The Design and Implementation of the FreeBSD Operating System, Second Edition
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FreeBSD/Linux Kernel Cross Reference
sys/kern/vfs_getcwd.c

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    1 /* $NetBSD: vfs_getcwd.c,v 1.25 2004/03/23 13:22:05 junyoung Exp $ */
    2 
    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  * 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 NetBSD
   21  *        Foundation, Inc. and its contributors.
   22  * 4. Neither the name of The NetBSD Foundation nor the names of its
   23  *    contributors may be used to endorse or promote products derived
   24  *    from this software without specific prior written permission.
   25  *
   26  * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
   27  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
   28  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
   29  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
   30  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
   31  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
   32  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
   33  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
   34  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
   35  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
   36  * POSSIBILITY OF SUCH DAMAGE.
   37  */
   38 
   39 #include <sys/cdefs.h>
   40 __KERNEL_RCSID(0, "$NetBSD: vfs_getcwd.c,v 1.25 2004/03/23 13:22:05 junyoung Exp $");
   41 
   42 #include <sys/param.h>
   43 #include <sys/systm.h>
   44 #include <sys/namei.h>
   45 #include <sys/filedesc.h>
   46 #include <sys/kernel.h>
   47 #include <sys/file.h>
   48 #include <sys/stat.h>
   49 #include <sys/vnode.h>
   50 #include <sys/mount.h>
   51 #include <sys/proc.h>
   52 #include <sys/uio.h>
   53 #include <sys/malloc.h>
   54 #include <sys/dirent.h>
   55 #include <ufs/ufs/dir.h>        /* XXX only for DIRBLKSIZ */
   56 
   57 #include <sys/sa.h>
   58 #include <sys/syscallargs.h>
   59 
   60 static int
   61 getcwd_scandir(struct vnode **, struct vnode **,
   62     char **, char *, struct proc *);
   63 static int
   64 getcwd_getcache(struct vnode **, struct vnode **,
   65     char **, char *);
   66 
   67 #define DIRENT_MINSIZE (sizeof(struct dirent) - (MAXNAMLEN + 1) + 4)
   68 
   69 /*
   70  * Vnode variable naming conventions in this file:
   71  *
   72  * rvp: the current root we're aiming towards.
   73  * lvp, *lvpp: the "lower" vnode
   74  * uvp, *uvpp: the "upper" vnode.
   75  *
   76  * Since all the vnodes we're dealing with are directories, and the
   77  * lookups are going *up* in the filesystem rather than *down*, the
   78  * usual "pvp" (parent) or "dvp" (directory) naming conventions are
   79  * too confusing.
   80  */
   81 
   82 /*
   83  * XXX Will infinite loop in certain cases if a directory read reliably
   84  *      returns EINVAL on last block.
   85  * XXX is EINVAL the right thing to return if a directory is malformed?
   86  */
   87 
   88 /*
   89  * XXX Untested vs. mount -o union; probably does the wrong thing.
   90  */
   91 
   92 /*
   93  * Find parent vnode of *lvpp, return in *uvpp
   94  *
   95  * If we care about the name, scan it looking for name of directory
   96  * entry pointing at lvp.
   97  *
   98  * Place the name in the buffer which starts at bufp, immediately
   99  * before *bpp, and move bpp backwards to point at the start of it.
  100  *
  101  * On entry, *lvpp is a locked vnode reference; on exit, it is vput and NULL'ed
  102  * On exit, *uvpp is either NULL or is a locked vnode reference.
  103  */
  104 static int
  105 getcwd_scandir(lvpp, uvpp, bpp, bufp, p)
  106         struct vnode **lvpp;
  107         struct vnode **uvpp;
  108         char **bpp;
  109         char *bufp;
  110         struct proc *p;
  111 {
  112         int     error = 0;
  113         int     eofflag;
  114         off_t   off;
  115         int     tries;
  116         struct uio uio;
  117         struct iovec iov;
  118         char   *dirbuf = NULL;
  119         int     dirbuflen;
  120         ino_t   fileno;
  121         struct vattr va;
  122         struct vnode *uvp = NULL;
  123         struct vnode *lvp = *lvpp;
  124         struct componentname cn;
  125         int len, reclen;
  126         tries = 0;
  127 
  128         /*
  129          * If we want the filename, get some info we need while the
  130          * current directory is still locked.
