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 1.37 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
53 private int is_tar(const unsigned char *, size_t);
54 private int from_oct(int, const char *); /* Decode octal number */
55
56 static const char tartype[][32] = {
57 "tar archive",
58 "POSIX tar archive",
59 "POSIX tar archive (GNU)",
60 };
61
62 protected int
file_is_tar(struct magic_set * ms,const unsigned char * buf,size_t nbytes)63 file_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 */
92 private int
is_tar(const unsigned char * buf,size_t nbytes)93 is_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 */
132 private int
from_oct(int digs,const char * where)133 from_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
