kernel/syscall/readlink.c

   1 /*
   2  * CDDL HEADER START
   3  *
   4  * The contents of this file are subject to the terms of the
   5  * Common Development and Distribution License (the "License").
   6  * You may not use this file except in compliance with the License.
   7  *
   8  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
   9  * or http://www.opensolaris.org/os/licensing.
  10  * See the License for the specific language governing permissions
  11  * and limitations under the License.
  12  *
  13  * When distributing Covered Code, include this CDDL HEADER in each
  14  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
  15  * If applicable, add the following below this CDDL HEADER, with the
  16  * fields enclosed by brackets "[]" replaced with your own identifying
  17  * information: Portions Copyright [yyyy] [name of copyright owner]
  18  *
  19  * CDDL HEADER END
  20  */
  21
  22 /*
  23  * Copyright (c) 1994, 2010, Oracle and/or its affiliates. All rights reserved.
  24  */
  25
  26 /*      Copyright (c) 1983, 1984, 1985, 1986, 1987, 1988, 1989 AT&T     */
  27 /*        All Rights Reserved   */
  28
  29 /*
  30  * Portions of this source code were derived from Berkeley 4.3 BSD
  31  * under license from the Regents of the University of California.
  32  */
  33
  34 #include <sys/param.h>
  35 #include <sys/isa_defs.h>
  36 #include <sys/types.h>
  37 #include <sys/sysmacros.h>
  38 #include <sys/cred.h>
  39 #include <sys/systm.h>
  40 #include <sys/errno.h>
  41 #include <sys/pathname.h>
  42 #include <sys/vnode.h>
  43 #include <sys/file.h>
  44 #include <sys/fcntl.h>
  45 #include <sys/uio.h>
  46 #include <sys/debug.h>
  47 #include <sys/fs_subr.h>
  48 #include <c2/audit.h>
  49
  50 /*
  51  * Read the contents of a symbolic link.
  52  */
  53 ssize_t
  54 readlinkat(int dfd, char *name, char *buf, size_t count)
  55 {
  56         vnode_t *startvp;
  57         vnode_t *vp;
  58         struct iovec aiov;
  59         struct uio auio;
  60         int error;
  61         struct vattr vattr;
  62         ssize_t cnt;
  63         int estale_retry = 0;
  64
  65         if ((cnt = (ssize_t)count) < 0)
  66                 return (set_errno(EINVAL));
  67         if (name == NULL)
  68                 return (set_errno(EFAULT));
  69         if ((error = fgetstartvp(dfd, name, &startvp)) != 0)
  70                 return (set_errno(error));
  71
  72 lookup:
  73         if (AU_AUDITING() && startvp != NULL)
  74                 audit_setfsat_path(1);
  75         if (error = lookupnameat(name, UIO_USERSPACE, NO_FOLLOW,
  76             NULLVPP, &vp, startvp)) {
  77                 if (error == ESTALE && fs_need_estale_retry(estale_retry++))
  78                         goto lookup;
  79                 goto out;
  80         }
  81
  82         if (vp->v_type != VLNK) {
  83                 /*
  84                  * Ask the underlying filesystem if it wants this
  85                  * object to look like a symlink at user-level.
  86                  */
  87                 vattr.va_mask = AT_TYPE;
  88                 error = fop_getattr(vp, &vattr, 0, CRED(), NULL);
  89                 if (error || vattr.va_type != VLNK) {
  90                         VN_RELE(vp);
  91                         if ((error == ESTALE) &&
  92                             fs_need_estale_retry(estale_retry++))
  93                                 goto lookup;
  94                         error = EINVAL;
  95                         goto out;
  96                 }
  97         }
  98         aiov.iov_base = buf;
  99         aiov.iov_len = cnt;
 100         auio.uio_iov = &aiov;
 101         auio.uio_iovcnt = 1;
 102         auio.uio_loffset = 0;
 103         auio.uio_segflg = UIO_USERSPACE;
 104         auio.uio_extflg = UIO_COPY_CACHED;
 105         auio.uio_resid = cnt;
 106         error = fop_readlink(vp, &auio, CRED(), NULL);
 107         VN_RELE(vp);
 108         if (error == ESTALE && fs_need_estale_retry(estale_retry++))
 109                 goto lookup;
 110 out:
 111         if (startvp != NULL)
 112                 VN_RELE(startvp);
 113         if (error)
 114                 return (set_errno(error));
 115         return ((ssize_t)(cnt - auio.uio_resid));
 116 }
 117
 118 #ifdef _SYSCALL32_IMPL
 119 /*
 120  * readlink32() intentionally returns a ssize_t rather than ssize32_t;
 121  * see the comments above read32 for details.
 122  */
 123
 124 ssize_t
 125 readlinkat32(int dfd, caddr32_t name, caddr32_t buf, size32_t count)
 126 {
 127         return ((ssize32_t)readlinkat(dfd, (char *)(uintptr_t)name,
 128             (char *)(uintptr_t)buf, (ssize32_t)count));
 129 }
 130
 131 #endif  /* _SYSCALL32_IMPL */