efa7a97b |
1 | /* -*-c-*- |
2 | * |
194363d4 |
3 | * $Id: checkpath.c,v 1.6 2004/04/08 01:36:22 mdw Exp $ |
efa7a97b |
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 | |
efa7a97b |
29 | /*----- Header files ------------------------------------------------------*/ |
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 | |
d7b5ee0c |
47 | #include "checkpath.h" |
efa7a97b |
48 | |
49 | /*----- Data structures ---------------------------------------------------*/ |
50 | |
51 | /* --- An item in the directory list --- * |
52 | * |
53 | * Each directory becomes an element on a list which is manipulated in a |
54 | * stack-like way. |
55 | */ |
56 | |
57 | struct elt { |
58 | struct elt *e_link; /* Pointer to the next one along */ |
59 | size_t e_offset; /* Offset of name in path string */ |
60 | unsigned e_flags; /* Various useful flags */ |
61 | char e_name[1]; /* Name of the directory */ |
62 | }; |
63 | |
7868d789 |
64 | #define f_sticky 1u /* Directory has sticky bit set */ |
efa7a97b |
65 | |
7868d789 |
66 | #define f_last 1u /* This is the final item to check */ |
efa7a97b |
67 | |
68 | /*----- Static variables --------------------------------------------------*/ |
69 | |
70 | static struct elt rootnode = { 0, 0, 0 }; /* Root of the list */ |
71 | static struct elt *sp; /* Stack pointer for list */ |
72462155 |
72 | static dstr d = DSTR_INIT; /* Current path string */ |
efa7a97b |
73 | |
74 | /*----- Main code ---------------------------------------------------------*/ |
75 | |
76 | /* --- @splitpath@ --- * |
77 | * |
78 | * Arguments: @const char *path@ = path string to break apart |
79 | * @struct elt *tail@ = tail block to attach to end of list |
80 | * |
81 | * Returns: Pointer to the new list head. |
82 | * |
83 | * Use: Breaks a path string into directories and adds each one |
84 | * as a node on the list, in the right order. These can then |
85 | * be pushed onto the directory stack as required. |
86 | */ |
87 | |
88 | static struct elt *splitpath(const char *path, struct elt *tail) |
89 | { |
90 | struct elt *head, **ee = &head, *e; |
91 | |
92 | while (*path) { |
93 | size_t n; |
94 | |
95 | /* --- Either a leading `/', or a doubled one --- * |
96 | * |
97 | * Either way, ignore it. |
98 | */ |
99 | |
100 | if (*path == '/') { |
101 | path++; |
102 | continue; |
103 | } |
104 | |
105 | /* --- Skip to the next directory separator --- * |
106 | * |
107 | * Build a list element for it, and link it on. |
108 | */ |
109 | |
110 | n = strcspn(path, "/"); |
111 | e = xmalloc(sizeof(struct elt) + n + 1); |
112 | memcpy(e->e_name, path, n); |
113 | e->e_name[n] = 0; |
114 | e->e_flags = 0; |
115 | *ee = e; |
116 | ee = &e->e_link; |
117 | path += n; |
118 | } |
119 | |
120 | /* --- Done --- */ |
121 | |
122 | *ee = tail; |
123 | return (head); |
124 | } |
125 | |
126 | /* --- @pop@ --- * |
127 | * |
128 | * Arguments: --- |
129 | * |
130 | * Returns: --- |
131 | * |
132 | * Use: Removes the top item from the directory stack. |
133 | */ |
134 | |
135 | static void pop(void) |
136 | { |
137 | if (sp->e_link) { |
138 | struct elt *e = sp->e_link; |
139 | d.len = sp->e_offset; |
140 | DPUTZ(&d); |
141 | sp = e; |
142 | } |
143 | } |
144 | |
145 | /* --- @popall@ --- * |
146 | * |
147 | * Arguments: --- |
148 | * |
149 | * Returns: --- |
150 | * |
151 | * Use: Removes all the items from the directory stack. |
152 | */ |
153 | |
154 | static void popall(void) |
155 | { |
156 | while (sp->e_link) |
157 | pop(); |
158 | } |
