src/src/mime.c

   1 /* $Cambridge: exim/src/src/mime.c,v 1.19 2009/11/11 10:08:02 nm4 Exp $ */
   2
   3 /*************************************************
   4 *     Exim - an Internet mail transport agent    *
   5 *************************************************/
   6
   7 /* Copyright (c) Tom Kistner <tom@duncanthrax.net> 2004 */
   8 /* License: GPL */
   9
  10 #include "exim.h"
  11 #ifdef WITH_CONTENT_SCAN
  12 #include "mime.h"
  13 #include <sys/stat.h>
  14
  15 FILE *mime_stream = NULL;
  16 uschar *mime_current_boundary = NULL;
  17
  18 /*************************************************
  19 * set MIME anomaly level + text                  *
  20 *************************************************/
  21
  22 /* Small wrapper to set the two expandables which
  23    give info on detected "problems" in MIME
  24    encodings. Those are defined in mime.h. */
  25
  26 void mime_set_anomaly(int level, char *text) {
  27   mime_anomaly_level = level;
  28   mime_anomaly_text = US text;
  29 }
  30
  31
  32 /*************************************************
  33 * decode quoted-printable chars                  *
  34 *************************************************/
  35
  36 /* gets called when we hit a =
  37    returns: new pointer position
  38    result code in c:
  39           -2 - decode error
  40           -1 - soft line break, no char
  41            0-255 - char to write
  42 */
  43
  44 uschar *mime_decode_qp_char(uschar *qp_p, int *c) {
  45   uschar *initial_pos = qp_p;
  46
  47   /* advance one char */
  48   qp_p++;
  49
  50   /* Check for two hex digits and decode them */
  51   if (isxdigit(*qp_p) && isxdigit(qp_p[1])) {
  52     /* Do hex conversion */
  53     if (isdigit(*qp_p)) {*c = *qp_p - '0';}
  54     else {*c = toupper(*qp_p) - 'A' + 10;};
  55     *c <<= 4;
  56     if (isdigit(qp_p[1])) {*c |= qp_p[1] - '0';}
  57     else {*c |= toupper(qp_p[1]) - 'A' + 10;};
  58     return qp_p + 2;
  59   };
  60
  61   /* tab or whitespace may follow just ignore it if it precedes \n */
  62   while (*qp_p == '\t' || *qp_p == ' ' || *qp_p == '\r')
  63     qp_p++;
  64
  65   if (*qp_p == '\n') {
  66     /* hit soft line break */
  67     *c = -1;
  68     return qp_p;
  69   };
  70
  71   /* illegal char here */
  72   *c = -2;
  73   return initial_pos;
  74 }
  75
  76
  77 /* just dump MIME part without any decoding */
  78 static int mime_decode_asis(FILE* in, FILE* out, uschar* boundary)
  79 {
  80   int len, size = 0;
  81   uschar buffer[MIME_MAX_LINE_LENGTH];
  82
  83   while(fgets(CS buffer, MIME_MAX_LINE_LENGTH, mime_stream) != NULL) {
  84     if (boundary != NULL
  85       && Ustrncmp(buffer, "--", 2) == 0
  86       && Ustrncmp((buffer+2), boundary, Ustrlen(boundary)) == 0
  87     )
  88       break;
  89
  90     len = Ustrlen(buffer);
  91     if (fwrite(buffer, 1, (size_t)len, out) < len)
  92       return -1;
  93     size += len;
  94   } /* while */
  95   return size;
  96 }
  97
  98
  99 /* decode base64 MIME part */
 100 static int mime_decode_base64(FILE* in, FILE* out, uschar* boundary)
 101 {
 102   uschar ibuf[MIME_MAX_LINE_LENGTH], obuf[MIME_MAX_LINE_LENGTH];
 103   uschar *ipos, *opos;
 104   size_t len, size = 0;
 105   int bytestate = 0;
 106
 107   opos = obuf;
 108
 109   while (Ufgets(ibuf, MIME_MAX_LINE_LENGTH, in) != NULL)
 110   {
 111     if (boundary != NULL
 112       && Ustrncmp(ibuf, "--", 2) == 0
 113       && Ustrncmp((ibuf+2), boundary, Ustrlen(boundary)) == 0
 114     )
 115       break;
 116
 117     for (ipos = ibuf ; *ipos != '\r' && *ipos != '\n' && *ipos != 0; ++ipos) {
 118       /* skip padding */
 119       if (*ipos == '=') {
 120         ++bytestate;
 121         continue;
 122       }
 123       /* skip bad characters */
 124       if (mime_b64[*ipos] == 128) {
