dotlock.c

   1 /*@ S-nail - a mail user agent derived from Berkeley Mail.
   2  *@ n_dotlock(): creation of an exclusive "dotlock" file.
   3  *
   4  * Copyright (c) 2015 Steffen (Daode) Nurpmeso <sdaoden@users.sf.net>.
   5  */
   6 #undef n_FILE
   7 #define n_FILE dotlock
   8
   9 #ifndef HAVE_AMALGAMATION
  10 # include "nail.h"
  11 #endif
  12
  13 #include <sys/wait.h>
  14
  15 #ifdef HAVE_DOTLOCK
  16 # include "dotlock.h"
  17 #endif
  18
  19 /* XXX Our Popen() main() takes void, temporary global data store */
  20 #ifdef HAVE_DOTLOCK
  21 static enum n_file_lock_type a_dotlock_flt;
  22 static int a_dotlock_fd;
  23 struct n_dotlock_info *a_dotlock_dip;
  24 #endif
  25
  26 /* main() of fork(2)ed dot file locker */
  27 #ifdef HAVE_DOTLOCK
  28 static int a_dotlock_main(void);
  29 #endif
  30
  31 #ifdef HAVE_DOTLOCK
  32 static int
  33 a_dotlock_main(void){
  34    /* Use PATH_MAX not NAME_MAX to catch those "we proclaim the minimum value"
  35     * problems (SunOS), since the pathconf(3) value comes too late! */
  36    char name[PATH_MAX +1];
  37    struct n_dotlock_info di;
  38    struct stat stb, fdstb;
  39    enum n_dotlock_state dls;
  40    char const *cp;
  41    int fd;
  42    enum n_file_lock_type flt;
  43    NYD_ENTER;
  44
  45    /* Ignore SIGPIPE, we'll see EPIPE and "fall through" */
  46    safe_signal(SIGPIPE, SIG_IGN);
  47
  48    /* Get the arguments "passed to us" */
  49    flt = a_dotlock_flt;
  50    fd = a_dotlock_fd;
  51    UNUSED(fd);
  52    di = *a_dotlock_dip;
  53
  54    /* chdir(2)? */
  55 jislink:
  56    dls = n_DLS_CANT_CHDIR | n_DLS_ABANDON;
  57
  58    if((cp = strrchr(di.di_file_name, '/')) != NULL){
  59       char const *fname = cp + 1;
  60
  61       while(PTRCMP(cp - 1, >, di.di_file_name) && cp[-1] == '/')
  62          --cp;
  63       cp = savestrbuf(di.di_file_name, PTR2SIZE(cp - di.di_file_name));
  64       if(chdir(cp))
  65          goto jmsg;
  66
  67       di.di_file_name = fname;
  68    }
  69
  70    /* So we're here, but then again the file can be a symbolic link!
  71     * This is however only true if we do not have realpath(3) available since
  72     * that'll have resolved the path already otherwise; nonetheless, let
  73     * readlink(2) be a precondition for dotlocking and keep this code */
  74    if(lstat(cp = di.di_file_name, &stb) == -1)
  75       goto jmsg;
  76    if(S_ISLNK(stb.st_mode)){
  77       /* Use salloc() and hope we stay in builtin buffer.. */
  78       char *x;
  79       size_t i;
  80       ssize_t sr;
  81
  82       for(x = NULL, i = PATH_MAX;; i += PATH_MAX){
  83          x = salloc(i +1);
  84          sr = readlink(cp, x, i);
  85          if(sr <= 0){
  86             dls = n_DLS_FISHY | n_DLS_ABANDON;
  87             goto jmsg;
  88          }
  89          if(UICMP(z, sr, <, i)){
  90             x[sr] = '\0';
  91             i = (size_t)sr;
  92             break;
  93          }
  94       }
  95       di.di_file_name = x;
  96       goto jislink;
  97    }
  98
  99    dls = n_DLS_FISHY | n_DLS_ABANDON;
 100
 101    /* Bail out if the file has changed its identity in the meanwhile */
 102    if(fstat(fd, &fdstb) == -1 ||
 103          fdstb.st_dev != stb.st_dev || fdstb.st_ino != stb.st_ino ||
 104          fdstb.st_uid != stb.st_uid || fdstb.st_gid != stb.st_gid ||
 105          fdstb.st_mode != stb.st_mode)
 106       goto jmsg;
 107
 108    /* Be aware, even if the error is false!  Note the shared code in dotlock.h
