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 * 4. 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 */
36
37 #include <sys/cdefs.h>
38 __FBSDID("$FreeBSD$");
39
40 #include "opt_capsicum.h"
41 #include "opt_ktrace.h"
42
43 #include <sys/param.h>
44 #include <sys/systm.h>
45 #include <sys/kernel.h>
46 #include <sys/capsicum.h>
47 #include <sys/fcntl.h>
48 #include <sys/jail.h>
49 #include <sys/lock.h>
50 #include <sys/mutex.h>
51 #include <sys/namei.h>
52 #include <sys/vnode.h>
53 #include <sys/mount.h>
54 #include <sys/filedesc.h>
55 #include <sys/proc.h>
56 #include <sys/sdt.h>
57 #include <sys/syscallsubr.h>
58 #include <sys/sysctl.h>
59 #ifdef KTRACE
60 #include <sys/ktrace.h>
61 #endif
62
63 #include <security/audit/audit.h>
64 #include <security/mac/mac_framework.h>
65
66 #include <vm/uma.h>
67
68 #define NAMEI_DIAGNOSTIC 1
69 #undef NAMEI_DIAGNOSTIC
70
71 SDT_PROVIDER_DECLARE(vfs);
72 SDT_PROBE_DEFINE3(vfs, namei, lookup, entry, "struct vnode *", "char *",
73 "unsigned long");
74 SDT_PROBE_DEFINE2(vfs, namei, lookup, return, "int", "struct vnode *");
75
76 /*
77 * Allocation zone for namei
78 */
79 uma_zone_t namei_zone;
80 /*
81 * Placeholder vnode for mp traversal
82 */
83 static struct vnode *vp_crossmp;
84
85 static void
nameiinit(void * dummy __unused)86 nameiinit(void *dummy __unused)
87 {
88
89 namei_zone = uma_zcreate("NAMEI", MAXPATHLEN, NULL, NULL, NULL, NULL,
90 UMA_ALIGN_PTR, 0);
91 getnewvnode("crossmp", NULL, &dead_vnodeops, &vp_crossmp);
92 vn_lock(vp_crossmp, LK_EXCLUSIVE);
93 VN_LOCK_ASHARE(vp_crossmp);
94 VOP_UNLOCK(vp_crossmp, 0);
95 }
96 SYSINIT(vfs, SI_SUB_VFS, SI_ORDER_SECOND, nameiinit, NULL);
97
98 static int lookup_shared = 1;
99 SYSCTL_INT(_vfs, OID_AUTO, lookup_shared, CTLFLAG_RWTUN, &lookup_shared, 0,
100 "Enables/Disables shared locks for path name translation");
101
102 static void
namei_cleanup_cnp(struct componentname * cnp)103 namei_cleanup_cnp(struct componentname *cnp)
104 {
105 uma_zfree(namei_zone, cnp->cn_pnbuf);
106 #ifdef DIAGNOSTIC
107 cnp->cn_pnbuf = NULL;
108 cnp->cn_nameptr = NULL;
109 #endif
110 }
111
112 static int
namei_handle_root(struct nameidata * ndp,struct vnode ** dpp)113 namei_handle_root(struct nameidata *ndp, struct vnode **dpp)
114 {
115 struct componentname *cnp;
116
117 cnp = &ndp->ni_cnd;
118 if (ndp->ni_strictrelative != 0) {
119 #ifdef KTRACE
120 if (KTRPOINT(curthread, KTR_CAPFAIL))
121 ktrcapfail(CAPFAIL_LOOKUP, NULL, NULL);
122 #endif
123 return (ENOTCAPABLE);
124 }
125 while (*(cnp->cn_nameptr) == '/') {
126 cnp->cn_nameptr++;
127 ndp->ni_pathlen--;
128 }
129 *dpp = ndp->ni_rootdir;
130 VREF(*dpp);
131 return (0);
132 }
133
134 /*
135 * Convert a pathname into a pointer to a locked vnode.
136 *
137 * The FOLLOW flag is set when symbolic links are to be followed
138 * when they occur at the end of the name translation process.
139 * Symbolic links are always followed for all other pathname
140 * components other than the last.
141 *
142 * The segflg defines whether the name is to be copied from user
143 * space or kernel space.
144 *
145 * Overall outline of namei:
146 *
147 * copy in name
148 * get starting directory
149 * while (!done && !error) {
150 * call lookup to search path.
151 * if symbolic link, massage name in buffer and continue
152 * }
153 */
154 int
namei(struct nameidata * ndp)155 namei(struct nameidata *ndp)
156 {
157 struct filedesc *fdp; /* pointer to file descriptor state */
158 char *cp; /* pointer into pathname argument */
159 struct vnode *dp; /* the directory we are searching */
160 struct iovec aiov; /* uio for reading symbolic links */
161 struct uio auio;
162 int error, linklen, startdir_used;
163 struct componentname *cnp = &ndp->ni_cnd;
164 struct thread *td = cnp->cn_thread;
165 struct proc *p = td->td_proc;
166
167 ndp->ni_cnd.cn_cred = ndp->ni_cnd.cn_thread->td_ucred;
168 KASSERT(cnp->cn_cred && p, ("namei: bad cred/proc"));
169 KASSERT((cnp->cn_nameiop & (~OPMASK)) == 0,
170 ("namei: nameiop contaminated with flags"));
171 KASSERT((cnp->cn_flags & OPMASK) == 0,
172 ("namei: flags contaminated with nameiops"));
173 MPASS(ndp->ni_startdir == NULL || ndp->ni_startdir->v_type == VDIR ||
174 ndp->ni_startdir->v_type == VBAD);
175 if (!lookup_shared)
176 cnp->cn_flags &= ~LOCKSHARED;
177 fdp = p->p_fd;
178
179 /* We will set this ourselves if we need it. */
180 cnp->cn_flags &= ~TRAILINGSLASH;
181
182 /*
183 * Get a buffer for the name to be translated, and copy the
184 * name into the buffer.
