src/src/mime.c

   1 /* $Cambridge: exim/src/src/mime.c,v 1.15 2006/09/05 15:34:41 ph10 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
  78 uschar *mime_parse_line(uschar *buffer, uschar *data, uschar *encoding, int *num_decoded) {
  79
  80   if (encoding == NULL) {
  81     /* no encoding type at all */
  82     NO_DECODING:
  83     memcpy(data, buffer, Ustrlen(buffer));
  84     data[(Ustrlen(buffer))] = 0;
  85     *num_decoded = Ustrlen(data);
  86     return data;
  87   }
  88   else if (Ustrcmp(encoding,"base64") == 0) {
  89     uschar *p = buffer;
  90     int offset = 0;
  91
  92     /* ----- BASE64 ---------------------------------------------------- */
  93     /* NULL out '\r' and '\n' chars */
  94     while (Ustrrchr(p,'\r') != NULL) {
  95       *(Ustrrchr(p,'\r')) = '\0';
  96     };
  97     while (Ustrrchr(p,'\n') != NULL) {
  98       *(Ustrrchr(p,'\n')) = '\0';
  99     };
 100
 101     while (*(p+offset) != '\0') {
 102       /* hit illegal char ? */
 103       if (mime_b64[*(p+offset)] == 128) {
 104         mime_set_anomaly(MIME_ANOMALY_BROKEN_BASE64);
 105         offset++;
 106       }
 107       else {
 108         *p = mime_b64[*(p+offset)];
 109         p++;
 110       };
 111     };
 112     *p = 255;
 113
 114     /* line is translated, start bit shifting */
 115     p = buffer;
 116     *num_decoded = 0;
 117     while(*p != 255) {
 118       uschar tmp_c;
 119
 120       /* byte 0 ---------------------- */
 121       if (*(p+1) == 255) {
 122         break;
 123       }
 124       data[(*num_decoded)] = *p;
 125       data[(*num_decoded)] <<= 2;
 126       tmp_c = *(p+1);
 127       tmp_c >>= 4;
 128       data[(*num_decoded)] |= tmp_c;
 129       (*num_decoded)++;
 130       p++;
 131       /* byte 1 ---------------------- */
 132       if (*(p+1) == 255) {
 133         break;
 134       }
 135       data[(*num_decoded)] = *p;
 136       data[(*num_decoded)] <<= 4;
 137       tmp_c = *(p+1);
 138       tmp_c >>= 2;
 139       data[(*num_decoded)] |= tmp_c;
 140       (*num_decoded)++;
 141       p++;
 142       /* byte 2 ---------------------- */
 143       if (*(p+1) == 255) {
 144         break;
 145       }
 146       data[(*num_decoded)] = *p;
 147       data[(*num_decoded)] <<= 6;
 148       data[(*num_decoded)] |= *(p+1);
 149       (*num_decoded)++;
 150       p+=2;
 151
 152     };
 153     return data;
 154     /* ----------------------------------------------------------------- */
 155   }
 156   else if (Ustrcmp(encoding,"quoted-printable") == 0) {
 157     uschar *p = buffer;
 158
 159     /* ----- QP -------------------------------------------------------- */
 160     *num_decoded = 0;
 161     while (*p != 0) {
 162       if (*p == '=') {
 163         int decode_qp_result;
 164
 165         p = mime_decode_qp_char(p,&decode_qp_result);
 166
 167         if (decode_qp_result == -2) {
 168           /* Error from decoder. p is unchanged. */
 169           mime_set_anomaly(MIME_ANOMALY_BROKEN_QP);
 170           data[(*num_decoded)] = '=';
 171           (*num_decoded)++;
 172           p++;
 173         }
 174         else if (decode_qp_result == -1) {
 175           break;
 176         }
 177         else if (decode_qp_result >= 0) {
 178           data[(*num_decoded)] = decode_qp_result;
 179           (*num_decoded)++;
 180         };
 181       }
 182       else {
 183         data[(*num_decoded)] = *p;
 184         (*num_decoded)++;
 185         p++;
 186       };
 187     };
 188     return data;
 189     /* ----------------------------------------------------------------- */
 190   }
 191   /* unknown encoding type, just dump as-is */
 192   else goto NO_DECODING;
 193 }
 194
 195
 196 FILE *mime_get_decode_file(uschar *pname, uschar *fname) {
 197   FILE *f = NULL;
 198   uschar *filename;
 199
 200   filename = (uschar *)malloc(2048);
 201
 202   if ((pname != NULL) && (fname != NULL)) {
 203     (void)string_format(filename, 2048, "%s/%s", pname, fname);
 204     f = modefopen(filename,"wb+",SPOOL_MODE);
 205   }
 206   else if (pname == NULL) {
 207     f = modefopen(fname,"wb+",SPOOL_MODE);
 208   }
 209   else if (fname == NULL) {
 210     int file_nr = 0;
 211     int result = 0;
 212
 213     /* must find first free sequential filename */
 214     do {
 215       struct stat mystat;
 216       (void)string_format(filename,2048,"%s/%s-%05u", pname, message_id, file_nr);
 217       file_nr++;
 218       /* security break */
 219       if (file_nr >= 1024)
