/*
* Text detection based on ascmagic.c from the file(1) utility.
*
* Portions Copyright (C) 2013-2019 Cisco Systems, Inc. and/or its affiliates. All rights reserved.
* Portions Copyright (C) 2008-2013 Sourcefire, Inc.
*
* Copyright (c) Ian F. Darwin 1986-1995.
* Software written by Ian F. Darwin and others;
* maintained 1995-present by Christos Zoulas and others.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice immediately at the beginning of the file, without modification,
* this list of conditions, and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE FOR
* ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#if HAVE_CONFIG_H
#include "clamav-config.h"
#endif
#include <stdio.h>
#include <string.h>
#include <memory.h>
#include <ctype.h>
#include <stdlib.h>
#ifdef HAVE_UNISTD_H
#include <unistd.h>
#endif
#include "clamav.h"
#include "filetypes.h"
#include "textdet.h"
#include "others.h"
#define F 0 /* character never appears in text */
#define T 1 /* character appears in plain ASCII text */
#define I 2 /* character appears in ISO-8859 text */
#define X 3 /* character appears in non-ISO extended ASCII (Mac, IBM PC) */
// clang-format off
static char text_chars[256] = {
/* BEL BS HT LF FF CR */
F, F, F, F, F, F, F, T, T, T, T, F, T, T, F, F, /* 0x0X */
/* ESC */
F, F, F, F, F, F, F, F, F, F, F, T, F, F, F, F, /* 0x1X */
T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, /* 0x2X */
T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, /* 0x3X */
T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, /* 0x4X */
T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, /* 0x5X */
T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, /* 0x6X */
T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, F, /* 0x7X */
/* NEL */
X, X, X, X, X, T, X, X, X, X, X, X, X, X, X, X, /* 0x8X */
X, X, X, X, X, X, X, X, X, X, X, X, X, X, X, X, /* 0x9X */
I, I, I, I, I, I, I, I, I, I, I, I, I, I, I, I, /* 0xaX */
I, I, I, I, I, I, I, I, I, I, I, I, I, I, I, I, /* 0xbX */
I, I, I, I, I, I, I, I, I, I, I, I, I, I, I, I, /* 0xcX */
I, I, I, I, I, I, I, I, I, I, I, I, I, I, I, I, /* 0xdX */
I, I, I, I, I, I, I, I, I, I, I, I, I, I, I, I, /* 0xeX */
I, I, I, I, I, I, I, I, I, I, I, I, I, I, I, I /* 0xfX */
};
// clang-format on
static int td_isascii(const unsigned char *buf, unsigned int len)
{
unsigned int i;
// @TODO: UTF8 BOM Detection.
// The following BOM detection results in False Negatives in regression testing
// which can be eliminated by adding a condition to call cli_scanhtml for CL_TYPE_TEXT_UTF8
// in scanners.c:cli_scanraw(). However, cli_scanhtml was written for ASCII and has
// not been validated to correctly handle multibyte UTF8.
// /* Check for the Byte-Order-Mark for UTF-8 */
// if ((len >= 3) &&
// (buf[0] == 0xEF) &&
// (buf[1] == 0xBB) &&
// (buf[2] == 0xBF))
// {
// return 0;
// }
/* Validate that the data all falls within the bounds of
* plain ASCII, ISO-8859 text, and non-ISO extended ASCII (Mac, IBM PC)
*/
for (i = 0; i < len; i++)
if (text_chars[buf[i]] == F)
return 0;
return 1;
}
static int td_isutf8(const unsigned char *buf, unsigned int len)
{
unsigned int i, j, gotone = 0;
for (i = 0; i < len; i++) {
if ((buf[i] & 0x80) == 0) { /* 0xxxxxxx is plain ASCII */
/*
* Even if the whole file is valid UTF-8 sequences,
* still reject it if it uses weird control characters.
*/
if (text_chars[buf[i]] != T)
return 0;
} else if ((buf[i] & 0x40) == 0) { /* 10xxxxxx never 1st byte */
return 0;
} else { /* 11xxxxxx begins UTF-8 */
unsigned int following;
if ((buf[i] & 0x20) == 0) { /* 110xxxxx */
/* c = buf[i] & 0x1f; */
following = 1;
} else if ((buf[i] & 0x10) == 0) { /* 1110xxxx */
/* c = buf[i] & 0x0f; */
following = 2;
} else if ((buf[i] & 0x08) == 0) { /* 11110xxx */
/* c = buf[i] & 0x07; */
following = 3;
} else if ((buf[i] & 0x04) == 0) { /* 111110xx */
/* c = buf[i] & 0x03; */
following = 4;
} else if ((buf[i] & 0x02) == 0) { /* 1111110x */
/* c = buf[i] & 0x01; */
following = 5;
} else {
return 0;
}
for (j = 0; j < following; j++) {
if (++i >= len)
return gotone;
if ((buf[i] & 0x80) == 0 || (buf[i] & 0x40))
return 0;
/* c = (c << 6) + (buf[i] & 0x3f); */
}
gotone = 1;
}
}
return gotone;
}
static int td_isutf16(const unsigned char *buf, unsigned int len)
{
unsigned int be = 1, nobom = 0, i, c, bad = 0, high = 0;
if (len < 2)
return 0;
if (buf[0] == 0xff && buf[1] == 0xfe)
be = 0;
else if (buf[0] == 0xfe && buf[1] == 0xff)
be = 1;
else
nobom = 1;
for (i = 2; i + 1 < len; i += 2) {
if (be)
c = buf[i + 1] + 256 * buf[i];
else
c = buf[i] + 256 * buf[i + 1];
if (c == 0xfffe)
return 0;
if (c < 128 && text_chars[c] != T) {
if (nobom)
return 0;
else
bad++;
} else if (c >= 128) {
high++;
}
}
// if (nobom && high >= len / 4)
// return 0;
if (!nobom && bad >= len / 2)
return 0;
return 1 + be;
}
cli_file_t cli_texttype(const unsigned char *buf, unsigned int len)
{
int ret;
if (td_isascii(buf, len)) {
cli_dbgmsg("Recognized ASCII text\n");
return CL_TYPE_TEXT_ASCII;
} else if (td_isutf8(buf, len)) {
cli_dbgmsg("Recognized UTF-8 character data\n");
return CL_TYPE_TEXT_UTF8;
} else if ((ret = td_isutf16(buf, len))) {
cli_dbgmsg("Recognized %s character data\n", (ret == 1) ? "UTF-16LE" : "UTF-16BE");
return (ret == 1) ? CL_TYPE_TEXT_UTF16LE : CL_TYPE_TEXT_UTF16BE;
} else {
cli_dbgmsg("Recognized binary data\n");
return CL_TYPE_BINARY_DATA;
}
}