185 */
186 if ((cnp->cn_flags & HASBUF) == 0)
187 cnp->cn_pnbuf = uma_zalloc(namei_zone, M_WAITOK);
188 if (ndp->ni_segflg == UIO_SYSSPACE)
189 error = copystr(ndp->ni_dirp, cnp->cn_pnbuf,
190 MAXPATHLEN, (size_t *)&ndp->ni_pathlen);
191 else
192 error = copyinstr(ndp->ni_dirp, cnp->cn_pnbuf,
193 MAXPATHLEN, (size_t *)&ndp->ni_pathlen);
194
195 /*
196 * Don't allow empty pathnames.
197 */
198 if (error == 0 && *cnp->cn_pnbuf == '\0')
199 error = ENOENT;
200
201 #ifdef CAPABILITY_MODE
202 /*
203 * In capability mode, lookups must be "strictly relative" (i.e.
204 * not an absolute path, and not containing '..' components) to
205 * a real file descriptor, not the pseudo-descriptor AT_FDCWD.
206 */
207 if (error == 0 && IN_CAPABILITY_MODE(td) &&
208 (cnp->cn_flags & NOCAPCHECK) == 0) {
209 ndp->ni_strictrelative = 1;
210 if (ndp->ni_dirfd == AT_FDCWD) {
211 #ifdef KTRACE
212 if (KTRPOINT(td, KTR_CAPFAIL))
213 ktrcapfail(CAPFAIL_LOOKUP, NULL, NULL);
214 #endif
215 error = ECAPMODE;
216 }
217 }
218 #endif
219 if (error != 0) {
220 namei_cleanup_cnp(cnp);
221 ndp->ni_vp = NULL;
222 return (error);
223 }
224 ndp->ni_loopcnt = 0;
225 #ifdef KTRACE
226 if (KTRPOINT(td, KTR_NAMEI)) {
227 KASSERT(cnp->cn_thread == curthread,
228 ("namei not using curthread"));
229 ktrnamei(cnp->cn_pnbuf);
230 }
231 #endif
232 /*
233 * Get starting point for the translation.
234 */
235 FILEDESC_SLOCK(fdp);
236 ndp->ni_rootdir = fdp->fd_rdir;
237 VREF(ndp->ni_rootdir);
238 ndp->ni_topdir = fdp->fd_jdir;
239
240 /*
241 * If we are auditing the kernel pathname, save the user pathname.
242 */
243 if (cnp->cn_flags & AUDITVNODE1)
244 AUDIT_ARG_UPATH1(td, ndp->ni_dirfd, cnp->cn_pnbuf);
245 if (cnp->cn_flags & AUDITVNODE2)
246 AUDIT_ARG_UPATH2(td, ndp->ni_dirfd, cnp->cn_pnbuf);
247
248 startdir_used = 0;
249 dp = NULL;
250 cnp->cn_nameptr = cnp->cn_pnbuf;
251 if (cnp->cn_pnbuf[0] == '/') {
252 error = namei_handle_root(ndp, &dp);
253 } else {
254 if (ndp->ni_startdir != NULL) {
255 dp = ndp->ni_startdir;
256 startdir_used = 1;
257 } else if (ndp->ni_dirfd == AT_FDCWD) {
258 dp = fdp->fd_cdir;
259 VREF(dp);
260 } else {
261 cap_rights_t rights;
262
263 rights = ndp->ni_rightsneeded;
264 cap_rights_set(&rights, CAP_LOOKUP);
265
266 if (cnp->cn_flags & AUDITVNODE1)
267 AUDIT_ARG_ATFD1(ndp->ni_dirfd);
268 if (cnp->cn_flags & AUDITVNODE2)
269 AUDIT_ARG_ATFD2(ndp->ni_dirfd);
270 error = fgetvp_rights(td, ndp->ni_dirfd,
271 &rights, &ndp->ni_filecaps, &dp);
272 if (error == EINVAL)
273 error = ENOTDIR;
274 #ifdef CAPABILITIES
275 /*
276 * If file descriptor doesn't have all rights,
277 * all lookups relative to it must also be
278 * strictly relative.
279 */
280 CAP_ALL(&rights);
281 if (!cap_rights_contains(&ndp->ni_filecaps.fc_rights,
282 &rights) ||
283 ndp->ni_filecaps.fc_fcntls != CAP_FCNTL_ALL ||
284 ndp->ni_filecaps.fc_nioctls != -1) {
285 ndp->ni_strictrelative = 1;
286 }
287 #endif
288 }
289 if (error == 0 && dp->v_type != VDIR)
290 error = ENOTDIR;
291 }
292 FILEDESC_SUNLOCK(fdp);
293 if (ndp->ni_startdir != NULL && !startdir_used)
294 vrele(ndp->ni_startdir);
295 if (error != 0) {
296 if (dp != NULL)
297 vrele(dp);
298 vrele(ndp->ni_rootdir);
299 namei_cleanup_cnp(cnp);
300 return (error);
301 }
302 SDT_PROBE3(vfs, namei, lookup, entry, dp, cnp->cn_pnbuf,
303 cnp->cn_flags);
304 for (;;) {
305 ndp->ni_startdir = dp;
306 error = lookup(ndp);
307 if (error != 0) {
308 vrele(ndp->ni_rootdir);
309 namei_cleanup_cnp(cnp);
310 SDT_PROBE2(vfs, namei, lookup, return, error, NULL);
311 return (error);
312 }
313 /*
314 * If not a symbolic link, we're done.
