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1 | /* -*-c-*- |
2 | * |
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3 | * $Id: checkpath.c,v 1.4 2001/01/25 22:16:02 mdw Exp $ |
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4 | * |
5 | * Check a path for safety |
6 | * |
7 | * (c) 1999 Mark Wooding |
8 | */ |
9 | |
10 | /*----- Licensing notice --------------------------------------------------* |
11 | * |
12 | * This file is part of chkpath. |
13 | * |
14 | * chkpath is free software; you can redistribute it and/or modify |
15 | * it under the terms of the GNU General Public License as published by |
16 | * the Free Software Foundation; either version 2 of the License, or |
17 | * (at your option) any later version. |
18 | * |
19 | * chkpath is distributed in the hope that it will be useful, |
20 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
21 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
22 | * GNU General Public License for more details. |
23 | * |
24 | * You should have received a copy of the GNU General Public License |
25 | * along with chkpath; if not, write to the Free Software Foundation, |
26 | * Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. |
27 | */ |
28 | |
29 | /*----- Revision history --------------------------------------------------* |
30 | * |
31 | * $Log: checkpath.c,v $ |
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32 | * Revision 1.4 2001/01/25 22:16:02 mdw |
33 | * Make flags be unsigned. |
34 | * |
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35 | * Revision 1.3 1999/05/21 22:07:20 mdw |
36 | * Take advantage of new dynamic string macros. |
37 | * |
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38 | * Revision 1.2 1999/05/18 20:49:12 mdw |
39 | * Use a dynamic string for reading symlinks. |
40 | * |
41 | * Revision 1.1.1.1 1999/04/06 20:12:07 mdw |
42 | * Import new project. |
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43 | * |
44 | */ |
45 | |
46 | /*----- Header files ------------------------------------------------------*/ |
47 | |
48 | #include <errno.h> |
49 | #include <stdarg.h> |
50 | #include <stdio.h> |
51 | #include <stdlib.h> |
52 | #include <string.h> |
53 | |
54 | #include <sys/types.h> |
55 | #include <sys/stat.h> |
56 | #include <unistd.h> |
57 | |
58 | #include <pwd.h> |
59 | #include <grp.h> |
60 | |
61 | #include <mLib/alloc.h> |
62 | #include <mLib/dstr.h> |
63 | |
64 | #include "path.h" |
65 | |
66 | /*----- Data structures ---------------------------------------------------*/ |
67 | |
68 | /* --- An item in the directory list --- * |
69 | * |
70 | * Each directory becomes an element on a list which is manipulated in a |
71 | * stack-like way. |
72 | */ |
73 | |
74 | struct elt { |
75 | struct elt *e_link; /* Pointer to the next one along */ |
76 | size_t e_offset; /* Offset of name in path string */ |
77 | unsigned e_flags; /* Various useful flags */ |
78 | char e_name[1]; /* Name of the directory */ |
79 | }; |
80 | |
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81 | #define f_sticky 1u /* Directory has sticky bit set */ |
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82 | |
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83 | #define f_last 1u /* This is the final item to check */ |
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84 | |
85 | /*----- Static variables --------------------------------------------------*/ |
86 | |
87 | static struct elt rootnode = { 0, 0, 0 }; /* Root of the list */ |
88 | static struct elt *sp; /* Stack pointer for list */ |
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89 | static dstr d = DSTR_INIT; /* Current path string */ |
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90 | |
91 | /*----- Main code ---------------------------------------------------------*/ |
92 | |
93 | /* --- @splitpath@ --- * |
94 | * |
95 | * Arguments: @const char *path@ = path string to break apart |
96 | * @struct elt *tail@ = tail block to attach to end of list |
97 | * |
98 | * Returns: Pointer to the new list head. |
99 | * |