 220         break;
 221       result = stat(CS filename,&mystat);
 222     }
 223     while(result != -1);
 224     f = modefopen(filename,"wb+",SPOOL_MODE);
 225   };
 226
 227   /* set expansion variable */
 228   mime_decoded_filename = filename;
 229
 230   return f;
 231 }
 232
 233
 234 int mime_decode(uschar **listptr) {
 235   int sep = 0;
 236   uschar *list = *listptr;
 237   uschar *option;
 238   uschar option_buffer[1024];
 239   uschar decode_path[1024];
 240   FILE *decode_file = NULL;
 241   uschar *buffer = NULL;
 242   uschar *decode_buffer = NULL;
 243   long f_pos = 0;
 244   unsigned int size_counter = 0;
 245
 246   if (mime_stream == NULL)
 247     return FAIL;
 248
 249   f_pos = ftell(mime_stream);
 250
 251   /* build default decode path (will exist since MBOX must be spooled up) */
 252   (void)string_format(decode_path,1024,"%s/scan/%s",spool_directory,message_id);
 253
 254   /* reserve a line and decoder buffer to work in */
 255   buffer = (uschar *)malloc(MIME_MAX_LINE_LENGTH+1);
 256   if (buffer == NULL) {
 257     log_write(0, LOG_PANIC,
 258                  "decode ACL condition: can't allocate %d bytes of memory.", MIME_MAX_LINE_LENGTH+1);
 259     return DEFER;
 260   };
 261
 262   decode_buffer = (uschar *)malloc(MIME_MAX_LINE_LENGTH+1);
 263   if (decode_buffer == NULL) {
 264     log_write(0, LOG_PANIC,
 265                  "decode ACL condition: can't allocate %d bytes of memory.", MIME_MAX_LINE_LENGTH+1);
 266     return DEFER;
 267   };
 268
 269   /* try to find 1st option */
 270   if ((option = string_nextinlist(&list, &sep,
 271                                   option_buffer,
 272                                   sizeof(option_buffer))) != NULL) {
 273
 274     /* parse 1st option */
 275     if ( (Ustrcmp(option,"false") == 0) || (Ustrcmp(option,"0") == 0) ) {
 276       /* explicitly no decoding */
 277       return FAIL;
 278     };
 279
 280     if (Ustrcmp(option,"default") == 0) {
 281       /* explicit default path + file names */
 282       goto DEFAULT_PATH;
 283     };
 284
 285     if (option[0] == '/') {
 286       struct stat statbuf;
 287
 288       memset(&statbuf,0,sizeof(statbuf));
 289
 290       /* assume either path or path+file name */
 291       if ( (stat(CS option, &statbuf) == 0) && S_ISDIR(statbuf.st_mode) )
 292         /* is directory, use it as decode_path */
 293         decode_file = mime_get_decode_file(option, NULL);
 294       else
 295         /* does not exist or is a file, use as full file name */
 296         decode_file = mime_get_decode_file(NULL, option);
 297     }
 298     else
 299       /* assume file name only, use default path */
 300       decode_file = mime_get_decode_file(decode_path, option);
 301   }
 302   else
 303     /* no option? patch default path */
 304     DEFAULT_PATH: decode_file = mime_get_decode_file(decode_path, NULL);
 305
 306   if (decode_file == NULL)
 307     return DEFER;
 308
 309   /* read data linewise and dump it to the file,
 310      while looking for the current boundary */
 311   while(fgets(CS buffer, MIME_MAX_LINE_LENGTH, mime_stream) != NULL) {
 312     uschar *decoded_line = NULL;
 313     int decoded_line_length = 0;
 314
 315     if (mime_current_boundary != NULL) {
 316       /* boundary line must start with 2 dashes */
 317       if (Ustrncmp(buffer,"--",2) == 0) {
 318         if (Ustrncmp((buffer+2),mime_current_boundary,Ustrlen(mime_current_boundary)) == 0)
 319           break;
 320       };
 321     };
 322
 323     decoded_line = mime_parse_line(buffer, decode_buffer, mime_content_transfer_encoding, &decoded_line_length);
 324
 325     /* write line to decode file */
 326     if (fwrite(decoded_line, 1, decoded_line_length, decode_file) < decoded_line_length) {
 327       /* error/short write */
 328       clearerr(mime_stream);
 329       fseek(mime_stream,f_pos,SEEK_SET);
 330       return DEFER;
 331     };
 332     size_counter += decoded_line_length;
 333
 334     if (size_counter > 1023) {
 335       if ((mime_content_size + (size_counter / 1024)) < 65535)
 336         mime_content_size += (size_counter / 1024);
 337       else
 338         mime_content_size = 65535;
 339       size_counter = (size_counter % 1024);
 340     };
 341
 342   }
 343
 344   (void)fclose(decode_file);
 345
 346   clearerr(mime_stream);
 347   fseek(mime_stream,f_pos,SEEK_SET);
 348
 349   /* round up remaining size bytes to one k */
 350   if (size_counter) {
 351     mime_content_size++;
 352   };