315 */
316 if ((cnp->cn_flags & ISSYMLINK) == 0) {
317 vrele(ndp->ni_rootdir);
318 if ((cnp->cn_flags & (SAVENAME | SAVESTART)) == 0) {
319 namei_cleanup_cnp(cnp);
320 } else
321 cnp->cn_flags |= HASBUF;
322
323 SDT_PROBE2(vfs, namei, lookup, return, 0, ndp->ni_vp);
324 return (0);
325 }
326 if (ndp->ni_loopcnt++ >= MAXSYMLINKS) {
327 error = ELOOP;
328 break;
329 }
330 #ifdef MAC
331 if ((cnp->cn_flags & NOMACCHECK) == 0) {
332 error = mac_vnode_check_readlink(td->td_ucred,
333 ndp->ni_vp);
334 if (error != 0)
335 break;
336 }
337 #endif
338 if (ndp->ni_pathlen > 1)
339 cp = uma_zalloc(namei_zone, M_WAITOK);
340 else
341 cp = cnp->cn_pnbuf;
342 aiov.iov_base = cp;
343 aiov.iov_len = MAXPATHLEN;
344 auio.uio_iov = &aiov;
345 auio.uio_iovcnt = 1;
346 auio.uio_offset = 0;
347 auio.uio_rw = UIO_READ;
348 auio.uio_segflg = UIO_SYSSPACE;
349 auio.uio_td = td;
350 auio.uio_resid = MAXPATHLEN;
351 error = VOP_READLINK(ndp->ni_vp, &auio, cnp->cn_cred);
352 if (error != 0) {
353 if (ndp->ni_pathlen > 1)
354 uma_zfree(namei_zone, cp);
355 break;
356 }
357 linklen = MAXPATHLEN - auio.uio_resid;
358 if (linklen == 0) {
359 if (ndp->ni_pathlen > 1)
360 uma_zfree(namei_zone, cp);
361 error = ENOENT;
362 break;
363 }
364 if (linklen + ndp->ni_pathlen >= MAXPATHLEN) {
365 if (ndp->ni_pathlen > 1)
366 uma_zfree(namei_zone, cp);
367 error = ENAMETOOLONG;
368 break;
369 }
370 if (ndp->ni_pathlen > 1) {
371 bcopy(ndp->ni_next, cp + linklen, ndp->ni_pathlen);
372 uma_zfree(namei_zone, cnp->cn_pnbuf);
373 cnp->cn_pnbuf = cp;
374 } else
375 cnp->cn_pnbuf[linklen] = '\0';
376 ndp->ni_pathlen += linklen;
377 vput(ndp->ni_vp);
378 dp = ndp->ni_dvp;
379 /*
380 * Check if root directory should replace current directory.
381 */
382 cnp->cn_nameptr = cnp->cn_pnbuf;
383 if (*(cnp->cn_nameptr) == '/') {
384 vrele(dp);
385 error = namei_handle_root(ndp, &dp);
386 if (error != 0) {
387 vrele(ndp->ni_rootdir);
388 namei_cleanup_cnp(cnp);
389 return (error);
390 }
391 }
392 }
393 vrele(ndp->ni_rootdir);
394 namei_cleanup_cnp(cnp);
395 vput(ndp->ni_vp);
396 ndp->ni_vp = NULL;
397 vrele(ndp->ni_dvp);
398 SDT_PROBE2(vfs, namei, lookup, return, error, NULL);
399 return (error);
400 }
401
402 static int
compute_cn_lkflags(struct mount * mp,int lkflags,int cnflags)403 compute_cn_lkflags(struct mount *mp, int lkflags, int cnflags)
404 {
405
406 if (mp == NULL || ((lkflags & LK_SHARED) &&
407 (!(mp->mnt_kern_flag & MNTK_LOOKUP_SHARED) ||
408 ((cnflags & ISDOTDOT) &&
409 (mp->mnt_kern_flag & MNTK_LOOKUP_EXCL_DOTDOT))))) {
410 lkflags &= ~LK_SHARED;
411 lkflags |= LK_EXCLUSIVE;
412 }
413 lkflags |= LK_NODDLKTREAT;
414 return (lkflags);
415 }
416
417 static __inline int
needs_exclusive_leaf(struct mount * mp,int flags)418 needs_exclusive_leaf(struct mount *mp, int flags)
419 {
420
421 /*
422 * Intermediate nodes can use shared locks, we only need to
423 * force an exclusive lock for leaf nodes.
424 */
425 if ((flags & (ISLASTCN | LOCKLEAF)) != (ISLASTCN | LOCKLEAF))
426 return (0);
427
428 /* Always use exclusive locks if LOCKSHARED isn't set. */
429 if (!(flags & LOCKSHARED))
430 return (1);
431
432 /*
433 * For lookups during open(), if the mount point supports
434 * extended shared operations, then use a shared lock for the
435 * leaf node, otherwise use an exclusive lock.
436 */
437 if ((flags & ISOPEN) != 0)
438 return (!MNT_EXTENDED_SHARED(mp));
439
440 /*
441 * Lookup requests outside of open() that specify LOCKSHARED
442 * only need a shared lock on the leaf vnode.
443 */
444 return (0);
445 }
446
447 /*
448 * Search a pathname.
449 * This is a very central and rather complicated routine.
450 *
451 * The pathname is pointed to by ni_ptr and is of length ni_pathlen.
452 * The starting directory is taken from ni_startdir. The pathname is
453 * descended until done, or a symbolic link is encountered. The variable
454 * ni_more is clear if the path is completed; it is set to one if a
455 * symbolic link needing interpretation is encountered.
456 *
457 * The flag argument is LOOKUP, CREATE, RENAME, or DELETE depending on
458 * whether the name is to be looked up, created, renamed, or deleted.
459 * When CREATE, RENAME, or DELETE is specified, information usable in
460 * creating, renaming, or deleting a directory entry may be calculated.
461 * If flag has LOCKPARENT or'ed into it, the parent directory is returned
462 * locked. If flag has WANTPARENT or'ed into it, the parent directory is
463 * returned unlocked. Otherwise the parent directory is not returned. If
464 * the target of the pathname exists and LOCKLEAF is or'ed into the flag
465 * the target is returned locked, otherwise it is returned unlocked.
466 * When creating or renaming and LOCKPARENT is specified, the target may not
467 * be ".". When deleting and LOCKPARENT is specified, the target may be ".".
468 *
469 * Overall outline of lookup:
470 *
471 * dirloop:
472 * identify next component of name at ndp->ni_ptr
473 * handle degenerate case where name is null string
474 * if .. and crossing mount points and on mounted filesys, find parent
475 * call VOP_LOOKUP routine for next component name
476 * directory vnode returned in ni_dvp, unlocked unless LOCKPARENT set
477 * component vnode returned in ni_vp (if it exists), locked.
