Commit | Line | Data |
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efa7a97b | 1 | /* -*-c-*- |
2 | * | |
efa7a97b | 3 | * Check a path for safety |
4 | * | |
5 | * (c) 1999 Mark Wooding | |
6 | */ | |
7 | ||
263d6e0d | 8 | /*----- Licensing notice --------------------------------------------------* |
efa7a97b | 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. | |
263d6e0d | 16 | * |
efa7a97b | 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. | |
263d6e0d | 21 | * |
efa7a97b | 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 | ||
efa7a97b | 27 | /*----- Header files ------------------------------------------------------*/ |
28 | ||
9c42854d MW |
29 | #include "config.h" |
30 | ||
efa7a97b | 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> | |
a2965015 | 46 | #include <mLib/macros.h> |
efa7a97b | 47 | |
d7b5ee0c | 48 | #include "checkpath.h" |
efa7a97b | 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 | ||
7868d789 | 65 | #define f_sticky 1u /* Directory has sticky bit set */ |
efa7a97b | 66 | |
7868d789 | 67 | #define f_last 1u /* This is the final item to check */ |
efa7a97b | 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 */ | |
72462155 | 73 | static dstr d = DSTR_INIT; /* Current path string */ |
efa7a97b | 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) | |
d8e11317 | 156 | { while (sp->e_link) pop(); } |
efa7a97b | 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 | * | |
d7b5ee0c | 178 | * Arguments: @const struct checkpath *cp@ = pointer to context |
179 | * @unsigned what@ = what sort of report is this? | |
efa7a97b | 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 | ||
d7b5ee0c | 189 | static void report(const struct checkpath *cp, unsigned what, int verbose, |
efa7a97b | 190 | const char *p, const char *msg, ...) |
191 | { | |
d8e11317 MW |
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 | ||
efa7a97b | 203 | /* --- Decide whether to bin this message --- */ |
204 | ||
205 | if (!cp->cp_report || verbose > cp->cp_verbose || !(cp->cp_what & what)) | |
206 | return; | |
207 | ||
d8e11317 MW |
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 | ||
efa7a97b | 215 | /* --- Format the message nicely --- */ |
216 | ||
d8e11317 MW |
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; | |
efa7a97b | 254 | } |
d8e11317 MW |
255 | q++; |
256 | } else { | |
257 | n = strcspn(q, "%"); | |
258 | DPUTM(&d, q, n); | |
259 | q += n; | |
efa7a97b | 260 | } |
d8e11317 MW |
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); | |
efa7a97b | 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 | |
d7b5ee0c | 274 | * @const struct checkpath *cp@ = pointer to caller parameters |
efa7a97b | 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 | ||
d7b5ee0c | 282 | static unsigned sanity(const char *p, struct stat *st, |
283 | const struct checkpath *cp, unsigned f) | |
efa7a97b | 284 | { |
d7b5ee0c | 285 | unsigned bad = 0; |
286 | int stickyok = 0; | |
d8e11317 MW |
287 | int i; |
288 | unsigned b; | |
d7b5ee0c | 289 | |
290 | if (S_ISDIR(st->st_mode) && | |
291 | (!(f & f_last) || (cp->cp_what & CP_STICKYOK))) | |
292 | stickyok = 01000; | |
efa7a97b | 293 | |
294 | /* --- Check for world-writability --- */ | |
295 | ||
296 | if ((cp->cp_what & CP_WRWORLD) && | |
d7b5ee0c | 297 | (st->st_mode & (0002 | stickyok)) == 0002) { |
efa7a97b | 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)) && | |
d7b5ee0c | 305 | (st->st_mode & (0020 | stickyok)) == 0020) { |
d8e11317 | 306 | b = CP_WRGRP; |
d7b5ee0c | 307 | |
308 | if (cp->cp_what & CP_WROTHGRP) { | |
309 | b = CP_WROTHGRP; | |
efa7a97b | 310 | for (i = 0; i < cp->cp_gids; i++) { |
311 | if (st->st_gid == cp->cp_gid[i]) | |
d7b5ee0c | 312 | b = cp->cp_what & CP_WRGRP; |
efa7a97b | 313 | } |
d7b5ee0c | 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); | |
efa7a97b | 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 | ||
d7b5ee0c | 336 | /* --- @checkpath@ --- * |
efa7a97b | 337 | * |
338 | * Arguments: @const char *p@ = directory name which needs checking | |
d7b5ee0c | 339 | * @const struct checkpath *cp@ = parameters for the check |
efa7a97b | 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 | ||
d7b5ee0c | 347 | unsigned checkpath(const char *p, const struct checkpath *cp) |
efa7a97b | 348 | { |
349 | char cwd[PATH_MAX]; | |
350 | struct elt *e, *ee; | |
351 | struct stat st; | |
d7b5ee0c | 352 | unsigned bad = 0; |
efa7a97b | 353 | |
72462155 | 354 | /* --- Initialize stack pointer and path string --- */ |
efa7a97b | 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)) { | |
72462155 | 420 | dstr buf = DSTR_INIT; |
efa7a97b | 421 | int i; |
422 | ||
423 | /* --- Resolve the link --- */ | |
424 | ||
558a9b22 | 425 | dstr_ensure(&buf, st.st_size + 1); |
426 | if ((i = readlink(d.buf, buf.buf, buf.sz)) < 0) { | |
efa7a97b | 427 | report(cp, CP_ERROR, 0, d.buf, "can't readlink: %e"); |
428 | bad |= CP_ERROR; | |
429 | break; | |
430 | } | |
558a9b22 | 431 | buf.buf[i] = 0; |
432 | report(cp, CP_SYMLINK, 2, d.buf, "symlink -> `%s'", buf.buf); | |
efa7a97b | 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 | ||
558a9b22 | 451 | if (buf.buf[0] == '/') |
efa7a97b | 452 | popall(); |
453 | else | |
454 | pop(); | |
558a9b22 | 455 | ee = splitpath(buf.buf, ee); |
456 | dstr_destroy(&buf); | |
efa7a97b | 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 | ||
a2965015 | 492 | /* --- @checkpath_addgid@ --- * |
efa7a97b | 493 | * |
d7b5ee0c | 494 | * Arguments: @struct checkpath *cp@ = pointer to block to fill in |
a2965015 | 495 | * @gid_t g@ = group id to add |
efa7a97b | 496 | * |
a2965015 | 497 | * Returns: Zero if successful, nonzero if the array is full. |
efa7a97b | 498 | * |
a2965015 | 499 | * Use: Adds the group @g@ to the structure. |
efa7a97b | 500 | */ |
501 | ||
a2965015 | 502 | int checkpath_addgid(struct checkpath *cp, gid_t g) |
efa7a97b | 503 | { |
a2965015 MW |
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 | */ | |
efa7a97b | 537 | |
a2965015 MW |
538 | int checkpath_setgid(struct checkpath *cp) |
539 | { return (checkpath_addgid(cp, getgid())); } | |
263d6e0d | 540 | |
a2965015 MW |
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); | |
efa7a97b | 557 | for (i = 0; i < n; i++) { |
a2965015 MW |
558 | if (checkpath_addgid(cp, gg[i])) |
559 | return (-1); | |
efa7a97b | 560 | } |
a2965015 MW |
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); | |
efa7a97b | 581 | } |
582 | ||
583 | /*----- That's all, folks -------------------------------------------------*/ |