1 /* $NetBSD: vfs_getcwd.c,v 1.61 2021/06/29 22:39:21 dholland Exp $ */
2
3 /*-
4 * Copyright (c) 1999, 2020 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 __KERNEL_RCSID(0, "$NetBSD: vfs_getcwd.c,v 1.61 2021/06/29 22:39:21 dholland Exp $");
34
35 #include <sys/param.h>
36 #include <sys/systm.h>
37 #include <sys/namei.h>
38 #include <sys/filedesc.h>
39 #include <sys/kernel.h>
40 #include <sys/file.h>
41 #include <sys/stat.h>
42 #include <sys/vnode.h>
43 #include <sys/mount.h>
44 #include <sys/proc.h>
45 #include <sys/uio.h>
46 #include <sys/kmem.h>
47 #include <sys/dirent.h>
48 #include <sys/kauth.h>
49
50 #include <ufs/ufs/dir.h> /* XXX only for DIRBLKSIZ */
51
52 #include <sys/syscallargs.h>
53
54 /*
55 * Vnode variable naming conventions in this file:
56 *
57 * rvp: the current root we're aiming towards.
58 * lvp, *lvpp: the "lower" vnode
59 * uvp, *uvpp: the "upper" vnode.
60 *
61 * Since all the vnodes we're dealing with are directories, and the
62 * lookups are going *up* in the filesystem rather than *down*, the
63 * usual "pvp" (parent) or "dvp" (directory) naming conventions are
64 * too confusing.
65 */
66
67 /*
68 * XXX Will infinite loop in certain cases if a directory read reliably
69 * returns EINVAL on last block.
70 * XXX is EINVAL the right thing to return if a directory is malformed?
71 */
72
73 /*
74 * XXX Untested vs. mount -o union; probably does the wrong thing.
75 */
76
77 /*
78 * Find parent vnode of *lvpp, return in *uvpp
79 *
80 * If we care about the name, scan it looking for name of directory
81 * entry pointing at lvp.
82 *
83 * Place the name in the buffer which starts at bufp, immediately
84 * before *bpp, and move bpp backwards to point at the start of it.
85 *
86 * On entry, *lvpp is a locked vnode reference; on exit, it is vput and NULL'ed
87 * On exit, *uvpp is either NULL or is a locked vnode reference.
88 */
89 static int
getcwd_scandir(struct vnode * lvp,struct vnode ** uvpp,char ** bpp,char * bufp,struct lwp * l)90 getcwd_scandir(struct vnode *lvp, struct vnode **uvpp, char **bpp,
91 char *bufp, struct lwp *l)
92 {
93 int error = 0;
94 int eofflag;
95 off_t off;
96 int tries;
97 struct uio uio;
98 struct iovec iov;
99 char *dirbuf = NULL;
100 int dirbuflen;
101 ino_t fileno;
102 struct vattr va;
103 struct vnode *uvp = NULL;
104 kauth_cred_t cred = l->l_cred;
105 struct componentname cn;
106 int len, reclen;
107 tries = 0;
108
109 /* Need exclusive for UFS VOP_GETATTR (itimes) & VOP_LOOKUP. */
110 KASSERT(VOP_ISLOCKED(lvp) == LK_EXCLUSIVE);
111
112 /*
113 * If we want the filename, get some info we need while the
114 * current directory is still locked.
115 */
116 if (bufp != NULL) {
117 error = VOP_GETATTR(lvp, &va, cred);
118 if (error) {
119 VOP_UNLOCK(lvp);
120 *uvpp = NULL;
121 return error;
122 }
123 }
124
125 /*
126 * Ok, we have to do it the hard way..
127 * Next, get parent vnode using lookup of ..
