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

/*
 * Copyright (c) The Exim Maintainers 2015 - 2026
 * Copyright (c) Tom Kistner <tom@duncanthrax.net> 2004 - 2015
 * License: GPL
 * SPDX-License-Identifier: GPL-2.0-or-later
 */

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

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

static mime_header mime_header_list[] = {
  /*	name			namelen		value */
  { US"content-type:",              13, &mime_content_type },
  { US"content-disposition:",       20, &mime_content_disposition },
  { US"content-transfer-encoding:", 26, &mime_content_transfer_encoding },
  { US"content-id:",                11, &mime_content_id },
  { US"content-description:",       20, &mime_content_description }
};

static mime_parameter mime_parameter_list[] = {
  /*	name	namelen	 value */
  { US"name",     4, &mime_filename },
  { US"filename", 8, &mime_filename },
  { US"charset",  7, &mime_charset  },
  { US"boundary", 8, &mime_boundary }
};


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

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

void
mime_set_anomaly(int idx)
{
struct anom {
  int level;
  const uschar * text;
} anom[] = { {1, CUS"Broken Quoted-Printable encoding detected"},
	     {2, CUS"Broken BASE64 encoding detected"} };

mime_anomaly_level = anom[idx].level;
mime_anomaly_text =  anom[idx].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
*/

static const uschar *
mime_decode_qp_char(const uschar * qp_p, int * c)
{
const 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 */
  *c = (isdigit(*qp_p) ? *qp_p - '0' : toupper(*qp_p) - 'A' + 10) <<4;
  qp_p++;
  *c |= isdigit(*qp_p) ? *qp_p - '0' : toupper(*qp_p) - 'A' + 10;
  return qp_p + 1;
  }

/* 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 ssize_t
mime_decode_asis(FILE * in, FILE * out, const uschar * boundary)
{
ssize_t len, size = 0;
uschar buffer[MIME_MAX_LINE_LENGTH];

while(fgets(CS buffer, MIME_MAX_LINE_LENGTH, mime_stream) != NULL)
  {
  if (  boundary
     && 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 quoted-printable MIME part */
static ssize_t
mime_decode_qp(FILE * in, FILE * out, const uschar * boundary)
{
uschar ibuf[MIME_MAX_LINE_LENGTH], obuf[MIME_MAX_LINE_LENGTH];
const uschar * ipos;
uschar * opos;
ssize_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)
    {
    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++ = '=';
	++ipos;
	}
      else if (decode_qp_result == -1)
	break;
      else if (decode_qp_result >= 0)
	*opos++ = decode_qp_result;
      }
    else
      *opos++ = *ipos++;
    }
  /* something to write? */
  if ((len = opos - obuf) > 0)
    {
    if (fwrite(obuf, 1, len, out) != len) return -1; /* error */
    size += len;
    }
  }
return size;
}


/*
Return open filehandle for combo of path and file.
Side-effect: set mime_decoded_filename, to copy in allocated mem
*/

static FILE *
mime_get_decode_file(uschar *pname, uschar *fname)
{
if (pname && fname)
  mime_decoded_filename = string_sprintf("%s/%s", pname, fname);
else if (!pname)
  mime_decoded_filename = string_copy(fname);
else if (!fname)
  {
  int file_nr = 0;
  int result = 0;

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

return modefopen(mime_decoded_filename, "wb+", SPOOL_MODE);
}


int
mime_decode(const uschar ** listptr)
{
int sep = 0;
const uschar * list = *listptr;
uschar * option;
uschar * decode_path;
FILE * decode_file = NULL;
long f_pos = 0;
ssize_t size_counter = 0;
ssize_t (*decode_function)(FILE *, FILE *, const uschar *);

if (!mime_stream || (f_pos = ftell(mime_stream)) < 0)
  return FAIL;

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

/* try to find 1st option */
if ((option = string_nextinlist(&list, &sep, NULL, 0)))
  {
  /* 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)
  return DEFER;

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

size_counter = decode_function(mime_stream, decode_file, mime_current_boundary);

clearerr(mime_stream);
if (fseek(mime_stream, f_pos, SEEK_SET))
  return DEFER;