 125         mime_set_anomaly(MIME_ANOMALY_BROKEN_BASE64);
 126         continue;
 127       }
 128       /* simple state-machine */
 129       switch((bytestate++) & 3) {
 130         case 0:
 131           *opos = mime_b64[*ipos] << 2;
 132            break;
 133         case 1:
 134           *opos |= mime_b64[*ipos] >> 4;
 135           ++opos;
 136           *opos = mime_b64[*ipos] << 4;
 137           break;
 138         case 2:
 139           *opos |= mime_b64[*ipos] >> 2;
 140           ++opos;
 141           *opos = mime_b64[*ipos] << 6;
 142           break;
 143         case 3:
 144           *opos |= mime_b64[*ipos];
 145           ++opos;
 146           break;
 147       } /* switch */
 148     } /* for */
 149     /* something to write? */
 150     len = opos - obuf;
 151     if (len > 0) {
 152       if (fwrite(obuf, 1, len, out) != len)
 153         return -1; /* error */
 154       size += len;
 155       /* copy incomplete last byte to start of obuf, where we continue */
 156       if ((bytestate & 3) != 0)
 157         *obuf = *opos;
 158       opos = obuf;
 159     }
 160   } /* while */
 161
 162   /* write out last byte if it was incomplete */
 163   if (bytestate & 3) {
 164       if (fwrite(obuf, 1, 1, out) != 1)
 165           return -1;
 166       ++size;
 167   }
 168
 169   return size;
 170 }
 171
 172
 173 /* decode quoted-printable MIME part */
 174 static int mime_decode_qp(FILE* in, FILE* out, uschar* boundary)
 175 {
 176   uschar ibuf[MIME_MAX_LINE_LENGTH], obuf[MIME_MAX_LINE_LENGTH];
 177   uschar *ipos, *opos;
 178   size_t len, size = 0;
 179
 180   while (fgets(CS ibuf, MIME_MAX_LINE_LENGTH, in) != NULL)
 181   {
 182     if (boundary != NULL
 183       && Ustrncmp(ibuf, "--", 2) == 0
 184       && Ustrncmp((ibuf+2), boundary, Ustrlen(boundary)) == 0
 185     )
 186       break; /* todo: check for missing boundary */
 187
 188     ipos = ibuf;
 189     opos = obuf;
 190
 191     while (*ipos != 0) {
 192       if (*ipos == '=') {
 193         int decode_qp_result;
 194
 195         ipos = mime_decode_qp_char(ipos, &decode_qp_result);
 196
 197         if (decode_qp_result == -2) {
 198           /* Error from decoder. ipos is unchanged. */
 199           mime_set_anomaly(MIME_ANOMALY_BROKEN_QP);
 200           *opos = '=';
 201           ++opos;
 202           ++ipos;
 203         }
 204         else if (decode_qp_result == -1) {
 205           break;
 206         }
 207         else if (decode_qp_result >= 0) {
 208           *opos = decode_qp_result;
 209           ++opos;
 210         }
 211       }
 212       else {
 213         *opos = *ipos;
 214         ++opos;
 215         ++ipos;
 216       }
 217     }
 218     /* something to write? */
 219     len = opos - obuf;
 220     if (len > 0) {
 221       if (fwrite(obuf, 1, len, out) != len)
 222         return -1; /* error */
 223       size += len;
 224     }
 225   }
 226   return size;
 227 }
 228
 229
 230 FILE *mime_get_decode_file(uschar *pname, uschar *fname) {
 231   FILE *f = NULL;
 232   uschar *filename;
 233
 234   filename = (uschar *)malloc(2048);
 235
 236   if ((pname != NULL) && (fname != NULL)) {
 237     (void)string_format(filename, 2048, "%s/%s", pname, fname);
 238     f = modefopen(filename,"wb+",SPOOL_MODE);
 239   }
 240   else if (pname == NULL) {
 241     f = modefopen(fname,"wb+",SPOOL_MODE);
 242   }
 243   else if (fname == NULL) {
 244     int file_nr = 0;
 245     int result = 0;
 246
 247     /* must find first free sequential filename */
 248     do {
 249       struct stat mystat;
 250       (void)string_format(filename,2048,"%s/%s-%05u", pname, message_id, file_nr);
 251       file_nr++;
 252       /* security break */
 253       if (file_nr >= 1024)
 254         break;
 255       result = stat(CS filename,&mystat);
 256     }