128 */
129 cn.cn_nameiop = LOOKUP;
130 cn.cn_flags = ISLASTCN | ISDOTDOT | RDONLY;
131 cn.cn_cred = cred;
132 cn.cn_nameptr = "..";
133 cn.cn_namelen = 2;
134
135 /* At this point, lvp is locked */
136 error = VOP_LOOKUP(lvp, uvpp, &cn);
137 VOP_UNLOCK(lvp);
138 if (error) {
139 *uvpp = NULL;
140 return error;
141 }
142 uvp = *uvpp;
143 /* If we don't care about the pathname, we're done */
144 if (bufp == NULL) {
145 return 0;
146 }
147
148 fileno = va.va_fileid;
149
150 /* I guess UFS_DIRBLKSIZ is a good guess at a good size to use? */
151 dirbuflen = UFS_DIRBLKSIZ;
152 if (dirbuflen < va.va_blocksize)
153 dirbuflen = va.va_blocksize;
154 dirbuf = kmem_alloc(dirbuflen, KM_SLEEP);
155
156 /* Now lvp is unlocked, try to lock uvp */
157 error = vn_lock(uvp, LK_SHARED);
158 if (error) {
159 vrele(uvp);
160 *uvpp = NULL;
161 return error;
162 }
163
164 #if 0
165 unionread:
166 #endif
167 off = 0;
168 do {
169 /* call VOP_READDIR of parent */
170 iov.iov_base = dirbuf;
171 iov.iov_len = dirbuflen;
172
173 uio.uio_iov = &iov;
174 uio.uio_iovcnt = 1;
175 uio.uio_offset = off;
176 uio.uio_resid = dirbuflen;
177 uio.uio_rw = UIO_READ;
178 UIO_SETUP_SYSSPACE(&uio);
179
180 eofflag = 0;
181
182 error = VOP_READDIR(uvp, &uio, cred, &eofflag, 0, 0);
183
184 off = uio.uio_offset;
185
186 /*
187 * Try again if NFS tosses its cookies.
188 * XXX this can still loop forever if the directory is busted
189 * such that the second or subsequent page of it always
190 * returns EINVAL
191 */
192 if ((error == EINVAL) && (tries < 3)) {
193 off = 0;
194 tries++;
195 continue; /* once more, with feeling */
196 }
197
198 if (!error) {
199 char *cpos;
200 struct dirent *dp;
201
202 cpos = dirbuf;
203 tries = 0;
204
205 /* scan directory page looking for matching vnode */
206 for (len = (dirbuflen - uio.uio_resid); len > 0;
207 len -= reclen) {
208 dp = (struct dirent *) cpos;
209 reclen = dp->d_reclen;
210
211 /* check for malformed directory.. */
212 if (reclen < _DIRENT_MINSIZE(dp) ||
213 reclen > len) {
214 error = EINVAL;
215 goto out;
216 }
217 /*
218 * XXX should perhaps do VOP_LOOKUP to
219 * check that we got back to the right place,
220 * but getting the locking games for that
221 * right would be heinous.
222 */
223 if ((dp->d_type != DT_WHT) &&
224 (dp->d_fileno == fileno)) {
225 char *bp = *bpp;
226
227 bp -= dp->d_namlen;
228 if (bp <= bufp) {
229 error = ERANGE;
230 goto out;
231 }
232 memcpy(bp, dp->d_name, dp->d_namlen);
233 error = 0;
234 *bpp = bp;
235 goto out;
236 }
237 cpos += reclen;
238 }
239 } else
240 goto out;
241 } while (!eofflag);
242 #if 0
243 /*
244 * Deal with mount -o union, which unions only the
245 * root directory of the mount.
246 */
247 if ((uvp->v_vflag & VV_ROOT) &&
248 (uvp->v_mount->mnt_flag & MNT_UNION)) {
249 struct vnode *tvp = uvp;
250
251 uvp = uvp->v_mount->mnt_vnodecovered;
252 vput(tvp);
253 vref(uvp);
254 *uvpp = uvp;
255 vn_lock(uvp, LK_SHARED | LK_RETRY);
256 goto unionread;
257 }
258 #endif
259 error = ENOENT;
260
261 out:
262 VOP_UNLOCK(uvp);
263 kmem_free(dirbuf, dirbuflen);
264 return error;
265 }
266
267 /*
268 * common routine shared by sys___getcwd() and vn_isunder()
269 */
270 int
getcwd_common(struct vnode * lvp,struct vnode * rvp,char ** bpp,char * bufp,int limit,int flags,struct lwp * l)271 getcwd_common(struct vnode *lvp, struct vnode *rvp, char **bpp, char *bufp,
272 int limit, int flags, struct lwp *l)
273 {
274 struct cwdinfo *cwdi = l->l_proc->p_cwdi;
275 kauth_cred_t cred = l->l_cred;
276 struct vnode *uvp = NULL;
277 char *bp = NULL;
278 int error;
279 accmode_t accmode = VEXEC;
280
281 error = 0;
282 if (rvp == NULL) {
283 rvp = cwdi->cwdi_rdir;
284 if (rvp == NULL)
285 rvp = rootvnode;
286 }
287
288 vref(rvp);
289 vref(lvp);
290
291 /*
292 * Error handling invariant:
293 * Before a `goto out':
294 * lvp is either NULL, or held.