478 * if result vnode is mounted on and crossing mount points,
479 * find mounted on vnode
480 * if more components of name, do next level at dirloop
481 * return the answer in ni_vp, locked if LOCKLEAF set
482 * if LOCKPARENT set, return locked parent in ni_dvp
483 * if WANTPARENT set, return unlocked parent in ni_dvp
484 */
485 int
lookup(struct nameidata * ndp)486 lookup(struct nameidata *ndp)
487 {
488 char *cp; /* pointer into pathname argument */
489 struct vnode *dp = 0; /* the directory we are searching */
490 struct vnode *tdp; /* saved dp */
491 struct mount *mp; /* mount table entry */
492 struct prison *pr;
493 int docache; /* == 0 do not cache last component */
494 int wantparent; /* 1 => wantparent or lockparent flag */
495 int rdonly; /* lookup read-only flag bit */
496 int error = 0;
497 int dpunlocked = 0; /* dp has already been unlocked */
498 struct componentname *cnp = &ndp->ni_cnd;
499 int lkflags_save;
500 int ni_dvp_unlocked;
501
502 /*
503 * Setup: break out flag bits into variables.
504 */
505 ni_dvp_unlocked = 0;
506 wantparent = cnp->cn_flags & (LOCKPARENT | WANTPARENT);
507 KASSERT(cnp->cn_nameiop == LOOKUP || wantparent,
508 ("CREATE, DELETE, RENAME require LOCKPARENT or WANTPARENT."));
509 docache = (cnp->cn_flags & NOCACHE) ^ NOCACHE;
510 if (cnp->cn_nameiop == DELETE ||
511 (wantparent && cnp->cn_nameiop != CREATE &&
512 cnp->cn_nameiop != LOOKUP))
513 docache = 0;
514 rdonly = cnp->cn_flags & RDONLY;
515 cnp->cn_flags &= ~ISSYMLINK;
516 ndp->ni_dvp = NULL;
517 /*
518 * We use shared locks until we hit the parent of the last cn then
519 * we adjust based on the requesting flags.
520 */
521 if (lookup_shared)
522 cnp->cn_lkflags = LK_SHARED;
523 else
524 cnp->cn_lkflags = LK_EXCLUSIVE;
525 dp = ndp->ni_startdir;
526 ndp->ni_startdir = NULLVP;
527 vn_lock(dp,
528 compute_cn_lkflags(dp->v_mount, cnp->cn_lkflags | LK_RETRY,
529 cnp->cn_flags));
530
531 dirloop:
532 /*
533 * Search a new directory.
534 *
535 * The last component of the filename is left accessible via
536 * cnp->cn_nameptr for callers that need the name. Callers needing
537 * the name set the SAVENAME flag. When done, they assume
538 * responsibility for freeing the pathname buffer.
539 */
540 cnp->cn_consume = 0;
541 for (cp = cnp->cn_nameptr; *cp != 0 && *cp != '/'; cp++)
542 continue;
543 cnp->cn_namelen = cp - cnp->cn_nameptr;
544 if (cnp->cn_namelen > NAME_MAX) {
545 error = ENAMETOOLONG;
546 goto bad;
547 }
548 #ifdef NAMEI_DIAGNOSTIC
549 { char c = *cp;
550 *cp = '\0';
551 printf("{%s}: ", cnp->cn_nameptr);
552 *cp = c; }
553 #endif
554 ndp->ni_pathlen -= cnp->cn_namelen;
555 ndp->ni_next = cp;
556
557 /*
558 * Replace multiple slashes by a single slash and trailing slashes
559 * by a null. This must be done before VOP_LOOKUP() because some
560 * fs's don't know about trailing slashes. Remember if there were
561 * trailing slashes to handle symlinks, existing non-directories
562 * and non-existing files that won't be directories specially later.
563 */
564 while (*cp == '/' && (cp[1] == '/' || cp[1] == '\0')) {
565 cp++;
566 ndp->ni_pathlen--;
567 if (*cp == '\0') {
568 *ndp->ni_next = '\0';
569 cnp->cn_flags |= TRAILINGSLASH;
570 }
571 }
572 ndp->ni_next = cp;
573
574 cnp->cn_flags |= MAKEENTRY;
575 if (*cp == '\0' && docache == 0)
576 cnp->cn_flags &= ~MAKEENTRY;
577 if (cnp->cn_namelen == 2 &&
578 cnp->cn_nameptr[1] == '.' && cnp->cn_nameptr[0] == '.')
579 cnp->cn_flags |= ISDOTDOT;
580 else
581 cnp->cn_flags &= ~ISDOTDOT;
582 if (*ndp->ni_next == 0)
583 cnp->cn_flags |= ISLASTCN;
584 else
585 cnp->cn_flags &= ~ISLASTCN;
586
587 if ((cnp->cn_flags & ISLASTCN) != 0 &&
588 cnp->cn_namelen == 1 && cnp->cn_nameptr[0] == '.' &&
589 (cnp->cn_nameiop == DELETE || cnp->cn_nameiop == RENAME)) {
590 error = EINVAL;
591 goto bad;
592 }
593
594 /*
595 * Check for degenerate name (e.g. / or "")
596 * which is a way of talking about a directory,
597 * e.g. like "/." or ".".
598 */
599 if (cnp->cn_nameptr[0] == '\0') {
600 if (dp->v_type != VDIR) {
601 error = ENOTDIR;
602 goto bad;
603 }
604 if (cnp->cn_nameiop != LOOKUP) {
605 error = EISDIR;
606 goto bad;
607 }
608 if (wantparent) {
609 ndp->ni_dvp = dp;
610 VREF(dp);
611 }
612 ndp->ni_vp = dp;
613
614 if (cnp->cn_flags & AUDITVNODE1)
615 AUDIT_ARG_VNODE1(dp);
616 else if (cnp->cn_flags & AUDITVNODE2)
617 AUDIT_ARG_VNODE2(dp);
618
619 if (!(cnp->cn_flags & (LOCKPARENT | LOCKLEAF)))
620 VOP_UNLOCK(dp, 0);
621 /* XXX This should probably move to the top of function. */
622 if (cnp->cn_flags & SAVESTART)
623 panic("lookup: SAVESTART");
624 goto success;
625 }
626
627 /*
628 * Handle "..": five special cases.
629 * 0. If doing a capability lookup, return ENOTCAPABLE (this is a
630 * fairly conservative design choice, but it's the only one that we
631 * are satisfied guarantees the property we're looking for).
632 * 1. Return an error if this is the last component of
633 * the name and the operation is DELETE or RENAME.
