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 1.44 2019/02/20 02:35:27 christos 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(const char *, size_t);	/* Decode octal number */
55
56static const char tartype[][32] = {	/* should be equal to messages */
57	"tar archive",			/* found in ../magic/Magdir/archive */
58	"POSIX tar archive",
59	"POSIX tar archive (GNU)",	/*  */
60};
61
62protected int
63file_is_tar(struct magic_set *ms, const struct buffer *b)
64{
65	const unsigned char *buf = CAST(const unsigned char *, b->fbuf);
66	size_t nbytes = b->flen;
67	/*
68	 * Do the tar test first, because if the first file in the tar
69	 * archive starts with a dot, we can confuse it with an nroff file.
70	 */
71	int tar;
72	int mime = ms->flags & MAGIC_MIME;
73
74	if ((ms->flags & (MAGIC_APPLE|MAGIC_EXTENSION)) != 0)
75		return 0;
76
77	tar = is_tar(buf, nbytes);
78	if (tar < 1 || tar > 3)
79		return 0;
80
81	if (mime == MAGIC_MIME_ENCODING)
82		return 1;
83
84	if (file_printf(ms, "%s", mime ? "application/x-tar" :
85	    tartype[tar - 1]) == -1)
86		return -1;
87
88	return 1;
89}
90
91/*
92 * Return
93 *	0 if the checksum is bad (i.e., probably not a tar archive),
94 *	1 for old UNIX tar file,
95 *	2 for Unix Std (POSIX) tar file,
96 *	3 for GNU tar file.
97 */
98private int
99is_tar(const unsigned char *buf, size_t nbytes)
100{
101	const union record *header = RCAST(const union record *,
102	    RCAST(const void *, buf));
103	size_t i;
104	int sum, recsum;
105	const unsigned char *p, *ep;
106
107	if (nbytes < sizeof(*header))
108		return 0;
109
110	recsum = from_oct(header->header.chksum, sizeof(header->header.chksum));
111
112	sum = 0;
113	p = header->charptr;
114	ep = header->charptr + sizeof(*header);
115	while (p < ep)
116		sum += *p++;
117
118	/* Adjust checksum to count the "chksum" field as blanks. */
119	for (i = 0; i < sizeof(header->header.chksum); i++)
120		sum -= header->header.chksum[i];
121	sum += ' ' * sizeof(header->header.chksum);
122
123	if (sum != recsum)
124		return 0;	/* Not a tar archive */
125
126	if (strncmp(header->header.magic, GNUTMAGIC,
127	    sizeof(header->header.magic)) == 0)
128		return 3;		/* GNU Unix Standard tar archive */
129
130	if (strncmp(header->header.magic, TMAGIC,
131	    sizeof(header->header.magic)) == 0)
132		return 2;		/* Unix Standard tar archive */
133
134	return 1;			/* Old fashioned tar archive */
135}
136
137
138/*
139 * Quick and dirty octal conversion.
140 *
141 * Result is -1 if the field is invalid (all blank, or non-octal).
142 */
143private int
144from_oct(const char *where, size_t digs)
145{
146	int	value;
147
148	if (digs == 0)
149		return -1;
150
151	while (isspace(CAST(unsigned char, *where))) {	/* Skip spaces */
152		where++;
153		if (digs-- == 0)
154			return -1;		/* All blank field */
155	}
156	value = 0;
157	while (digs > 0 && isodigit(*where)) {	/* Scan til non-octal */
158		value = (value << 3) | (*where++ - '0');
159		digs--;
160	}
161
162	if (digs > 0 && *where && !isspace(CAST(unsigned char, *where)))
163		return -1;			/* Ended on non-(space/NUL) */
164
165	return value;
166}
167