  131          */
  132         if (bufp != NULL) {
  133                 error = VOP_GETATTR(lvp, &va, p->p_ucred, p);
  134                 if (error) {
  135                         vput(lvp);
  136                         *lvpp = NULL;
  137                         *uvpp = NULL;
  138                         return error;
  139                 }
  140         }
  141 
  142         /*
  143          * Ok, we have to do it the hard way..
  144          * Next, get parent vnode using lookup of ..
  145          */
  146         cn.cn_nameiop = LOOKUP;
  147         cn.cn_flags = ISLASTCN | ISDOTDOT | RDONLY;
  148         cn.cn_proc = p;
  149         cn.cn_cred = p->p_ucred;
  150         cn.cn_pnbuf = NULL;
  151         cn.cn_nameptr = "..";
  152         cn.cn_namelen = 2;
  153         cn.cn_hash = 0;
  154         cn.cn_consume = 0;
  155 
  156         /*
  157          * At this point, lvp is locked and will be unlocked by the lookup.
  158          * On successful return, *uvpp will be locked
  159          */
  160         error = VOP_LOOKUP(lvp, uvpp, &cn);
  161         if (error) {
  162                 vput(lvp);
  163                 *lvpp = NULL;
  164                 *uvpp = NULL;
  165                 return error;
  166         }
  167         uvp = *uvpp;
  168 
  169         /* If we don't care about the pathname, we're done */
  170         if (bufp == NULL) {
  171                 vrele(lvp);
  172                 *lvpp = NULL;
  173                 return 0;
  174         }
  175 
  176         fileno = va.va_fileid;
  177 
  178         dirbuflen = DIRBLKSIZ;
  179         if (dirbuflen < va.va_blocksize)
  180                 dirbuflen = va.va_blocksize;
  181         dirbuf = (char *)malloc(dirbuflen, M_TEMP, M_WAITOK);
  182 
  183 #if 0
  184 unionread:
  185 #endif
  186         off = 0;
  187         do {
  188                 /* call VOP_READDIR of parent */
  189                 iov.iov_base = dirbuf;
  190                 iov.iov_len = dirbuflen;
  191 
  192                 uio.uio_iov = &iov;
  193                 uio.uio_iovcnt = 1;
  194                 uio.uio_offset = off;
  195                 uio.uio_resid = dirbuflen;
  196                 uio.uio_segflg = UIO_SYSSPACE;
  197                 uio.uio_rw = UIO_READ;
  198                 uio.uio_procp = p;
  199 
  200                 eofflag = 0;
  201 
  202                 error = VOP_READDIR(uvp, &uio, p->p_ucred, &eofflag, 0, 0);
  203 
  204                 off = uio.uio_offset;
  205 
  206                 /*
  207                  * Try again if NFS tosses its cookies.
  208                  * XXX this can still loop forever if the directory is busted
  209                  * such that the second or subsequent page of it always
  210                  * returns EINVAL
  211                  */
  212                 if ((error == EINVAL) && (tries < 3)) {
  213                         off = 0;
  214                         tries++;
  215                         continue;       /* once more, with feeling */
  216                 }
  217 
  218                 if (!error) {
  219                         char   *cpos;
  220                         struct dirent *dp;
  221 
  222                         cpos = dirbuf;
  223                         tries = 0;
  224 
  225                         /* scan directory page looking for matching vnode */
  226                         for (len = (dirbuflen - uio.uio_resid); len > 0;
  227                             len -= reclen) {
  228                                 dp = (struct dirent *) cpos;
  229                                 reclen = dp->d_reclen;
  230 
  231                                 /* check for malformed directory.. */
  232                                 if (reclen < DIRENT_MINSIZE) {
  233                                         error = EINVAL;
  234                                         goto out;
  235                                 }
  236                                 /*
  237                                  * XXX should perhaps do VOP_LOOKUP to
  238                                  * check that we got back to the right place,
  239                                  * but getting the locking games for that
  240                                  * right would be heinous.