 257     while(result != -1);
 258     f = modefopen(filename,"wb+",SPOOL_MODE);
 259   };
 260
 261   /* set expansion variable */
 262   mime_decoded_filename = filename;
 263
 264   return f;
 265 }
 266
 267
 268 int mime_decode(uschar **listptr) {
 269   int sep = 0;
 270   uschar *list = *listptr;
 271   uschar *option;
 272   uschar option_buffer[1024];
 273   uschar decode_path[1024];
 274   FILE *decode_file = NULL;
 275   long f_pos = 0;
 276   unsigned int size_counter = 0;
 277   int (*decode_function)(FILE*, FILE*, uschar*);
 278
 279   if (mime_stream == NULL)
 280     return FAIL;
 281
 282   f_pos = ftell(mime_stream);
 283
 284   /* build default decode path (will exist since MBOX must be spooled up) */
 285   (void)string_format(decode_path,1024,"%s/scan/%s",spool_directory,message_id);
 286
 287   /* try to find 1st option */
 288   if ((option = string_nextinlist(&list, &sep,
 289                                   option_buffer,
 290                                   sizeof(option_buffer))) != NULL) {
 291
 292     /* parse 1st option */
 293     if ( (Ustrcmp(option,"false") == 0) || (Ustrcmp(option,"0") == 0) ) {
 294       /* explicitly no decoding */
 295       return FAIL;
 296     };
 297
 298     if (Ustrcmp(option,"default") == 0) {
 299       /* explicit default path + file names */
 300       goto DEFAULT_PATH;
 301     };
 302
 303     if (option[0] == '/') {
 304       struct stat statbuf;
 305
 306       memset(&statbuf,0,sizeof(statbuf));
 307
 308       /* assume either path or path+file name */
 309       if ( (stat(CS option, &statbuf) == 0) && S_ISDIR(statbuf.st_mode) )
 310         /* is directory, use it as decode_path */
 311         decode_file = mime_get_decode_file(option, NULL);
 312       else
 313         /* does not exist or is a file, use as full file name */
 314         decode_file = mime_get_decode_file(NULL, option);
 315     }
 316     else
 317       /* assume file name only, use default path */
 318       decode_file = mime_get_decode_file(decode_path, option);
 319   }
 320   else
 321     /* no option? patch default path */
 322     DEFAULT_PATH: decode_file = mime_get_decode_file(decode_path, NULL);
 323
 324   if (decode_file == NULL)
 325     return DEFER;
 326
 327   /* decode according to mime type */
 328   if (mime_content_transfer_encoding == NULL)
 329     /* no encoding, dump as-is */
 330     decode_function = mime_decode_asis;
 331   else if (Ustrcmp(mime_content_transfer_encoding, "base64") == 0)
 332     decode_function = mime_decode_base64;
 333   else if (Ustrcmp(mime_content_transfer_encoding, "quoted-printable") == 0)
 334     decode_function = mime_decode_qp;
 335   else
 336     /* unknown encoding type, just dump as-is */
 337     decode_function = mime_decode_asis;
 338
 339   size_counter = decode_function(mime_stream, decode_file, mime_current_boundary);
 340
 341   clearerr(mime_stream);
 342   fseek(mime_stream, f_pos, SEEK_SET);
 343
 344   if (fclose(decode_file) != 0 || size_counter < 0)
 345     return DEFER;
 346
 347   /* round up to the next KiB */
 348   mime_content_size = (size_counter + 1023) / 1024;
 349
 350   return OK;
 351 }
 352
 353 int mime_get_header(FILE *f, uschar *header) {
 354   int c = EOF;
 355   int done = 0;
 356   int header_value_mode = 0;
 357   int header_open_brackets = 0;
 358   int num_copied = 0;
 359
 360   while(!done) {
 361
 362     c = fgetc(f);
 363     if (c == EOF) break;
 364
 365     /* always skip CRs */
 366     if (c == '\r') continue;
 367
 368     if (c == '\n') {
 369       if (num_copied > 0) {
 370         /* look if next char is '\t' or ' ' */
 371         c = fgetc(f);
 372         if (c == EOF) break;
 373         if ( (c == '\t') || (c == ' ') ) continue;
 374         (void)ungetc(c,f);
 375       };
