is_tar.c

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/*  $OpenBSD: is_tar.c,v 1.10 2009/10/27 23:59:37 deraadt Exp $ */
/*
 * 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.
 */
/*
 * is_tar() -- figure out whether file is a tar archive.
 *
 * Stolen (by the author!) from the public domain tar program:
 * Public Domain version written 26 Aug 1985 John Gilmore (ihnp4!hoptoad!gnu).
 *
 * @(#)list.c 1.18 9/23/86 Public Domain - gnu
 *
 * Comments changed and some code/comments reformatted
 * for file command by Ian Darwin.
 */
#include <rz_userconf.h>
 
#if !USE_LIB_MAGIC
 
#include "file.h"
#include <string.h>
#include <ctype.h>
#include <sys/types.h>
#include "tar.h"
 
static const char tartype[][32] = {
    "tar archive",
    "POSIX tar archive",
    "POSIX tar archive (GNU)",
};
 
/*
 * Quick and dirty octal conversion.
 *
 * Result is -1 if the field is invalid (all blank, or nonoctal).
 */
#define isodigit(c) (((c) >= '0') && ((c) <= '7'))
static int from_oct(int digs, const char *where) {
    int value = 0;
    while (isspace((ut8)*where)) { /* Skip spaces */
        where++;
        if (--digs <= 0) {
            return -1; /* All blank field */
        }
    }
    while (digs > 0 && isodigit(*where)) { /* Scan til nonoctal */
        value = (value << 3) | (*where++ - '0');
        --digs;
    }
    if (digs > 0 && *where && !isspace((ut8)*where)) {
        return -1; /* Ended on non-space/nul */
    }
    return value;
}
 
/*
 * Return
 *  0 if the checksum is bad (i.e., probably not a tar archive),
 *  1 for old UNIX tar file,
 *  2 for Unix Std (POSIX) tar file,
 *  3 for GNU tar file.
 */
static int is_tar(const ut8 *buf, size_t nbytes) {
    const union record *header = (const union record *)(const void *)buf;
    int i, sum, recsum;
    const char *p;
 
    if (nbytes < sizeof(union record)) {
        return 0;
    }
 
    recsum = from_oct(8, header->header.chksum);
 
    sum = 0;
    p = header->charptr;
    for (i = sizeof(union record); --i >= 0;) {
        /*
         * We cannot use ut8 here because of old compilers,
         * e.g. V7.
         */
        sum += 0xFF & *p++;
    }
 
    /* Adjust checksum to count the "chksum" field as blanks. */
    for (i = sizeof header->header.chksum; --i >= 0;) {
        sum -= 0xFF & header->header.chksum[i];
    }
    sum += ' ' * sizeof header->header.chksum;
    if (sum != recsum) {
        return 0; /* Not a tar archive */
    }
    if (strcmp(header->header.magic, GNUTMAGIC) == 0) {
        return 3; /* GNU Unix Standard tar archive */
    }
    if (strcmp(header->header.magic, TMAGIC) == 0) {
        return 2; /* Unix Standard tar archive */
    }
    return 1; /* Old fashioned tar archive */
}
 
int file_is_tar(RzMagic *ms, const ut8 *buf, size_t nbytes) {
    /*
     * Do the tar test first, because if the first file in the tar
     * archive starts with a dot, we can confuse it with an nroff file.
     */
    int tar = is_tar(buf, nbytes);
    int mime = ms->flags & RZ_MAGIC_MIME;
 
    if (tar < 1 || tar > 3) {
        return 0;
    }
    if (mime == RZ_MAGIC_MIME_ENCODING) {
        return 0;
    }
    if (file_printf(ms, mime ? "application/x-tar" : tartype[tar - 1]) == -1) {
        return -1;
    }
    return 1;
}
#endif