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

   1 /* -*-c-*-
   2  *
   3  * $Id: path.c,v 1.4 2001/01/25 22:16:02 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: path.c,v $
  32  * Revision 1.4  2001/01/25 22:16:02  mdw
  33  * Make flags be unsigned.
  34  *
  35  * Revision 1.3  1999/05/21 22:07:20  mdw
  36  * Take advantage of new dynamic string macros.
  37  *
  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.
  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
  81 #define f_sticky 1u                     /* Directory has sticky bit set */
  82
  83 #define f_last 1u                       /* This is the final item to check */
  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 */
  89 static dstr d = DSTR_INIT;              /* Current path string */
  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) {
 219     dstr d = DSTR_INIT;
 220     va_list ap;
 221     const char *q = msg;
 222     size_t n;
 223     int e = errno;
 224
 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
 359   /* --- Initialize stack pointer and path string --- */
 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)) {
 425       dstr buf = DSTR_INIT;
 426       int i;
 427
 428       /* --- Resolve the link --- */
 429
 430       dstr_ensure(&buf, st.st_size + 1);
 431       if ((i = readlink(d.buf, buf.buf, buf.sz)) < 0) {
 432         report(cp, CP_ERROR, 0, d.buf, "can't readlink: %e");
 433         bad |= CP_ERROR;
 434         break;
 435       }
 436       buf.buf[i] = 0;
 437       report(cp, CP_SYMLINK, 2, d.buf, "symlink -> `%s'", buf.buf);
 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
 456       if (buf.buf[0] == '/')
 457         popall();
 458       else
 459         pop();
 460       ee = splitpath(buf.buf, ee);
 461       dstr_destroy(&buf);
 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 -------------------------------------------------*/