  241                                  */
  242                                 if ((dp->d_type != DT_WHT) &&
  243                                     (dp->d_fileno == fileno)) {
  244                                         char *bp = *bpp;
  245 
  246                                         bp -= dp->d_namlen;
  247                                         if (bp <= bufp) {
  248                                                 error = ERANGE;
  249                                                 goto out;
  250                                         }
  251                                         memcpy(bp, dp->d_name, dp->d_namlen);
  252                                         error = 0;
  253                                         *bpp = bp;
  254                                         goto out;
  255                                 }
  256                                 cpos += reclen;
  257                         }
  258                 } else
  259                         goto out;
  260         } while (!eofflag);
  261 #if 0
  262         /*
  263          * Deal with mount -o union, which unions only the
  264          * root directory of the mount.
  265          */
  266         if ((uvp->v_flag & VROOT) &&
  267             (uvp->v_mount->mnt_flag & MNT_UNION)) {
  268                 struct vnode *tvp = uvp;
  269 
  270                 uvp = uvp->v_mount->mnt_vnodecovered;
  271                 vput(tvp);
  272                 VREF(uvp);
  273                 *uvpp = uvp;
  274                 error = vn_lock(uvp, LK_EXCLUSIVE | LK_RETRY);
  275                 if (error != 0) {
  276                         vrele(uvp);
  277                         *uvpp = uvp = NULL;
  278                         goto out;
  279                 }
  280                 goto unionread;
  281         }
  282 #endif
  283         error = ENOENT;
  284 
  285 out:
  286         vrele(lvp);
  287         *lvpp = NULL;
  288         free(dirbuf, M_TEMP);
  289         return error;
  290 }
  291 
  292 /*
  293  * Look in the vnode-to-name reverse cache to see if
  294  * we can find things the easy way.
  295  *
  296  * XXX vget failure path is untested.
  297  *
  298  * On entry, *lvpp is a locked vnode reference.
  299  * On exit, one of the following is the case:
  300  *      0) Both *lvpp and *uvpp are NULL and failure is returned.
  301  *      1) *uvpp is NULL, *lvpp remains locked and -1 is returned (cache miss)
  302  *      2) *uvpp is a locked vnode reference, *lvpp is vput and NULL'ed
  303  *         and 0 is returned (cache hit)
  304  */
  305 
  306 static int
  307 getcwd_getcache(lvpp, uvpp, bpp, bufp)
  308         struct vnode **lvpp, **uvpp;
  309         char **bpp;
  310         char *bufp;
  311 {
  312         struct vnode *lvp, *uvp = NULL;
  313         char *obp = *bpp;
  314         int error;
  315 
  316         lvp = *lvpp;
  317 
  318         /*
  319          * This returns 0 on a cache hit, -1 on a clean cache miss,
  320          * or an errno on other failure.
  321          */
  322         error = cache_revlookup(lvp, uvpp, bpp, bufp);
  323         if (error) {
  324                 if (error != -1) {
  325                         vput(lvp);
  326                         *lvpp = NULL;
  327                         *uvpp = NULL;
  328                 }
  329                 return error;
  330         }
  331         uvp = *uvpp;
  332 
  333         /*
  334          * Since we're going up, we have to release the current lock
  335          * before we take the parent lock.
  336          */
  337 
  338         VOP_UNLOCK(lvp, 0);
  339 
  340         error = vget(uvp, LK_EXCLUSIVE | LK_RETRY);
  341         /*
  342          * Verify that vget succeeded while we were waiting for the
  343          * lock.
  344          */
  345         if (error) {
  346                 /*
  347                  * Oops, we missed.  If the vget failed try to get our
  348                  * lock back; if that works, rewind the `bp' and tell
  349                  * caller to try things the hard way, otherwise give
  350                  * up.
