The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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FreeBSD/Linux Kernel Cross Reference
sys/compat/linux/linux_getcwd.c

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    1 /* $OpenBSD: linux_getcwd.c,v 1.2 2001/05/16 12:50:21 ho Exp $ */
    2 /* $NetBSD: vfs_getcwd.c,v 1.3.2.3 1999/07/11 10:24:09 sommerfeld Exp $ */
    3 /*-
    4  * Copyright (c) 1999 The NetBSD Foundation, Inc.
    5  * All rights reserved.
    6  *
    7  * This code is derived from software contributed to The NetBSD Foundation
    8  * by Bill Sommerfeld.
    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  *
   19  * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
   20  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
   21  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
   22  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
   23  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
   24  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
   25  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
   26  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
   27  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
   28  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
   29  * POSSIBILITY OF SUCH DAMAGE.
   30  */
   31 
   32 #include <sys/cdefs.h>
   33 __FBSDID("$FreeBSD: releng/9.0/sys/compat/linux/linux_getcwd.c 204523 2010-03-01 17:20:04Z joel $");
   34 
   35 #include "opt_compat.h"
   36 
   37 #include <sys/param.h>
   38 #include <sys/systm.h>
   39 #include <sys/namei.h>
   40 #include <sys/filedesc.h>
   41 #include <sys/kernel.h>
   42 #include <sys/file.h>
   43 #include <sys/stat.h>
   44 #include <sys/syscallsubr.h>
   45 #include <sys/vnode.h>
   46 #include <sys/mount.h>
   47 #include <sys/proc.h>
   48 #include <sys/uio.h>
   49 #include <sys/malloc.h>
   50 #include <sys/dirent.h>
   51 #include <ufs/ufs/dir.h>        /* XXX only for DIRBLKSIZ */
   52 
   53 #ifdef COMPAT_LINUX32
   54 #include <machine/../linux32/linux.h>
   55 #include <machine/../linux32/linux32_proto.h>
   56 #else
   57 #include <machine/../linux/linux.h>
   58 #include <machine/../linux/linux_proto.h>
   59 #endif
   60 #include <compat/linux/linux_util.h>
   61 
   62 #include <security/mac/mac_framework.h>
   63 
   64 static int
   65 linux_getcwd_scandir(struct vnode **, struct vnode **,
   66     char **, char *, struct thread *);
   67 static int
   68 linux_getcwd_common(struct vnode *, struct vnode *,
   69                    char **, char *, int, int, struct thread *);
   70 
   71 #define DIRENT_MINSIZE (sizeof(struct dirent) - (MAXNAMLEN+1) + 4)
   72 
   73 /*
   74  * Vnode variable naming conventions in this file:
   75  *
   76  * rvp: the current root we're aiming towards.
   77  * lvp, *lvpp: the "lower" vnode
   78  * uvp, *uvpp: the "upper" vnode.
   79  *
   80  * Since all the vnodes we're dealing with are directories, and the
   81  * lookups are going *up* in the filesystem rather than *down*, the
   82  * usual "pvp" (parent) or "dvp" (directory) naming conventions are
   83  * too confusing.
   84  */
   85 
   86 /*
   87  * XXX Will infinite loop in certain cases if a directory read reliably
   88  *      returns EINVAL on last block.
   89  * XXX is EINVAL the right thing to return if a directory is malformed?
   90  */
   91 
   92 /*
   93  * XXX Untested vs. mount -o union; probably does the wrong thing.
   94  */
   95 
   96 /*
   97  * Find parent vnode of *lvpp, return in *uvpp
   98  *
   99  * If we care about the name, scan it looking for name of directory
  100  * entry pointing at lvp.
  101  *
  102  * Place the name in the buffer which starts at bufp, immediately
  103  * before *bpp, and move bpp backwards to point at the start of it.
  104  *
  105  * On entry, *lvpp is a locked vnode reference; on exit, it is vput and NULL'ed
  106  * On exit, *uvpp is either NULL or is a locked vnode reference.
