| 1 | /* -*-c-*- |
| 2 | * |
| 3 | * Check a path for safety |
| 4 | * |
| 5 | * (c) 1999 Mark Wooding |
| 6 | */ |
| 7 | |
| 8 | /*----- Licensing notice --------------------------------------------------* |
| 9 | * |
| 10 | * This file is part of chkpath. |
| 11 | * |
| 12 | * chkpath is free software; you can redistribute it and/or modify |
| 13 | * it under the terms of the GNU General Public License as published by |
| 14 | * the Free Software Foundation; either version 2 of the License, or |
| 15 | * (at your option) any later version. |
| 16 | * |
| 17 | * chkpath is distributed in the hope that it will be useful, |
| 18 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 19 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 20 | * GNU General Public License for more details. |
| 21 | * |
| 22 | * You should have received a copy of the GNU General Public License |
| 23 | * along with chkpath; if not, write to the Free Software Foundation, |
| 24 | * Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. |
| 25 | */ |
| 26 | |
| 27 | /*----- Header files ------------------------------------------------------*/ |
| 28 | |
| 29 | #include "config.h" |
| 30 | |
| 31 | #include <errno.h> |
| 32 | #include <stdarg.h> |
| 33 | #include <stdio.h> |
| 34 | #include <stdlib.h> |
| 35 | #include <string.h> |
| 36 | |
| 37 | #include <sys/types.h> |
| 38 | #include <sys/stat.h> |
| 39 | #include <unistd.h> |
| 40 | |
| 41 | #include <pwd.h> |
| 42 | #include <grp.h> |
| 43 | |
| 44 | #include <mLib/alloc.h> |
| 45 | #include <mLib/dstr.h> |
| 46 | #include <mLib/macros.h> |
| 47 | |
| 48 | #include "checkpath.h" |
| 49 | |
| 50 | /*----- Data structures ---------------------------------------------------*/ |
| 51 | |
| 52 | /* --- An item in the directory list --- * |
| 53 | * |
| 54 | * Each directory becomes an element on a list which is manipulated in a |
| 55 | * stack-like way. |
| 56 | */ |
| 57 | |
| 58 | struct elt { |
| 59 | struct elt *e_link; /* Pointer to the next one along */ |
| 60 | size_t e_offset; /* Offset of name in path string */ |
| 61 | unsigned e_flags; /* Various useful flags */ |
| 62 | char e_name[1]; /* Name of the directory */ |
| 63 | }; |
| 64 | |
| 65 | #define f_sticky 1u /* Directory has sticky bit set */ |
| 66 | |
| 67 | #define f_last 1u /* This is the final item to check */ |
| 68 | |
| 69 | /*----- Static variables --------------------------------------------------*/ |
| 70 | |
| 71 | static struct elt rootnode = { 0, 0, 0 }; /* Root of the list */ |
| 72 | static struct elt *sp; /* Stack pointer for list */ |
| 73 | static dstr d = DSTR_INIT; /* Current path string */ |
| 74 | |
| 75 | /*----- Main code ---------------------------------------------------------*/ |
| 76 | |
| 77 | /* --- @splitpath@ --- * |
| 78 | * |
| 79 | * Arguments: @const char *path@ = path string to break apart |
| 80 | * @struct elt *tail@ = tail block to attach to end of list |
| 81 | * |