 376       /* end of the header, terminate with ';' */
 377       c = ';';
 378       done = 1;
 379     };
 380
 381     /* skip control characters */
 382     if (c < 32) continue;
 383
 384     if (header_value_mode) {
 385       /* --------- value mode ----------- */
 386       /* skip leading whitespace */
 387       if ( ((c == '\t') || (c == ' ')) && (header_value_mode == 1) )
 388         continue;
 389
 390       /* we have hit a non-whitespace char, start copying value data */
 391       header_value_mode = 2;
 392
 393       /* skip quotes */
 394       if (c == '"') continue;
 395
 396       /* leave value mode on ';' */
 397       if (c == ';') {
 398         header_value_mode = 0;
 399       };
 400       /* -------------------------------- */
 401     }
 402     else {
 403       /* -------- non-value mode -------- */
 404       /* skip whitespace + tabs */
 405       if ( (c == ' ') || (c == '\t') )
 406         continue;
 407       if (c == '\\') {
 408         /* quote next char. can be used
 409         to escape brackets. */
 410         c = fgetc(f);
 411         if (c == EOF) break;
 412       }
 413       else if (c == '(') {
 414         header_open_brackets++;
 415         continue;
 416       }
 417       else if ((c == ')') && header_open_brackets) {
 418         header_open_brackets--;
 419         continue;
 420       }
 421       else if ( (c == '=') && !header_open_brackets ) {
 422         /* enter value mode */
 423         header_value_mode = 1;
 424       };
 425
 426       /* skip chars while we are in a comment */
 427       if (header_open_brackets > 0)
 428         continue;
 429       /* -------------------------------- */
 430     };
 431
 432     /* copy the char to the buffer */
 433     header[num_copied] = (uschar)c;
 434     /* raise counter */
 435     num_copied++;
 436
 437     /* break if header buffer is full */
 438     if (num_copied > MIME_MAX_HEADER_SIZE-1) {
 439       done = 1;
 440     };
 441   };
 442
 443   if ((num_copied > 0) && (header[num_copied-1] != ';')) {
 444     header[num_copied-1] = ';';
 445   };
 446
 447   /* 0-terminate */
 448   header[num_copied] = '\0';
 449
 450   /* return 0 for EOF or empty line */
 451   if ((c == EOF) || (num_copied == 1))
 452     return 0;
 453   else
 454     return 1;
 455 }
 456
 457
 458 int mime_acl_check(uschar *acl, FILE *f, struct mime_boundary_context *context,
 459                    uschar **user_msgptr, uschar **log_msgptr) {
 460   int rc = OK;
 461   uschar *header = NULL;
 462   struct mime_boundary_context nested_context;
 463
 464   /* reserve a line buffer to work in */
 465   header = (uschar *)malloc(MIME_MAX_HEADER_SIZE+1);
 466   if (header == NULL) {
 467     log_write(0, LOG_PANIC,
 468                  "MIME ACL: can't allocate %d bytes of memory.", MIME_MAX_HEADER_SIZE+1);
 469     return DEFER;
 470   };
 471
 472   /* Not actually used at the moment, but will be vital to fixing
 473    * some RFC 2046 nonconformance later... */
 474   nested_context.parent = context;
 475
 476   /* loop through parts */
 477   while(1) {
 478
 479     /* reset all per-part mime variables */
 480     mime_anomaly_level     = 0;
 481     mime_anomaly_text      = NULL;
 482     mime_boundary          = NULL;
 483     mime_charset           = NULL;
 484     mime_decoded_filename  = NULL;
 485     mime_filename          = NULL;
 486     mime_content_description = NULL;
 487     mime_content_disposition = NULL;
 488     mime_content_id        = NULL;
 489     mime_content_transfer_encoding = NULL;
 490     mime_content_type      = NULL;
 491     mime_is_multipart      = 0;
 492     mime_content_size      = 0;
 493
 494     /*
 495     If boundary is null, we assume that *f is positioned on the start of headers (for example,
 496     at the very beginning of a message.