100 | * Use: Breaks a path string into directories and adds each one |
101 | * as a node on the list, in the right order. These can then |
102 | * be pushed onto the directory stack as required. |
103 | */ |
104 | |
105 | static struct elt *splitpath(const char *path, struct elt *tail) |
106 | { |
107 | struct elt *head, **ee = &head, *e; |
108 | |
109 | while (*path) { |
110 | size_t n; |
111 | |
112 | /* --- Either a leading `/', or a doubled one --- * |
113 | * |
114 | * Either way, ignore it. |
115 | */ |
116 | |
117 | if (*path == '/') { |
118 | path++; |
119 | continue; |
120 | } |
121 | |
122 | /* --- Skip to the next directory separator --- * |
123 | * |
124 | * Build a list element for it, and link it on. |
125 | */ |
126 | |
127 | n = strcspn(path, "/"); |
128 | e = xmalloc(sizeof(struct elt) + n + 1); |
129 | memcpy(e->e_name, path, n); |
130 | e->e_name[n] = 0; |
131 | e->e_flags = 0; |
132 | *ee = e; |
133 | ee = &e->e_link; |
134 | path += n; |
135 | } |
136 | |
137 | /* --- Done --- */ |
138 | |
139 | *ee = tail; |
140 | return (head); |
141 | } |
142 | |
143 | /* --- @pop@ --- * |
144 | * |
145 | * Arguments: --- |
146 | * |
147 | * Returns: --- |
148 | * |
149 | * Use: Removes the top item from the directory stack. |
150 | */ |
151 | |
152 | static void pop(void) |
153 | { |
154 | if (sp->e_link) { |
155 | struct elt *e = sp->e_link; |
156 | d.len = sp->e_offset; |
157 | DPUTZ(&d); |
158 | sp = e; |
159 | } |
160 | } |
161 | |
162 | /* --- @popall@ --- * |
163 | * |
164 | * Arguments: --- |
165 | * |
166 | * Returns: --- |
167 | * |
168 | * Use: Removes all the items from the directory stack. |
169 | */ |
170 | |
171 | static void popall(void) |
172 | { |
173 | while (sp->e_link) |
174 | pop(); |
175 | } |
176 | |
177 | /* --- @push@ --- * |
178 | * |
179 | * Arguments: @struct elt *e@ = pointer to directory element |
180 | * |
181 | * Returns: --- |
182 | * |
183 | * Use: Pushes a new subdirectory onto the stack. |
184 | */ |
185 | |
186 | static void push(struct elt *e) |
187 | { |
188 | e->e_link = sp; |
189 | e->e_offset = d.len; |
190 | DPUTC(&d, '/'); |
191 | DPUTS(&d, e->e_name); |
192 | sp = e; |
193 | } |
194 | |
195 | /* --- @report@ --- * |
196 | * |
197 | * Arguments: @struct chkpath *cp@ = pointer to context |
198 | * @int what@ = what sort of report is this? |
199 | * @int verbose@ = how verbose is this? |
200 | * @const char *p@ = what path does it refer to? |
201 | * @const char *msg@ = the message to give to the user |
202 | * |
203 | * Returns: --- |
204 | * |
205 | * Use: Formats and presents messages to the client. |
206 | */ |
207 | |
208 | static void report(struct chkpath *cp, int what, int verbose, |
209 | const char *p, const char *msg, ...) |
210 | { |
211 | /* --- Decide whether to bin this message --- */ |
212 | |
213 | if (!cp->cp_report || verbose > cp->cp_verbose || !(cp->cp_what & what)) |
214 | return; |
215 | |
216 | /* --- Format the message nicely --- */ |
217 | |
218 | if (cp->cp_what & CP_REPORT) { |
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219 | dstr d = DSTR_INIT; |
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220 | va_list ap; |
221 | const char *q = msg; |
222 | size_t n; |
223 | int e = errno; |
224 | |
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225 | va_start(ap, msg); |
226 | if (verbose > 1) |
227 | dstr_puts(&d, "[ "); |
228 | if (p) |
229 | dstr_putf(&d, "Path: %s: ", p); |
230 | while (*q) { |
231 | if (*q == '%') { |
232 | q++; |
233 | switch (*q) { |
234 | case 'e': |
235 | dstr_puts(&d, strerror(e)); |
236 | break; |
237 | case 'u': { |
238 | uid_t u = (uid_t)va_arg(ap, int); |
239 | struct passwd *pw = getpwuid(u); |
240 | if (pw) |
241 | dstr_putf(&d, "`%s'", pw->pw_name); |
242 | else |
243 | dstr_putf(&d, "%i", (int)u); |
244 | } break; |
245 | case 'g': { |
246 | gid_t g = (gid_t)va_arg(ap, int); |
247 | struct group *gr = getgrgid(g); |
248 | if (gr) |
249 | dstr_putf(&d, "`%s'", gr->gr_name); |
250 | else |
251 | dstr_putf(&d, "%i", (int)g); |
252 | } break; |
253 | case 's': { |
254 | const char *s = va_arg(ap, const char *); |
