mdw@git.distorted.org.uk Git - checkpath/blob - checkpath.c

   1 /* -*-c-*-
   2  *
   3  * $Id: checkpath.c,v 1.1 1999/04/06 20:12:07 mdw Exp $
   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 $
  32  * Revision 1.1  1999/04/06 20:12:07  mdw
  33  * Initial revision
  34  *
  35  */
  36
  37 /*----- Header files ------------------------------------------------------*/
  38
  39 #include <errno.h>
  40 #include <stdarg.h>
  41 #include <stdio.h>
  42 #include <stdlib.h>
  43 #include <string.h>
  44
  45 #include <sys/types.h>
  46 #include <sys/stat.h>
  47 #include <unistd.h>
  48
  49 #include <pwd.h>
  50 #include <grp.h>
  51
  52 #include <mLib/alloc.h>
  53 #include <mLib/dstr.h>
  54
  55 #include "path.h"
  56
  57 /*----- Data structures ---------------------------------------------------*/
  58
  59 /* --- An item in the directory list --- *
  60  *
  61  * Each directory becomes an element on a list which is manipulated in a
  62  * stack-like way.
  63  */
  64
  65 struct elt {
  66   struct elt *e_link;                   /* Pointer to the next one along */
  67   size_t e_offset;                      /* Offset of name in path string */
  68   unsigned e_flags;                     /* Various useful flags */
  69   char e_name[1];                       /* Name of the directory */
  70 };
  71
  72 enum {
  73   f_sticky = 1                          /* Directory has sticky bit set */
  74 };
  75
  76 enum {
  77   f_last = 1                            /* This is the final item to check */
  78 };
  79
  80 /*----- Static variables --------------------------------------------------*/
  81
  82 static struct elt rootnode = { 0, 0, 0 }; /* Root of the list */
  83 static struct elt *sp;                  /* Stack pointer for list */
  84 static dstr d;                          /* Current path string */
  85
  86 /*----- Main code ---------------------------------------------------------*/
  87
  88 /* --- @splitpath@ --- *
  89  *
  90  * Arguments:   @const char *path@ = path string to break apart
  91  *              @struct elt *tail@ = tail block to attach to end of list
  92  *
  93  * Returns:     Pointer to the new list head.
  94  *
  95  * Use:         Breaks a path string into directories and adds each one
  96  *              as a node on the list, in the right order.  These can then
  97  *              be pushed onto the directory stack as required.
  98  */
  99
 100 static struct elt *splitpath(const char *path, struct elt *tail)
 101 {
 102   struct elt *head, **ee = &head, *e;
 103
 104   while (*path) {
 105     size_t n;
 106
 107     /* --- Either a leading `/', or a doubled one --- *
 108      *
 109      * Either way, ignore it.
 110      */
 111
 112     if (*path == '/') {
 113       path++;
 114       continue;
 115     }
 116
 117     /* --- Skip to the next directory separator --- *
 118      *
 119      * Build a list element for it, and link it on.
 120      */
 121
 122     n = strcspn(path, "/");
 123     e = xmalloc(sizeof(struct elt) + n + 1);
 124     memcpy(e->e_name, path, n);
 125     e->e_name[n] = 0;
 126     e->e_flags = 0;
 127     *ee = e;
 128     ee = &e->e_link;
 129     path += n;
 130   }
 131
 132   /* --- Done --- */
 133
 134   *ee = tail;
 135   return (head);
 136 }
 137
 138 /* --- @pop@ --- *
 139  *
 140  * Arguments:   ---
 141  *
 142  * Returns:     ---
 143  *
 144  * Use:         Removes the top item from the directory stack.
 145  */
 146
 147 static void pop(void)
 148 {
 149   if (sp->e_link) {
 150     struct elt *e = sp->e_link;
 151     d.len = sp->e_offset;
 152     DPUTZ(&d);
 153     sp = e;
 154   }
 155 }
 156
 157 /* --- @popall@ --- *
 158  *
 159  * Arguments:   ---
 160  *
 161  * Returns:     ---
 162  *
 163  * Use:         Removes all the items from the directory stack.
 164  */
 165
 166 static void popall(void)
 167 {
 168   while (sp->e_link)
 169     pop();
 170 }
 171
 172 /* --- @push@ --- *
 173  *
 174  * Arguments:   @struct elt *e@ = pointer to directory element
 175  *
 176  * Returns:     ---
 177  *
 178  * Use:         Pushes a new subdirectory onto the stack.
 179  */
 180
 181 static void push(struct elt *e)
 182 {
 183   e->e_link = sp;
 184   e->e_offset = d.len;
 185   DPUTC(&d, '/');
 186   DPUTS(&d, e->e_name);
 187   sp = e;
 188 }
 189
 190 /* --- @report@ --- *
 191  *
 192  * Arguments:   @struct chkpath *cp@ = pointer to context
 193  *              @int what@ = what sort of report is this?
 194  *              @int verbose@ = how verbose is this?
 195  *              @const char *p@ = what path does it refer to?
 196  *              @const char *msg@ = the message to give to the user
 197  *
 198  * Returns:     ---
 199  *
 200  * Use:         Formats and presents messages to the client.
