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. All advertising materials mentioning features or use of this software
  19  *    must display the following acknowledgement:
  20  *      This product includes software developed by the University of
  21  *      California, Berkeley and its contributors.
  22  * 4. Neither the name of the University nor the names of its contributors
  23  *    may be used to endorse or promote products derived from this software
  24  *    without specific prior written permission.
  25  *
  26  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  27  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  28  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  29  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  30  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  31  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  32  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  33  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  34  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  35  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  36  * SUCH DAMAGE.
  37  *
  38  *      @(#)vfs_lookup.c        8.4 (Berkeley) 2/16/94
  39  * $FreeBSD: src/sys/kern/vfs_lookup.c,v 1.38.2.3 2001/08/31 19:36:49 dillon Exp $
  40  * $DragonFly: src/sys/kern/vfs_lookup.c,v 1.23 2006/08/12 00:26:20 dillon Exp $
  41  */
  42
  43 #include "opt_ktrace.h"
  44
  45 #include <sys/param.h>
  46 #include <sys/systm.h>
  47 #include <sys/kernel.h>
  48 #include <sys/vnode.h>
  49 #include <sys/mount.h>
  50 #include <sys/filedesc.h>
  51 #include <sys/proc.h>
  52 #include <sys/namei.h>
  53 #include <sys/sysctl.h>
  54
  55 #ifdef KTRACE
  56 #include <sys/ktrace.h>
  57 #endif
  58
  59 #include <vm/vm_zone.h>
  60
  61 int varsym_enable = 0;
  62 SYSCTL_INT(_vfs, OID_AUTO, varsym_enable, CTLFLAG_RW, &varsym_enable, 0,
  63             "Enable Variant Symlinks");
  64
  65 /*
  66  * OLD API FUNCTION
  67  *
  68  * Relookup a path name component.  This function is only used by the
  69  * old API *_rename() code under very specific conditions.  CNP_LOCKPARENT
  70  * must be set in the cnp.  dvp must be unlocked on entry and will be left
  71  * unlocked if an error occurs.
  72  *
  73  * The returned *vpp will be NULL if an error occurs.  Note that no error
  74  * will occur (error == 0) for CREATE requests on a non-existant target, but
  75  * *vpp will be NULL in that case.  Both dvp and *vpp (if not NULL) will be
  76  * locked in the no-error case.   No additional references are made to dvp,
  77  * only the locking state changes.
  78  */
  79 int
  80 relookup(struct vnode *dvp, struct vnode **vpp, struct componentname *cnp)
  81 {
  82         int rdonly;                     /* lookup read-only flag bit */
  83         int error = 0;
  84
  85         /*
  86          * Setup: break out flag bits into variables.
  87          */
  88         KKASSERT(cnp->cn_flags & CNP_LOCKPARENT);
  89         KKASSERT(cnp->cn_flags & CNP_PDIRUNLOCK);
  90         vn_lock(dvp, LK_EXCLUSIVE | LK_RETRY);
  91         cnp->cn_flags &= ~CNP_PDIRUNLOCK;
  92
  93         *vpp = NULL;
  94         rdonly = cnp->cn_flags & CNP_RDONLY;
  95
  96         /*
  97          * Search a new directory.
  98          */
  99
 100         /*
 101          * Degenerate lookups (e.g. "/", "..", derived from "/.", etc)
 102          * are not allowed.
 103          */
 104         if (cnp->cn_nameptr[0] == '\0') {
 105                 error = EISDIR;
 106                 goto bad;
 107         }
 108         if (cnp->cn_flags & CNP_ISDOTDOT)
 109                 panic ("relookup: lookup on dot-dot");
 110
 111         /*
 112          * We now have a segment name to search for, and a directory to search.
 113          */
 114         if ((error = VOP_OLD_LOOKUP(dvp, vpp, cnp)) != 0) {
 115                 KASSERT(*vpp == NULL, ("leaf should be empty"));
 116                 if (error != EJUSTRETURN)
 117                         goto bad;
 118                 /*
 119                  * If creating and at end of pathname, then can consider
 120                  * allowing file to be created.
 121                  */
 122                 if (rdonly) {
 123                         error = EROFS;
 124                         goto bad;
 125                 }
 126                 /*
 127                  * We return with ni_vp NULL to indicate that the entry
 128                  * doesn't currently exist, leaving a pointer to the
 129                  * (possibly locked) directory inode in ndp->ni_dvp.
 130                  */
 131                 return (0);
 132         }
 133
 134         /*
 135          * Check for symbolic link
 136          */
 137         KASSERT((*vpp)->v_type != VLNK || !(cnp->cn_flags & CNP_FOLLOW),
 138             ("relookup: symlink found.\n"));
 139
 140         /*
 141          * Disallow directory write attempts on read-only file systems.
 142          */
 143         if (rdonly && (cnp->cn_nameiop == NAMEI_DELETE ||
 144                         cnp->cn_nameiop == NAMEI_RENAME)) {
 145                 error = EROFS;
 146                 goto bad;
 147         }
 148         KKASSERT((cnp->cn_flags & CNP_PDIRUNLOCK) == 0);
 149         return (0);
 150
 151 bad:
 152         if ((cnp->cn_flags & CNP_PDIRUNLOCK) == 0) {
 153                 cnp->cn_flags |= CNP_PDIRUNLOCK;
 154                 vn_unlock(dvp);
 155         }
 156         if (*vpp) {
 157                 vput(*vpp);
 158                 *vpp = NULL;
 159         }
 160         return (error);
 161 }
 162