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

   1 /* -*-c-*-
   2  *
   3  * Check a path for safety
   4  *
   5  * (c) 1999 Mark Wooding
   6  */
   7
   8 /*----- Licensing notice --------------------------------------------------*
   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.
  16  *
  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.
  21  *
  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
  27 /*----- Header files ------------------------------------------------------*/
  28
  29 #include "config.h"
  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
  47 #include "checkpath.h"
  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
  64 #define f_sticky 1u                     /* Directory has sticky bit set */
  65
  66 #define f_last 1u                       /* This is the final item to check */
  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 */
  72 static dstr d = DSTR_INIT;              /* Current path string */
  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   { while (sp->e_link) pop(); }
 156
 157 /* --- @push@ --- *
 158  *
 159  * Arguments:   @struct elt *e@ = pointer to directory element
 160  *
 161  * Returns:     ---
 162  *
 163  * Use:         Pushes a new subdirectory onto the stack.
 164  */
 165
 166 static void push(struct elt *e)
 167 {
 168   e->e_link = sp;
 169   e->e_offset = d.len;
 170   DPUTC(&d, '/');
 171   DPUTS(&d, e->e_name);
 172   sp = e;
 173 }
 174
 175 /* --- @report@ --- *
 176  *
 177  * Arguments:   @const struct checkpath *cp@ = pointer to context
 178  *              @unsigned what@ = what sort of report is this?
 179  *              @int verbose@ = how verbose is this?
 180  *              @const char *p@ = what path does it refer to?
 181  *              @const char *msg@ = the message to give to the user
 182  *
 183  * Returns:     ---
 184  *
 185  * Use:         Formats and presents messages to the client.
 186  */
 187
 188 static void report(const struct checkpath *cp, unsigned what, int verbose,
 189                    const char *p, const char *msg, ...)
 190 {
 191   dstr d = DSTR_INIT;
 192   va_list ap;
 193   const char *q = msg;
 194   const char *s;
 195   size_t n;
 196   int e = errno;
 197   uid_t u;
 198   struct passwd *pw;
 199   gid_t g;
 200   struct group *gr;
 201
 202   /* --- Decide whether to bin this message --- */
 203
 204   if (!cp->cp_report || verbose > cp->cp_verbose || !(cp->cp_what & what))
 205     return;
 206
 207   /* --- If no reporting, do the easy thing --- */
 208
 209   if (!(cp->cp_what & CP_REPORT)) {
 210     cp->cp_report(what, verbose, p, 0, cp->cp_arg);
 211     return;
 212   }
 213
 214   /* --- Format the message nicely --- */
 215
 216   va_start(ap, msg);
 217   if (verbose > 1)
 218     dstr_puts(&d, "[ ");
 219   if (p)
 220     dstr_putf(&d, "Path: %s: ", p);
 221   while (*q) {
 222     if (*q == '%') {
 223       q++;
 224       switch (*q) {
 225         case 'e':
 226           dstr_puts(&d, strerror(e));
 227           break;
 228         case 'u':
 229           u = (uid_t)va_arg(ap, int);
 230           if ((pw = getpwuid(u)) != 0)
 231             dstr_putf(&d, "`%s'", pw->pw_name);
 232           else
 233             dstr_putf(&d, "%i", (int)u);
 234           break;
 235         case 'g':
 236           g = (gid_t)va_arg(ap, int);
 237           if ((gr = getgrgid(g)) != 0)
 238             dstr_putf(&d, "`%s'", gr->gr_name);
 239           else
 240             dstr_putf(&d, "%i", (int)g);
 241           break;
 242         case 's':
 243           s = va_arg(ap, const char *);
 244           dstr_puts(&d, s);
 245           break;
 246         case '%':
 247           dstr_putc(&d, '%');
 248           break;
 249         default:
 250           dstr_putc(&d, '%');
 251           dstr_putc(&d, *q);
 252           break;
 253       }
 254       q++;
 255     } else {
 256       n = strcspn(q, "%");
 257       DPUTM(&d, q, n);
 258       q += n;
 259     }
 260   }
 261   if (verbose > 1)
 262     dstr_puts(&d, " ]");
 263   DPUTZ(&d);
 264   cp->cp_report(what, verbose, p, d.buf, cp->cp_arg);
 265   dstr_destroy(&d);
 266   va_end(ap);
 267 }
 268
 269 /* --- @sanity@ --- *
 270  *
 271  * Arguments:   @const char *p@ = name of directory to check
 272  *              @struct stat *st@ = pointer to @stat@(2) block for it
 273  *              @const struct checkpath *cp@ = pointer to caller parameters
 274  *              @unsigned f@ = various flags
 275  *
 276  * Returns:     Zero if everything's OK, else bitmask of problems.
 277  *
 278  * Use:         Performs the main load of sanity-checking on a directory.
