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/*
* 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 file_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 "file.h"
#ifndef lint
FILE_RCSID("@(#)$File: is_tar.c,v 1.50 2022/12/26 17:31:14 christos Exp $")
#endif
#include "magic.h"
#include <string.h>
#include <ctype.h>
#include "tar.h"
#define isodigit(c) ( ((c) >= '0') && ((c) <= '7') )
file_private int is_tar(const unsigned char *, size_t);
file_private int from_oct(const char *, size_t); /* Decode octal number */
static const char tartype[][32] = { /* should be equal to messages */
"tar archive", /* found in ../magic/Magdir/archive */
"POSIX tar archive",
"POSIX tar archive (GNU)", /* */
};
file_protected int
file_is_tar(struct magic_set *ms, const struct buffer *b)
{
const unsigned char *buf = CAST(const unsigned char *, b->fbuf);
size_t nbytes = b->flen;
/*
* 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;
int mime = ms->flags & MAGIC_MIME;
if ((ms->flags & (MAGIC_APPLE|MAGIC_EXTENSION)) != 0)
return 0;
tar = is_tar(buf, nbytes);
if (tar < 1 || tar > 3)
return 0;
if (mime == MAGIC_MIME_ENCODING)
return 1;
if (file_printf(ms, "%s", mime ? "application/x-tar" :
tartype[tar - 1]) == -1)
return -1;
return 1;
}
/*
* 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.
*/
file_private int
is_tar(const unsigned char *buf, size_t nbytes)
{
static const char gpkg_match[] = "/gpkg-1";
const union record *header = RCAST(const union record *,
RCAST(const void *, buf));
size_t i;
int sum, recsum;
const unsigned char *p, *ep;
const char *nulp;
if (nbytes < sizeof(*header))
return 0;
/* If the file looks like Gentoo GLEP 78 binary package (GPKG),
* don't waste time on further checks and fall back to magic rules.
*/
nulp = CAST(const char *,
memchr(header->header.name, 0, sizeof(header->header.name)));
if (nulp != NULL && nulp >= header->header.name + sizeof(gpkg_match) &&
memcmp(nulp - sizeof(gpkg_match) + 1, gpkg_match,
sizeof(gpkg_match)) == 0)
return 0;
recsum = from_oct(header->header.chksum, sizeof(header->header.chksum));
sum = 0;
p = header->charptr;
ep = header->charptr + sizeof(*header);
while (p < ep)
sum += *p++;
/* Adjust checksum to count the "chksum" field as blanks. */
for (i = 0; i < sizeof(header->header.chksum); i++)
sum -= header->header.chksum[i];
sum += ' ' * sizeof(header->header.chksum);
if (sum != recsum)
return 0; /* Not a tar archive */
if (strncmp(header->header.magic, GNUTMAGIC,
sizeof(header->header.magic)) == 0)
return 3; /* GNU Unix Standard tar archive */
if (strncmp(header->header.magic, TMAGIC,
sizeof(header->header.magic)) == 0)
return 2; /* Unix Standard tar archive */
return 1; /* Old fashioned tar archive */
}
/*
* Quick and dirty octal conversion.
*
* Result is -1 if the field is invalid (all blank, or non-octal).
*/
file_private int
from_oct(const char *where, size_t digs)
{
int value;
if (digs == 0)
return -1;
while (isspace(CAST(unsigned char, *where))) { /* Skip spaces */
where++;
if (digs-- == 0)
return -1; /* All blank field */
}
value = 0;
while (digs > 0 && isodigit(*where)) { /* Scan til non-octal */
value = (value << 3) | (*where++ - '0');
digs--;
}
if (digs > 0 && *where && !isspace(CAST(unsigned char, *where)))
return -1; /* Ended on non-(space/NUL) */
return value;
}
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