634 * 2. If at root directory (e.g. after chroot)
635 * or at absolute root directory
636 * then ignore it so can't get out.
637 * 3. If this vnode is the root of a mounted
638 * filesystem, then replace it with the
639 * vnode which was mounted on so we take the
640 * .. in the other filesystem.
641 * 4. If the vnode is the top directory of
642 * the jail or chroot, don't let them out.
643 */
644 if (cnp->cn_flags & ISDOTDOT) {
645 if (ndp->ni_strictrelative != 0) {
646 #ifdef KTRACE
647 if (KTRPOINT(curthread, KTR_CAPFAIL))
648 ktrcapfail(CAPFAIL_LOOKUP, NULL, NULL);
649 #endif
650 error = ENOTCAPABLE;
651 goto bad;
652 }
653 if ((cnp->cn_flags & ISLASTCN) != 0 &&
654 (cnp->cn_nameiop == DELETE || cnp->cn_nameiop == RENAME)) {
655 error = EINVAL;
656 goto bad;
657 }
658 for (;;) {
659 for (pr = cnp->cn_cred->cr_prison; pr != NULL;
660 pr = pr->pr_parent)
661 if (dp == pr->pr_root)
662 break;
663 if (dp == ndp->ni_rootdir ||
664 dp == ndp->ni_topdir ||
665 dp == rootvnode ||
666 pr != NULL ||
667 ((dp->v_vflag & VV_ROOT) != 0 &&
668 (cnp->cn_flags & NOCROSSMOUNT) != 0)) {
669 ndp->ni_dvp = dp;
670 ndp->ni_vp = dp;
671 VREF(dp);
672 goto nextname;
673 }
674 if ((dp->v_vflag & VV_ROOT) == 0)
675 break;
676 if (dp->v_iflag & VI_DOOMED) { /* forced unmount */
677 error = ENOENT;
678 goto bad;
679 }
680 tdp = dp;
681 dp = dp->v_mount->mnt_vnodecovered;
682 VREF(dp);
683 vput(tdp);
684 vn_lock(dp,
685 compute_cn_lkflags(dp->v_mount, cnp->cn_lkflags |
686 LK_RETRY, ISDOTDOT));
687 }
688 }
689
690 /*
691 * We now have a segment name to search for, and a directory to search.
692 */
693 unionlookup:
694 #ifdef MAC
695 if ((cnp->cn_flags & NOMACCHECK) == 0) {
696 error = mac_vnode_check_lookup(cnp->cn_thread->td_ucred, dp,
697 cnp);
698 if (error)
699 goto bad;
700 }
701 #endif
702 ndp->ni_dvp = dp;
703 ndp->ni_vp = NULL;
704 ASSERT_VOP_LOCKED(dp, "lookup");
705 /*
706 * If we have a shared lock we may need to upgrade the lock for the
707 * last operation.
708 */
709 if (dp != vp_crossmp &&
710 VOP_ISLOCKED(dp) == LK_SHARED &&
711 (cnp->cn_flags & ISLASTCN) && (cnp->cn_flags & LOCKPARENT))
712 vn_lock(dp, LK_UPGRADE|LK_RETRY);
713 if ((dp->v_iflag & VI_DOOMED) != 0) {
714 error = ENOENT;
715 goto bad;
716 }
717 /*
718 * If we're looking up the last component and we need an exclusive
719 * lock, adjust our lkflags.
720 */
721 if (needs_exclusive_leaf(dp->v_mount, cnp->cn_flags))
722 cnp->cn_lkflags = LK_EXCLUSIVE;
723 #ifdef NAMEI_DIAGNOSTIC
724 vprint("lookup in", dp);
725 #endif
726 lkflags_save = cnp->cn_lkflags;
727 cnp->cn_lkflags = compute_cn_lkflags(dp->v_mount, cnp->cn_lkflags,
728 cnp->cn_flags);
729 if ((error = VOP_LOOKUP(dp, &ndp->ni_vp, cnp)) != 0) {
730 cnp->cn_lkflags = lkflags_save;
731 KASSERT(ndp->ni_vp == NULL, ("leaf should be empty"));
732 #ifdef NAMEI_DIAGNOSTIC
733 printf("not found\n");
734 #endif
735 if ((error == ENOENT) &&
736 (dp->v_vflag & VV_ROOT) && (dp->v_mount != NULL) &&
737 (dp->v_mount->mnt_flag & MNT_UNION)) {
738 tdp = dp;
739 dp = dp->v_mount->mnt_vnodecovered;
740 VREF(dp);
741 vput(tdp);
742 vn_lock(dp,
743 compute_cn_lkflags(dp->v_mount, cnp->cn_lkflags |
744 LK_RETRY, cnp->cn_flags));
745 goto unionlookup;
746 }
747
748 if (error != EJUSTRETURN)
749 goto bad;
750 /*
751 * At this point, we know we're at the end of the
752 * pathname. If creating / renaming, we can consider
753 * allowing the file or directory to be created / renamed,
754 * provided we're not on a read-only filesystem.
755 */
756 if (rdonly) {
757 error = EROFS;
758 goto bad;
759 }
760 /* trailing slash only allowed for directories */
761 if ((cnp->cn_flags & TRAILINGSLASH) &&
762 !(cnp->cn_flags & WILLBEDIR)) {
763 error = ENOENT;
764 goto bad;
765 }
766 if ((cnp->cn_flags & LOCKPARENT) == 0)
767 VOP_UNLOCK(dp, 0);
768 /*
769 * We return with ni_vp NULL to indicate that the entry
770 * doesn't currently exist, leaving a pointer to the
771 * (possibly locked) directory vnode in ndp->ni_dvp.
772 */
773 if (cnp->cn_flags & SAVESTART) {
774 ndp->ni_startdir = ndp->ni_dvp;
775 VREF(ndp->ni_startdir);
776 }
777 goto success;
778 } else
779 cnp->cn_lkflags = lkflags_save;
780 #ifdef NAMEI_DIAGNOSTIC
781 printf("found\n");
782 #endif
783 /*
784 * Take into account any additional components consumed by
785 * the underlying filesystem.
