[exim.git] / src / src / mime.c

/* $Cambridge: exim/src/src/mime.c,v 1.19 2009/11/11 10:08:02 nm4 Exp $ */

/*************************************************
*     Exim - an Internet mail transport agent    *
*************************************************/

/* Copyright (c) Tom Kistner <tom@duncanthrax.net> 2004 */
/* License: GPL */

#include "exim.h"
#ifdef WITH_CONTENT_SCAN
#include "mime.h"
#include <sys/stat.h>

FILE *mime_stream = NULL;
uschar *mime_current_boundary = NULL;

/*************************************************
* set MIME anomaly level + text                  *
*************************************************/

/* Small wrapper to set the two expandables which
   give info on detected "problems" in MIME
   encodings. Those are defined in mime.h. */

void mime_set_anomaly(int level, const char *text) {
  mime_anomaly_level = level;
  mime_anomaly_text = CUS text;
}


/*************************************************
* decode quoted-printable chars                  *
*************************************************/

/* gets called when we hit a =
   returns: new pointer position
   result code in c:
          -2 - decode error
          -1 - soft line break, no char
           0-255 - char to write
*/

uschar *mime_decode_qp_char(uschar *qp_p, int *c) {
  uschar *initial_pos = qp_p;

  /* advance one char */
  qp_p++;

  /* Check for two hex digits and decode them */
  if (isxdigit(*qp_p) && isxdigit(qp_p[1])) {
    /* Do hex conversion */
    if (isdigit(*qp_p)) {*c = *qp_p - '0';}
    else {*c = toupper(*qp_p) - 'A' + 10;};
    *c <<= 4;
    if (isdigit(qp_p[1])) {*c |= qp_p[1] - '0';}
    else {*c |= toupper(qp_p[1]) - 'A' + 10;};
    return qp_p + 2;
  };

  /* tab or whitespace may follow just ignore it if it precedes \n */
  while (*qp_p == '\t' || *qp_p == ' ' || *qp_p == '\r')
    qp_p++;

  if (*qp_p == '\n') {
    /* hit soft line break */
    *c = -1;
    return qp_p;
  };

  /* illegal char here */
  *c = -2;
  return initial_pos;
}


/* just dump MIME part without any decoding */
static int mime_decode_asis(FILE* in, FILE* out, uschar* boundary)
{
  int len, size = 0;
  uschar buffer[MIME_MAX_LINE_LENGTH];

  while(fgets(CS buffer, MIME_MAX_LINE_LENGTH, mime_stream) != NULL) {
    if (boundary != NULL
      && Ustrncmp(buffer, "--", 2) == 0
      && Ustrncmp((buffer+2), boundary, Ustrlen(boundary)) == 0
    )
      break;

    len = Ustrlen(buffer);
    if (fwrite(buffer, 1, (size_t)len, out) < len)
      return -1;
    size += len;
  } /* while */
  return size;
}


/* decode base64 MIME part */
static int mime_decode_base64(FILE* in, FILE* out, uschar* boundary)
{
  uschar ibuf[MIME_MAX_LINE_LENGTH], obuf[MIME_MAX_LINE_LENGTH];
  uschar *ipos, *opos;
  size_t len, size = 0;
  int bytestate = 0;

  opos = obuf;

  while (Ufgets(ibuf, MIME_MAX_LINE_LENGTH, in) != NULL)
  {
    if (boundary != NULL
      && Ustrncmp(ibuf, "--", 2) == 0
      && Ustrncmp((ibuf+2), boundary, Ustrlen(boundary)) == 0
    )
      break;

    for (ipos = ibuf ; *ipos != '\r' && *ipos != '\n' && *ipos != 0; ++ipos) {
      /* skip padding */
      if (*ipos == '=') {
        ++bytestate;
        continue;
      }
      /* skip bad characters */
      if (mime_b64[*ipos] == 128) {
        mime_set_anomaly(MIME_ANOMALY_BROKEN_BASE64);
        continue;
      }
      /* simple state-machine */
      switch((bytestate++) & 3) {
        case 0:
          *opos = mime_b64[*ipos] << 2;
           break;
        case 1:
          *opos |= mime_b64[*ipos] >> 4;
          ++opos;
          *opos = mime_b64[*ipos] << 4;
          break;
        case 2:
          *opos |= mime_b64[*ipos] >> 2;
          ++opos;
          *opos = mime_b64[*ipos] << 6;
          break;
        case 3:
          *opos |= mime_b64[*ipos];
          ++opos;
          break;
      } /* switch */
    } /* for */
    /* something to write? */
    len = opos - obuf;
    if (len > 0) {
      if (fwrite(obuf, 1, len, out) != len)
        return -1; /* error */
      size += len;
      /* copy incomplete last byte to start of obuf, where we continue */
      if ((bytestate & 3) != 0)
        *obuf = *opos;
      opos = obuf;
    }
  } /* while */