  107  */
  108 static int
  109 linux_getcwd_scandir(lvpp, uvpp, bpp, bufp, td)
  110         struct vnode **lvpp;
  111         struct vnode **uvpp;
  112         char **bpp;
  113         char *bufp;
  114         struct thread *td;
  115 {
  116         int     error = 0;
  117         int     eofflag;
  118         off_t   off;
  119         int     tries;
  120         struct uio uio;
  121         struct iovec iov;
  122         char   *dirbuf = NULL;
  123         int     dirbuflen;
  124         ino_t   fileno;
  125         struct vattr va;
  126         struct vnode *uvp = NULL;
  127         struct vnode *lvp = *lvpp;      
  128         struct componentname cn;
  129         int len, reclen;
  130         tries = 0;
  131 
  132         /*
  133          * If we want the filename, get some info we need while the
  134          * current directory is still locked.
  135          */
  136         if (bufp != NULL) {
  137                 error = VOP_GETATTR(lvp, &va, td->td_ucred);
  138                 if (error) {
  139                         vput(lvp);
  140                         *lvpp = NULL;
  141                         *uvpp = NULL;
  142                         return error;
  143                 }
  144         }
  145 
  146         /*
  147          * Ok, we have to do it the hard way..
  148          * Next, get parent vnode using lookup of ..
  149          */
  150         cn.cn_nameiop = LOOKUP;
  151         cn.cn_flags = ISLASTCN | ISDOTDOT | RDONLY;
  152         cn.cn_thread = td;
  153         cn.cn_cred = td->td_ucred;
  154         cn.cn_pnbuf = NULL;
  155         cn.cn_nameptr = "..";
  156         cn.cn_namelen = 2;
  157         cn.cn_consume = 0;
  158         cn.cn_lkflags = LK_SHARED;
  159         
  160         /*
  161          * At this point, lvp is locked and will be unlocked by the lookup.
  162          * On successful return, *uvpp will be locked
  163          */
  164 #ifdef MAC
  165         error = mac_vnode_check_lookup(td->td_ucred, lvp, &cn);
  166         if (error == 0)
  167 #endif
  168                 error = VOP_LOOKUP(lvp, uvpp, &cn);
  169         if (error) {
  170                 vput(lvp);
  171                 *lvpp = NULL;
  172                 *uvpp = NULL;
  173                 return error;
  174         }
  175         uvp = *uvpp;
  176 
  177         /* If we don't care about the pathname, we're done */
  178         if (bufp == NULL) {
  179                 vput(lvp);
  180                 *lvpp = NULL;
  181                 return 0;
  182         }
  183         
  184         fileno = va.va_fileid;
  185 
  186         dirbuflen = DIRBLKSIZ;
  187         if (dirbuflen < va.va_blocksize)
  188                 dirbuflen = va.va_blocksize;
  189         dirbuf = (char *)malloc(dirbuflen, M_TEMP, M_WAITOK);
  190 
  191 #if 0
  192 unionread:
  193 #endif
  194         off = 0;
  195         do {
  196                 /* call VOP_READDIR of parent */
  197                 iov.iov_base = dirbuf;
  198                 iov.iov_len = dirbuflen;
  199 
  200                 uio.uio_iov = &iov;
  201                 uio.uio_iovcnt = 1;
  202                 uio.uio_offset = off;
  203                 uio.uio_resid = dirbuflen;
  204                 uio.uio_segflg = UIO_SYSSPACE;
  205                 uio.uio_rw = UIO_READ;
  206                 uio.uio_td = td;
  207 
  208                 eofflag = 0;
  209 
  210 #ifdef MAC
  211                 error = mac_vnode_check_readdir(td->td_ucred, uvp);
  212                 if (error == 0)
  213 #endif /* MAC */
  214                         error = VOP_READDIR(uvp, &uio, td->td_ucred, &eofflag,
  215                             0, 0);
  216 
  217                 off = uio.uio_offset;
  218 
  219                 /*
  220                  * Try again if NFS tosses its cookies.