786 */
787 if (cnp->cn_consume > 0) {
788 cnp->cn_nameptr += cnp->cn_consume;
789 ndp->ni_next += cnp->cn_consume;
790 ndp->ni_pathlen -= cnp->cn_consume;
791 cnp->cn_consume = 0;
792 }
793
794 dp = ndp->ni_vp;
795
796 /*
797 * Check to see if the vnode has been mounted on;
798 * if so find the root of the mounted filesystem.
799 */
800 while (dp->v_type == VDIR && (mp = dp->v_mountedhere) &&
801 (cnp->cn_flags & NOCROSSMOUNT) == 0) {
802 if (vfs_busy(mp, 0))
803 continue;
804 vput(dp);
805 if (dp != ndp->ni_dvp)
806 vput(ndp->ni_dvp);
807 else
808 vrele(ndp->ni_dvp);
809 vref(vp_crossmp);
810 ndp->ni_dvp = vp_crossmp;
811 error = VFS_ROOT(mp, compute_cn_lkflags(mp, cnp->cn_lkflags,
812 cnp->cn_flags), &tdp);
813 vfs_unbusy(mp);
814 if (vn_lock(vp_crossmp, LK_SHARED | LK_NOWAIT))
815 panic("vp_crossmp exclusively locked or reclaimed");
816 if (error) {
817 dpunlocked = 1;
818 goto bad2;
819 }
820 ndp->ni_vp = dp = tdp;
821 }
822
823 /*
824 * Check for symbolic link
825 */
826 if ((dp->v_type == VLNK) &&
827 ((cnp->cn_flags & FOLLOW) || (cnp->cn_flags & TRAILINGSLASH) ||
828 *ndp->ni_next == '/')) {
829 cnp->cn_flags |= ISSYMLINK;
830 if (dp->v_iflag & VI_DOOMED) {
831 /*
832 * We can't know whether the directory was mounted with
833 * NOSYMFOLLOW, so we can't follow safely.
834 */
835 error = ENOENT;
836 goto bad2;
837 }
838 if (dp->v_mount->mnt_flag & MNT_NOSYMFOLLOW) {
839 error = EACCES;
840 goto bad2;
841 }
842 /*
843 * Symlink code always expects an unlocked dvp.
844 */
845 if (ndp->ni_dvp != ndp->ni_vp) {
846 VOP_UNLOCK(ndp->ni_dvp, 0);
847 ni_dvp_unlocked = 1;
848 }
849 goto success;
850 }
851
852 nextname:
853 /*
854 * Not a symbolic link that we will follow. Continue with the
855 * next component if there is any; otherwise, we're done.
856 */
857 KASSERT((cnp->cn_flags & ISLASTCN) || *ndp->ni_next == '/',
858 ("lookup: invalid path state."));
859 if (*ndp->ni_next == '/') {
860 cnp->cn_nameptr = ndp->ni_next;
861 while (*cnp->cn_nameptr == '/') {
862 cnp->cn_nameptr++;
863 ndp->ni_pathlen--;
864 }
865 if (ndp->ni_dvp != dp)
866 vput(ndp->ni_dvp);
867 else
868 vrele(ndp->ni_dvp);
869 goto dirloop;
870 }
871 /*
872 * If we're processing a path with a trailing slash,
873 * check that the end result is a directory.
874 */
875 if ((cnp->cn_flags & TRAILINGSLASH) && dp->v_type != VDIR) {
876 error = ENOTDIR;
877 goto bad2;
878 }
879 /*
880 * Disallow directory write attempts on read-only filesystems.
881 */
882 if (rdonly &&
883 (cnp->cn_nameiop == DELETE || cnp->cn_nameiop == RENAME)) {
884 error = EROFS;
885 goto bad2;
886 }
887 if (cnp->cn_flags & SAVESTART) {
888 ndp->ni_startdir = ndp->ni_dvp;
889 VREF(ndp->ni_startdir);
890 }
891 if (!wantparent) {
892 ni_dvp_unlocked = 2;
893 if (ndp->ni_dvp != dp)
894 vput(ndp->ni_dvp);
895 else
896 vrele(ndp->ni_dvp);
897 } else if ((cnp->cn_flags & LOCKPARENT) == 0 && ndp->ni_dvp != dp) {
898 VOP_UNLOCK(ndp->ni_dvp, 0);
899 ni_dvp_unlocked = 1;
900 }
901
902 if (cnp->cn_flags & AUDITVNODE1)
903 AUDIT_ARG_VNODE1(dp);
904 else if (cnp->cn_flags & AUDITVNODE2)
905 AUDIT_ARG_VNODE2(dp);
906
907 if ((cnp->cn_flags & LOCKLEAF) == 0)
908 VOP_UNLOCK(dp, 0);
909 success:
910 /*
911 * Because of lookup_shared we may have the vnode shared locked, but
912 * the caller may want it to be exclusively locked.
913 */
914 if (needs_exclusive_leaf(dp->v_mount, cnp->cn_flags) &&
915 VOP_ISLOCKED(dp) != LK_EXCLUSIVE) {
916 vn_lock(dp, LK_UPGRADE | LK_RETRY);
917 if (dp->v_iflag & VI_DOOMED) {
918 error = ENOENT;
919 goto bad2;
920 }
921 }
922 return (0);
923
924 bad2:
925 if (ni_dvp_unlocked != 2) {
926 if (dp != ndp->ni_dvp && !ni_dvp_unlocked)
927 vput(ndp->ni_dvp);
928 else
929 vrele(ndp->ni_dvp);
930 }
931 bad:
932 if (!dpunlocked)
933 vput(dp);
934 ndp->ni_vp = NULL;
935 return (error);
936 }
937
938 /*
939 * relookup - lookup a path name component
940 * Used by lookup to re-acquire things.
941 */
942 int
relookup(struct vnode * dvp,struct vnode ** vpp,struct componentname * cnp)943 relookup(struct vnode *dvp, struct vnode **vpp, struct componentname *cnp)
944 {
945 struct vnode *dp = 0; /* the directory we are searching */
946 int wantparent; /* 1 => wantparent or lockparent flag */
947 int rdonly; /* lookup read-only flag bit */
948 int error = 0;
949
950 KASSERT(cnp->cn_flags & ISLASTCN,
951 ("relookup: Not given last component."));
952 /*
953 * Setup: break out flag bits into variables.