255 | dstr_puts(&d, s); |
256 | } break; |
257 | case '%': |
258 | dstr_putc(&d, '%'); |
259 | break; |
260 | default: |
261 | dstr_putc(&d, '%'); |
262 | dstr_putc(&d, *q); |
263 | break; |
264 | } |
265 | q++; |
266 | } else { |
267 | n = strcspn(q, "%"); |
268 | DPUTM(&d, q, n); |
269 | q += n; |
270 | } |
271 | } |
272 | if (verbose > 1) |
273 | dstr_puts(&d, " ]"); |
274 | DPUTZ(&d); |
275 | cp->cp_report(what, verbose, p, d.buf, cp->cp_arg); |
276 | dstr_destroy(&d); |
277 | va_end(ap); |
278 | } else |
279 | cp->cp_report(what, verbose, p, 0, cp->cp_arg); |
280 | } |
281 | |
282 | /* --- @sanity@ --- * |
283 | * |
284 | * Arguments: @const char *p@ = name of directory to check |
285 | * @struct stat *st@ = pointer to @stat@(2) block for it |
286 | * @struct chkpath *cp@ = pointer to caller parameters |
287 | * @unsigned f@ = various flags |
288 | * |
289 | * Returns: Zero if everything's OK, else bitmask of problems. |
290 | * |
291 | * Use: Performs the main load of sanity-checking on a directory. |
292 | */ |
293 | |
294 | static int sanity(const char *p, struct stat *st, |
295 | struct chkpath *cp, unsigned f) |
296 | { |
297 | int bad = 0; |
298 | int sticky = (cp->cp_what & CP_STICKYOK) || !(f & f_last) ? 01000 : 0; |
299 | |
300 | /* --- Check for world-writability --- */ |
301 | |
302 | if ((cp->cp_what & CP_WRWORLD) && |
303 | (st->st_mode & (0002 | sticky)) == 0002) { |
304 | bad |= CP_WRWORLD; |
305 | report(cp, CP_WRWORLD, 1, p, "** world writable **"); |
306 | } |
307 | |
308 | /* --- Check for group-writability --- */ |
309 | |
310 | if ((cp->cp_what & (CP_WRGRP | CP_WROTHGRP)) && |
311 | (st->st_mode & (0020 | sticky)) == 0020) { |
312 | if (cp->cp_what & CP_WRGRP) { |
313 | bad |= CP_WRGRP; |
314 | report(cp, CP_WRGRP, 1, p, "writable by group %g", st->st_gid); |
315 | } else { |
316 | int i; |
317 | for (i = 0; i < cp->cp_gids; i++) { |
318 | if (st->st_gid == cp->cp_gid[i]) |
319 | goto good_gid; |
320 | } |
321 | bad |= CP_WROTHGRP; |
322 | report(cp, CP_WROTHGRP, 1, p, "writable by group %g", st->st_gid); |
323 | good_gid:; |
324 | } |
325 | } |
326 | |
327 | /* --- Check for user-writability --- */ |
328 | |
329 | if ((cp->cp_what & CP_WROTHUSR) && |
330 | st->st_uid != cp->cp_uid && |
331 | st->st_uid != 0) { |
332 | bad |= CP_WROTHUSR; |
333 | report(cp, CP_WROTHUSR, 1, p, "owner is user %u", st->st_uid); |
334 | } |
335 | |
336 | /* --- Done sanity check --- */ |
337 | |
338 | return (bad); |
339 | } |
340 | |
341 | /* --- @path_check@ --- * |
342 | * |
343 | * Arguments: @const char *p@ = directory name which needs checking |
344 | * @struct chkpath *cp@ = caller parameters for the check |
345 | * |
346 | * Returns: Zero if all is well, otherwise bitmask of problems. |
347 | * |
348 | * Use: Scrutinises a directory path to see what evil things other |
349 | * users could do to it. |
350 | */ |
351 | |
352 | int path_check(const char *p, struct chkpath *cp) |
353 | { |
354 | char cwd[PATH_MAX]; |
355 | struct elt *e, *ee; |
356 | struct stat st; |
357 | int bad = 0; |
358 | |
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359 | /* --- Initialize stack pointer and path string --- */ |
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360 | |
361 | sp = &rootnode; |
362 | dstr_destroy(&d); |
363 | |
364 | /* --- Try to find the current directory --- */ |
365 | |
366 | if (!getcwd(cwd, sizeof(cwd))) { |
367 | report(cp, CP_ERROR, 0, 0, "can't find current directory: %e"); |
368 | return (CP_ERROR); |
369 | } |
370 | |
371 | /* --- Check that the root directory is OK --- */ |
372 | |
373 | if (stat("/", &st)) { |
374 | report(cp, CP_ERROR, 0, 0, "can't stat root directory: %e"); |
375 | return (CP_ERROR); |
376 | } |
377 | |
378 | report(cp, CP_REPORT, 3, p, "begin scan"); |
379 | bad |= sanity("/", &st, cp, 0); |
380 | |
381 | /* --- Get the initial list of things to process --- */ |
382 | |
383 | ee = splitpath(p, 0); |
384 | if (*p != '/') |
385 | ee = splitpath(cwd, ee); |
386 | |
387 | /* --- While there are list items which still need doing --- */ |
388 | |
389 | while (ee) { |