  /* write out last byte if it was incomplete */
  if (bytestate & 3) {
      if (fwrite(obuf, 1, 1, out) != 1)
          return -1;
      ++size;
  }

  return size;
}


/* decode quoted-printable MIME part */
static int mime_decode_qp(FILE* in, FILE* out, uschar* boundary)
{
  uschar ibuf[MIME_MAX_LINE_LENGTH], obuf[MIME_MAX_LINE_LENGTH];
  uschar *ipos, *opos;
  size_t len, size = 0;

  while (fgets(CS ibuf, MIME_MAX_LINE_LENGTH, in) != NULL)
  {
    if (boundary != NULL
      && Ustrncmp(ibuf, "--", 2) == 0
      && Ustrncmp((ibuf+2), boundary, Ustrlen(boundary)) == 0
    )
      break; /* todo: check for missing boundary */

    ipos = ibuf;
    opos = obuf;

    while (*ipos != 0) {
      if (*ipos == '=') {
        int decode_qp_result;

        ipos = mime_decode_qp_char(ipos, &decode_qp_result);

        if (decode_qp_result == -2) {
          /* Error from decoder. ipos is unchanged. */
          mime_set_anomaly(MIME_ANOMALY_BROKEN_QP);
          *opos = '=';
          ++opos;
          ++ipos;
        }
        else if (decode_qp_result == -1) {
          break;
        }
        else if (decode_qp_result >= 0) {
          *opos = decode_qp_result;
          ++opos;
        }
      }
      else {
        *opos = *ipos;
        ++opos;
        ++ipos;
      }
    }
    /* something to write? */
    len = opos - obuf;
    if (len > 0) {
      if (fwrite(obuf, 1, len, out) != len)
        return -1; /* error */
      size += len;
    }
  }
  return size;
}


FILE *mime_get_decode_file(uschar *pname, uschar *fname) {
  FILE *f = NULL;
  uschar *filename;

  filename = (uschar *)malloc(2048);

  if ((pname != NULL) && (fname != NULL)) {
    (void)string_format(filename, 2048, "%s/%s", pname, fname);
    f = modefopen(filename,"wb+",SPOOL_MODE);
  }
  else if (pname == NULL) {
    f = modefopen(fname,"wb+",SPOOL_MODE);
  }
  else if (fname == NULL) {
    int file_nr = 0;
    int result = 0;

    /* must find first free sequential filename */
    do {
      struct stat mystat;
      (void)string_format(filename,2048,"%s/%s-%05u", pname, message_id, file_nr);
      file_nr++;
      /* security break */
      if (file_nr >= 1024)
        break;
      result = stat(CS filename,&mystat);
    }
    while(result != -1);
    f = modefopen(filename,"wb+",SPOOL_MODE);
  };

  /* set expansion variable */
  mime_decoded_filename = filename;

  return f;
}


int mime_decode(uschar **listptr) {
  int sep = 0;
  uschar *list = *listptr;
  uschar *option;
  uschar option_buffer[1024];
  uschar decode_path[1024];
  FILE *decode_file = NULL;
  long f_pos = 0;
  unsigned int size_counter = 0;
  int (*decode_function)(FILE*, FILE*, uschar*);

  if (mime_stream == NULL)
    return FAIL;

  f_pos = ftell(mime_stream);

  /* build default decode path (will exist since MBOX must be spooled up) */
  (void)string_format(decode_path,1024,"%s/scan/%s",spool_directory,message_id);

  /* try to find 1st option */
  if ((option = string_nextinlist(&list, &sep,
                                  option_buffer,
                                  sizeof(option_buffer))) != NULL) {