 353
 354   return OK;
 355 }
 356
 357 int mime_get_header(FILE *f, uschar *header) {
 358   int c = EOF;
 359   int done = 0;
 360   int header_value_mode = 0;
 361   int header_open_brackets = 0;
 362   int num_copied = 0;
 363
 364   while(!done) {
 365
 366     c = fgetc(f);
 367     if (c == EOF) break;
 368
 369     /* always skip CRs */
 370     if (c == '\r') continue;
 371
 372     if (c == '\n') {
 373       if (num_copied > 0) {
 374         /* look if next char is '\t' or ' ' */
 375         c = fgetc(f);
 376         if (c == EOF) break;
 377         if ( (c == '\t') || (c == ' ') ) continue;
 378         (void)ungetc(c,f);
 379       };
 380       /* end of the header, terminate with ';' */
 381       c = ';';
 382       done = 1;
 383     };
 384
 385     /* skip control characters */
 386     if (c < 32) continue;
 387
 388     if (header_value_mode) {
 389       /* --------- value mode ----------- */
 390       /* skip leading whitespace */
 391       if ( ((c == '\t') || (c == ' ')) && (header_value_mode == 1) )
 392         continue;
 393
 394       /* we have hit a non-whitespace char, start copying value data */
 395       header_value_mode = 2;
 396
 397       /* skip quotes */
 398       if (c == '"') continue;
 399
 400       /* leave value mode on ';' */
 401       if (c == ';') {
 402         header_value_mode = 0;
 403       };
 404       /* -------------------------------- */
 405     }
 406     else {
 407       /* -------- non-value mode -------- */
 408       /* skip whitespace + tabs */
 409       if ( (c == ' ') || (c == '\t') )
 410         continue;
 411       if (c == '\\') {
 412         /* quote next char. can be used
 413         to escape brackets. */
 414         c = fgetc(f);
 415         if (c == EOF) break;
 416       }
 417       else if (c == '(') {
 418         header_open_brackets++;
 419         continue;
 420       }
 421       else if ((c == ')') && header_open_brackets) {
 422         header_open_brackets--;
 423         continue;
 424       }
 425       else if ( (c == '=') && !header_open_brackets ) {
 426         /* enter value mode */
 427         header_value_mode = 1;
 428       };
 429
 430       /* skip chars while we are in a comment */
 431       if (header_open_brackets > 0)
 432         continue;
 433       /* -------------------------------- */
 434     };
 435
 436     /* copy the char to the buffer */
 437     header[num_copied] = (uschar)c;
 438     /* raise counter */
 439     num_copied++;
 440
 441     /* break if header buffer is full */
 442     if (num_copied > MIME_MAX_HEADER_SIZE-1) {
 443       done = 1;
 444     };
 445   };
 446
 447   if ((num_copied > 0) && (header[num_copied-1] != ';')) {
 448     header[num_copied-1] = ';';
 449   };
 450
 451   /* 0-terminate */
 452   header[num_copied] = '\0';
 453
 454   /* return 0 for EOF or empty line */
 455   if ((c == EOF) || (num_copied == 1))
 456     return 0;
 457   else
 458     return 1;
 459 }
 460
 461
 462 int mime_acl_check(uschar *acl, FILE *f, struct mime_boundary_context *context,
 463                    uschar **user_msgptr, uschar **log_msgptr) {
 464   int rc = OK;
 465   uschar *header = NULL;
 466   struct mime_boundary_context nested_context;
 467
 468   /* reserve a line buffer to work in */
 469   header = (uschar *)malloc(MIME_MAX_HEADER_SIZE+1);
 470   if (header == NULL) {
 471     log_write(0, LOG_PANIC,
 472                  "MIME ACL: can't allocate %d bytes of memory.", MIME_MAX_HEADER_SIZE+1);
 473     return DEFER;
 474   };
 475
 476   /* Not actually used at the moment, but will be vital to fixing
 477    * some RFC 2046 nonconformance later... */
 478   nested_context.parent = context;
 479
 480   /* loop through parts */
 481   while(1) {
 482
 483     /* reset all per-part mime variables */
 484     mime_anomaly_level     = 0;
 485     mime_anomaly_text      = NULL;
 486     mime_boundary          = NULL;
 487     mime_charset           = NULL;
 488     mime_decoded_filename  = NULL;
 489     mime_filename          = NULL;
 490     mime_content_description = NULL;
 491     mime_content_disposition = NULL;
 492     mime_content_id        = NULL;
 493     mime_content_transfer_encoding = NULL;
 494     mime_content_type      = NULL;
 495     mime_is_multipart      = 0;
 496     mime_content_size      = 0;
 497
 498     /*
 499     If boundary is null, we assume that *f is positioned on the start of headers (for example,
 500     at the very beginning of a message.