159 | |
160 | /* --- @push@ --- * |
161 | * |
162 | * Arguments: @struct elt *e@ = pointer to directory element |
163 | * |
164 | * Returns: --- |
165 | * |
166 | * Use: Pushes a new subdirectory onto the stack. |
167 | */ |
168 | |
169 | static void push(struct elt *e) |
170 | { |
171 | e->e_link = sp; |
172 | e->e_offset = d.len; |
173 | DPUTC(&d, '/'); |
174 | DPUTS(&d, e->e_name); |
175 | sp = e; |
176 | } |
177 | |
178 | /* --- @report@ --- * |
179 | * |
d7b5ee0c |
180 | * Arguments: @const struct checkpath *cp@ = pointer to context |
181 | * @unsigned what@ = what sort of report is this? |
efa7a97b |
182 | * @int verbose@ = how verbose is this? |
183 | * @const char *p@ = what path does it refer to? |
184 | * @const char *msg@ = the message to give to the user |
185 | * |
186 | * Returns: --- |
187 | * |
188 | * Use: Formats and presents messages to the client. |
189 | */ |
190 | |
d7b5ee0c |
191 | static void report(const struct checkpath *cp, unsigned what, int verbose, |
efa7a97b |
192 | const char *p, const char *msg, ...) |
193 | { |
194 | /* --- Decide whether to bin this message --- */ |
195 | |
196 | if (!cp->cp_report || verbose > cp->cp_verbose || !(cp->cp_what & what)) |
197 | return; |
198 | |
199 | /* --- Format the message nicely --- */ |
200 | |
201 | if (cp->cp_what & CP_REPORT) { |
72462155 |
202 | dstr d = DSTR_INIT; |
efa7a97b |
203 | va_list ap; |
204 | const char *q = msg; |
205 | size_t n; |
206 | int e = errno; |
207 | |
efa7a97b |
208 | va_start(ap, msg); |
209 | if (verbose > 1) |
210 | dstr_puts(&d, "[ "); |
211 | if (p) |
212 | dstr_putf(&d, "Path: %s: ", p); |
213 | while (*q) { |
214 | if (*q == '%') { |
215 | q++; |
216 | switch (*q) { |
217 | case 'e': |
218 | dstr_puts(&d, strerror(e)); |
219 | break; |
220 | case 'u': { |
221 | uid_t u = (uid_t)va_arg(ap, int); |
222 | struct passwd *pw = getpwuid(u); |
223 | if (pw) |
224 | dstr_putf(&d, "`%s'", pw->pw_name); |
225 | else |
226 | dstr_putf(&d, "%i", (int)u); |
227 | } break; |
228 | case 'g': { |
229 | gid_t g = (gid_t)va_arg(ap, int); |
230 | struct group *gr = getgrgid(g); |
231 | if (gr) |
232 | dstr_putf(&d, "`%s'", gr->gr_name); |
233 | else |
234 | dstr_putf(&d, "%i", (int)g); |
235 | } break; |
236 | case 's': { |
237 | const char *s = va_arg(ap, const char *); |
238 | dstr_puts(&d, s); |
239 | } break; |
240 | case '%': |
241 | dstr_putc(&d, '%'); |
242 | break; |
243 | default: |
244 | dstr_putc(&d, '%'); |
245 | dstr_putc(&d, *q); |
246 | break; |
247 | } |
248 | q++; |
249 | } else { |
250 | n = strcspn(q, "%"); |
251 | DPUTM(&d, q, n); |
252 | q += n; |
253 | } |
254 | } |
255 | if (verbose > 1) |
256 | dstr_puts(&d, " ]"); |
257 | DPUTZ(&d); |
258 | cp->cp_report(what, verbose, p, d.buf, cp->cp_arg); |
259 | dstr_destroy(&d); |
260 | va_end(ap); |
261 | } else |
262 | cp->cp_report(what, verbose, p, 0, cp->cp_arg); |
263 | } |
264 | |
265 | /* --- @sanity@ --- * |
266 | * |
267 | * Arguments: @const char *p@ = name of directory to check |
268 | * @struct stat *st@ = pointer to @stat@(2) block for it |
d7b5ee0c |
269 | * @const struct checkpath *cp@ = pointer to caller parameters |
efa7a97b |
270 | * @unsigned f@ = various flags |
271 | * |
272 | * Returns: Zero if everything's OK, else bitmask of problems. |
273 | * |
274 | * Use: Performs the main load of sanity-checking on a directory. |
275 | */ |
276 | |
d7b5ee0c |
277 | static unsigned sanity(const char *p, struct stat *st, |
278 | const struct checkpath *cp, unsigned f) |