| 82 | * Returns: Pointer to the new list head. |
| 83 | * |
| 84 | * Use: Breaks a path string into directories and adds each one |
| 85 | * as a node on the list, in the right order. These can then |
| 86 | * be pushed onto the directory stack as required. |
| 87 | */ |
| 88 | |
| 89 | static struct elt *splitpath(const char *path, struct elt *tail) |
| 90 | { |
| 91 | struct elt *head, **ee = &head, *e; |
| 92 | |
| 93 | while (*path) { |
| 94 | size_t n; |
| 95 | |
| 96 | /* --- Either a leading `/', or a doubled one --- * |
| 97 | * |
| 98 | * Either way, ignore it. |
| 99 | */ |
| 100 | |
| 101 | if (*path == '/') { |
| 102 | path++; |
| 103 | continue; |
| 104 | } |
| 105 | |
| 106 | /* --- Skip to the next directory separator --- * |
| 107 | * |
| 108 | * Build a list element for it, and link it on. |
| 109 | */ |
| 110 | |
| 111 | n = strcspn(path, "/"); |
| 112 | e = xmalloc(sizeof(struct elt) + n + 1); |
| 113 | memcpy(e->e_name, path, n); |
| 114 | e->e_name[n] = 0; |
| 115 | e->e_flags = 0; |
| 116 | *ee = e; |
| 117 | ee = &e->e_link; |
| 118 | path += n; |
| 119 | } |
| 120 | |
| 121 | /* --- Done --- */ |
| 122 | |
| 123 | *ee = tail; |
| 124 | return (head); |
| 125 | } |
| 126 | |
| 127 | /* --- @pop@ --- * |
| 128 | * |
| 129 | * Arguments: --- |
| 130 | * |
| 131 | * Returns: --- |
| 132 | * |
| 133 | * Use: Removes the top item from the directory stack. |
| 134 | */ |
| 135 | |
| 136 | static void pop(void) |
| 137 | { |
| 138 | if (sp->e_link) { |
| 139 | struct elt *e = sp->e_link; |
| 140 | d.len = sp->e_offset; |
| 141 | DPUTZ(&d); |
| 142 | sp = e; |
| 143 | } |
| 144 | } |
| 145 | |
| 146 | /* --- @popall@ --- * |
| 147 | * |
| 148 | * Arguments: --- |
| 149 | * |
| 150 | * Returns: --- |
| 151 | * |
| 152 | * Use: Removes all the items from the directory stack. |
| 153 | */ |
| 154 | |
| 155 | static void popall(void) |
| 156 | { while (sp->e_link) pop(); } |
| 157 | |
| 158 | /* --- @push@ --- * |
| 159 | * |
| 160 | * Arguments: @struct elt *e@ = pointer to directory element |
| 161 | * |
| 162 | * Returns: --- |
| 163 | * |
| 164 | * Use: Pushes a new subdirectory onto the stack. |
| 165 | */ |
| 166 | |
| 167 | static void push(struct elt *e) |
| 168 | { |
| 169 | e->e_link = sp; |
| 170 | e->e_offset = d.len; |
| 171 | DPUTC(&d, '/'); |
| 172 | DPUTS(&d, e->e_name); |
| 173 | sp = e; |
| 174 | } |
| 175 | |
| 176 | /* --- @report@ --- * |
| 177 | * |
| 178 | * Arguments: @const struct checkpath *cp@ = pointer to context |
| 179 | * @unsigned what@ = what sort of report is this? |
| 180 | * @int verbose@ = how verbose is this? |
| 181 | * @const char *p@ = what path does it refer to? |
| 182 | * @const char *msg@ = the message to give to the user |
| 183 | * |
| 184 | * Returns: --- |
| 185 | * |
| 186 | * Use: Formats and presents messages to the client. |
| 187 | */ |
| 188 | |
| 189 | static void report(const struct checkpath *cp, unsigned what, int verbose, |