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;
}


static int
mime_get_header(FILE * f, uschar * header)
{
int c = EOF;
enum hdr_parse_state {
  hdr_nonvalue, hdr_val_whitespace, hdr_value, hdr_quotedvalue
  } header_value_mode = hdr_nonvalue;
int header_open_brackets = 0, num_copied = 0;

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

  if (c < 32 && c != '\t') continue;	/* skip non-tab control chars, inc CR */

  if (header_value_mode > hdr_nonvalue)			/* value modes */
    {
    if (header_value_mode == hdr_val_whitespace)	/* leading WS mode */
      {
      if (c == '\t' || c == ' ')
	continue;				/* skip leading whitespace */

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

    if (c == '"')				/* flip "quoted" mode */
      header_value_mode = header_value_mode == hdr_value
			? hdr_quotedvalue : hdr_value;

    /* leave value mode on unquoted ';' */
    if (header_value_mode == hdr_value && c == ';')
      header_value_mode = hdr_nonvalue;
    }
  else							/* non-value mode */
    {
    /* skip whitespace + tabs */
    if (c == ' ' || c == '\t')
      continue;
    if (c == '\\')
      {
      /* quote next char. can be used
      to escape brackets. */
      if ((c = fgetc(f)) == 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 = hdr_val_whitespace;

    /* 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;

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

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 */
return c == EOF || num_copied == 1 ? 0 : 1;
}


/* reset all per-part mime variables */
static void
mime_vars_reset(void)
{
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;
}


/* Grab a parameter value, dealing with quoting.

Arguments:
 str	Input string.  Updated on return to point to terminating ; or NUL

Return:
 Allocated string with parameter value
*/
static uschar *
mime_param_val(const uschar ** sp)
{
const uschar * s = *sp;
gstring * val = NULL;

/* debug_printf_indent("   considering paramval '%s'\n", s); */

while (*s && *s != ';')		/* ; terminates */
  if (*s == '"')
    {
    s++;			/* skip opening " */
    while (*s && *s != '"')	/* " protects ; */
      val = string_catn(val, s++, 1);
    if (*s) s++;		/* skip closing " */
    }
  else
    val = string_catn(val, s++, 1);
*sp = s;
return string_from_gstring(val);
}

static const uschar *
mime_next_semicolon(const uschar * s)
{
while (*s && *s != ';')		/* ; terminates */
  if (*s == '"')
    {
    s++;			/* skip opening " */
    while (*s && *s != '"')	/* " protects ; */
      s++;
    if (*s) s++;		/* skip closing " */
    }
  else
    s++;
return s;
}


static uschar *
rfc2231_to_2047(const uschar * fname, const uschar * charset, int * len)
{
gstring * val = string_catn(NULL, US"=?", 2);
uschar c;

if (charset)
  val = string_cat(val, charset);
val = string_catn(val, US"?Q?", 3);

while ((c = *fname))
  if (c == '%' && isxdigit(fname[1]) && isxdigit(fname[2]))
    {
    val = string_catn(val, US"=", 1);
    val = string_catn(val, ++fname, 2);
    fname += 2;
    }
  else
    val = string_catn(val, fname++, 1);

val = string_catn(val, US"?=", 2);
*len = gstring_length(val);
return string_from_gstring(val);
}


/* Walk the params. For those in the given list, write the value to the
pointer in the list.
*/

void
mime_hdr_value_decode(const uschar * p,
  mime_parameter * paramlist, unsigned nparam, const uschar * header)
{
gstring * mime_fname = NULL, * mime_fname_rfc2231 = NULL;
uschar * mime_filename_charset = NULL;
BOOL decoding_failed = FALSE;

/* grab all param=value tags on the remaining line,
check if they are interesting */

while (Uskip_whitespace(&p))
  {
  DEBUG(acl)
    debug_printf_indent("MIME:   considering paramlist '%s'\n", p);