 109     * *requires* that it is possible to create a filename at least one byte
 110     * longer than di_lock_name! */
 111    do/* while(0) breaker */{
 112 # ifdef HAVE_PATHCONF
 113       long pc;
 114 # endif
 115       int i = snprintf(name, sizeof name, "%s.lock", di.di_file_name);
 116
 117       /* fd is a file, not portable to use for _PC_NAME_MAX */
 118       if(i < 0){
 119 jenametool:
 120          dls = n_DLS_NAMETOOLONG | n_DLS_ABANDON;
 121          goto jmsg;
 122       }
 123 # ifdef HAVE_PATHCONF
 124       errno = 0;
 125       if((pc = pathconf(".", _PC_NAME_MAX)) == -1){
 126          /* errno unchanged: no limit */
 127          if(errno == 0)
 128             break;
 129       }else if(pc - 1 >= (long)i)
 130          break;
 131       else
 132          goto jenametool;
 133 # endif
 134       if(UICMP(z, NAME_MAX - 1, <, (uiz_t)i))
 135          goto jenametool;
 136    }while(0);
 137
 138    di.di_lock_name = name;
 139
 140    /* We are in the directory of the mailbox for which we have to create
 141     * a dotlock file for.  We don't know wether we have realpath(3) available,
 142     * and manually resolving the path is due especially given that S-nail
 143     * supports the special "%:" syntax to warp any file into a "system
 144     * mailbox"; there may also be multiple system mailbox directories...
 145     * So what we do is that we fstat(2) the mailbox and check its UID and
 146     * GID against that of our own process: if any of those mismatch we must
 147     * either assume a directory we are not allowed to write in, or that we run
 148     * via -u/$USER/%USER as someone else, in which case we favour our
 149     * privilege-separated dotlock process */
 150    assert(cp != NULL); /* Ugly: avoid a useless var and reuse that one */
 151    if(access(".", W_OK)){
 152       /* This may however also indicate a read-only filesystem, which is not
 153        * really an error from our point of view since the mailbox will degrade
 154        * to a readonly one for which no dotlock is needed, then, and errors
 155        * may arise only due to actions which require box modifications */
 156       if(errno == EROFS){
 157          dls = n_DLS_ROFS | n_DLS_ABANDON;
 158          goto jmsg;
 159       }
 160       cp = NULL;
 161    }
 162    if(cp == NULL || stb.st_uid != user_id || stb.st_gid != group_id){
 163       char itoabuf[64];
 164       char const *args[13];
 165
 166       snprintf(itoabuf, sizeof itoabuf, "%" PRIuZ, di.di_pollmsecs);
 167       args[ 0] = PRIVSEP;
 168       args[ 1] = (flt == FLT_READ ? "rdotlock" : "wdotlock");
 169       args[ 2] = "mailbox";   args[ 3] = di.di_file_name;
 170       args[ 4] = "name";      args[ 5] = di.di_lock_name;
 171       args[ 6] = "hostname";  args[ 7] = di.di_hostname;
 172       args[ 8] = "randstr";   args[ 9] = di.di_randstr;
 173       args[10] = "pollmsecs"; args[11] = itoabuf;
 174       args[12] = NULL;
 175       execv(LIBEXECDIR "/" UAGENT "-privsep", UNCONST(args));
 176
 177       dls = n_DLS_NOEXEC;
 178       write(STDOUT_FILENO, &dls, sizeof dls);
 179       /* But fall through and try it with normal privileges! */
 180    }
 181
 182    /* So let's try and call it ourselfs!  Note that we don't block signals just
 183     * like our privsep child does, the user will anyway be able to remove his
 184     * file again, and if we're in -u/$USER mode then we are allowed to access
 185     * the user's box: shall we leave behind a stale dotlock then at least we
