1/*
2 * Copyright (c) Ian F. Darwin 1986-1995.
3 * Software written by Ian F. Darwin and others;
4 * maintained 1995-present by Christos Zoulas and others.
5 *
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions
8 * are met:
9 * 1. Redistributions of source code must retain the above copyright
10 *    notice immediately at the beginning of the file, without modification,
11 *    this list of conditions, and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 *    notice, this list of conditions and the following disclaimer in the
14 *    documentation and/or other materials provided with the distribution.
15 *
16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
17 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
18 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
19 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE FOR
20 * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
21 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
22 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
23 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
24 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
25 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
26 * SUCH DAMAGE.
27 */
28/*
29 * is_tar() -- figure out whether file is a tar archive.
30 *
31 * Stolen (by the author!) from the public domain tar program:
32 * Public Domain version written 26 Aug 1985 John Gilmore (ihnp4!hoptoad!gnu).
33 *
34 * @(#)list.c 1.18 9/23/86 Public Domain - gnu
35 *
36 * Comments changed and some code/comments reformatted
37 * for file command by Ian Darwin.
38 */
39
40#include "file.h"
41
42#ifndef lint
43FILE_RCSID("@(#)$File: is_tar.c,v 1.37 2010/11/30 14:58:53 rrt Exp $")
44#endif
45
46#include "magic.h"
47#include <string.h>
48#include <ctype.h>
49#include "tar.h"
50
51#define	isodigit(c)	( ((c) >= '0') && ((c) <= '7') )
52
53private int is_tar(const unsigned char *, size_t);
54private int from_oct(int, const char *);	/* Decode octal number */
55
56static const char tartype[][32] = {
57	"tar archive",
58	"POSIX tar archive",
59	"POSIX tar archive (GNU)",
60};
61
62protected int
63file_is_tar(struct magic_set *ms, const unsigned char *buf, size_t nbytes)
64{
65	/*
66	 * Do the tar test first, because if the first file in the tar
67	 * archive starts with a dot, we can confuse it with an nroff file.
68	 */
69	int tar;
70	int mime = ms->flags & MAGIC_MIME;
71
72	if ((ms->flags & MAGIC_APPLE) != 0)
73		return 0;
74
75	tar = is_tar(buf, nbytes);
76	if (tar < 1 || tar > 3)
77		return 0;
78
79	if (file_printf(ms, "%s", mime ? "application/x-tar" :
80	    tartype[tar - 1]) == -1)
81		return -1;
82	return 1;
83}
84
85/*
86 * Return
87 *	0 if the checksum is bad (i.e., probably not a tar archive),
88 *	1 for old UNIX tar file,
89 *	2 for Unix Std (POSIX) tar file,
90 *	3 for GNU tar file.
91 */
92private int
93is_tar(const unsigned char *buf, size_t nbytes)
94{
95	const union record *header = (const union record *)(const void *)buf;
96	int	i;
97	int	sum, recsum;
98	const unsigned char	*p;
99
100	if (nbytes < sizeof(union record))
101		return 0;
102
103	recsum = from_oct(8,  header->header.chksum);
104
105	sum = 0;
106	p = header->charptr;
107	for (i = sizeof(union record); --i >= 0;)
108		sum += *p++;
109
110	/* Adjust checksum to count the "chksum" field as blanks. */
111	for (i = sizeof(header->header.chksum); --i >= 0;)
112		sum -= header->header.chksum[i];
113	sum += ' ' * sizeof header->header.chksum;
114
115	if (sum != recsum)
116		return 0;	/* Not a tar archive */
117
118	if (strcmp(header->header.magic, GNUTMAGIC) == 0)
119		return 3;		/* GNU Unix Standard tar archive */
120	if (strcmp(header->header.magic, TMAGIC) == 0)
121		return 2;		/* Unix Standard tar archive */
122
123	return 1;			/* Old fashioned tar archive */
124}
125
126
127/*
128 * Quick and dirty octal conversion.
129 *
130 * Result is -1 if the field is invalid (all blank, or non-octal).
131 */
132private int
133from_oct(int digs, const char *where)
134{
135	int	value;
136
137	while (isspace((unsigned char)*where)) {	/* Skip spaces */
138		where++;
139		if (--digs <= 0)
140			return -1;		/* All blank field */
141	}
142	value = 0;
143	while (digs > 0 && isodigit(*where)) {	/* Scan til non-octal */
144		value = (value << 3) | (*where++ - '0');
145		--digs;
146	}
147
148	if (digs > 0 && *where && !isspace((unsigned char)*where))
149		return -1;			/* Ended on non-(space/NUL) */
150
151	return value;
152}
153