295 * uvp is either NULL, or held.
296 */
297
298 if (bufp)
299 bp = *bpp;
300
301 /*
302 * this loop will terminate when one of the following happens:
303 * - we hit the root
304 * - getdirentries or lookup fails
305 * - we run out of space in the buffer.
306 */
307 if (lvp == rvp) {
308 if (bp)
309 *(--bp) = '/';
310 goto out;
311 }
312 do {
313 /*
314 * access check here is optional, depending on
315 * whether or not caller cares.
316 */
317 int chkaccess = (flags & GETCWD_CHECK_ACCESS);
318 bool locked = false;
319
320 /*
321 * step up if we're a covered vnode..
322 * check access on the first vnode only.
323 */
324 if (lvp->v_vflag & VV_ROOT) {
325 vn_lock(lvp, LK_SHARED | LK_RETRY);
326 if (chkaccess) {
327 error = VOP_ACCESS(lvp, accmode, cred);
328 if (error) {
329 VOP_UNLOCK(lvp);
330 goto out;
331 }
332 chkaccess = 0;
333 }
334 while (lvp->v_vflag & VV_ROOT) {
335 struct vnode *tvp;
336
337 if (lvp == rvp) {
338 VOP_UNLOCK(lvp);
339 goto out;
340 }
341
342 tvp = lvp->v_mount->mnt_vnodecovered;
343 /*
344 * hodie natus est radici frater
345 */
346 if (tvp == NULL) {
347 VOP_UNLOCK(lvp);
348 error = ENOENT;
349 goto out;
350 }
351 vref(tvp);
352 vput(lvp);
353 lvp = tvp;
354 if (lvp->v_vflag & VV_ROOT)
355 vn_lock(lvp, LK_SHARED | LK_RETRY);
356 }
357 }
358
359 /* Do we need to check access to the directory? */
360 if (chkaccess && !cache_have_id(lvp)) {
361 /* Need exclusive for UFS VOP_GETATTR (itimes) & VOP_LOOKUP. */
362 vn_lock(lvp, LK_EXCLUSIVE | LK_RETRY);
363 error = VOP_ACCESS(lvp, accmode, cred);
364 if (error) {
365 VOP_UNLOCK(lvp);
366 goto out;
367 }
368 chkaccess = 0;
369 locked = true;
370 }
371
372 /*
373 * Look in the name cache; if that fails, look in the
374 * directory..
375 */
376 error = cache_revlookup(lvp, &uvp, &bp, bufp, chkaccess,
377 accmode);
378 if (error == -1) {
379 if (!locked) {
380 locked = true;
381 vn_lock(lvp, LK_EXCLUSIVE | LK_RETRY);
382 }
383 if (lvp->v_type != VDIR) {
384 VOP_UNLOCK(lvp);
385 error = ENOTDIR;
386 goto out;
387 }
388 error = getcwd_scandir(lvp, &uvp, &bp, bufp, l);
389 /* lvp now unlocked */
390 } else if (locked) {
391 VOP_UNLOCK(lvp);
392 }
393 if (error)
394 goto out;
395 #if DIAGNOSTIC
396 if (bufp && (bp <= bufp)) {
397 panic("getcwd: oops, went back too far");
398 }
399 #endif
400 accmode = VEXEC | VREAD;
401 if (bp)
402 *(--bp) = '/';
403 vrele(lvp);
404 lvp = uvp;
405 uvp = NULL;
406 limit--;
407 } while ((lvp != rvp) && (limit > 0));
408
409 out:
410 if (bpp)
411 *bpp = bp;
412 if (uvp)
413 vrele(uvp);
414 if (lvp)
415 vrele(lvp);
416 vrele(rvp);
417 return error;
418 }
419
420 /*
421 * Check if one directory can be found inside another in the directory
422 * hierarchy.
423 *
424 * Intended to be used in chroot, chdir, fchdir, etc., to ensure that
425 * chroot() actually means something.
426 */
427 int
vn_isunder(struct vnode * lvp,struct vnode * rvp,struct lwp * l)428 vn_isunder(struct vnode *lvp, struct vnode *rvp, struct lwp *l)
429 {
430 int error;
431
432 error = getcwd_common(lvp, rvp, NULL, NULL, MAXPATHLEN / 2, 0, l);
433
434 if (!error)
435 return 1;
436 else
437 return 0;
438 }
439
440 /*
441 * Returns true if proc p1's root directory equal to or under p2's
442 * root directory.
