vfs_getcwd.c revision 1.60
1 /* $NetBSD: vfs_getcwd.c,v 1.60 2020/05/16 18:31:50 christos 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 1.60 2020/05/16 18:31:50 christos 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 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 cn.cn_consume = 0; 135 136 /* At this point, lvp is locked */ 137 error = VOP_LOOKUP(lvp, uvpp, &cn); 138 VOP_UNLOCK(lvp); 139 if (error) { 140 *uvpp = NULL; 141 return error; 142 } 143 uvp = *uvpp; 144 /* If we don't care about the pathname, we're done */ 145 if (bufp == NULL) { 146 return 0; 147 } 148 149 fileno = va.va_fileid; 150 151 /* I guess UFS_DIRBLKSIZ is a good guess at a good size to use? */ 152 dirbuflen = UFS_DIRBLKSIZ; 153 if (dirbuflen < va.va_blocksize) 154 dirbuflen = va.va_blocksize; 155 dirbuf = kmem_alloc(dirbuflen, KM_SLEEP); 156 157 /* Now lvp is unlocked, try to lock uvp */ 158 error = vn_lock(uvp, LK_SHARED); 159 if (error) { 160 vrele(uvp); 161 *uvpp = NULL; 162 return error; 163 } 164 165 #if 0 166 unionread: 167 #endif 168 off = 0; 169 do { 170 /* call VOP_READDIR of parent */ 171 iov.iov_base = dirbuf; 172 iov.iov_len = dirbuflen; 173 174 uio.uio_iov = &iov; 175 uio.uio_iovcnt = 1; 176 uio.uio_offset = off; 177 uio.uio_resid = dirbuflen; 178 uio.uio_rw = UIO_READ; 179 UIO_SETUP_SYSSPACE(&uio); 180 181 eofflag = 0; 182 183 error = VOP_READDIR(uvp, &uio, cred, &eofflag, 0, 0); 184 185 off = uio.uio_offset; 186 187 /* 188 * Try again if NFS tosses its cookies. 189 * XXX this can still loop forever if the directory is busted 190 * such that the second or subsequent page of it always 191 * returns EINVAL 192 */ 193 if ((error == EINVAL) && (tries < 3)) { 194 off = 0; 195 tries++; 196 continue; /* once more, with feeling */ 197 } 198 199 if (!error) { 200 char *cpos; 201 struct dirent *dp; 202 203 cpos = dirbuf; 204 tries = 0; 205 206 /* scan directory page looking for matching vnode */ 207 for (len = (dirbuflen - uio.uio_resid); len > 0; 208 len -= reclen) { 209 dp = (struct dirent *) cpos; 210 reclen = dp->d_reclen; 211 212 /* check for malformed directory.. */ 213 if (reclen < _DIRENT_MINSIZE(dp) || 214 reclen > len) { 215 error = EINVAL; 216 goto out; 217 } 218 /* 219 * XXX should perhaps do VOP_LOOKUP to 220 * check that we got back to the right place, 221 * but getting the locking games for that 222 * right would be heinous. 223 */ 224 if ((dp->d_type != DT_WHT) && 225 (dp->d_fileno == fileno)) { 226 char *bp = *bpp; 227 228 bp -= dp->d_namlen; 229 if (bp <= bufp) { 230 error = ERANGE; 231 goto out; 232 } 233 memcpy(bp, dp->d_name, dp->d_namlen); 234 error = 0; 235 *bpp = bp; 236 goto out; 237 } 238 cpos += reclen; 239 } 240 } else 241 goto out; 242 } while (!eofflag); 243 #if 0 244 /* 245 * Deal with mount -o union, which unions only the 246 * root directory of the mount. 247 */ 248 if ((uvp->v_vflag & VV_ROOT) && 249 (uvp->v_mount->mnt_flag & MNT_UNION)) { 250 struct vnode *tvp = uvp; 251 252 uvp = uvp->v_mount->mnt_vnodecovered; 253 vput(tvp); 254 vref(uvp); 255 *uvpp = uvp; 256 vn_lock(uvp, LK_SHARED | LK_RETRY); 257 goto unionread; 258 } 259 #endif 260 error = ENOENT; 261 262 out: 263 VOP_UNLOCK(uvp); 264 kmem_free(dirbuf, dirbuflen); 265 return error; 266 } 267 268 /* 269 * common routine shared by sys___getcwd() and vn_isunder() 270 */ 271 int 272 getcwd_common(struct vnode *lvp, struct