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 file_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 1.50 2022/12/26 17:31:14 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
53file_private int is_tar(const unsigned char *, size_t);
54file_private 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
62file_protected 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 */
98file_private int
99is_tar(const unsigned char *buf, size_t nbytes)
100{
101	static const char gpkg_match[] = "/gpkg-1";
102
103	const union record *header = RCAST(const union record *,
104	    RCAST(const void *, buf));
105	size_t i;
106	int sum, recsum;
107	const unsigned char *p, *ep;
108	const char *nulp;
109
110	if (nbytes < sizeof(*header))
111		return 0;
112
113	/* If the file looks like Gentoo GLEP 78 binary package (GPKG),
114	 * don't waste time on further checks and fall back to magic rules.
115	 */
116	nulp = CAST(const char *,
117	    memchr(header->header.name, 0, sizeof(header->header.name)));
118	if (nulp != NULL && nulp >= header->header.name + sizeof(gpkg_match) &&
119	    memcmp(nulp - sizeof(gpkg_match) + 1, gpkg_match,
120	    sizeof(gpkg_match)) == 0)
121	    return 0;
122
123	recsum = from_oct(header->header.chksum, sizeof(header->header.chksum));
124
125	sum = 0;
126	p = header->charptr;
127	ep = header->charptr + sizeof(*header);
128	while (p < ep)
129		sum += *p++;
130
131	/* Adjust checksum to count the "chksum" field as blanks. */
132	for (i = 0; i < sizeof(header->header.chksum); i++)
133		sum -= header->header.chksum[i];
134	sum += ' ' * sizeof(header->header.chksum);
135
136	if (sum != recsum)
137		return 0;	/* Not a tar archive */
138
139	if (strncmp(header->header.magic, GNUTMAGIC,
140	    sizeof(header->header.magic)) == 0)
141		return 3;		/* GNU Unix Standard tar archive */
142
143	if (strncmp(header->header.magic, TMAGIC,
144	    sizeof(header->header.magic)) == 0)
145		return 2;		/* Unix Standard tar archive */
146
147	return 1;			/* Old fashioned tar archive */
148}
149
150
151/*
152 * Quick and dirty octal conversion.
153 *
154 * Result is -1 if the field is invalid (all blank, or non-octal).
155 */
156file_private int
157from_oct(const char *where, size_t digs)
158{
159	int	value;
160
161	if (digs == 0)
162		return -1;
163
164	while (isspace(CAST(unsigned char, *where))) {	/* Skip spaces */
165		where++;
166		if (digs-- == 0)
167			return -1;		/* All blank field */
168	}
169	value = 0;
170	while (digs > 0 && isodigit(*where)) {	/* Scan til non-octal */
171		value = (value << 3) | (*where++ - '0');
172		digs--;
173	}
174
175	if (digs > 0 && *where && !isspace(CAST(unsigned char, *where)))
176		return -1;			/* Ended on non-(space/NUL) */
177
178	return value;
179}
180