efa7a97b |
279 | { |
d7b5ee0c |
280 | unsigned bad = 0; |
281 | int stickyok = 0; |
282 | |
283 | if (S_ISDIR(st->st_mode) && |
284 | (!(f & f_last) || (cp->cp_what & CP_STICKYOK))) |
285 | stickyok = 01000; |
efa7a97b |
286 | |
287 | /* --- Check for world-writability --- */ |
288 | |
289 | if ((cp->cp_what & CP_WRWORLD) && |
d7b5ee0c |
290 | (st->st_mode & (0002 | stickyok)) == 0002) { |
efa7a97b |
291 | bad |= CP_WRWORLD; |
292 | report(cp, CP_WRWORLD, 1, p, "** world writable **"); |
293 | } |
294 | |
295 | /* --- Check for group-writability --- */ |
296 | |
297 | if ((cp->cp_what & (CP_WRGRP | CP_WROTHGRP)) && |
d7b5ee0c |
298 | (st->st_mode & (0020 | stickyok)) == 0020) { |
299 | int i; |
300 | unsigned b = CP_WRGRP; |
301 | |
302 | if (cp->cp_what & CP_WROTHGRP) { |
303 | b = CP_WROTHGRP; |
efa7a97b |
304 | for (i = 0; i < cp->cp_gids; i++) { |
305 | if (st->st_gid == cp->cp_gid[i]) |
d7b5ee0c |
306 | b = cp->cp_what & CP_WRGRP; |
efa7a97b |
307 | } |
d7b5ee0c |
308 | } |
309 | if (b) { |
310 | bad |= b; |
311 | report(cp, b, 1, p, "writable by %sgroup %g", |
312 | (b == CP_WROTHGRP) ? "other " : "", st->st_gid); |
efa7a97b |
313 | } |
314 | } |
315 | |
316 | /* --- Check for user-writability --- */ |
317 | |
318 | if ((cp->cp_what & CP_WROTHUSR) && |
319 | st->st_uid != cp->cp_uid && |
320 | st->st_uid != 0) { |
321 | bad |= CP_WROTHUSR; |
322 | report(cp, CP_WROTHUSR, 1, p, "owner is user %u", st->st_uid); |
323 | } |
324 | |
325 | /* --- Done sanity check --- */ |
326 | |
327 | return (bad); |
328 | } |
329 | |
d7b5ee0c |
330 | /* --- @checkpath@ --- * |
efa7a97b |
331 | * |
332 | * Arguments: @const char *p@ = directory name which needs checking |
d7b5ee0c |
333 | * @const struct checkpath *cp@ = parameters for the check |
efa7a97b |
334 | * |
335 | * Returns: Zero if all is well, otherwise bitmask of problems. |
336 | * |
337 | * Use: Scrutinises a directory path to see what evil things other |
338 | * users could do to it. |
339 | */ |
340 | |
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341 | unsigned checkpath(const char *p, const struct checkpath *cp) |
efa7a97b |
342 | { |
343 | char cwd[PATH_MAX]; |
344 | struct elt *e, *ee; |
345 | struct stat st; |
d7b5ee0c |
346 | unsigned bad = 0; |
efa7a97b |
347 | |
72462155 |
348 | /* --- Initialize stack pointer and path string --- */ |
efa7a97b |
349 | |
350 | sp = &rootnode; |
351 | dstr_destroy(&d); |
352 | |
353 | /* --- Try to find the current directory --- */ |
354 | |
355 | if (!getcwd(cwd, sizeof(cwd))) { |
356 | report(cp, CP_ERROR, 0, 0, "can't find current directory: %e"); |
357 | return (CP_ERROR); |
358 | } |
359 | |
360 | /* --- Check that the root directory is OK --- */ |
361 | |
362 | if (stat("/", &st)) { |
363 | report(cp, CP_ERROR, 0, 0, "can't stat root directory: %e"); |
364 | return (CP_ERROR); |
365 | } |
366 | |
367 | report(cp, CP_REPORT, 3, p, "begin scan"); |
368 | bad |= sanity("/", &st, cp, 0); |
369 | |
370 | /* --- Get the initial list of things to process --- */ |
371 | |
372 | ee = splitpath(p, 0); |
373 | if (*p != '/') |
374 | ee = splitpath(cwd, ee); |
375 | |
376 | /* --- While there are list items which still need doing --- */ |
377 | |
378 | while (ee) { |
379 | e = ee->e_link; |
380 | |
381 | /* --- Strip off simple `.' elements --- */ |
382 | |
383 | if (strcmp(ee->e_name, ".") == 0) { |
384 | free(ee); |
385 | ee = e; |
386 | continue; |
387 | } |
388 | |
389 | /* --- Backtrack on `..' elements --- */ |
390 | |