| 190 | const char *p, const char *msg, ...) |
| 191 | { |
| 192 | dstr d = DSTR_INIT; |
| 193 | va_list ap; |
| 194 | const char *q = msg; |
| 195 | const char *s; |
| 196 | size_t n; |
| 197 | int e = errno; |
| 198 | uid_t u; |
| 199 | struct passwd *pw; |
| 200 | gid_t g; |
| 201 | struct group *gr; |
| 202 | |
| 203 | /* --- Decide whether to bin this message --- */ |
| 204 | |
| 205 | if (!cp->cp_report || verbose > cp->cp_verbose || !(cp->cp_what & what)) |
| 206 | return; |
| 207 | |
| 208 | /* --- If no reporting, do the easy thing --- */ |
| 209 | |
| 210 | if (!(cp->cp_what & CP_REPORT)) { |
| 211 | cp->cp_report(what, verbose, p, 0, cp->cp_arg); |
| 212 | return; |
| 213 | } |
| 214 | |
| 215 | /* --- Format the message nicely --- */ |
| 216 | |
| 217 | va_start(ap, msg); |
| 218 | if (verbose > 1) |
| 219 | dstr_puts(&d, "[ "); |
| 220 | if (p) |
| 221 | dstr_putf(&d, "Path: %s: ", p); |
| 222 | while (*q) { |
| 223 | if (*q == '%') { |
| 224 | q++; |
| 225 | switch (*q) { |
| 226 | case 'e': |
| 227 | dstr_puts(&d, strerror(e)); |
| 228 | break; |
| 229 | case 'u': |
| 230 | u = (uid_t)va_arg(ap, int); |
| 231 | if ((pw = getpwuid(u)) != 0) |
| 232 | dstr_putf(&d, "`%s'", pw->pw_name); |
| 233 | else |
| 234 | dstr_putf(&d, "%i", (int)u); |
| 235 | break; |
| 236 | case 'g': |
| 237 | g = (gid_t)va_arg(ap, int); |
| 238 | if ((gr = getgrgid(g)) != 0) |
| 239 | dstr_putf(&d, "`%s'", gr->gr_name); |
| 240 | else |
| 241 | dstr_putf(&d, "%i", (int)g); |
| 242 | break; |
| 243 | case 's': |
| 244 | s = va_arg(ap, const char *); |
| 245 | dstr_puts(&d, s); |
| 246 | break; |
| 247 | case '%': |
| 248 | dstr_putc(&d, '%'); |
| 249 | break; |
| 250 | default: |
| 251 | dstr_putc(&d, '%'); |
| 252 | dstr_putc(&d, *q); |
| 253 | break; |
| 254 | } |
| 255 | q++; |
| 256 | } else { |
| 257 | n = strcspn(q, "%"); |
| 258 | DPUTM(&d, q, n); |
| 259 | q += n; |
| 260 | } |
| 261 | } |
| 262 | if (verbose > 1) |
| 263 | dstr_puts(&d, " ]"); |
| 264 | DPUTZ(&d); |
| 265 | cp->cp_report(what, verbose, p, d.buf, cp->cp_arg); |
| 266 | dstr_destroy(&d); |
| 267 | va_end(ap); |
| 268 | } |
| 269 | |
| 270 | /* --- @sanity@ --- * |
| 271 | * |
| 272 | * Arguments: @const char *p@ = name of directory to check |
| 273 | * @struct stat *st@ = pointer to @stat@(2) block for it |
| 274 | * @const struct checkpath *cp@ = pointer to caller parameters |
| 275 | * @unsigned f@ = various flags |
| 276 | * |
| 277 | * Returns: Zero if everything's OK, else bitmask of problems. |
| 278 | * |
| 279 | * Use: Performs the main load of sanity-checking on a directory. |
| 280 | */ |
| 281 | |
| 282 | static unsigned sanity(const char *p, struct stat *st, |
| 283 | const struct checkpath *cp, unsigned f) |
| 284 | { |
| 285 | unsigned bad = 0; |
| 286 | int stickyok = 0; |
| 287 | int i; |
| 288 | unsigned b; |
| 289 | |
| 290 | if (S_ISDIR(st->st_mode) && |
| 291 | (!(f & f_last) || (cp->cp_what & CP_STICKYOK))) |
| 292 | stickyok = 01000; |
| 293 | |