 497     If a boundary is given, we must first advance to it to reach the start of the next header
 498     block.
 499     */
 500
 501     /* NOTE -- there's an error here -- RFC2046 specifically says to
 502      * check for outer boundaries.  This code doesn't do that, and
 503      * I haven't fixed this.
 504      *
 505      * (I have moved partway towards adding support, however, by adding
 506      * a "parent" field to my new boundary-context structure.)
 507      */
 508     if (context != NULL) {
 509       while(fgets(CS header, MIME_MAX_HEADER_SIZE, f) != NULL) {
 510         /* boundary line must start with 2 dashes */
 511         if (Ustrncmp(header,"--",2) == 0) {
 512           if (Ustrncmp((header+2),context->boundary,Ustrlen(context->boundary)) == 0) {
 513             /* found boundary */
 514             if (Ustrncmp((header+2+Ustrlen(context->boundary)),"--",2) == 0) {
 515               /* END boundary found */
 516               debug_printf("End boundary found %s\n", context->boundary);
 517               return rc;
 518             }
 519             else {
 520               debug_printf("Next part with boundary %s\n", context->boundary);
 521             };
 522             /* can't use break here */
 523             goto DECODE_HEADERS;
 524           }
 525         };
 526       }
 527       /* Hit EOF or read error. Ugh. */
 528       debug_printf("Hit EOF ...\n");
 529       return rc;
 530     };
 531
 532     DECODE_HEADERS:
 533     /* parse headers, set up expansion variables */
 534     while(mime_get_header(f,header)) {
 535       int i;
 536       /* loop through header list */
 537       for (i = 0; i < mime_header_list_size; i++) {
 538         uschar *header_value = NULL;
 539         int header_value_len = 0;
 540
 541         /* found an interesting header? */
 542         if (strncmpic(mime_header_list[i].name,header,mime_header_list[i].namelen) == 0) {
 543           uschar *p = header + mime_header_list[i].namelen;
 544           /* yes, grab the value (normalize to lower case)
 545              and copy to its corresponding expansion variable */
 546           while(*p != ';') {
 547             *p = tolower(*p);
 548             p++;
 549           };
 550           header_value_len = (p - (header + mime_header_list[i].namelen));
 551           header_value = (uschar *)malloc(header_value_len+1);
 552           memset(header_value,0,header_value_len+1);
 553           p = header + mime_header_list[i].namelen;
 554           Ustrncpy(header_value, p, header_value_len);
 555           debug_printf("Found %s MIME header, value is '%s'\n", mime_header_list[i].name, header_value);
 556           *((uschar **)(mime_header_list[i].value)) = header_value;
 557
 558           /* make p point to the next character after the closing ';' */
 559           p += (header_value_len+1);
 560
 561           /* grab all param=value tags on the remaining line, check if they are interesting */
 562           NEXT_PARAM_SEARCH: while (*p != 0) {
 563             int j;
 564             for (j = 0; j < mime_parameter_list_size; j++) {
 565               uschar *param_value = NULL;
 566               int param_value_len = 0;
 567
 568               /* found an interesting parameter? */
 569               if (strncmpic(mime_parameter_list[j].name,p,mime_parameter_list[j].namelen) == 0) {
 570                 uschar *q = p + mime_parameter_list[j].namelen;
 571                 /* yes, grab the value and copy to its corresponding expansion variable */
 572                 while(*q != ';') q++;
 573                 param_value_len = (q - (p + mime_parameter_list[j].namelen));
 574                 param_value = (uschar *)malloc(param_value_len+1);
 575                 memset(param_value,0,param_value_len+1);
 576                 q = p + mime_parameter_list[j].namelen;
 577                 Ustrncpy(param_value, q, param_value_len);
 578                 param_value = rfc2047_decode(param_value, check_rfc2047_length, NULL, 32, &param_value_len, &q);
 579                 debug_printf("Found %s MIME parameter in %s header, value is '%s'\n", mime_parameter_list[j].name, mime_header_list[i].name, param_value);
 580                 *((uschar **)(mime_parameter_list[j].value)) = param_value;
 581                 p += (mime_parameter_list[j].namelen + param_value_len + 1);
 582                 goto NEXT_PARAM_SEARCH;
 583               };
 584             }
 585             /* There is something, but not one of our interesting parameters.