 279  */
 280
 281 static unsigned sanity(const char *p, struct stat *st,
 282                        const struct checkpath *cp, unsigned f)
 283 {
 284   unsigned bad = 0;
 285   int stickyok = 0;
 286   int i;
 287   unsigned b;
 288
 289   if (S_ISDIR(st->st_mode) &&
 290       (!(f & f_last) || (cp->cp_what & CP_STICKYOK)))
 291     stickyok = 01000;
 292
 293   /* --- Check for world-writability --- */
 294
 295   if ((cp->cp_what & CP_WRWORLD) &&
 296       (st->st_mode & (0002 | stickyok)) == 0002) {
 297     bad |= CP_WRWORLD;
 298     report(cp, CP_WRWORLD, 1, p, "** world writable **");
 299   }
 300
 301   /* --- Check for group-writability --- */
 302
 303   if ((cp->cp_what & (CP_WRGRP | CP_WROTHGRP)) &&
 304       (st->st_mode & (0020 | stickyok)) == 0020) {
 305     b = CP_WRGRP;
 306
 307     if (cp->cp_what & CP_WROTHGRP) {
 308       b = CP_WROTHGRP;
 309       for (i = 0; i < cp->cp_gids; i++) {
 310         if (st->st_gid == cp->cp_gid[i])
 311           b = cp->cp_what & CP_WRGRP;
 312       }
 313     }
 314     if (b) {
 315       bad |= b;
 316       report(cp, b, 1, p, "writable by %sgroup %g",
 317              (b == CP_WROTHGRP) ? "other " : "", st->st_gid);
 318     }
 319   }
 320
 321   /* --- Check for user-writability --- */
 322
 323   if ((cp->cp_what & CP_WROTHUSR) &&
 324       st->st_uid != cp->cp_uid &&
 325       st->st_uid != 0) {
 326     bad |= CP_WROTHUSR;
 327     report(cp, CP_WROTHUSR, 1, p, "owner is user %u", st->st_uid);
 328   }
 329
 330   /* --- Done sanity check --- */
 331
 332   return (bad);
 333 }
 334
 335 /* --- @checkpath@ --- *
 336  *
 337  * Arguments:   @const char *p@ = directory name which needs checking
 338  *              @const struct checkpath *cp@ = parameters for the check
 339  *
 340  * Returns:     Zero if all is well, otherwise bitmask of problems.
 341  *
 342  * Use:         Scrutinises a directory path to see what evil things other
 343  *              users could do to it.
 344  */
 345
 346 unsigned checkpath(const char *p, const struct checkpath *cp)
 347 {
 348   char cwd[PATH_MAX];
 349   struct elt *e, *ee;
 350   struct stat st;
 351   unsigned bad = 0;
 352
 353   /* --- Initialize stack pointer and path string --- */
 354
 355   sp = &rootnode;
 356   dstr_destroy(&d);
 357
 358   /* --- Try to find the current directory --- */
 359
 360   if (!getcwd(cwd, sizeof(cwd))) {
 361     report(cp, CP_ERROR, 0, 0, "can't find current directory: %e");
 362     return (CP_ERROR);
 363   }
 364
 365   /* --- Check that the root directory is OK --- */
 366
 367   if (stat("/", &st)) {
 368     report(cp, CP_ERROR, 0, 0, "can't stat root directory: %e");
 369     return (CP_ERROR);
 370   }
 371
 372   report(cp, CP_REPORT, 3, p, "begin scan");
 373   bad |= sanity("/", &st, cp, 0);
 374
 375   /* --- Get the initial list of things to process --- */
 376
 377   ee = splitpath(p, 0);
 378   if (*p != '/')
 379     ee = splitpath(cwd, ee);
 380
 381   /* --- While there are list items which still need doing --- */
 382
 383   while (ee) {
 384     e = ee->e_link;
 385
 386     /* --- Strip off simple `.' elements --- */
 387
 388     if (strcmp(ee->e_name, ".") == 0) {
 389       free(ee);
 390       ee = e;
 391       continue;
 392     }
 393
 394     /* --- Backtrack on `..' elements --- */
 395
 396     else if (strcmp(ee->e_name, "..") == 0) {
 397       pop();
 398       free(ee);
 399       ee = e;
 400       continue;
 401     }
 402
 403     /* --- Everything else gets pushed on the end --- */
 404
 405     push(ee);
 406     ee = e;
 407
 408     /* --- Find out what sort of a thing this is --- */
 409
 410     if (lstat(d.buf, &st)) {
 411       report(cp, CP_ERROR, 0, d.buf, "can't stat: %e");
 412       bad |= CP_ERROR;
 413       break;
 414     }
 415
 416     /* --- Handle symbolic links specially --- */
 417
 418     if (S_ISLNK(st.st_mode)) {
 419       dstr buf = DSTR_INIT;
 420       int i;
 421
 422       /* --- Resolve the link --- */
 423
 424       dstr_ensure(&buf, st.st_size + 1);
 425       if ((i = readlink(d.buf, buf.buf, buf.sz)) < 0) {
 426         report(cp, CP_ERROR, 0, d.buf, "can't readlink: %e");
 427         bad |= CP_ERROR;
 428         break;
 429       }
 430       buf.buf[i] = 0;
 431       report(cp, CP_SYMLINK, 2, d.buf, "symlink -> `%s'", buf.buf);
 432
 433       /* --- Handle sticky parents --- *
 434        *
 435        * If I make a symlink in a sticky directory, I can later modify it.
 436        * However, nobody else can (except the owner of the directory, and
 437        * we'll already have noticed that if we care).
 438        */
 439
 440       if ((cp->cp_what & CP_WROTHUSR) &&
 441           (sp->e_link->e_flags & f_sticky) &&
 442           st.st_uid != cp->cp_uid && st.st_uid != 0) {
 443         bad |= CP_WROTHUSR;
 444         report(cp, CP_WROTHUSR, 1, d.buf,
 445                "symlink modifiable by user %u", st.st_uid);
 446       }
 447
 448       /* --- Sort out what to do from here --- */
 449
 450       if (buf.buf[0] == '/')
 451         popall();
 452       else
 453         pop();
 454       ee = splitpath(buf.buf, ee);
 455       dstr_destroy(&buf);
 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 /* --- @checkpath_setids@ --- *
 492  *
 493  * Arguments:   @struct checkpath *cp@ = pointer to block to fill in
 494  *
 495  * Returns:     ---
 496  *
 497  * Use:         Fills in the user ids and things in the structure.
 498  */
 499
 500 void checkpath_setids(struct checkpath *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 -------------------------------------------------*/