  /* look for interesting parameters */
  for (mime_parameter * mp = paramlist; mp < paramlist + nparam; mp++)
    if (strncmpic(mp->name, p, mp->namelen) == 0)
      {
      p += mp->namelen;
      if (*p == '*')			/* RFC 2231 */
	{
	while (isdigit(*++p)) ;		/* ignore cont-cnt values */
	if (*p == '*') p++;		/* step over sep chset mark */
	if (*p == '=')
	  {
	  uschar * p2;
	  p++;				/* step over = */
	  p2 = mime_param_val(&p);	/* p now trailing ; or NUL */

	  if (p2 && *p2)			/* p2 is the dequoted value */
	    {
	    uschar * err_msg;
	    const uschar * fname = p2;
	    int slen;

	    /* build up an un-decoded filename over successive
	    filename*= parameters (for use when 2047 decode fails) */

	    mime_fname_rfc2231 = string_cat(mime_fname_rfc2231, p2);

	    if (!decoding_failed)
	      {
	      if (!mime_filename_charset)
		{			/* try for RFC 2231 chset/lang */
		uschar * s = p2;

		/* look for a ' in the raw paramval */
		while(*s != '\'' && *s) s++;	/* s is 1st ' or NUL */

		if (*s)				/* there was a ' */
		  {
		  int size;
		  if ((size = s-p2) > 0)
		    mime_filename_charset = string_copyn(p2, size);

		  if (*(fname = s)) fname++;
		  while(*fname == '\'') fname++;    /*fname is after 2nd '*/
		  }
		}

	      DEBUG(acl)
		debug_printf_indent("MIME:    charset %s fname '%s'\n",
		  mime_filename_charset ? mime_filename_charset : US"<NULL>",
		  fname);

	      fname = rfc2231_to_2047(fname, mime_filename_charset,
					    &slen);
	      DEBUG(acl)
		debug_printf_indent("MIME:    2047-name %s\n", fname);

	      fname = rfc2047_decode(fname, FALSE, NULL, ' ', NULL, &err_msg);
	      DEBUG(acl) debug_printf_indent("MIME:    plain-name %s\n", fname);

	      if (!fname || Ustrlen(fname) == slen)
		decoding_failed = TRUE;
	      else if (mp->value == &mime_filename)
		{
		/* build up a decoded filename over successive
		filename*= parameters */

		mime_fname = string_cat(mime_fname, fname);
		mime_filename = string_from_gstring(mime_fname);
		}
	      }	/*!decoding_failed*/
	    }	/*p2*/

	  if (*p) p++;			/* p is past ; */
	  goto param_done;		/* done matching param names */
	  }		/*2231 param coding extension*/
	}
      else if (*p == '=')
	{		/* non-2231 param */
	uschar * p3, * dummy_errstr;

	/* grab the value and copy to its expansion variable */

	p++;				/* step over = */
	p3 = mime_param_val(&p);		/* p now trailing ; or NUL */

	*mp->value = p3 && *p3
	  ? rfc2047_decode(p3, check_rfc2047_length, NULL, 32, NULL,
	      &dummy_errstr)
	  : NULL;
	DEBUG(acl) debug_printf_indent(
	  "MIME:  found %s parameter in %s header, value '%s'\n",
	  mp->name, header, *mp->value);

	if (*p) p++;			/* p is past ; */
	goto param_done;			/* done matching param names */
	}
      }					/* interesting parameters */

  /* There is something, but not one of our interesting parameters.
  Advance past the next semicolon */

  p = mime_next_semicolon(p);
  if (*p) p++;
param_done: ;
  }					/* param scan on line */

if (strncmpic(CUS"content-disposition:", header, 20) == 0)
  {
  if (decoding_failed)
    mime_filename = string_from_gstring(mime_fname_rfc2231);

  DEBUG(acl) debug_printf_indent(
    "MIME:  found %s parameter in Content-Disposition header, value is '%s'\n",
    "filename", mime_filename);
  }
}

#define MIME_MAX_DEPTH 64

/* Called from run_mime_acl() (receive.c) and also (directly) recursively.
The toplevel call supplies a NULL mime_boundary_context.