  221                  * XXX this can still loop forever if the directory is busted
  222                  * such that the second or subsequent page of it always
  223                  * returns EINVAL
  224                  */
  225                 if ((error == EINVAL) && (tries < 3)) {
  226                         off = 0;
  227                         tries++;
  228                         continue;       /* once more, with feeling */
  229                 }
  230 
  231                 if (!error) {
  232                         char   *cpos;
  233                         struct dirent *dp;
  234                         
  235                         cpos = dirbuf;
  236                         tries = 0;
  237                                 
  238                         /* scan directory page looking for matching vnode */ 
  239                         for (len = (dirbuflen - uio.uio_resid); len > 0; len -= reclen) {
  240                                 dp = (struct dirent *) cpos;
  241                                 reclen = dp->d_reclen;
  242 
  243                                 /* check for malformed directory.. */
  244                                 if (reclen < DIRENT_MINSIZE) {
  245                                         error = EINVAL;
  246                                         goto out;
  247                                 }
  248                                 /*
  249                                  * XXX should perhaps do VOP_LOOKUP to
  250                                  * check that we got back to the right place,
  251                                  * but getting the locking games for that
  252                                  * right would be heinous.
  253                                  */
  254                                 if ((dp->d_type != DT_WHT) &&
  255                                     (dp->d_fileno == fileno)) {
  256                                         char *bp = *bpp;
  257                                         bp -= dp->d_namlen;
  258                                         
  259                                         if (bp <= bufp) {
  260                                                 error = ERANGE;
  261                                                 goto out;
  262                                         }
  263                                         bcopy(dp->d_name, bp, dp->d_namlen);
  264                                         error = 0;
  265                                         *bpp = bp;
  266                                         goto out;
  267                                 }
  268                                 cpos += reclen;
  269                         }
  270                 }
  271         } while (!eofflag);
  272         error = ENOENT;
  273                 
  274 out:
  275         vput(lvp);
  276         *lvpp = NULL;
  277         free(dirbuf, M_TEMP);
  278         return error;
  279 }
  280 
  281 
  282 /*
  283  * common routine shared by sys___getcwd() and linux_vn_isunder()
  284  */
  285 
  286 #define GETCWD_CHECK_ACCESS 0x0001
  287 
  288 static int
  289 linux_getcwd_common (lvp, rvp, bpp, bufp, limit, flags, td)
  290         struct vnode *lvp;
  291         struct vnode *rvp;
  292         char **bpp;
  293         char *bufp;
  294         int limit;
  295         int flags;
  296         struct thread *td;
  297 {
  298         struct filedesc *fdp = td->td_proc->p_fd;
  299         struct vnode *uvp = NULL;
  300         char *bp = NULL;
  301         int error;
  302         accmode_t accmode = VEXEC;
  303 
  304         if (rvp == NULL) {
  305                 rvp = fdp->fd_rdir;
  306                 if (rvp == NULL)
  307                         rvp = rootvnode;
  308         }
  309         
  310         VREF(rvp);
  311         VREF(lvp);
  312 
  313         /*
  314          * Error handling invariant:
  315          * Before a `goto out':
  316          *      lvp is either NULL, or locked and held.
  317          *      uvp is either NULL, or locked and held.
  318          */
  319 
  320         error = vn_lock(lvp, LK_EXCLUSIVE | LK_RETRY);
  321         if (error != 0)
  322                 panic("vn_lock LK_RETRY returned error %d", error);
  323         if (bufp)
  324                 bp = *bpp;
  325         /*
  326          * this loop will terminate when one of the following happens:
  327          *      - we hit the root
  328          *      - getdirentries or lookup fails
  329          *      - we run out of space in the buffer.
  330          */
  331         if (lvp == rvp) {
  332                 if (bp)
  333                         *(--bp) = '/';
  334                 goto out;
  335         }
  336         do {
  337                 if (lvp->v_type != VDIR) {
  338                         error = ENOTDIR;
  339                         goto out;
  340                 }
  341                 
  342                 /*
  343                  * access check here is optional, depending on
  344                  * whether or not caller cares.
  345                  */
  346                 if (flags & GETCWD_CHECK_ACCESS) {
  347                         error = VOP_ACCESS(lvp, accmode, td->td_ucred, td);
  348                         if (error)
  349                                 goto out;
  350                         accmode = VEXEC|VREAD;
  351                 }
  352                 
  353                 /*
  354                  * step up if we're a covered vnode..