vnode *rvp, char **bpp, char *bufp, 273 int limit, int flags, struct lwp *l) 274 { 275 struct cwdinfo *cwdi = l->l_proc->p_cwdi; 276 kauth_cred_t cred = l->l_cred; 277 struct vnode *uvp = NULL; 278 char *bp = NULL; 279 int error; 280 accmode_t accmode = VEXEC; 281 282 error = 0; 283 if (rvp == NULL) { 284 rvp = cwdi->cwdi_rdir; 285 if (rvp == NULL) 286 rvp = rootvnode; 287 } 288 289 vref(rvp); 290 vref(lvp); 291 292 /* 293 * Error handling invariant: 294 * Before a `goto out': 295 * lvp is either NULL, or held. 296 * uvp is either NULL, or held. 297 */ 298 299 if (bufp) 300 bp = *bpp; 301 302 /* 303 * this loop will terminate when one of the following happens: 304 * - we hit the root 305 * - getdirentries or lookup fails 306 * - we run out of space in the buffer. 307 */ 308 if (lvp == rvp) { 309 if (bp) 310 *(--bp) = '/'; 311 goto out; 312 } 313 do { 314 /* 315 * access check here is optional, depending on 316 * whether or not caller cares. 317 */ 318 int chkaccess = (flags & GETCWD_CHECK_ACCESS); 319 bool locked = false; 320 321 /* 322 * step up if we're a covered vnode.. 323 * check access on the first vnode only. 324 */ 325 if (lvp->v_vflag & VV_ROOT) { 326 vn_lock(lvp, LK_SHARED | LK_RETRY); 327 if (chkaccess) { 328 error = VOP_ACCESS(lvp, accmode, cred); 329 if (error) { 330 VOP_UNLOCK(lvp); 331 goto out; 332 } 333 chkaccess = 0; 334 } 335 while (lvp->v_vflag & VV_ROOT) { 336 struct vnode *tvp; 337 338 if (lvp == rvp) { 339 VOP_UNLOCK(lvp); 340 goto out; 341 } 342 343 tvp = lvp->v_mount->mnt_vnodecovered; 344 /* 345 * hodie natus est radici frater 346 */ 347 if (tvp == NULL) { 348 VOP_UNLOCK(lvp); 349 error = ENOENT; 350 goto out; 351 } 352 vref(tvp); 353 vput(lvp); 354 lvp = tvp; 355 if (lvp->v_vflag & VV_ROOT) 356 vn_lock(lvp, LK_SHARED | LK_RETRY); 357 } 358 } 359 360 /* Do we need to check access to the directory? */ 361 if (chkaccess && !cache_have_id(lvp)) { 362 /* Need exclusive for UFS VOP_GETATTR (itimes) & VOP_LOOKUP. */ 363 vn_lock(lvp, LK_EXCLUSIVE | LK_RETRY); 364 error = VOP_ACCESS(lvp, accmode, cred); 365 if (error) { 366 VOP_UNLOCK(lvp); 367 goto out; 368 } 369 chkaccess = 0; 370 locked = true; 371 } 372 373 /* 374 * Look in the name cache; if that fails, look in the 375 * directory.. 376 */ 377 error = cache_revlookup(lvp, &uvp, &bp, bufp, chkaccess, 378 accmode); 379 if (error == -1) { 380 if (!locked) { 381 locked = true; 382 vn_lock(lvp, LK_EXCLUSIVE | LK_RETRY); 383 } 384 if (lvp->v_type != VDIR) { 385 VOP_UNLOCK(lvp); 386 error = ENOTDIR; 387 goto out; 388 } 389 error = getcwd_scandir(lvp, &uvp, &bp, bufp, l); 390 /* lvp now unlocked */ 391 } else if (locked) { 392 VOP_UNLOCK(lvp); 393 } 394 if (error) 395 goto out; 396 #if DIAGNOSTIC 397 if (bufp && (bp <= bufp)) { 398 panic("getcwd: oops, went back too far"); 399 } 400 #endif 401 accmode = VEXEC | VREAD; 402 if (bp) 403 *(--bp) = '/'; 404 vrele(lvp); 405 lvp = uvp; 406 uvp = NULL; 407 limit--; 408 } while ((lvp != rvp) && (limit > 0)); 409 410 out: 411 if (bpp) 412 *bpp = bp; 413 if (uvp) 414 vrele(uvp); 415 if (lvp) 416 vrele(lvp); 417 vrele(rvp); 418 return error; 419 } 420 421 /* 422 * Check if one directory can be found inside another in the directory 423 * hierarchy. 424 * 425 * Intended to be used in chroot, chdir, fchdir, etc., to ensure that 426 * chroot() actually means something. 