    /* parse 1st option */
    if ( (Ustrcmp(option,"false") == 0) || (Ustrcmp(option,"0") == 0) ) {
      /* explicitly no decoding */
      return FAIL;
    };

    if (Ustrcmp(option,"default") == 0) {
      /* explicit default path + file names */
      goto DEFAULT_PATH;
    };

    if (option[0] == '/') {
      struct stat statbuf;

      memset(&statbuf,0,sizeof(statbuf));

      /* assume either path or path+file name */
      if ( (stat(CS option, &statbuf) == 0) && S_ISDIR(statbuf.st_mode) )
        /* is directory, use it as decode_path */
        decode_file = mime_get_decode_file(option, NULL);
      else
        /* does not exist or is a file, use as full file name */
        decode_file = mime_get_decode_file(NULL, option);
    }
    else
      /* assume file name only, use default path */
      decode_file = mime_get_decode_file(decode_path, option);
  }
  else
    /* no option? patch default path */
    DEFAULT_PATH: decode_file = mime_get_decode_file(decode_path, NULL);

  if (decode_file == NULL)
    return DEFER;

  /* decode according to mime type */
  if (mime_content_transfer_encoding == NULL)
    /* no encoding, dump as-is */
    decode_function = mime_decode_asis;
  else if (Ustrcmp(mime_content_transfer_encoding, "base64") == 0)
    decode_function = mime_decode_base64;
  else if (Ustrcmp(mime_content_transfer_encoding, "quoted-printable") == 0)
    decode_function = mime_decode_qp;
  else
    /* unknown encoding type, just dump as-is */
    decode_function = mime_decode_asis;

  size_counter = decode_function(mime_stream, decode_file, mime_current_boundary);

  clearerr(mime_stream);
  fseek(mime_stream, f_pos, SEEK_SET);

  if (fclose(decode_file) != 0 || size_counter < 0)
    return DEFER;

  /* round up to the next KiB */
  mime_content_size = (size_counter + 1023) / 1024;

  return OK;
}

int mime_get_header(FILE *f, uschar *header) {
  int c = EOF;
  int done = 0;
  int header_value_mode = 0;
  int header_open_brackets = 0;
  int num_copied = 0;

  while(!done) {

    c = fgetc(f);
    if (c == EOF) break;

    /* always skip CRs */
    if (c == '\r') continue;

    if (c == '\n') {
      if (num_copied > 0) {
        /* look if next char is '\t' or ' ' */
        c = fgetc(f);
        if (c == EOF) break;
        if ( (c == '\t') || (c == ' ') ) continue;
        (void)ungetc(c,f);
      };
      /* end of the header, terminate with ';' */
      c = ';';
      done = 1;
    };

    /* skip control characters */
    if (c < 32) continue;

    if (header_value_mode) {
      /* --------- value mode ----------- */
      /* skip leading whitespace */
      if ( ((c == '\t') || (c == ' ')) && (header_value_mode == 1) )
        continue;

      /* we have hit a non-whitespace char, start copying value data */
      header_value_mode = 2;

      /* skip quotes */
      if (c == '"') continue;

      /* leave value mode on ';' */
      if (c == ';') {
        header_value_mode = 0;
      };
      /* -------------------------------- */
    }
    else {
      /* -------- non-value mode -------- */
      /* skip whitespace + tabs */
      if ( (c == ' ') || (c == '\t') )
        continue;
      if (c == '\\') {
        /* quote next char. can be used
        to escape brackets. */
        c = fgetc(f);
        if (c == EOF) break;
      }
      else if (c == '(') {
        header_open_brackets++;
        continue;
      }
      else if ((c == ')') && header_open_brackets) {
        header_open_brackets--;
        continue;
      }
      else if ( (c == '=') && !header_open_brackets ) {
        /* enter value mode */
        header_value_mode = 1;
      };

      /* skip chars while we are in a comment */
      if (header_open_brackets > 0)
        continue;
      /* -------------------------------- */
    };

    /* copy the char to the buffer */
    header[num_copied] = (uschar)c;
    /* raise counter */
    num_copied++;

    /* break if header buffer is full */
    if (num_copied > MIME_MAX_HEADER_SIZE-1) {
      done = 1;
    };
  };

  if ((num_copied > 0) && (header[num_copied-1] != ';')) {
    header[num_copied-1] = ';';
  };