| 294 | /* --- Check for world-writability --- */ |
| 295 | |
| 296 | if ((cp->cp_what & CP_WRWORLD) && |
| 297 | (st->st_mode & (0002 | stickyok)) == 0002) { |
| 298 | bad |= CP_WRWORLD; |
| 299 | report(cp, CP_WRWORLD, 1, p, "** world writable **"); |
| 300 | } |
| 301 | |
| 302 | /* --- Check for group-writability --- */ |
| 303 | |
| 304 | if ((cp->cp_what & (CP_WRGRP | CP_WROTHGRP)) && |
| 305 | (st->st_mode & (0020 | stickyok)) == 0020) { |
| 306 | b = CP_WRGRP; |
| 307 | |
| 308 | if (cp->cp_what & CP_WROTHGRP) { |
| 309 | b = CP_WROTHGRP; |
| 310 | for (i = 0; i < cp->cp_gids; i++) { |
| 311 | if (st->st_gid == cp->cp_gid[i]) |
| 312 | b = cp->cp_what & CP_WRGRP; |
| 313 | } |
| 314 | } |
| 315 | if (b) { |
| 316 | bad |= b; |
| 317 | report(cp, b, 1, p, "writable by %sgroup %g", |
| 318 | (b == CP_WROTHGRP) ? "other " : "", st->st_gid); |
| 319 | } |
| 320 | } |
| 321 | |
| 322 | /* --- Check for user-writability --- */ |
| 323 | |
| 324 | if ((cp->cp_what & CP_WROTHUSR) && |
| 325 | st->st_uid != cp->cp_uid && |
| 326 | st->st_uid != 0) { |
| 327 | bad |= CP_WROTHUSR; |
| 328 | report(cp, CP_WROTHUSR, 1, p, "owner is user %u", st->st_uid); |
| 329 | } |
| 330 | |
| 331 | /* --- Done sanity check --- */ |
| 332 | |
| 333 | return (bad); |
| 334 | } |
| 335 | |
| 336 | /* --- @checkpath@ --- * |
| 337 | * |
| 338 | * Arguments: @const char *p@ = directory name which needs checking |
| 339 | * @const struct checkpath *cp@ = parameters for the check |
| 340 | * |
| 341 | * Returns: Zero if all is well, otherwise bitmask of problems. |
| 342 | * |
| 343 | * Use: Scrutinises a directory path to see what evil things other |
| 344 | * users could do to it. |
| 345 | */ |
| 346 | |
| 347 | unsigned checkpath(const char *p, const struct checkpath *cp) |
| 348 | { |
| 349 | char cwd[PATH_MAX]; |
| 350 | struct elt *e, *ee; |
| 351 | struct stat st; |
| 352 | unsigned bad = 0; |
| 353 | |
| 354 | /* --- Initialize stack pointer and path string --- */ |
| 355 | |
| 356 | sp = &rootnode; |
| 357 | dstr_destroy(&d); |
| 358 | |
| 359 | /* --- Try to find the current directory --- */ |
| 360 | |
| 361 | if (!getcwd(cwd, sizeof(cwd))) { |
| 362 | report(cp, CP_ERROR, 0, 0, "can't find current directory: %e"); |
| 363 | return (CP_ERROR); |
| 364 | } |
| 365 | |
| 366 | /* --- Check that the root directory is OK --- */ |
| 367 | |
| 368 | if (stat("/", &st)) { |
| 369 | report(cp, CP_ERROR, 0, 0, "can't stat root directory: %e"); |
| 370 | return (CP_ERROR); |
| 371 | } |
| 372 | |
| 373 | report(cp, CP_REPORT, 3, p, "begin scan"); |
| 374 | bad |= sanity("/", &st, cp, 0); |
| 375 | |
| 376 | /* --- Get the initial list of things to process --- */ |
| 377 | |
| 378 | ee = splitpath(p, 0); |
| 379 | if (*p != '/') |
| 380 | ee = splitpath(cwd, ee); |
| 381 | |
| 382 | /* --- While there are list items which still need doing --- */ |
| 383 | |
| 384 | while (ee) { |
| 385 | e = ee->e_link; |
| 386 | |