 186     * start a friendly human conversation.  Since we cannot handle SIGKILL and
 187     * SIGSTOP malicious things could happen whatever we do */
 188    safe_signal(SIGHUP, SIG_IGN);
 189    safe_signal(SIGINT, SIG_IGN);
 190    safe_signal(SIGQUIT, SIG_IGN);
 191    safe_signal(SIGTERM, SIG_IGN);
 192
 193    NYD;
 194    dls = a_dotlock_create(&di);
 195    NYD;
 196
 197    /* Finally: notify our parent about the actual lock state.. */
 198 jmsg:
 199    write(STDOUT_FILENO, &dls, sizeof dls);
 200    close(STDOUT_FILENO);
 201
 202    /* ..then eventually wait until we shall remove the lock again, which will
 203     * be notified via the read returning */
 204    if(dls == n_DLS_NONE){
 205       read(STDIN_FILENO, &dls, sizeof dls);
 206
 207       unlink(name);
 208    }
 209    NYD_LEAVE;
 210    return EXIT_OK;
 211 }
 212 #endif /* HAVE_DOTLOCK */
 213
 214 FL FILE *
 215 n_dotlock(char const *fname, int fd, enum n_file_lock_type flt,
 216       off_t off, off_t len, size_t pollmsecs){
 217 #undef _DOMSG
 218 #ifdef HAVE_DOTLOCK
 219 # define _DOMSG() n_err(_("Creating dotlock for \"%s\" "), fname)
 220 #else
 221 # define _DOMSG() n_err(_("Trying to lock file \"%s\" "), fname)
 222 #endif
 223
 224 #ifdef HAVE_DOTLOCK
 225    int cpipe[2];
 226    struct n_dotlock_info di;
 227    enum n_dotlock_state dls;
 228    char const *emsg;
 229 #endif
 230    int serrno;
 231    union {size_t tries; int (*ptf)(void); char const *sh; ssize_t r;} u;
 232    bool_t flocked, didmsg;
 233    FILE *rv;
 234    NYD_ENTER;
 235
 236    rv = NULL;
 237    didmsg = FAL0;
 238    UNINIT(serrno, 0);
 239 #ifdef HAVE_DOTLOCK
 240    emsg = NULL;
 241 #endif
 242
 243    if(options & OPT_D_VV){
 244       _DOMSG();
 245       didmsg = TRUM1;
 246    }
 247
 248    flocked = FAL0;
 249    for(u.tries = 0; !n_file_lock(fd, flt, off, len, 0);)
 250       switch((serrno = errno)){
 251       case EACCES:
 252       case EAGAIN:
 253       case ENOLCK:
 254          if(pollmsecs > 0 && ++u.tries < FILE_LOCK_TRIES){
 255             if(!didmsg)
 256                _DOMSG();
 257             n_err(".");
 258             didmsg = TRUM1;
 259             n_msleep(pollmsecs, FAL0);
 260             continue;
 261          }
 262          /* FALLTHRU */
 263       default:
 264          goto jleave;
 265       }
 266    flocked = TRU1;
 267
 268 #ifndef HAVE_DOTLOCK
 269 jleave:
 270    if(didmsg == TRUM1)
 271       n_err("\n");
 272    if(flocked)
 273       rv = (FILE*)-1;
 274    else
 275       errno = serrno;
 276    NYD_LEAVE;
 277    return rv;
 278
 279 #else
 280    /* Create control-pipe for our dot file locker process, which will remove
 281     * the lock and terminate once the pipe is closed, for whatever reason */
 282    if(pipe_cloexec(cpipe) == -1){
 283       serrno = errno;
 284       emsg = N_("  Can't create file lock control pipe\n");
 285       goto jemsg;
 286    }
 287
 288    /* And the locker process itself; it'll be a (rather cheap) thread only
 289     * unless the lock has to be placed in the system spool and we have our
 290     * privilege-separated dotlock program available, in which case that will be
 291     * executed and do "it" with changed group-id */
 292    di.di_file_name = fname;
 293    di.di_pollmsecs = pollmsecs;
 294    /* Initialize some more stuff; query the two strings in the parent in order
 295     * to cache the result of the former and anyway minimalize child page-ins.