  /* 0-terminate */
  header[num_copied] = '\0';

  /* return 0 for EOF or empty line */
  if ((c == EOF) || (num_copied == 1))
    return 0;
  else
    return 1;
}


int mime_acl_check(uschar *acl, FILE *f, struct mime_boundary_context *context,
                   uschar **user_msgptr, uschar **log_msgptr) {
  int rc = OK;
  uschar *header = NULL;
  struct mime_boundary_context nested_context;

  /* reserve a line buffer to work in */
  header = (uschar *)malloc(MIME_MAX_HEADER_SIZE+1);
  if (header == NULL) {
    log_write(0, LOG_PANIC,
                 "MIME ACL: can't allocate %d bytes of memory.", MIME_MAX_HEADER_SIZE+1);
    return DEFER;
  };

  /* Not actually used at the moment, but will be vital to fixing
   * some RFC 2046 nonconformance later... */
  nested_context.parent = context;

  /* loop through parts */
  while(1) {

    /* reset all per-part mime variables */
    mime_anomaly_level     = 0;
    mime_anomaly_text      = NULL;
    mime_boundary          = NULL;
    mime_charset           = NULL;
    mime_decoded_filename  = NULL;
    mime_filename          = NULL;
    mime_content_description = NULL;
    mime_content_disposition = NULL;
    mime_content_id        = NULL;
    mime_content_transfer_encoding = NULL;
    mime_content_type      = NULL;
    mime_is_multipart      = 0;
    mime_content_size      = 0;

    /*
    If boundary is null, we assume that *f is positioned on the start of headers (for example,
    at the very beginning of a message.
    If a boundary is given, we must first advance to it to reach the start of the next header
    block.
    */

    /* NOTE -- there's an error here -- RFC2046 specifically says to
     * check for outer boundaries.  This code doesn't do that, and
     * I haven't fixed this.
     *
     * (I have moved partway towards adding support, however, by adding
     * a "parent" field to my new boundary-context structure.)
     */
    if (context != NULL) {
      while(fgets(CS header, MIME_MAX_HEADER_SIZE, f) != NULL) {
        /* boundary line must start with 2 dashes */
        if (Ustrncmp(header,"--",2) == 0) {
          if (Ustrncmp((header+2),context->boundary,Ustrlen(context->boundary)) == 0) {
            /* found boundary */
            if (Ustrncmp((header+2+Ustrlen(context->boundary)),"--",2) == 0) {
              /* END boundary found */
              debug_printf("End boundary found %s\n", context->boundary);
              return rc;
            }
            else {
              debug_printf("Next part with boundary %s\n", context->boundary);
            };
            /* can't use break here */
            goto DECODE_HEADERS;
          }
        };
      }
      /* Hit EOF or read error. Ugh. */
      debug_printf("Hit EOF ...\n");
      return rc;
    };

    DECODE_HEADERS:
    /* parse headers, set up expansion variables */
    while(mime_get_header(f,header)) {
      int i;
      /* loop through header list */
      for (i = 0; i < mime_header_list_size; i++) {
        uschar *header_value = NULL;
        int header_value_len = 0;

        /* found an interesting header? */
        if (strncmpic(mime_header_list[i].name,header,mime_header_list[i].namelen) == 0) {
          uschar *p = header + mime_header_list[i].namelen;
          /* yes, grab the value (normalize to lower case)
             and copy to its corresponding expansion variable */
          while(*p != ';') {
            *p = tolower(*p);
            p++;
          };
          header_value_len = (p - (header + mime_header_list[i].namelen));
          header_value = (uschar *)malloc(header_value_len+1);
          memset(header_value,0,header_value_len+1);
          p = header + mime_header_list[i].namelen;
          Ustrncpy(header_value, p, header_value_len);
          debug_printf("Found %s MIME header, value is '%s'\n", mime_header_list[i].name, header_value);
          *((uschar **)(mime_header_list[i].value)) = header_value;

          /* make p point to the next character after the closing ';' */
          p += (header_value_len+1);

          /* grab all param=value tags on the remaining line, check if they are interesting */
          NEXT_PARAM_SEARCH: while (*p != 0) {
            int j;
            for (j = 0; j < mime_parameter_list_size; j++) {
              uschar *param_value = NULL;
              int param_value_len = 0;