391 | else if (strcmp(ee->e_name, "..") == 0) { |
392 | pop(); |
393 | free(ee); |
394 | ee = e; |
395 | continue; |
396 | } |
397 | |
398 | /* --- Everything else gets pushed on the end --- */ |
399 | |
400 | push(ee); |
401 | ee = e; |
402 | |
403 | /* --- Find out what sort of a thing this is --- */ |
404 | |
405 | if (lstat(d.buf, &st)) { |
406 | report(cp, CP_ERROR, 0, d.buf, "can't stat: %e"); |
407 | bad |= CP_ERROR; |
408 | break; |
409 | } |
410 | |
411 | /* --- Handle symbolic links specially --- */ |
412 | |
413 | if (S_ISLNK(st.st_mode)) { |
72462155 |
414 | dstr buf = DSTR_INIT; |
efa7a97b |
415 | int i; |
416 | |
417 | /* --- Resolve the link --- */ |
418 | |
558a9b22 |
419 | dstr_ensure(&buf, st.st_size + 1); |
420 | if ((i = readlink(d.buf, buf.buf, buf.sz)) < 0) { |
efa7a97b |
421 | report(cp, CP_ERROR, 0, d.buf, "can't readlink: %e"); |
422 | bad |= CP_ERROR; |
423 | break; |
424 | } |
558a9b22 |
425 | buf.buf[i] = 0; |
426 | report(cp, CP_SYMLINK, 2, d.buf, "symlink -> `%s'", buf.buf); |
efa7a97b |
427 | |
428 | /* --- Handle sticky parents --- * |
429 | * |
430 | * If I make a symlink in a sticky directory, I can later modify it. |
431 | * However, nobody else can (except the owner of the directory, and |
432 | * we'll already have noticed that if we care). |
433 | */ |
434 | |
435 | if ((cp->cp_what & CP_WROTHUSR) && |
436 | (sp->e_link->e_flags & f_sticky) && |
437 | st.st_uid != cp->cp_uid && st.st_uid != 0) { |
438 | bad |= CP_WROTHUSR; |
439 | report(cp, CP_WROTHUSR, 1, d.buf, |
440 | "symlink modifiable by user %u", st.st_uid); |
441 | } |
442 | |
443 | /* --- Sort out what to do from here --- */ |
444 | |
558a9b22 |
445 | if (buf.buf[0] == '/') |
efa7a97b |
446 | popall(); |
447 | else |
448 | pop(); |
558a9b22 |
449 | ee = splitpath(buf.buf, ee); |
450 | dstr_destroy(&buf); |
efa7a97b |
451 | continue; |
452 | } |
453 | |
454 | /* --- Run the sanity check on this path element --- */ |
455 | |
456 | bad |= sanity(d.buf, &st, cp, ee ? 0 : f_last); |
457 | |
458 | if (S_ISDIR(st.st_mode)) { |
459 | if (st.st_mode & 01000) |
460 | sp->e_flags |= f_sticky; |
461 | report(cp, CP_REPORT, 4, d.buf, "directory"); |
462 | continue; |
463 | } |
464 | |
465 | /* --- Something else I don't understand --- */ |
466 | |
467 | break; |
468 | } |
469 | |
470 | /* --- Check for leftover junk --- */ |
471 | |
472 | if (ee) { |
473 | if (!(bad & CP_ERROR)) |
474 | report(cp, CP_ERROR, 0, 0, "junk left over after reaching leaf"); |
475 | while (ee) { |
476 | e = ee->e_link; |
477 | free(ee); |
478 | ee = e; |
479 | } |
480 | } |
481 | |
482 | popall(); |
483 | return (bad); |
484 | } |
485 | |
d7b5ee0c |
486 | /* --- @checkpath_setids@ --- * |
efa7a97b |
487 | * |
d7b5ee0c |
488 | * Arguments: @struct checkpath *cp@ = pointer to block to fill in |
efa7a97b |
489 | * |
d7b5ee0c |
490 | * Returns: --- |
efa7a97b |
491 | * |
492 | * Use: Fills in the user ids and things in the structure. |
493 | */ |
494 | |
d7b5ee0c |
495 | void checkpath_setids(struct checkpath *cp) |
efa7a97b |
496 | { |
497 | int n, i; |
498 | gid_t g = getgid(); |
499 | |
500 | cp->cp_uid = getuid(); |
501 | n = getgroups(sizeof(cp->cp_gid) / sizeof(cp->cp_gid[0]), cp->cp_gid); |
502 | |
503 | for (i = 0; i < n; i++) { |
504 | if (cp->cp_gid[i] == g) |
505 | goto gid_ok; |
506 | } |
507 | cp->cp_gid[n++] = g; |
508 | gid_ok: |
509 | cp->cp_gids = n; |
510 | } |
511 | |
512 | /*----- That's all, folks -------------------------------------------------*/ |