Returns:       OK         access is granted by an ACCEPT verb
               DISCARD    access is granted by a DISCARD verb
               FAIL       access is denied
               FAIL_DROP  access is denied; drop the connection
               DEFER      can't tell at the moment
               ERROR      disaster
*/

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

if (depth >= MIME_MAX_DEPTH)
  {
  log_write(LOG_MAIN, "MIME acl condition fail: excessive nesting depth");
  return FAIL;
  }

/* reserve a line buffer to work in.  Assume tainted data. */
header = store_get(MIME_MAX_HEADER_SIZE+1, GET_TAINTED);

/* 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_vars_reset();

  /* 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) for (;;)
    {
    if (!fgets(CS header, MIME_MAX_HEADER_SIZE, f))
      {
      /* Hit EOF or read error. Ugh. */
      DEBUG(acl) debug_printf_indent("MIME: Hit EOF ...\n");
      return rc;
      }

    /* boundary line must start with 2 dashes */
    if (  Ustrncmp(header, "--", 2) == 0
       && Ustrncmp(header+2, context->boundary, Ustrlen(context->boundary)) == 0
       )
      {			/* found boundary */
      if (Ustrncmp((header+2+Ustrlen(context->boundary)), "--", 2) == 0)
	{
	/* END boundary found */
	DEBUG(acl) debug_printf_indent("MIME: End boundary found %s\n",
	  context->boundary);
	return rc;
	}

      DEBUG(acl) debug_printf_indent("MIME: Next part with boundary %s\n",
	context->boundary);
      break;
      }
    }

  /* parse headers, set up expansion variables */
  while (mime_get_header(f, header))

    /* look for interesting headers */
    for (struct mime_header * mh = mime_header_list;
	 mh < mime_header_list + nelem(mime_header_list);
	 mh++) if (strncmpic(mh->name, header, mh->namelen) == 0)
      {
      const uschar * p = header + mh->namelen, * p1;

      /* grab the value (normalize to lower case)
      and copy to its corresponding expansion variable */

      for (p1 = p; *p1 != ';' && *p1; p1++) ;
      *mh->value = string_copynlc(p, p1-p);
      DEBUG(acl) debug_printf_indent("MIME: found %s header, value is '%s'\n",
	mh->name, *mh->value);

      if (*(p = p1)) p++;			/* jump past the ; */

      mime_hdr_value_decode(p, mime_parameter_list, nelem(mime_parameter_list),
			    header);
      break;
      }	/* interesting headers */

  /* set additional flag variables (easier access) */
  if (  mime_content_type
     && 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 && nested_context.boundary 
     && Ustrncmp(mime_content_type,"multipart",9) == 0)
    {
    DEBUG(acl)
      debug_printf_indent("MIME: Entering multipart recursion, boundary '%s'\n",
	nested_context.boundary);

    nested_context.context =
      context && context->context == MBC_ATTACHMENT
      ? MBC_ATTACHMENT
      :    Ustrcmp(mime_content_type,"multipart/alternative") == 0
	|| Ustrcmp(mime_content_type,"multipart/related") == 0
      ? MBC_COVERLETTER_ALL
      : MBC_COVERLETTER_ONESHOT;

    rc = mime_acl_check(acl, f, &nested_context, user_msgptr, log_msgptr,
			depth+1);
    if (rc != OK) break;
    }
  else if (  mime_content_type
	  && Ustrncmp(mime_content_type,"message/rfc822",14) == 0)
    {
    const uschar * rfc822name = NULL;
    uschar * filename;
    int file_nr = 0;
    int result = 0;

    /* must find first free sequential filename */
    for (gstring * g = string_get(64); result != -1; gstring_reset(g))
      {
      struct stat mystat;
      g = string_fmt_append(g,
	"%s/scan/%s/__rfc822_%05u", spool_directory, message_id, file_nr++);
      /* security break */
      if (file_nr >= 128)
	goto NO_RFC822;
      result = stat(CS (filename = string_from_gstring(g)), &mystat);
      }

    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)		/* decoding failed */
      {
      log_write(LOG_MAIN,
	   "MIME acl condition warning - could not decode RFC822 MIME part to file.");
      rc = DEFER;
      goto out;
      }
    mime_decoded_filename = NULL;
    }

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

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

out:
mime_vars_reset();
return rc;
}

#endif	/*WITH_CONTENT_SCAN*/

/* vi: aw ai sw=2
*/
