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
43 FILE_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
53 file_private int is_tar(const unsigned char *, size_t);
54 file_private int from_oct(const char *, size_t); /* Decode octal number */
55
56 static 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
62 file_protected int
file_is_tar(struct magic_set * ms,const struct buffer * b)63 file_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 */
98 file_private int
is_tar(const unsigned char * buf,size_t nbytes)99 is_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 */
156 file_private int
from_oct(const char * where,size_t digs)157 from_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