  351                  */
  352                 *uvpp = NULL;
  353                 error = vn_lock(lvp, LK_EXCLUSIVE | LK_RETRY);
  354                 if (error == 0) {
  355                         *bpp = obp;
  356                         return -1;
  357                 }
  358         }
  359         vrele(lvp);
  360         *lvpp = NULL;
  361 
  362         return error;
  363 }
  364 
  365 /*
  366  * common routine shared by sys___getcwd() and vn_isunder()
  367  */
  368 
  369 int
  370 getcwd_common(lvp, rvp, bpp, bufp, limit, flags, p)
  371         struct vnode *lvp;
  372         struct vnode *rvp;
  373         char **bpp;
  374         char *bufp;
  375         int limit;
  376         int flags;
  377         struct proc *p;
  378 {
  379         struct cwdinfo *cwdi = p->p_cwdi;
  380         struct vnode *uvp = NULL;
  381         char *bp = NULL;
  382         int error;
  383         int perms = VEXEC;
  384 
  385         if (rvp == NULL) {
  386                 rvp = cwdi->cwdi_rdir;
  387                 if (rvp == NULL)
  388                         rvp = rootvnode;
  389         }
  390 
  391         VREF(rvp);
  392         VREF(lvp);
  393 
  394         /*
  395          * Error handling invariant:
  396          * Before a `goto out':
  397          *      lvp is either NULL, or locked and held.
  398          *      uvp is either NULL, or locked and held.
  399          */
  400 
  401         error = vn_lock(lvp, LK_EXCLUSIVE | LK_RETRY);
  402         if (error) {
  403                 vrele(lvp);
  404                 lvp = NULL;
  405                 goto out;
  406         }
  407         if (bufp)
  408                 bp = *bpp;
  409         /*
  410          * this loop will terminate when one of the following happens:
  411          *      - we hit the root
  412          *      - getdirentries or lookup fails
  413          *      - we run out of space in the buffer.
  414          */
  415         if (lvp == rvp) {
  416                 if (bp)
  417                         *(--bp) = '/';
  418                 goto out;
  419         }
  420         do {
  421                 if (lvp->v_type != VDIR) {
  422                         error = ENOTDIR;
  423                         goto out;
  424                 }
  425 
  426                 /*
  427                  * access check here is optional, depending on
  428                  * whether or not caller cares.
  429                  */
  430                 if (flags & GETCWD_CHECK_ACCESS) {
  431                         error = VOP_ACCESS(lvp, perms, p->p_ucred, p);
  432                         if (error)
  433                                 goto out;
  434                         perms = VEXEC|VREAD;
  435                 }
  436 
  437                 /*
  438                  * step up if we're a covered vnode..
  439                  */
  440                 while (lvp->v_flag & VROOT) {
  441                         struct vnode *tvp;
  442 
  443                         if (lvp == rvp)
  444                                 goto out;
  445 
  446                         tvp = lvp;
  447                         lvp = lvp->v_mount->mnt_vnodecovered;
  448                         vput(tvp);
  449                         /*
  450                          * hodie natus est radici frater
  451                          */
  452                         if (lvp == NULL) {
  453                                 error = ENOENT;
  454                                 goto out;
  455                         }
  456                         VREF(lvp);
  457                         error = vn_lock(lvp, LK_EXCLUSIVE | LK_RETRY);
  458                         if (error != 0) {
  459                                 vrele(lvp);
  460                                 lvp = NULL;
  461                                 goto out;
  462                         }
  463                 }
  464                 /*
  465                  * Look in the name cache; if that fails, look in the
  466                  * directory..