| 387 | /* --- Strip off simple `.' elements --- */ |
| 388 | |
| 389 | if (strcmp(ee->e_name, ".") == 0) { |
| 390 | free(ee); |
| 391 | ee = e; |
| 392 | continue; |
| 393 | } |
| 394 | |
| 395 | /* --- Backtrack on `..' elements --- */ |
| 396 | |
| 397 | else if (strcmp(ee->e_name, "..") == 0) { |
| 398 | pop(); |
| 399 | free(ee); |
| 400 | ee = e; |
| 401 | continue; |
| 402 | } |
| 403 | |
| 404 | /* --- Everything else gets pushed on the end --- */ |
| 405 | |
| 406 | push(ee); |
| 407 | ee = e; |
| 408 | |
| 409 | /* --- Find out what sort of a thing this is --- */ |
| 410 | |
| 411 | if (lstat(d.buf, &st)) { |
| 412 | report(cp, CP_ERROR, 0, d.buf, "can't stat: %e"); |
| 413 | bad |= CP_ERROR; |
| 414 | break; |
| 415 | } |
| 416 | |
| 417 | /* --- Handle symbolic links specially --- */ |
| 418 | |
| 419 | if (S_ISLNK(st.st_mode)) { |
| 420 | dstr buf = DSTR_INIT; |
| 421 | int i; |
| 422 | |
| 423 | /* --- Resolve the link --- */ |
| 424 | |
| 425 | dstr_ensure(&buf, st.st_size + 1); |
| 426 | if ((i = readlink(d.buf, buf.buf, buf.sz)) < 0) { |
| 427 | report(cp, CP_ERROR, 0, d.buf, "can't readlink: %e"); |
| 428 | bad |= CP_ERROR; |
| 429 | break; |
| 430 | } |
| 431 | buf.buf[i] = 0; |
| 432 | report(cp, CP_SYMLINK, 2, d.buf, "symlink -> `%s'", buf.buf); |
| 433 | |
| 434 | /* --- Handle sticky parents --- * |
| 435 | * |
| 436 | * If I make a symlink in a sticky directory, I can later modify it. |
| 437 | * However, nobody else can (except the owner of the directory, and |
| 438 | * we'll already have noticed that if we care). |
| 439 | */ |
| 440 | |
| 441 | if ((cp->cp_what & CP_WROTHUSR) && |
| 442 | (sp->e_link->e_flags & f_sticky) && |
| 443 | st.st_uid != cp->cp_uid && st.st_uid != 0) { |
| 444 | bad |= CP_WROTHUSR; |
| 445 | report(cp, CP_WROTHUSR, 1, d.buf, |
| 446 | "symlink modifiable by user %u", st.st_uid); |
| 447 | } |
| 448 | |
| 449 | /* --- Sort out what to do from here --- */ |
| 450 | |
| 451 | if (buf.buf[0] == '/') |
| 452 | popall(); |
| 453 | else |
| 454 | pop(); |
| 455 | ee = splitpath(buf.buf, ee); |
| 456 | dstr_destroy(&buf); |
| 457 | continue; |
| 458 | } |
| 459 | |
| 460 | /* --- Run the sanity check on this path element --- */ |
| 461 | |
| 462 | bad |= sanity(d.buf, &st, cp, ee ? 0 : f_last); |
| 463 | |
| 464 | if (S_ISDIR(st.st_mode)) { |
| 465 | if (st.st_mode & 01000) |
| 466 | sp->e_flags |= f_sticky; |
| 467 | report(cp, CP_REPORT, 4, d.buf, "directory"); |
| 468 | continue; |
| 469 | } |
| 470 | |
| 471 | /* --- Something else I don't understand --- */ |
| 472 | |
| 473 | break; |
| 474 | } |
| 475 | |
| 476 | /* --- Check for leftover junk --- */ |
| 477 | |
| 478 | if (ee) { |
| 479 | if (!(bad & CP_ERROR)) |
| 480 | report(cp, CP_ERROR, 0, 0, "junk left over after reaching leaf"); |
| 481 | while (ee) { |
| 482 | e = ee->e_link; |
| 483 | free(ee); |
| 484 | ee = e; |
| 485 | } |
| 486 | } |
| 487 | |
| 488 | popall(); |
| 489 | return (bad); |
| 490 | } |
| 491 | |