 201  */
 202
 203 static void report(struct chkpath *cp, int what, int verbose,
 204                    const char *p, const char *msg, ...)
 205 {
 206   /* --- Decide whether to bin this message --- */
 207
 208   if (!cp->cp_report || verbose > cp->cp_verbose || !(cp->cp_what & what))
 209     return;
 210
 211   /* --- Format the message nicely --- */
 212
 213   if (cp->cp_what & CP_REPORT) {
 214     dstr d;
 215     va_list ap;
 216     const char *q = msg;
 217     size_t n;
 218     int e = errno;
 219
 220     dstr_create(&d);
 221     va_start(ap, msg);
 222     if (verbose > 1)
 223       dstr_puts(&d, "[ ");
 224     if (p)
 225       dstr_putf(&d, "Path: %s: ", p);
 226     while (*q) {
 227       if (*q == '%') {
 228         q++;
 229         switch (*q) {
 230           case 'e':
 231             dstr_puts(&d, strerror(e));
 232             break;
 233           case 'u': {
 234             uid_t u = (uid_t)va_arg(ap, int);
 235             struct passwd *pw = getpwuid(u);
 236             if (pw)
 237               dstr_putf(&d, "`%s'", pw->pw_name);
 238             else
 239               dstr_putf(&d, "%i", (int)u);
 240           } break;
 241           case 'g': {
 242             gid_t g = (gid_t)va_arg(ap, int);
 243             struct group *gr = getgrgid(g);
 244             if (gr)
 245               dstr_putf(&d, "`%s'", gr->gr_name);
 246             else
 247               dstr_putf(&d, "%i", (int)g);
 248           } break;
 249           case 's': {
 250             const char *s = va_arg(ap, const char *);
 251             dstr_puts(&d, s);
 252           } break;
 253           case '%':
 254             dstr_putc(&d, '%');
 255             break;
 256           default:
 257             dstr_putc(&d, '%');
 258             dstr_putc(&d, *q);
 259             break;
 260         }
 261         q++;
 262       } else {
 263         n = strcspn(q, "%");
 264         DPUTM(&d, q, n);
 265         q += n;
 266       }
 267     }
 268     if (verbose > 1)
 269       dstr_puts(&d, " ]");
 270     DPUTZ(&d);
 271     cp->cp_report(what, verbose, p, d.buf, cp->cp_arg);
 272     dstr_destroy(&d);
 273     va_end(ap);
 274   } else
 275     cp->cp_report(what, verbose, p, 0, cp->cp_arg);
 276 }
 277
 278 /* --- @sanity@ --- *
 279  *
 280  * Arguments:   @const char *p@ = name of directory to check
 281  *              @struct stat *st@ = pointer to @stat@(2) block for it
 282  *              @struct chkpath *cp@ = pointer to caller parameters
 283  *              @unsigned f@ = various flags
 284  *
 285  * Returns:     Zero if everything's OK, else bitmask of problems.
 286  *
 287  * Use:         Performs the main load of sanity-checking on a directory.
 288  */
 289
 290 static int sanity(const char *p, struct stat *st,
 291                   struct chkpath *cp, unsigned f)
 292 {
 293   int bad = 0;
 294   int sticky = (cp->cp_what & CP_STICKYOK) || !(f & f_last) ? 01000 : 0;
 295
 296   /* --- Check for world-writability --- */
 297
 298   if ((cp->cp_what & CP_WRWORLD) &&
 299       (st->st_mode & (0002 | sticky)) == 0002) {
 300     bad |= CP_WRWORLD;
 301     report(cp, CP_WRWORLD, 1, p, "** world writable **");
 302   }
 303
 304   /* --- Check for group-writability --- */
 305
 306   if ((cp->cp_what & (CP_WRGRP | CP_WROTHGRP)) &&
 307       (st->st_mode & (0020 | sticky)) == 0020) {
 308     if (cp->cp_what & CP_WRGRP) {
 309       bad |= CP_WRGRP;
 310       report(cp, CP_WRGRP, 1, p, "writable by group %g", st->st_gid);
 311     } else {
 312       int i;
 313       for (i = 0; i < cp->cp_gids; i++) {
 314         if (st->st_gid == cp->cp_gid[i])
 315           goto good_gid;
 316       }
 317       bad |= CP_WROTHGRP;
 318       report(cp, CP_WROTHGRP, 1, p, "writable by group %g", st->st_gid);
 319     good_gid:;
 320     }
 321   }
 322
 323   /* --- Check for user-writability --- */
 324
 325   if ((cp->cp_what & CP_WROTHUSR) &&
 326       st->st_uid != cp->cp_uid &&
 327       st->st_uid != 0) {
 328     bad |= CP_WROTHUSR;
 329     report(cp, CP_WROTHUSR, 1, p, "owner is user %u", st->st_uid);
 330   }
 331
 332   /* --- Done sanity check --- */
 333
 334   return (bad);
 335 }
 336
 337 /* --- @path_check@ --- *
 338  *
 339  * Arguments:   @const char *p@ = directory name which needs checking
 340  *              @struct chkpath *cp@ = caller parameters for the check
 341  *
 342  * Returns:     Zero if all is well, otherwise bitmask of problems.