 586                Advance to the next semicolon */
 587             while(*p != ';') p++;
 588             p++;
 589           };
 590         };
 591       };
 592     };
 593
 594     /* set additional flag variables (easier access) */
 595     if ( (mime_content_type != NULL) &&
 596          (Ustrncmp(mime_content_type,"multipart",9) == 0) )
 597       mime_is_multipart = 1;
 598
 599     /* Make a copy of the boundary pointer.
 600        Required since mime_boundary is global
 601        and can be overwritten further down in recursion */
 602     nested_context.boundary = mime_boundary;
 603
 604     /* raise global counter */
 605     mime_part_count++;
 606
 607     /* copy current file handle to global variable */
 608     mime_stream = f;
 609     mime_current_boundary = context ? context->boundary : 0;
 610
 611     /* Note the context */
 612     mime_is_coverletter = !(context && context->context == MBC_ATTACHMENT);
 613
 614     /* call ACL handling function */
 615     rc = acl_check(ACL_WHERE_MIME, NULL, acl, user_msgptr, log_msgptr);
 616
 617     mime_stream = NULL;
 618     mime_current_boundary = NULL;
 619
 620     if (rc != OK) break;
 621
 622     /* If we have a multipart entity and a boundary, go recursive */
 623     if ( (mime_content_type != NULL) &&
 624          (nested_context.boundary != NULL) &&
 625          (Ustrncmp(mime_content_type,"multipart",9) == 0) ) {
 626       debug_printf("Entering multipart recursion, boundary '%s'\n", nested_context.boundary);
 627
 628       if (context && context->context == MBC_ATTACHMENT)
 629         nested_context.context = MBC_ATTACHMENT;
 630       else if (!Ustrcmp(mime_content_type,"multipart/alternative")
 631             || !Ustrcmp(mime_content_type,"multipart/related"))
 632         nested_context.context = MBC_COVERLETTER_ALL;
 633       else
 634         nested_context.context = MBC_COVERLETTER_ONESHOT;
 635
 636       rc = mime_acl_check(acl, f, &nested_context, user_msgptr, log_msgptr);
 637       if (rc != OK) break;
 638     }
 639     else if ( (mime_content_type != NULL) &&
 640             (Ustrncmp(mime_content_type,"message/rfc822",14) == 0) ) {
 641       uschar *rfc822name = NULL;
 642       uschar filename[2048];
 643       int file_nr = 0;
 644       int result = 0;
 645
 646       /* must find first free sequential filename */
 647       do {
 648         struct stat mystat;
 649         (void)string_format(filename,2048,"%s/scan/%s/__rfc822_%05u", spool_directory, message_id, file_nr);
 650         file_nr++;
 651         /* security break */
 652         if (file_nr >= 128)
 653           goto NO_RFC822;
 654         result = stat(CS filename,&mystat);
 655       }
 656       while(result != -1);
 657
 658       rfc822name = filename;
 659
 660       /* decode RFC822 attachment */
 661       mime_decoded_filename = NULL;
 662       mime_stream = f;
 663       mime_current_boundary = context ? context->boundary : NULL;
 664       mime_decode(&rfc822name);
 665       mime_stream = NULL;
 666       mime_current_boundary = NULL;
 667       if (mime_decoded_filename == NULL) {
 668         /* decoding failed */
 669         log_write(0, LOG_MAIN,
 670              "mime_regex acl condition warning - could not decode RFC822 MIME part to file.");
 671         return DEFER;
 672       };
 673       mime_decoded_filename = NULL;
 674     };
 675
 676     NO_RFC822:
 677     /* If the boundary of this instance is NULL, we are finished here */
 678     if (context == NULL) break;
 679
 680     if (context->context == MBC_COVERLETTER_ONESHOT)
 681       context->context = MBC_ATTACHMENT;
 682
 683   };
 684
 685   return rc;
 686 }
 687
 688 #endif