
                        goto bad;
                }
                /* trailing slash only allowed for directories */
                if ((cnp->cn_flags & TRAILINGSLASH) &&
                    !(cnp->cn_flags & WILLBEDIR)) {
                        error = ENOENT;
                        goto bad;
                }
                if ((cnp->cn_flags & LOCKPARENT) == 0)
                        VOP_UNLOCK(dp);
                /*
                 * We return with ni_vp NULL to indicate that the entry
                 * doesn't currently exist, leaving a pointer to the
                 * (possibly locked) directory vnode in ndp->ni_dvp.
                 */
                goto success;
        }

good:
        dp = ndp->ni_vp;

        /*
         * Check for symbolic link
         */
        if ((dp->v_type == VLNK) &&
            ((cnp->cn_flags & FOLLOW) || (cnp->cn_flags & TRAILINGSLASH) ||
             *ndp->ni_next == '/')) {
                cnp->cn_flags |= ISSYMLINK;
                if (VN_IS_DOOMED(dp)) {
                        /*
                         * We can't know whether the directory was mounted with
                         * NOSYMFOLLOW, so we can't follow safely.
                         */
                        error = ENOENT;
                        goto bad2;
                }
                if (dp->v_mount->mnt_flag & MNT_NOSYMFOLLOW) {
                        error = EACCES;
                        goto bad2;
                }
                /*
                 * Symlink code always expects an unlocked dvp.
                 */
                if (ndp->ni_dvp != ndp->ni_vp) {
                        VOP_UNLOCK(ndp->ni_dvp);
                        ni_dvp_unlocked = 1;
                }
                goto success;
        }

        if ((vn_irflag_read(dp) & VIRF_MOUNTPOINT) != 0 &&
            (cnp->cn_flags & NOCROSSMOUNT) == 0) {
                error = vfs_lookup_cross_mount(ndp);
                if (error != 0)
                        goto bad_unlocked;
                /*
                 * FALLTHROUGH to nextname
                 */
                dp = ndp->ni_vp;
        }

nextname:
        /*
         * Not a symbolic link that we will follow.  Continue with the
         * next component if there is any; otherwise, we're done.
         */
        KASSERT((cnp->cn_flags & ISLASTCN) || *ndp->ni_next == '/',
            ("lookup: invalid path state."));
        if (relookup) {
                relookup = 0;
                ndp->ni_pathlen = prev_ni_pathlen;
                ndp->ni_next = prev_ni_next;
                if (ndp->ni_dvp != dp)
                        vput(ndp->ni_dvp);
                else
                        vrele(ndp->ni_dvp);
                goto dirloop;
        }
        if (cnp->cn_flags & ISDOTDOT) {
                error = nameicap_check_dotdot(ndp, ndp->ni_dvp);
                if (error != 0)
                        goto bad2;
        }
        if (*ndp->ni_next == '/') {
                cnp->cn_nameptr = ndp->ni_next;
                while (*cnp->cn_nameptr == '/') {
                        cnp->cn_nameptr++;
                        ndp->ni_pathlen--;
                }
                if (ndp->ni_dvp != dp)
                        vput(ndp->ni_dvp);
                else
                        vrele(ndp->ni_dvp);
                goto dirloop;
        }
        /*
         * If we're processing a path with a trailing slash,
         * check that the end result is a directory.
         */
        if ((cnp->cn_flags & TRAILINGSLASH) && dp->v_type != VDIR) {
                error = ENOTDIR;
                goto bad2;
        }
        /*
         * Disallow directory write attempts on read-only filesystems.
         */
        if (rdonly &&
            (cnp->cn_nameiop == DELETE || cnp->cn_nameiop == RENAME)) {
                error = EROFS;
                goto bad2;
        }
        if (!wantparent) {
                ni_dvp_unlocked = 2;
                if (ndp->ni_dvp != dp)
                        vput(ndp->ni_dvp);
                else
                        vrele(ndp->ni_dvp);
        } else if ((cnp->cn_flags & LOCKPARENT) == 0 && ndp->ni_dvp != dp) {
                VOP_UNLOCK(ndp->ni_dvp);
                ni_dvp_unlocked = 1;
        }

        if (cnp->cn_flags & AUDITVNODE1)
                AUDIT_ARG_VNODE1(dp);
        else if (cnp->cn_flags & AUDITVNODE2)
                AUDIT_ARG_VNODE2(dp);

        if ((cnp->cn_flags & LOCKLEAF) == 0)
                VOP_UNLOCK(dp);
success:
        /*
         * FIXME: for lookups which only cross a mount point to fetch the
         * root vnode, ni_dvp will be set to vp_crossmp. This can be a problem
         * if either WANTPARENT or LOCKPARENT is set.
         */
        /*
         * Because of shared lookup we may have the vnode shared locked, but
         * the caller may want it to be exclusively locked.
         */
        if (needs_exclusive_leaf(dp->v_mount, cnp->cn_flags) &&
            VOP_ISLOCKED(dp) != LK_EXCLUSIVE) {
                vn_lock(dp, LK_UPGRADE | LK_RETRY);
                if (VN_IS_DOOMED(dp)) {
                        error = ENOENT;
                        goto bad2;
                }
        }
success_right_lock:
        if (ndp->ni_vp != NULL) {
                if ((cnp->cn_flags & ISDOTDOT) == 0) {
                        error = nameicap_tracker_add(ndp, ndp->ni_vp);
                        if (error != 0)
                                goto bad2;
                }
                if ((cnp->cn_flags & (FAILIFEXISTS | ISSYMLINK)) == FAILIFEXISTS)
                        return (vfs_lookup_failifexists(ndp));
        }
        return (0);