390 | e = ee->e_link; |
391 | |
392 | /* --- Strip off simple `.' elements --- */ |
393 | |
394 | if (strcmp(ee->e_name, ".") == 0) { |
395 | free(ee); |
396 | ee = e; |
397 | continue; |
398 | } |
399 | |
400 | /* --- Backtrack on `..' elements --- */ |
401 | |
402 | else if (strcmp(ee->e_name, "..") == 0) { |
403 | pop(); |
404 | free(ee); |
405 | ee = e; |
406 | continue; |
407 | } |
408 | |
409 | /* --- Everything else gets pushed on the end --- */ |
410 | |
411 | push(ee); |
412 | ee = e; |
413 | |
414 | /* --- Find out what sort of a thing this is --- */ |
415 | |
416 | if (lstat(d.buf, &st)) { |
417 | report(cp, CP_ERROR, 0, d.buf, "can't stat: %e"); |
418 | bad |= CP_ERROR; |
419 | break; |
420 | } |
421 | |
422 | /* --- Handle symbolic links specially --- */ |
423 | |
424 | if (S_ISLNK(st.st_mode)) { |
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425 | dstr buf = DSTR_INIT; |
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426 | int i; |
427 | |
428 | /* --- Resolve the link --- */ |
429 | |
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430 | dstr_ensure(&buf, st.st_size + 1); |
431 | if ((i = readlink(d.buf, buf.buf, buf.sz)) < 0) { |
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432 | report(cp, CP_ERROR, 0, d.buf, "can't readlink: %e"); |
433 | bad |= CP_ERROR; |
434 | break; |
435 | } |
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436 | buf.buf[i] = 0; |
437 | report(cp, CP_SYMLINK, 2, d.buf, "symlink -> `%s'", buf.buf); |
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438 | |
439 | /* --- Handle sticky parents --- * |
440 | * |
441 | * If I make a symlink in a sticky directory, I can later modify it. |
442 | * However, nobody else can (except the owner of the directory, and |
443 | * we'll already have noticed that if we care). |
444 | */ |
445 | |
446 | if ((cp->cp_what & CP_WROTHUSR) && |
447 | (sp->e_link->e_flags & f_sticky) && |
448 | st.st_uid != cp->cp_uid && st.st_uid != 0) { |
449 | bad |= CP_WROTHUSR; |
450 | report(cp, CP_WROTHUSR, 1, d.buf, |
451 | "symlink modifiable by user %u", st.st_uid); |
452 | } |
453 | |
454 | /* --- Sort out what to do from here --- */ |
455 | |
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456 | if (buf.buf[0] == '/') |
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457 | popall(); |
458 | else |
459 | pop(); |
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460 | ee = splitpath(buf.buf, ee); |
461 | dstr_destroy(&buf); |
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462 | continue; |
463 | } |
464 | |
465 | /* --- Run the sanity check on this path element --- */ |
466 | |
467 | bad |= sanity(d.buf, &st, cp, ee ? 0 : f_last); |
468 | |
469 | if (S_ISDIR(st.st_mode)) { |
470 | if (st.st_mode & 01000) |
471 | sp->e_flags |= f_sticky; |
472 | report(cp, CP_REPORT, 4, d.buf, "directory"); |
473 | continue; |
474 | } |
475 | |
476 | /* --- Something else I don't understand --- */ |
477 | |
478 | break; |
479 | } |
480 | |
481 | /* --- Check for leftover junk --- */ |
482 | |
483 | if (ee) { |
484 | if (!(bad & CP_ERROR)) |
485 | report(cp, CP_ERROR, 0, 0, "junk left over after reaching leaf"); |
486 | while (ee) { |
487 | e = ee->e_link; |
488 | free(ee); |
489 | ee = e; |
490 | } |
491 | } |
492 | |
493 | popall(); |
494 | return (bad); |
495 | } |
496 | |
497 | /* --- @path_setids@ --- * |
498 | * |
499 | * Arguments: @struct chkpath *cp@ = pointer to block to fill in |
500 | * |
501 | * Returns: Zero if OK, else @-1@. |
502 | * |
503 | * Use: Fills in the user ids and things in the structure. |
504 | */ |
505 | |
506 | void path_setids(struct chkpath *cp) |
507 | { |
508 | int n, i; |
509 | gid_t g = getgid(); |
510 | |
511 | cp->cp_uid = getuid(); |
512 | n = getgroups(sizeof(cp->cp_gid) / sizeof(cp->cp_gid[0]), cp->cp_gid); |
513 | |
514 | for (i = 0; i < n; i++) { |
515 | if (cp->cp_gid[i] == g) |
516 | goto gid_ok; |
517 | } |
518 | cp->cp_gid[n++] = g; |
519 | gid_ok: |
520 | cp->cp_gids = n; |
521 | } |
522 | |
523 | /*----- That's all, folks -------------------------------------------------*/ |