| 492 | /* --- @checkpath_addgid@ --- * |
| 493 | * |
| 494 | * Arguments: @struct checkpath *cp@ = pointer to block to fill in |
| 495 | * @gid_t g@ = group id to add |
| 496 | * |
| 497 | * Returns: Zero if successful, nonzero if the array is full. |
| 498 | * |
| 499 | * Use: Adds the group @g@ to the structure. |
| 500 | */ |
| 501 | |
| 502 | int checkpath_addgid(struct checkpath *cp, gid_t g) |
| 503 | { |
| 504 | int i; |
| 505 | |
| 506 | for (i = 0; i < cp->cp_gids; i++) { |
| 507 | if (cp->cp_gid[i] == g) |
| 508 | return (0); |
| 509 | } |
| 510 | if (cp->cp_gids >= N(cp->cp_gid)) |
| 511 | return (-1); |
| 512 | cp->cp_gid[cp->cp_gids++] = g; |
| 513 | return (0); |
| 514 | } |
| 515 | |
| 516 | /* --- @checkpath_setuid@ --- * |
| 517 | * |
| 518 | * Arguments: @struct checkpath *cp@ = pointer to block to fill in |
| 519 | * |
| 520 | * Returns: --- |
| 521 | * |
| 522 | * Use: Fills in the @cp_uid@ slot of the structure with the real uid |
| 523 | * of the current process. |
| 524 | */ |
| 525 | |
| 526 | void checkpath_setuid(struct checkpath *cp) { cp->cp_uid = getuid(); } |
| 527 | |
| 528 | /* --- @checkpath_setgid@ --- * |
| 529 | * |
| 530 | * Arguments: @struct checkpath *cp@ = pointer to block to fill in |
| 531 | * |
| 532 | * Returns: Zero if successful, nonzero if the array is full. |
| 533 | * |
| 534 | * Use: Adds the real gid of the current process to the @cp_gid@ |
| 535 | * array. |
| 536 | */ |
| 537 | |
| 538 | int checkpath_setgid(struct checkpath *cp) |
| 539 | { return (checkpath_addgid(cp, getgid())); } |
| 540 | |
| 541 | /* --- @checkpath_setgroups@ --- * |
| 542 | * |
| 543 | * Arguments: @struct checkpath *cp@ = pointer to block to fill in |
| 544 | * |
| 545 | * Returns: Zero if successful, nonzero if the array is full. |
| 546 | * |
| 547 | * Use: Adds the current process's supplementary groups to the |
| 548 | * @cp_gid@ table. |
| 549 | */ |
| 550 | |
| 551 | int checkpath_setgroups(struct checkpath *cp) |
| 552 | { |
| 553 | int i, n; |
| 554 | gid_t gg[NGROUPS_MAX]; |
| 555 | |
| 556 | n = getgroups(N(gg), gg); |
| 557 | for (i = 0; i < n; i++) { |
| 558 | if (checkpath_addgid(cp, gg[i])) |
| 559 | return (-1); |
| 560 | } |
| 561 | return (0); |
| 562 | } |
| 563 | |
| 564 | /* --- @checkpath_setids@ --- * |
| 565 | * |
| 566 | * Arguments: @struct checkpath *cp@ = pointer to block to fill in |
| 567 | * |
| 568 | * Returns: --- |
| 569 | * |
| 570 | * Use: Fills in the user ids and things in the structure. This is |
| 571 | * equivalent to setting @cp_gids = 0@ and then calling |
| 572 | * @_setuid@, @_setgid@ and @_setgroups@. It can't fail. |
| 573 | */ |
| 574 | |
| 575 | void checkpath_setids(struct checkpath *cp) |
| 576 | { |
| 577 | cp->cp_gids = 0; |
| 578 | checkpath_setuid(cp); |
| 579 | checkpath_setgid(cp); |
| 580 | checkpath_setgroups(cp); |
| 581 | } |
| 582 | |
| 583 | /*----- That's all, folks -------------------------------------------------*/ |