954 */
955 wantparent = cnp->cn_flags & (LOCKPARENT|WANTPARENT);
956 KASSERT(wantparent, ("relookup: parent not wanted."));
957 rdonly = cnp->cn_flags & RDONLY;
958 cnp->cn_flags &= ~ISSYMLINK;
959 dp = dvp;
960 cnp->cn_lkflags = LK_EXCLUSIVE;
961 vn_lock(dp, LK_EXCLUSIVE | LK_RETRY);
962
963 /*
964 * Search a new directory.
965 *
966 * The last component of the filename is left accessible via
967 * cnp->cn_nameptr for callers that need the name. Callers needing
968 * the name set the SAVENAME flag. When done, they assume
969 * responsibility for freeing the pathname buffer.
970 */
971 #ifdef NAMEI_DIAGNOSTIC
972 printf("{%s}: ", cnp->cn_nameptr);
973 #endif
974
975 /*
976 * Check for "" which represents the root directory after slash
977 * removal.
978 */
979 if (cnp->cn_nameptr[0] == '\0') {
980 /*
981 * Support only LOOKUP for "/" because lookup()
982 * can't succeed for CREATE, DELETE and RENAME.
983 */
984 KASSERT(cnp->cn_nameiop == LOOKUP, ("nameiop must be LOOKUP"));
985 KASSERT(dp->v_type == VDIR, ("dp is not a directory"));
986
987 if (!(cnp->cn_flags & LOCKLEAF))
988 VOP_UNLOCK(dp, 0);
989 *vpp = dp;
990 /* XXX This should probably move to the top of function. */
991 if (cnp->cn_flags & SAVESTART)
992 panic("lookup: SAVESTART");
993 return (0);
994 }
995
996 if (cnp->cn_flags & ISDOTDOT)
997 panic ("relookup: lookup on dot-dot");
998
999 /*
1000 * We now have a segment name to search for, and a directory to search.
1001 */
1002 #ifdef NAMEI_DIAGNOSTIC
1003 vprint("search in:", dp);
1004 #endif
1005 if ((error = VOP_LOOKUP(dp, vpp, cnp)) != 0) {
1006 KASSERT(*vpp == NULL, ("leaf should be empty"));
1007 if (error != EJUSTRETURN)
1008 goto bad;
1009 /*
1010 * If creating and at end of pathname, then can consider
1011 * allowing file to be created.
1012 */
1013 if (rdonly) {
1014 error = EROFS;
1015 goto bad;
1016 }
1017 /* ASSERT(dvp == ndp->ni_startdir) */
1018 if (cnp->cn_flags & SAVESTART)
1019 VREF(dvp);
1020 if ((cnp->cn_flags & LOCKPARENT) == 0)
1021 VOP_UNLOCK(dp, 0);
1022 /*
1023 * We return with ni_vp NULL to indicate that the entry
1024 * doesn't currently exist, leaving a pointer to the
1025 * (possibly locked) directory vnode in ndp->ni_dvp.
1026 */
1027 return (0);
1028 }
1029
1030 dp = *vpp;
1031
1032 /*
1033 * Disallow directory write attempts on read-only filesystems.
1034 */
1035 if (rdonly &&
1036 (cnp->cn_nameiop == DELETE || cnp->cn_nameiop == RENAME)) {
1037 if (dvp == dp)
1038 vrele(dvp);
1039 else
1040 vput(dvp);
1041 error = EROFS;
1042 goto bad;
1043 }
1044 /*
1045 * Set the parent lock/ref state to the requested state.
1046 */
1047 if ((cnp->cn_flags & LOCKPARENT) == 0 && dvp != dp) {
1048 if (wantparent)
1049 VOP_UNLOCK(dvp, 0);
1050 else
1051 vput(dvp);
1052 } else if (!wantparent)
1053 vrele(dvp);
1054 /*
1055 * Check for symbolic link
1056 */
1057 KASSERT(dp->v_type != VLNK || !(cnp->cn_flags & FOLLOW),
1058 ("relookup: symlink found.\n"));
1059
1060 /* ASSERT(dvp == ndp->ni_startdir) */
1061 if (cnp->cn_flags & SAVESTART)
1062 VREF(dvp);
1063
1064 if ((cnp->cn_flags & LOCKLEAF) == 0)
1065 VOP_UNLOCK(dp, 0);
1066 return (0);
1067 bad:
1068 vput(dp);
1069 *vpp = NULL;
1070 return (error);
1071 }
1072
1073 void
NDINIT_ALL(struct nameidata * ndp,u_long op,u_long flags,enum uio_seg segflg,const char * namep,int dirfd,struct vnode * startdir,cap_rights_t * rightsp,struct thread * td)1074 NDINIT_ALL(struct nameidata *ndp, u_long op, u_long flags, enum uio_seg segflg,
1075 const char *namep, int dirfd, struct vnode *startdir, cap_rights_t *rightsp,
1076 struct thread *td)
1077 {
1078
1079 ndp->ni_cnd.cn_nameiop = op;
1080 ndp->ni_cnd.cn_flags = flags;
1081 ndp->ni_segflg = segflg;
1082 ndp->ni_dirp = namep;
1083 ndp->ni_dirfd = dirfd;
1084 ndp->ni_startdir = startdir;
1085 ndp->ni_strictrelative = 0;
1086 if (rightsp != NULL)
1087 ndp->ni_rightsneeded = *rightsp;
1088 else
1089 cap_rights_init(&ndp->ni_rightsneeded);
1090 filecaps_init(&ndp->ni_filecaps);
1091 ndp->ni_cnd.cn_thread = td;
1092 }
1093
1094 /*
1095 * Free data allocated by namei(); see namei(9) for details.