  467                  */
  468                 error = getcwd_getcache(&lvp, &uvp, &bp, bufp);
  469                 if (error == -1)
  470                         error = getcwd_scandir(&lvp, &uvp, &bp, bufp, p);
  471                 if (error)
  472                         goto out;
  473 #if DIAGNOSTIC
  474                 if (lvp != NULL)
  475                         panic("getcwd: oops, forgot to null lvp");
  476                 if (bufp && (bp <= bufp)) {
  477                         panic("getcwd: oops, went back too far");
  478                 }
  479 #endif
  480                 if (bp)
  481                         *(--bp) = '/';
  482                 lvp = uvp;
  483                 uvp = NULL;
  484                 limit--;
  485         } while ((lvp != rvp) && (limit > 0));
  486 
  487 out:
  488         if (bpp)
  489                 *bpp = bp;
  490         if (uvp)
  491                 vput(uvp);
  492         if (lvp)
  493                 vput(lvp);
  494         vrele(rvp);
  495         return error;
  496 }
  497 
  498 /*
  499  * Check if one directory can be found inside another in the directory
  500  * hierarchy.
  501  *
  502  * Intended to be used in chroot, chdir, fchdir, etc., to ensure that
  503  * chroot() actually means something.
  504  */
  505 int
  506 vn_isunder(lvp, rvp, p)
  507         struct vnode *lvp;
  508         struct vnode *rvp;
  509         struct proc *p;
  510 {
  511         int error;
  512 
  513         error = getcwd_common(lvp, rvp, NULL, NULL, MAXPATHLEN / 2, 0, p);
  514 
  515         if (!error)
  516                 return 1;
  517         else
  518                 return 0;
  519 }
  520 
  521 /*
  522  * Returns true if proc p1's root directory equal to or under p2's
  523  * root directory.
  524  *
  525  * Intended to be used from ptrace/procfs sorts of things.
  526  */
  527 
  528 int
  529 proc_isunder(p1, p2)
  530         struct proc *p1;
  531         struct proc *p2;
  532 {
  533         struct vnode *r1 = p1->p_cwdi->cwdi_rdir;
  534         struct vnode *r2 = p2->p_cwdi->cwdi_rdir;
  535 
  536         if (r1 == NULL)
  537                 return (r2 == NULL);
  538         else if (r2 == NULL)
  539                 return 1;
  540         else
  541                 return vn_isunder(r1, r2, p2);
  542 }
  543 
  544 /*
  545  * Find pathname of process's current directory.
  546  *
  547  * Use vfs vnode-to-name reverse cache; if that fails, fall back
  548  * to reading directory contents.
  549  */
  550 
  551 int
  552 sys___getcwd(l, v, retval)
  553         struct lwp *l;
  554         void   *v;
  555         register_t *retval;
  556 {
  557         struct sys___getcwd_args /* {
  558                 syscallarg(char *) bufp;
  559                 syscallarg(size_t) length;
  560         } */ *uap = v;
  561 
  562         int     error;
  563         char   *path;
  564         char   *bp, *bend;
  565         int     len = SCARG(uap, length);
  566         int     lenused;
  567 
  568         if (len > MAXPATHLEN * 4)
  569                 len = MAXPATHLEN * 4;
  570         else if (len < 2)
  571                 return ERANGE;
  572 
  573         path = (char *)malloc(len, M_TEMP, M_WAITOK);
  574         if (!path)
  575                 return ENOMEM;
  576 
  577         bp = &path[len];
  578         bend = bp;
  579         *(--bp) = '\0';
  580 
  581         /*
  582          * 5th argument here is "max number of vnodes to traverse".
  583          * Since each entry takes up at least 2 bytes in the output buffer,
  584          * limit it to N/2 vnodes for an N byte buffer.
  585          */
  586         error = getcwd_common(l->l_proc->p_cwdi->cwdi_cdir, NULL, &bp, path,
  587             len / 2, GETCWD_CHECK_ACCESS, l->l_proc);
  588 
  589         if (error)
  590                 goto out;
  591         lenused = bend - bp;
  592         *retval = lenused;
  593         /* put the result into user buffer */
  594         error = copyout(bp, SCARG(uap, bufp), lenused);
  595 
  596 out:
  597         free(path, M_TEMP);
  598         return error;
  599 }

Cache object: b2315a99169eaa815af40fcc8ef3cd89


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