              /* found an interesting parameter? */
              if (strncmpic(mime_parameter_list[j].name,p,mime_parameter_list[j].namelen) == 0) {
                uschar *q = p + mime_parameter_list[j].namelen;
                /* yes, grab the value and copy to its corresponding expansion variable */
                while(*q != ';') q++;
                param_value_len = (q - (p + mime_parameter_list[j].namelen));
                param_value = (uschar *)malloc(param_value_len+1);
                memset(param_value,0,param_value_len+1);
                q = p + mime_parameter_list[j].namelen;
                Ustrncpy(param_value, q, param_value_len);
                param_value = rfc2047_decode(param_value, check_rfc2047_length, NULL, 32, &param_value_len, &q);
                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);
                *((uschar **)(mime_parameter_list[j].value)) = param_value;
                p += (mime_parameter_list[j].namelen + param_value_len + 1);
                goto NEXT_PARAM_SEARCH;
              };
            }
            /* There is something, but not one of our interesting parameters.
               Advance to the next semicolon */
            while(*p != ';') p++;
            p++;
          };
        };
      };
    };

    /* set additional flag variables (easier access) */
    if ( (mime_content_type != NULL) &&
         (Ustrncmp(mime_content_type,"multipart",9) == 0) )
      mime_is_multipart = 1;

    /* Make a copy of the boundary pointer.
       Required since mime_boundary is global
       and can be overwritten further down in recursion */
    nested_context.boundary = mime_boundary;

    /* raise global counter */
    mime_part_count++;

    /* copy current file handle to global variable */
    mime_stream = f;
    mime_current_boundary = context ? context->boundary : 0;

    /* Note the context */
    mime_is_coverletter = !(context && context->context == MBC_ATTACHMENT);

    /* call ACL handling function */
    rc = acl_check(ACL_WHERE_MIME, NULL, acl, user_msgptr, log_msgptr);

    mime_stream = NULL;
    mime_current_boundary = NULL;

    if (rc != OK) break;

    /* If we have a multipart entity and a boundary, go recursive */
    if ( (mime_content_type != NULL) &&
         (nested_context.boundary != NULL) &&
         (Ustrncmp(mime_content_type,"multipart",9) == 0) ) {
      debug_printf("Entering multipart recursion, boundary '%s'\n", nested_context.boundary);

      if (context && context->context == MBC_ATTACHMENT)
        nested_context.context = MBC_ATTACHMENT;
      else if (!Ustrcmp(mime_content_type,"multipart/alternative")
            || !Ustrcmp(mime_content_type,"multipart/related"))
        nested_context.context = MBC_COVERLETTER_ALL;
      else
        nested_context.context = MBC_COVERLETTER_ONESHOT;

      rc = mime_acl_check(acl, f, &nested_context, user_msgptr, log_msgptr);
      if (rc != OK) break;
    }
    else if ( (mime_content_type != NULL) &&
            (Ustrncmp(mime_content_type,"message/rfc822",14) == 0) ) {
      uschar *rfc822name = NULL;
      uschar filename[2048];
      int file_nr = 0;
      int result = 0;

      /* must find first free sequential filename */
      do {
        struct stat mystat;
        (void)string_format(filename,2048,"%s/scan/%s/__rfc822_%05u", spool_directory, message_id, file_nr);
        file_nr++;
        /* security break */
        if (file_nr >= 128)
          goto NO_RFC822;
        result = stat(CS filename,&mystat);
      }
      while(result != -1);

      rfc822name = filename;

      /* decode RFC822 attachment */
      mime_decoded_filename = NULL;
      mime_stream = f;
      mime_current_boundary = context ? context->boundary : NULL;
      mime_decode(&rfc822name);
      mime_stream = NULL;
      mime_current_boundary = NULL;
      if (mime_decoded_filename == NULL) {
        /* decoding failed */
        log_write(0, LOG_MAIN,
             "mime_regex acl condition warning - could not decode RFC822 MIME part to file.");
        return DEFER;
      };
      mime_decoded_filename = NULL;
    };

    NO_RFC822:
    /* If the boundary of this instance is NULL, we are finished here */
    if (context == NULL) break;

    if (context->context == MBC_COVERLETTER_ONESHOT)
      context->context = MBC_ATTACHMENT;

  };

  return rc;
}

#endif