443 *
444 * Intended to be used from ptrace/procfs sorts of things.
445 */
446
447 int
proc_isunder(struct proc * p1,struct lwp * l2)448 proc_isunder(struct proc *p1, struct lwp *l2)
449 {
450 struct vnode *r1 = p1->p_cwdi->cwdi_rdir;
451 struct vnode *r2 = l2->l_proc->p_cwdi->cwdi_rdir;
452
453 if (r1 == NULL)
454 return (r2 == NULL);
455 else if (r2 == NULL)
456 return 1;
457 else
458 return vn_isunder(r1, r2, l2);
459 }
460
461 /*
462 * Find pathname of process's current directory.
463 *
464 * Use vfs vnode-to-name reverse cache; if that fails, fall back
465 * to reading directory contents.
466 */
467
468 int
sys___getcwd(struct lwp * l,const struct sys___getcwd_args * uap,register_t * retval)469 sys___getcwd(struct lwp *l, const struct sys___getcwd_args *uap, register_t *retval)
470 {
471 /* {
472 syscallarg(char *) bufp;
473 syscallarg(size_t) length;
474 } */
475
476 int error;
477 char *path;
478 char *bp, *bend;
479 int len = SCARG(uap, length);
480 int lenused;
481 struct cwdinfo *cwdi;
482
483 if (len > MAXPATHLEN * 4)
484 len = MAXPATHLEN * 4;
485 else if (len < 2)
486 return ERANGE;
487
488 path = kmem_alloc(len, KM_SLEEP);
489 bp = &path[len];
490 bend = bp;
491 *(--bp) = '\0';
492
493 /*
494 * 5th argument here is "max number of vnodes to traverse".
495 * Since each entry takes up at least 2 bytes in the output buffer,
496 * limit it to N/2 vnodes for an N byte buffer.
497 */
498 cwdi = l->l_proc->p_cwdi;
499 rw_enter(&cwdi->cwdi_lock, RW_READER);
500 error = getcwd_common(cwdi->cwdi_cdir, NULL, &bp, path,
501 len/2, GETCWD_CHECK_ACCESS, l);
502 rw_exit(&cwdi->cwdi_lock);
503
504 if (error)
505 goto out;
506 lenused = bend - bp;
507 *retval = lenused;
508 /* put the result into user buffer */
509 error = copyout(bp, SCARG(uap, bufp), lenused);
510
511 out:
512 kmem_free(path, len);
513 return error;
514 }
515
516 /*
517 * Try to find a pathname for a vnode. Since there is no mapping vnode ->
518 * parent directory, this needs the namecache to succeed. Caller holds a
519 * reference to the vnode.
520 */
521 int
vnode_to_path(char * path,size_t len,struct vnode * vp,struct lwp * curl,struct proc * p)522 vnode_to_path(char *path, size_t len, struct vnode *vp, struct lwp *curl,
523 struct proc *p)
524 {
525 struct proc *curp = curl->l_proc;
526 int error, lenused, elen;
527 char *bp, *bend;
528 struct vnode *dvp;
529
530 KASSERT(vrefcnt(vp) > 0);
531
532 bp = bend = &path[len];
533 *(--bp) = '\0';
534
535 error = cache_revlookup(vp, &dvp, &bp, path, false, 0);
536 if (error != 0)
537 return (error == -1 ? ENOENT : error);
538
539 *(--bp) = '/';
540 error = getcwd_common(dvp, NULL, &bp, path, len / 2,
541 GETCWD_CHECK_ACCESS, curl);
542 vrele(dvp);
543 if (error != 0)
544 return error;
545
546 /*
547 * Strip off emulation path for emulated processes looking at
548 * the maps file of a process of the same emulation. (Won't
549 * work if /emul/xxx is a symlink..)
550 */
551 if (curp->p_emul == p->p_emul && curp->p_emul->e_path != NULL) {
552 elen = strlen(curp->p_emul->e_path);
553 if (!strncmp(bp, curp->p_emul->e_path, elen))
554 bp = &bp[elen];
555 }
556
557 lenused = bend - bp;
558
559 memcpy(path, bp, lenused);
560 path[lenused] = '\0';
561
562 return 0;
563 }
564