 343  *
 344  * Use:         Scrutinises a directory path to see what evil things other
 345  *              users could do to it.
 346  */
 347
 348 int path_check(const char *p, struct chkpath *cp)
 349 {
 350   char cwd[PATH_MAX];
 351   struct elt *e, *ee;
 352   struct stat st;
 353   int bad = 0;
 354
 355   /* --- Initialise stack pointer and path string --- */
 356
 357   sp = &rootnode;
 358   dstr_destroy(&d);
 359
 360   /* --- Try to find the current directory --- */
 361
 362   if (!getcwd(cwd, sizeof(cwd))) {
 363     report(cp, CP_ERROR, 0, 0, "can't find current directory: %e");
 364     return (CP_ERROR);
 365   }
 366
 367   /* --- Check that the root directory is OK --- */
 368
 369   if (stat("/", &st)) {
 370     report(cp, CP_ERROR, 0, 0, "can't stat root directory: %e");
 371     return (CP_ERROR);
 372   }
 373
 374   report(cp, CP_REPORT, 3, p, "begin scan");
 375   bad |= sanity("/", &st, cp, 0);
 376
 377   /* --- Get the initial list of things to process --- */
 378
 379   ee = splitpath(p, 0);
 380   if (*p != '/')
 381     ee = splitpath(cwd, ee);
 382
 383   /* --- While there are list items which still need doing --- */
 384
 385   while (ee) {
 386     e = ee->e_link;
 387
 388     /* --- Strip off simple `.' elements --- */
 389
 390     if (strcmp(ee->e_name, ".") == 0) {
 391       free(ee);
 392       ee = e;
 393       continue;
 394     }
 395
 396     /* --- Backtrack on `..' elements --- */
 397
 398     else if (strcmp(ee->e_name, "..") == 0) {
 399       pop();
 400       free(ee);
 401       ee = e;
 402       continue;
 403     }
 404
 405     /* --- Everything else gets pushed on the end --- */
 406
 407     push(ee);
 408     ee = e;
 409
 410     /* --- Find out what sort of a thing this is --- */
 411
 412     if (lstat(d.buf, &st)) {
 413       report(cp, CP_ERROR, 0, d.buf, "can't stat: %e");
 414       bad |= CP_ERROR;
 415       break;
 416     }
 417
 418     /* --- Handle symbolic links specially --- */
 419
 420     if (S_ISLNK(st.st_mode)) {
 421       char buf[PATH_MAX];
 422       int i;
 423
 424       /* --- Resolve the link --- */
 425
 426       if ((i = readlink(d.buf, buf, sizeof(buf))) < 0) {
 427         report(cp, CP_ERROR, 0, d.buf, "can't readlink: %e");
 428         bad |= CP_ERROR;
 429         break;
 430       }
 431       buf[i] = 0;
 432       report(cp, CP_SYMLINK, 2, d.buf, "symlink -> `%s'", 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[0] == '/')
 452         popall();
 453       else
 454         pop();
 455       ee = splitpath(buf, ee);
 456       continue;
 457     }
 458
 459     /* --- Run the sanity check on this path element --- */
 460
 461     bad |= sanity(d.buf, &st, cp, ee ? 0 : f_last);
 462
 463     if (S_ISDIR(st.st_mode)) {
 464       if (st.st_mode & 01000)
 465         sp->e_flags |= f_sticky;
 466       report(cp, CP_REPORT, 4, d.buf, "directory");
 467       continue;
 468     }
 469
 470     /* --- Something else I don't understand --- */
 471
 472     break;
 473   }
 474
 475   /* --- Check for leftover junk --- */
 476
 477   if (ee) {
 478     if (!(bad & CP_ERROR))
 479       report(cp, CP_ERROR, 0, 0, "junk left over after reaching leaf");
 480     while (ee) {
 481       e = ee->e_link;
 482       free(ee);
 483       ee = e;
 484     }
 485   }
 486
 487   popall();
 488   return (bad);
 489 }
 490
 491 /* --- @path_setids@ --- *
 492  *
 493  * Arguments:   @struct chkpath *cp@ = pointer to block to fill in
 494  *
 495  * Returns:     Zero if OK, else @-1@.
 496  *
 497  * Use:         Fills in the user ids and things in the structure.
 498  */
 499
 500 void path_setids(struct chkpath *cp)
 501 {
 502   int n, i;
 503   gid_t g = getgid();
 504
 505   cp->cp_uid = getuid();
 506   n = getgroups(sizeof(cp->cp_gid) / sizeof(cp->cp_gid[0]), cp->cp_gid);
 507
 508   for (i = 0; i < n; i++) {
 509     if (cp->cp_gid[i] == g)
 510       goto gid_ok;
 511   }
 512   cp->cp_gid[n++] = g;
 513 gid_ok:
 514   cp->cp_gids = n;
 515 }
 516
 517 /*----- That's all, folks -------------------------------------------------*/