sys/kern/vfs_lookup.c

   1 /*
   2  * Copyright (c) 1982, 1986, 1989, 1993
   3  *      The Regents of the University of California.  All rights reserved.
   4  * (c) UNIX System Laboratories, Inc.
   5  * All or some portions of this file are derived from material licensed
   6  * to the University of California by American Telephone and Telegraph
   7  * Co. or Unix System Laboratories, Inc. and are reproduced herein with
   8  * the permission of UNIX System Laboratories, Inc.
   9  *
  10  * Redistribution and use in source and binary forms, with or without
  11  * modification, are permitted provided that the following conditions
  12  * are met:
  13  * 1. Redistributions of source code must retain the above copyright
  14  *    notice, this list of conditions and the following disclaimer.
  15  * 2. Redistributions in binary form must reproduce the above copyright
  16  *    notice, this list of conditions and the following disclaimer in the
  17  *    documentation and/or other materials provided with the distribution.
  18  * 3. Neither the name of the University nor the names of its contributors
  19  *    may be used to endorse or promote products derived from this software
  20  *    without specific prior written permission.
  21  *
  22  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  23  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  24  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  25  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  26  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  27  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  28  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  29  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  30  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  31  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  32  * SUCH DAMAGE.
  33  *
  34  *      @(#)vfs_lookup.c        8.4 (Berkeley) 2/16/94
  35  * $FreeBSD: src/sys/kern/vfs_lookup.c,v 1.38.2.3 2001/08/31 19:36:49 dillon Exp $
  36  */
  37
  38 #include "opt_ktrace.h"
  39
  40 #include <sys/param.h>
  41 #include <sys/systm.h>
  42 #include <sys/kernel.h>
  43 #include <sys/vnode.h>
  44 #include <sys/mount.h>
  45 #include <sys/filedesc.h>
  46 #include <sys/proc.h>
  47 #include <sys/namei.h>
  48 #include <sys/sysctl.h>
  49
  50 #ifdef KTRACE
  51 #include <sys/ktrace.h>
  52 #endif
  53
  54 #include <vm/vm_zone.h>
  55
  56 int varsym_enable = 0;
  57 SYSCTL_INT(_vfs, OID_AUTO, varsym_enable, CTLFLAG_RW, &varsym_enable, 0,
  58             "Enable Variant Symlinks");
  59
  60 /*
  61  * OLD API FUNCTION
  62  *
  63  * Relookup a path name component.  This function is only used by the
  64  * old API *_rename() code under very specific conditions.  CNP_LOCKPARENT
  65  * must be set in the cnp.  dvp must be unlocked on entry and will be left
  66  * unlocked if an error occurs.
  67  *
  68  * The returned *vpp will be NULL if an error occurs.  Note that no error
  69  * will occur (error == 0) for CREATE requests on a non-existant target, but
  70  * *vpp will be NULL in that case.  Both dvp and *vpp (if not NULL) will be
  71  * locked in the no-error case.   No additional references are made to dvp,
  72  * only the locking state changes.
  73  */
  74 int
  75 relookup(struct vnode *dvp, struct vnode **vpp, struct componentname *cnp)
  76 {
  77         int rdonly;                     /* lookup read-only flag bit */
  78         int error = 0;
  79
  80         /*
  81          * Setup: break out flag bits into variables.
  82          */
  83         KKASSERT(cnp->cn_flags & CNP_LOCKPARENT);
  84         KKASSERT(cnp->cn_flags & CNP_PDIRUNLOCK);
  85         vn_lock(dvp, LK_EXCLUSIVE | LK_RETRY);
  86         cnp->cn_flags &= ~CNP_PDIRUNLOCK;
  87
  88         *vpp = NULL;
  89         rdonly = cnp->cn_flags & CNP_RDONLY;
  90
  91         /*
  92          * Search a new directory.
  93          */
  94
  95         /*
  96          * Degenerate lookups (e.g. "/", "..", derived from "/.", etc)
  97          * are not allowed.
  98          */
  99         if (cnp->cn_nameptr[0] == '\0') {
 100                 error = EISDIR;
 101                 goto bad;
 102         }
 103         if (cnp->cn_flags & CNP_ISDOTDOT)
 104                 panic ("relookup: lookup on dot-dot");
 105
 106         /*
 107          * We now have a segment name to search for, and a directory to search.
 108          */
 109         if ((error = VOP_OLD_LOOKUP(dvp, vpp, cnp)) != 0) {
 110                 KASSERT(*vpp == NULL, ("leaf should be empty"));
 111                 if (error != EJUSTRETURN)
 112                         goto bad;
 113                 /*
 114                  * If creating and at end of pathname, then can consider
 115                  * allowing file to be created.
 116                  */
 117                 if (rdonly) {
 118                         error = EROFS;
 119                         goto bad;
 120                 }
 121                 /*
 122                  * We return with ni_vp NULL to indicate that the entry
 123                  * doesn't currently exist, leaving a pointer to the
 124                  * (possibly locked) directory inode in ndp->ni_dvp.
 125                  */
 126                 return (0);
 127         }
 128
 129         /*
 130          * Check for symbolic link
 131          */
 132         KASSERT((*vpp)->v_type != VLNK || !(cnp->cn_flags & CNP_FOLLOW),
 133             ("relookup: symlink found."));
 134
 135         /*
 136          * Disallow directory write attempts on read-only file systems.
 137          */
 138         if (rdonly && (cnp->cn_nameiop == NAMEI_DELETE ||
 139                         cnp->cn_nameiop == NAMEI_RENAME)) {
 140                 error = EROFS;
 141                 goto bad;
 142         }
 143         KKASSERT((cnp->cn_flags & CNP_PDIRUNLOCK) == 0);
 144         return (0);
 145
 146 bad:
 147         if ((cnp->cn_flags & CNP_PDIRUNLOCK) == 0) {
 148                 cnp->cn_flags |= CNP_PDIRUNLOCK;
 149                 vn_unlock(dvp);
 150         }
 151         if (*vpp) {
 152                 vput(*vpp);
 153                 *vpp = NULL;
 154         }
 155         return (error);
 156 }
 157