427 */ 428 int 429 vn_isunder(struct vnode *lvp, struct vnode *rvp, struct lwp *l) 430 { 431 int error; 432 433 error = getcwd_common(lvp, rvp, NULL, NULL, MAXPATHLEN / 2, 0, l); 434 435 if (!error) 436 return 1; 437 else 438 return 0; 439 } 440 441 /* 442 * Returns true if proc p1's root directory equal to or under p2's 443 * root directory. 444 * 445 * Intended to be used from ptrace/procfs sorts of things. 446 */ 447 448 int 449 proc_isunder(struct proc *p1, struct lwp *l2) 450 { 451 struct vnode *r1 = p1->p_cwdi->cwdi_rdir; 452 struct vnode *r2 = l2->l_proc->p_cwdi->cwdi_rdir; 453 454 if (r1 == NULL) 455 return (r2 == NULL); 456 else if (r2 == NULL) 457 return 1; 458 else 459 return vn_isunder(r1, r2, l2); 460 } 461 462 /* 463 * Find pathname of process's current directory. 464 * 465 * Use vfs vnode-to-name reverse cache; if that fails, fall back 466 * to reading directory contents. 467 */ 468 469 int 470 sys___getcwd(struct lwp *l, const struct sys___getcwd_args *uap, register_t *retval) 471 { 472 /* { 473 syscallarg(char *) bufp; 474 syscallarg(size_t) length; 475 } */ 476 477 int error; 478 char *path; 479 char *bp, *bend; 480 int len = SCARG(uap, length); 481 int lenused; 482 struct cwdinfo *cwdi; 483 484 if (len > MAXPATHLEN * 4) 485 len = MAXPATHLEN * 4; 486 else if (len < 2) 487 return ERANGE; 488 489 path = kmem_alloc(len, KM_SLEEP); 490 bp = &path[len]; 491 bend = bp; 492 *(--bp) = '\0'; 493 494 /* 495 * 5th argument here is "max number of vnodes to traverse". 496 * Since each entry takes up at least 2 bytes in the output buffer, 497 * limit it to N/2 vnodes for an N byte buffer. 498 */ 499 cwdi = l->l_proc->p_cwdi; 500 rw_enter(&cwdi->cwdi_lock, RW_READER); 501 error = getcwd_common(cwdi->cwdi_cdir, NULL, &bp, path, 502 len/2, GETCWD_CHECK_ACCESS, l); 503 rw_exit(&cwdi->cwdi_lock); 504 505 if (error) 506 goto out; 507 lenused = bend - bp; 508 *retval = lenused; 509 /* put the result into user buffer */ 510 error = copyout(bp, SCARG(uap, bufp), lenused); 511 512 out: 513 kmem_free(path, len); 514 return error; 515 } 516 517 /* 518 * Try to find a pathname for a vnode. Since there is no mapping vnode -> 519 * parent directory, this needs the namecache to succeed. Caller holds a 520 * reference to the vnode. 521 */ 522 int 523 vnode_to_path(char *path, size_t len, struct vnode *vp, struct lwp *curl, 524 struct proc *p) 525 { 526 struct proc *curp = curl->l_proc; 527 int error, lenused, elen; 528 char *bp, *bend; 529 struct vnode *dvp; 530 531 KASSERT(vrefcnt(vp) > 0); 532 533 bp = bend = &path[len]; 534 *(--bp) = '\0'; 535 536 error = cache_revlookup(vp, &dvp, &bp, path, false, 0); 537 if (error != 0) 538 return (error == -1 ? ENOENT : error); 539 540 *(--bp) = '/'; 541 error = getcwd_common(dvp, NULL, &bp, path, len / 2, 542 GETCWD_CHECK_ACCESS, curl); 543 vrele(dvp); 544 if (error != 0) 545 return error; 546 547 /* 548 * Strip off emulation path for emulated processes looking at 549 * the maps file of a process of the same emulation. (Won't 550 * work if /emul/xxx is a symlink..) 551 */ 552 if (curp->p_emul == p->p_emul && curp->p_emul->e_path != NULL) { 553 elen = strlen(curp->p_emul->e_path); 554 if (!strncmp(bp, curp->p_emul->e_path, elen)) 555 bp = &bp[elen]; 556 } 557 558 lenused = bend - bp; 559 560 memcpy(path, bp, lenused); 561 path[lenused] = '\0'; 562 563 return 0; 564 } 565
Indexes created Sun Sep 21 20:09:37 GMT 2025