 501     If a boundary is given, we must first advance to it to reach the start of the next header
 502     block.
 503     */
 504
 505     /* NOTE -- there's an error here -- RFC2046 specifically says to
 506      * check for outer boundaries.  This code doesn't do that, and
 507      * I haven't fixed this.
 508      *
 509      * (I have moved partway towards adding support, however, by adding
 510      * a "parent" field to my new boundary-context structure.)
 511      */
 512     if (context != NULL) {
 513       while(fgets(CS header, MIME_MAX_HEADER_SIZE, f) != NULL) {
 514         /* boundary line must start with 2 dashes */
 515         if (Ustrncmp(header,"--",2) == 0) {
 516           if (Ustrncmp((header+2),context->boundary,Ustrlen(context->boundary)) == 0) {
 517             /* found boundary */
 518             if (Ustrncmp((header+2+Ustrlen(context->boundary)),"--",2) == 0) {
 519               /* END boundary found */
 520               debug_printf("End boundary found %s\n", context->boundary);
 521               return rc;
 522             }
 523             else {
 524               debug_printf("Next part with boundary %s\n", context->boundary);
 525             };
 526             /* can't use break here */
 527             goto DECODE_HEADERS;
 528           }
 529         };
 530       }
 531       /* Hit EOF or read error. Ugh. */
 532       debug_printf("Hit EOF ...\n");
 533       return rc;
 534     };
 535
 536     DECODE_HEADERS:
 537     /* parse headers, set up expansion variables */
 538     while(mime_get_header(f,header)) {
 539       int i;
 540       /* loop through header list */
 541       for (i = 0; i < mime_header_list_size; i++) {
 542         uschar *header_value = NULL;
 543         int header_value_len = 0;
 544
 545         /* found an interesting header? */
 546         if (strncmpic(mime_header_list[i].name,header,mime_header_list[i].namelen) == 0) {
 547           uschar *p = header + mime_header_list[i].namelen;
 548           /* yes, grab the value (normalize to lower case)
 549              and copy to its corresponding expansion variable */
 550           while(*p != ';') {
 551             *p = tolower(*p);
 552             p++;
 553           };
 554           header_value_len = (p - (header + mime_header_list[i].namelen));
 555           header_value = (uschar *)malloc(header_value_len+1);
 556           memset(header_value,0,header_value_len+1);
 557           p = header + mime_header_list[i].namelen;
 558           Ustrncpy(header_value, p, header_value_len);
 559           debug_printf("Found %s MIME header, value is '%s'\n", mime_header_list[i].name, header_value);
 560           *((uschar **)(mime_header_list[i].value)) = header_value;
 561
 562           /* make p point to the next character after the closing ';' */
 563           p += (header_value_len+1);
 564
 565           /* grab all param=value tags on the remaining line, check if they are interesting */
 566           NEXT_PARAM_SEARCH: while (*p != 0) {
 567             int j;
 568             for (j = 0; j < mime_parameter_list_size; j++) {
 569               uschar *param_value = NULL;
 570               int param_value_len = 0;
 571
 572               /* found an interesting parameter? */
 573               if (strncmpic(mime_parameter_list[j].name,p,mime_parameter_list[j].namelen) == 0) {
 574                 uschar *q = p + mime_parameter_list[j].namelen;
 575                 /* yes, grab the value and copy to its corresponding expansion variable */
 576                 while(*q != ';') q++;
 577                 param_value_len = (q - (p + mime_parameter_list[j].namelen));
 578                 param_value = (uschar *)malloc(param_value_len+1);
 579                 memset(param_value,0,param_value_len+1);
 580                 q = p + mime_parameter_list[j].namelen;
 581                 Ustrncpy(param_value, q, param_value_len);
 582                 param_value = rfc2047_decode(param_value, check_rfc2047_length, NULL, 32, &param_value_len, &q);
 583                 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);
 584                 *((uschar **)(mime_parameter_list[j].value)) = param_value;
 585                 p += (mime_parameter_list[j].namelen + param_value_len + 1);
 586                 goto NEXT_PARAM_SEARCH;
 587               };
 588             }
 589             /* There is something, but not one of our interesting parameters.