bad2:
        if (ni_dvp_unlocked != 2) {
                if (dp != ndp->ni_dvp && !ni_dvp_unlocked)
                        vput(ndp->ni_dvp);
                else
                        vrele(ndp->ni_dvp);
        }
bad:
        vput(dp);
bad_unlocked:
        ndp->ni_vp = NULL;
        return (error);
}

/*
 * relookup - lookup a path name component
 *    Used by lookup to re-acquire things.
 */
int
vfs_relookup(struct vnode *dvp, struct vnode **vpp, struct componentname *cnp,
    bool refstart)
{
        struct vnode *dp = NULL;                /* the directory we are searching */
        int rdonly;                     /* lookup read-only flag bit */
        int error = 0;

        KASSERT(cnp->cn_flags & ISLASTCN,
            ("relookup: Not given last component."));
        /*
         * Setup: break out flag bits into variables.
         */
        KASSERT((cnp->cn_flags & (LOCKPARENT | WANTPARENT)) != 0,
            ("relookup: parent not wanted"));
        rdonly = cnp->cn_flags & RDONLY;
        cnp->cn_flags &= ~ISSYMLINK;
        dp = dvp;
        cnp->cn_lkflags = LK_EXCLUSIVE;
        vn_lock(dp, LK_EXCLUSIVE | LK_RETRY);

        /*
         * Search a new directory.
         *
         * See a comment in vfs_lookup for cnp->cn_nameptr.
         *
         * Check for "" which represents the root directory after slash
         * removal.
         */
        if (cnp->cn_nameptr[0] == '\0') {
                /*
                 * Support only LOOKUP for "/" because lookup()
                 * can't succeed for CREATE, DELETE and RENAME.
                 */
                KASSERT(cnp->cn_nameiop == LOOKUP, ("nameiop must be LOOKUP"));
                KASSERT(dp->v_type == VDIR, ("dp is not a directory"));

                if (!(cnp->cn_flags & LOCKLEAF))
                        VOP_UNLOCK(dp);
                *vpp = dp;
                /* XXX This should probably move to the top of function. */
                if (refstart)
                        panic("lookup: SAVESTART");
                return (0);
        }

        if (cnp->cn_flags & ISDOTDOT)
                panic ("relookup: lookup on dot-dot");

        /*
         * We now have a segment name to search for, and a directory to search.
         */
        if ((error = VOP_LOOKUP(dp, vpp, cnp)) != 0) {
                KASSERT(*vpp == NULL, ("leaf should be empty"));
                if (error != EJUSTRETURN)
                        goto bad;
                /*
                 * If creating and at end of pathname, then can consider
                 * allowing file to be created.
                 */
                if (rdonly) {
                        error = EROFS;
                        goto bad;
                }
                /* ASSERT(dvp == ndp->ni_startdir) */
                if (refstart)
                        vref(dvp);
                if ((cnp->cn_flags & LOCKPARENT) == 0)
                        VOP_UNLOCK(dp);
                /*
                 * We return with ni_vp NULL to indicate that the entry
                 * doesn't currently exist, leaving a pointer to the
                 * (possibly locked) directory vnode in ndp->ni_dvp.
                 */
                return (0);
        }

        dp = *vpp;

        /*
         * Disallow directory write attempts on read-only filesystems.
         */
        if (rdonly &&
            (cnp->cn_nameiop == DELETE || cnp->cn_nameiop == RENAME)) {
                if (dvp == dp)
                        vrele(dvp);
                else
                        vput(dvp);
                error = EROFS;
                goto bad;
        }
        /*
         * Set the parent lock/ref state to the requested state.
         */
        if ((cnp->cn_flags & LOCKPARENT) == 0 && dvp != dp)
                VOP_UNLOCK(dvp);
        /*
         * Check for symbolic link
         */
        KASSERT(dp->v_type != VLNK || !(cnp->cn_flags & FOLLOW),
            ("relookup: symlink found.\n"));

        /* ASSERT(dvp == ndp->ni_startdir) */
        if (refstart)
                vref(dvp);

        if ((cnp->cn_flags & LOCKLEAF) == 0)
                VOP_UNLOCK(dp);
        return (0);
bad:
        vput(dp);
        *vpp = NULL;
        return (error);
}

#ifdef INVARIANTS
/*
 * Validate the final state of ndp after the lookup.
 */
static void
NDVALIDATE_impl(struct nameidata *ndp, int line)
{
        struct componentname *cnp;

        cnp = &ndp->ni_cnd;
        if (cnp->cn_pnbuf == NULL)
                panic("%s: got no buf! called from %d", __func__, line);
}

#endif