  355                  */
  356                 while (lvp->v_vflag & VV_ROOT) {
  357                         struct vnode *tvp;
  358 
  359                         if (lvp == rvp)
  360                                 goto out;
  361                         
  362                         tvp = lvp;
  363                         lvp = lvp->v_mount->mnt_vnodecovered;
  364                         vput(tvp);
  365                         /*
  366                          * hodie natus est radici frater
  367                          */
  368                         if (lvp == NULL) {
  369                                 error = ENOENT;
  370                                 goto out;
  371                         }
  372                         VREF(lvp);
  373                         error = vn_lock(lvp, LK_EXCLUSIVE | LK_RETRY);
  374                         if (error != 0)
  375                                 panic("vn_lock LK_RETRY returned %d", error);
  376                 }
  377                 error = linux_getcwd_scandir(&lvp, &uvp, &bp, bufp, td);
  378                 if (error)
  379                         goto out;
  380 #ifdef DIAGNOSTIC               
  381                 if (lvp != NULL)
  382                         panic("getcwd: oops, forgot to null lvp");
  383                 if (bufp && (bp <= bufp)) {
  384                         panic("getcwd: oops, went back too far");
  385                 }
  386 #endif          
  387                 if (bp) 
  388                         *(--bp) = '/';
  389                 lvp = uvp;
  390                 uvp = NULL;
  391                 limit--;
  392         } while ((lvp != rvp) && (limit > 0)); 
  393 
  394 out:
  395         if (bpp)
  396                 *bpp = bp;
  397         if (uvp)
  398                 vput(uvp);
  399         if (lvp)
  400                 vput(lvp);
  401         vrele(rvp);
  402         return error;
  403 }
  404 
  405 
  406 /*
  407  * Find pathname of process's current directory.
  408  *
  409  * Use vfs vnode-to-name reverse cache; if that fails, fall back
  410  * to reading directory contents.
  411  */
  412 
  413 int
  414 linux_getcwd(struct thread *td, struct linux_getcwd_args *args)
  415 {
  416         caddr_t bp, bend, path;
  417         int error, len, lenused;
  418 
  419 #ifdef DEBUG
  420         if (ldebug(getcwd))
  421                 printf(ARGS(getcwd, "%p, %ld"), args->buf, (long)args->bufsize);
  422 #endif
  423 
  424         len = args->bufsize;
  425 
  426         if (len > MAXPATHLEN*4)
  427                 len = MAXPATHLEN*4;
  428         else if (len < 2)
  429                 return ERANGE;
  430 
  431         path = (char *)malloc(len, M_TEMP, M_WAITOK);
  432 
  433         error = kern___getcwd(td, path, UIO_SYSSPACE, len);
  434         if (!error) {
  435                 lenused = strlen(path) + 1;
  436                 if (lenused <= args->bufsize) {
  437                         td->td_retval[0] = lenused;
  438                         error = copyout(path, args->buf, lenused);
  439                 }
  440                 else
  441                         error = ERANGE;
  442         } else {
  443                 bp = &path[len];
  444                 bend = bp;
  445                 *(--bp) = '\0';
  446 
  447                 /*
  448                  * 5th argument here is "max number of vnodes to traverse".
  449                  * Since each entry takes up at least 2 bytes in the output buffer,
  450                  * limit it to N/2 vnodes for an N byte buffer.
  451                  */
  452 
  453                 mtx_lock(&Giant);
  454                 error = linux_getcwd_common (td->td_proc->p_fd->fd_cdir, NULL,
  455                     &bp, path, len/2, GETCWD_CHECK_ACCESS, td);
  456                 mtx_unlock(&Giant);
  457 
  458                 if (error)
  459                         goto out;
  460                 lenused = bend - bp;
  461                 td->td_retval[0] = lenused;
  462                 /* put the result into user buffer */
  463                 error = copyout(bp, args->buf, lenused);
  464         }
  465 out:
  466         free(path, M_TEMP);
  467         return (error);
  468 }
  469 

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