 590                Advance to the next semicolon */
 591             while(*p != ';') p++;
 592             p++;
 593           };
 594         };
 595       };
 596     };
 597
 598     /* set additional flag variables (easier access) */
 599     if ( (mime_content_type != NULL) &&
 600          (Ustrncmp(mime_content_type,"multipart",9) == 0) )
 601       mime_is_multipart = 1;
 602
 603     /* Make a copy of the boundary pointer.
 604        Required since mime_boundary is global
 605        and can be overwritten further down in recursion */
 606     nested_context.boundary = mime_boundary;
 607
 608     /* raise global counter */
 609     mime_part_count++;
 610
 611     /* copy current file handle to global variable */
 612     mime_stream = f;
 613     mime_current_boundary = context ? context->boundary : 0;
 614
 615     /* Note the context */
 616     mime_is_coverletter = !(context && context->context == MBC_ATTACHMENT);
 617
 618     /* call ACL handling function */
 619     rc = acl_check(ACL_WHERE_MIME, NULL, acl, user_msgptr, log_msgptr);
 620
 621     mime_stream = NULL;
 622     mime_current_boundary = NULL;
 623
 624     if (rc != OK) break;
 625
 626     /* If we have a multipart entity and a boundary, go recursive */
 627     if ( (mime_content_type != NULL) &&
 628          (nested_context.boundary != NULL) &&
 629          (Ustrncmp(mime_content_type,"multipart",9) == 0) ) {
 630       debug_printf("Entering multipart recursion, boundary '%s'\n", nested_context.boundary);
 631
 632       if (context && context->context == MBC_ATTACHMENT)
 633         nested_context.context = MBC_ATTACHMENT;
 634       else if (!Ustrcmp(mime_content_type,"multipart/alternative")
 635             || !Ustrcmp(mime_content_type,"multipart/related"))
 636         nested_context.context = MBC_COVERLETTER_ALL;
 637       else
 638         nested_context.context = MBC_COVERLETTER_ONESHOT;
 639
 640       rc = mime_acl_check(acl, f, &nested_context, user_msgptr, log_msgptr);
 641       if (rc != OK) break;
 642     }
 643     else if ( (mime_content_type != NULL) &&
 644             (Ustrncmp(mime_content_type,"message/rfc822",14) == 0) ) {
 645       uschar *rfc822name = NULL;
 646       uschar filename[2048];
 647       int file_nr = 0;
 648       int result = 0;
 649
 650       /* must find first free sequential filename */
 651       do {
 652         struct stat mystat;
 653         (void)string_format(filename,2048,"%s/scan/%s/__rfc822_%05u", spool_directory, message_id, file_nr);
 654         file_nr++;
 655         /* security break */
 656         if (file_nr >= 128)
 657           goto NO_RFC822;
 658         result = stat(CS filename,&mystat);
 659       }
 660       while(result != -1);
 661
 662       rfc822name = filename;
 663
 664       /* decode RFC822 attachment */
 665       mime_decoded_filename = NULL;
 666       mime_stream = f;
 667       mime_current_boundary = context ? context->boundary : NULL;
 668       mime_decode(&rfc822name);
 669       mime_stream = NULL;
 670       mime_current_boundary = NULL;
 671       if (mime_decoded_filename == NULL) {
 672         /* decoding failed */
 673         log_write(0, LOG_MAIN,
 674              "mime_regex acl condition warning - could not decode RFC822 MIME part to file.");
 675         return DEFER;
 676       };
 677       mime_decoded_filename = NULL;
 678     };
 679
 680     NO_RFC822:
 681     /* If the boundary of this instance is NULL, we are finished here */
 682     if (context == NULL) break;
 683
 684     if (context->context == MBC_COVERLETTER_ONESHOT)
 685       context->context = MBC_ATTACHMENT;
 686
 687   };
 688
 689   return rc;
 690 }
 691
 692 #endif