1096 */
1097 void
NDFREE(struct nameidata * ndp,const u_int flags)1098 NDFREE(struct nameidata *ndp, const u_int flags)
1099 {
1100 int unlock_dvp;
1101 int unlock_vp;
1102
1103 unlock_dvp = 0;
1104 unlock_vp = 0;
1105
1106 if (!(flags & NDF_NO_FREE_PNBUF) &&
1107 (ndp->ni_cnd.cn_flags & HASBUF)) {
1108 uma_zfree(namei_zone, ndp->ni_cnd.cn_pnbuf);
1109 ndp->ni_cnd.cn_flags &= ~HASBUF;
1110 }
1111 if (!(flags & NDF_NO_VP_UNLOCK) &&
1112 (ndp->ni_cnd.cn_flags & LOCKLEAF) && ndp->ni_vp)
1113 unlock_vp = 1;
1114 if (!(flags & NDF_NO_VP_RELE) && ndp->ni_vp) {
1115 if (unlock_vp) {
1116 vput(ndp->ni_vp);
1117 unlock_vp = 0;
1118 } else
1119 vrele(ndp->ni_vp);
1120 ndp->ni_vp = NULL;
1121 }
1122 if (unlock_vp)
1123 VOP_UNLOCK(ndp->ni_vp, 0);
1124 if (!(flags & NDF_NO_DVP_UNLOCK) &&
1125 (ndp->ni_cnd.cn_flags & LOCKPARENT) &&
1126 ndp->ni_dvp != ndp->ni_vp)
1127 unlock_dvp = 1;
1128 if (!(flags & NDF_NO_DVP_RELE) &&
1129 (ndp->ni_cnd.cn_flags & (LOCKPARENT|WANTPARENT))) {
1130 if (unlock_dvp) {
1131 vput(ndp->ni_dvp);
1132 unlock_dvp = 0;
1133 } else
1134 vrele(ndp->ni_dvp);
1135 ndp->ni_dvp = NULL;
1136 }
1137 if (unlock_dvp)
1138 VOP_UNLOCK(ndp->ni_dvp, 0);
1139 if (!(flags & NDF_NO_STARTDIR_RELE) &&
1140 (ndp->ni_cnd.cn_flags & SAVESTART)) {
1141 vrele(ndp->ni_startdir);
1142 ndp->ni_startdir = NULL;
1143 }
1144 }
1145
1146 /*
1147 * Determine if there is a suitable alternate filename under the specified
1148 * prefix for the specified path. If the create flag is set, then the
1149 * alternate prefix will be used so long as the parent directory exists.
1150 * This is used by the various compatiblity ABIs so that Linux binaries prefer
1151 * files under /compat/linux for example. The chosen path (whether under
1152 * the prefix or under /) is returned in a kernel malloc'd buffer pointed
1153 * to by pathbuf. The caller is responsible for free'ing the buffer from
1154 * the M_TEMP bucket if one is returned.
1155 */
1156 int
kern_alternate_path(struct thread * td,const char * prefix,const char * path,enum uio_seg pathseg,char ** pathbuf,int create,int dirfd)1157 kern_alternate_path(struct thread *td, const char *prefix, const char *path,
1158 enum uio_seg pathseg, char **pathbuf, int create, int dirfd)
1159 {
1160 struct nameidata nd, ndroot;
1161 char *ptr, *buf, *cp;
1162 size_t len, sz;
1163 int error;
1164
1165 buf = (char *) malloc(MAXPATHLEN, M_TEMP, M_WAITOK);
1166 *pathbuf = buf;
1167
1168 /* Copy the prefix into the new pathname as a starting point. */
1169 len = strlcpy(buf, prefix, MAXPATHLEN);
1170 if (len >= MAXPATHLEN) {
1171 *pathbuf = NULL;
1172 free(buf, M_TEMP);
1173 return (EINVAL);
1174 }
1175 sz = MAXPATHLEN - len;
1176 ptr = buf + len;
1177
1178 /* Append the filename to the prefix. */
1179 if (pathseg == UIO_SYSSPACE)
1180 error = copystr(path, ptr, sz, &len);
1181 else
1182 error = copyinstr(path, ptr, sz, &len);
1183
1184 if (error) {
1185 *pathbuf = NULL;
1186 free(buf, M_TEMP);
1187 return (error);
1188 }
1189
1190 /* Only use a prefix with absolute pathnames. */
1191 if (*ptr != '/') {
1192 error = EINVAL;
1193 goto keeporig;
1194 }
1195
1196 if (dirfd != AT_FDCWD) {
1197 /*
1198 * We want the original because the "prefix" is
1199 * included in the already opened dirfd.
1200 */
1201 bcopy(ptr, buf, len);
1202 return (0);
1203 }
1204
1205 /*
1206 * We know that there is a / somewhere in this pathname.
1207 * Search backwards for it, to find the file's parent dir
1208 * to see if it exists in the alternate tree. If it does,
1209 * and we want to create a file (cflag is set). We don't
1210 * need to worry about the root comparison in this case.
1211 */
1212
1213 if (create) {
1214 for (cp = &ptr[len] - 1; *cp != '/'; cp--);
1215 *cp = '\0';
1216
1217 NDINIT(&nd, LOOKUP, FOLLOW, UIO_SYSSPACE, buf, td);
1218 error = namei(&nd);
1219 *cp = '/';
1220 if (error != 0)
1221 goto keeporig;
1222 } else {
1223 NDINIT(&nd, LOOKUP, FOLLOW, UIO_SYSSPACE, buf, td);
1224
1225 error = namei(&nd);
1226 if (error != 0)
1227 goto keeporig;
1228
1229 /*
1230 * We now compare the vnode of the prefix to the one
1231 * vnode asked. If they resolve to be the same, then we
1232 * ignore the match so that the real root gets used.
1233 * This avoids the problem of traversing "../.." to find the
1234 * root directory and never finding it, because "/" resolves
1235 * to the emulation root directory. This is expensive :-(
1236 */
1237 NDINIT(&ndroot, LOOKUP, FOLLOW, UIO_SYSSPACE, prefix,
1238 td);
1239
1240 /* We shouldn't ever get an error from this namei(). */
1241 error = namei(&ndroot);
1242 if (error == 0) {
1243 if (nd.ni_vp == ndroot.ni_vp)
1244 error = ENOENT;
1245
1246 NDFREE(&ndroot, NDF_ONLY_PNBUF);
1247 vrele(ndroot.ni_vp);
1248 }
1249 }
1250
1251 NDFREE(&nd, NDF_ONLY_PNBUF);
1252 vrele(nd.ni_vp);
1253
1254 keeporig:
1255 /* If there was an error, use the original path name. */
1256 if (error)
1257 bcopy(ptr, buf, len);
1258 return (error);
1259 }
1260