 296     * Especially uname(3) may hang for multiple seconds when it is called the
 297     * first time! */
 298    di.di_hostname = nodename(FAL0);
 299    di.di_randstr = getrandstring(16);
 300    a_dotlock_flt = flt;
 301    a_dotlock_fd = fd;
 302    a_dotlock_dip = &di;
 303
 304    u.ptf = &a_dotlock_main;
 305    rv = Popen((char*)-1, "W", u.sh, NULL, cpipe[1]);
 306    serrno = errno;
 307
 308    close(cpipe[1]);
 309    if(rv == NULL){
 310       close(cpipe[0]);
 311       emsg = N_("  Can't create file lock process\n");
 312       goto jemsg;
 313    }
 314
 315    /* Let's check wether we were able to create the dotlock file */
 316    for(;;){
 317       u.r = read(cpipe[0], &dls, sizeof dls);
 318       if(UICMP(z, u.r, !=, sizeof dls)){
 319          serrno = (u.r != -1) ? EAGAIN : errno;
 320          dls = n_DLS_DUNNO | n_DLS_ABANDON;
 321       }else
 322          serrno = 0;
 323
 324       if(dls == n_DLS_NONE || (dls & n_DLS_ABANDON))
 325          close(cpipe[0]);
 326
 327       switch(dls & ~n_DLS_ABANDON){
 328       case n_DLS_NONE:
 329          goto jleave;
 330       case n_DLS_CANT_CHDIR:
 331          if(options & OPT_D_V)
 332             emsg = N_("  Can't change directory!  Please check permissions\n");
 333          serrno = EACCES;
 334          break;
 335       case n_DLS_NAMETOOLONG:
 336          emsg = N_("Resulting dotlock filename would be too long\n");
 337          serrno = EACCES;
 338          break;
 339       case n_DLS_ROFS:
 340          assert(dls & n_DLS_ABANDON);
 341          if(options & OPT_D_V)
 342             emsg = N_("  Read-only filesystem, not creating lock file\n");
 343          serrno = EROFS;
 344          break;
 345       case n_DLS_NOPERM:
 346          if(options & OPT_D_V)
 347             emsg = N_("  Can't create a lock file! Please check permissions\n"
 348                   "  (Maybe setting *dotlock-ignore-error* variable helps.)\n");
 349          serrno = EACCES;
 350          break;
 351       case n_DLS_NOEXEC:
 352          if(options & OPT_D_V)
 353             emsg = N_("  Can't find privilege-separated file lock program\n");
 354          serrno = ENOENT;
 355          break;
 356       case n_DLS_PRIVFAILED:
 357          emsg = N_("  Privilege-separated file lock program can't change "
 358                "privileges\n");
 359          serrno = EPERM;
 360          break;
 361       case n_DLS_EXIST:
 362          emsg = N_("  It seems there is a stale dotlock file?\n"
 363                "  Please remove the lock file manually, then retry\n");
 364          serrno = EEXIST;
 365          break;
 366       case n_DLS_FISHY:
 367          emsg = N_("  Fishy!  Is someone trying to \"steal\" foreign files?\n"
 368                "  Please check the mailbox file etc. manually, then retry\n");
 369          serrno = EAGAIN; /* ? Hack to ignore *dotlock-ignore-error* xxx */
 370          break;
 371       default:
 372       case n_DLS_DUNNO:
 373          emsg = N_("  Unspecified dotlock file control process error.\n"
 374                "  Like broken I/O pipe; this one is unlikely to happen\n");
 375          if(serrno != EAGAIN)
 376             serrno = EINVAL;
 377          break;
 378       case n_DLS_PING:
 379          if(!didmsg)
 380             _DOMSG();
 381          n_err(".");
 382          didmsg = TRUM1;
 383          continue;
 384       }
 385
 386       if(emsg != NULL){
 387          if(!didmsg){
 388             _DOMSG();
 389             didmsg = TRUM1;
 390          }
 391          if(didmsg == TRUM1)
 392             n_err("\n");
 393          didmsg = TRU1;
 394          n_err(V_(emsg));
 395          emsg = NULL;
 396       }
 397
 398       if(dls & n_DLS_ABANDON){
 399          Pclose(rv, FAL0);
 400          rv = NULL;
 401          break;
 402       }
 403    }
 404
 405 jleave:
 406    if(didmsg == TRUM1)
 407       n_err("\n");
 408    if(rv == NULL) {
 409       if(flocked && (serrno == EROFS ||
 410             (serrno != EAGAIN && serrno != EEXIST &&
 411              ok_blook(dotlock_ignore_error))))
 412          rv = (FILE*)-1;
 413       else
 414          errno = serrno;
 415    }
 416    NYD_LEAVE;
 417    return rv;
 418 jemsg:
 419    if(!didmsg)
 420       _DOMSG();
 421    n_err("\n");
 422    didmsg = TRU1;
 423    n_err(V_(emsg));
 424    goto jleave;
 425 #endif /* HAVE_DOTLOCK */
 426 #undef _DOMSG
 427 }
 428
 429 /* s-it-mode */