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
43 FILE_RCSID("@(#)$File: is_tar.c,v 1.41 2017/11/02 20:25:39 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 private int is_tar(const unsigned char *, size_t);
54 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 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 = 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 (file_printf(ms, "%s", mime ? "application/x-tar" :
82 tartype[tar - 1]) == -1)
83 return -1;
84 return 1;
85 }
86
87 /*
88 * Return
89 * 0 if the checksum is bad (i.e., probably not a tar archive),
90 * 1 for old UNIX tar file,
91 * 2 for Unix Std (POSIX) tar file,
92 * 3 for GNU tar file.
93 */
94 private int
is_tar(const unsigned char * buf,size_t nbytes)95 is_tar(const unsigned char *buf, size_t nbytes)
96 {
97 const union record *header = (const union record *)(const void *)buf;
98 size_t i;
99 int sum, recsum;
100 const unsigned char *p, *ep;
101
102 if (nbytes < sizeof(*header))
103 return 0;
104
105 recsum = from_oct(header->header.chksum, sizeof(header->header.chksum));
106
107 sum = 0;
108 p = header->charptr;
109 ep = header->charptr + sizeof(*header);
110 while (p < ep)
111 sum += *p++;
112
113 /* Adjust checksum to count the "chksum" field as blanks. */
114 for (i = 0; i < sizeof(header->header.chksum); i++)
115 sum -= header->header.chksum[i];
116 sum += ' ' * sizeof(header->header.chksum);
117
118 if (sum != recsum)
119 return 0; /* Not a tar archive */
120
121 if (strncmp(header->header.magic, GNUTMAGIC,
122 sizeof(header->header.magic)) == 0)
123 return 3; /* GNU Unix Standard tar archive */
124
125 if (strncmp(header->header.magic, TMAGIC,
126 sizeof(header->header.magic)) == 0)
127 return 2; /* Unix Standard tar archive */
128
129 return 1; /* Old fashioned tar archive */
130 }
131
132
133 /*
134 * Quick and dirty octal conversion.
135 *
136 * Result is -1 if the field is invalid (all blank, or non-octal).
137 */
138 private int
from_oct(const char * where,size_t digs)139 from_oct(const char *where, size_t digs)
140 {
141 int value;
142
143 if (digs == 0)
144 return -1;
145
146 while (isspace((unsigned char)*where)) { /* Skip spaces */
147 where++;
148 if (digs-- == 0)
149 return -1; /* All blank field */
150 }
151 value = 0;
152 while (digs > 0 && isodigit(*where)) { /* Scan til non-octal */
153 value = (value << 3) | (*where++ - '0');
154 digs--;
155 }
156
157 if (digs > 0 && *where && !isspace((unsigned char)*where))
158 return -1; /* Ended on non-(space/NUL) */
159
160 return value;
161 }
162