1 /*
2 * is_tar() -- figure out whether file is a tar archive.
3 *
4 * Stolen (by the author of the file utility!) from the public domain tar program:
5 * Public Domain version written 26 Aug 1985 John Gilmore (ihnp4!hoptoad!gnu).
6 *
7 * @(#)list.c 1.18 9/23/86 Public Domain - gnu
8 * $Id: is_tar.c,v 1.2 2006/06/17 21:00:44 tkojm Exp $
9 *
10 * Comments changed and some code/comments reformatted
11 * for file command by Ian Darwin.
12 */
13
14 #if HAVE_CONFIG_H
15 #include "clamav-config.h"
16 #endif
17
18 #include <string.h>
19 #include <ctype.h>
20 #include <sys/types.h>
21 #include "is_tar.h"
22
23 #include "clamav.h"
24 #include "others.h"
25
26 #define isodigit(c) (((c) >= '0') && ((c) <= '7'))
27
28 static int from_oct(int digs, char *where);
29
is_tar(const unsigned char * buf,unsigned int nbytes)30 int is_tar(const unsigned char *buf, unsigned int nbytes)
31 {
32 union record *header = (union record *)buf;
33 int i;
34 int sum, recsum;
35 char *p;
36
37 if (nbytes < sizeof(union record))
38 return 0;
39
40 recsum = from_oct(8, header->header.chksum);
41
42 sum = 0;
43 p = header->charptr;
44 for (i = sizeof(union record); --i >= 0;) {
45 /*
46 * We can't use unsigned char here because of old compilers,
47 * e.g. V7.
48 */
49 sum += 0xFF & *p++;
50 }
51
52 /* Adjust checksum to count the "chksum" field as blanks. */
53 for (i = sizeof(header->header.chksum); --i >= 0;)
54 sum -= 0xFF & header->header.chksum[i];
55 sum += ' ' * sizeof header->header.chksum;
56
57 if (sum != recsum)
58 return 0; /* Not a tar archive */
59
60 if (0 == strcmp(header->header.magic, TMAGIC))
61 return 2; /* Unix Standard tar archive */
62
63 return 1; /* Old fashioned tar archive */
64 }
65
66 /*
67 * Quick and dirty octal conversion.
68 *
69 * Result is -1 if the field is invalid (all blank, or nonoctal).
70 */
from_oct(int digs,char * where)71 static int from_oct(int digs, char *where)
72 {
73 int value;
74
75 while (isspace((unsigned char)*where)) { /* Skip spaces */
76 where++;
77 if (--digs <= 0)
78 return -1; /* All blank field */
79 }
80 value = 0;
81 while (digs > 0 && isodigit(*where)) { /* Scan til nonoctal */
82 value = (value << 3) | (*where++ - '0');
83 --digs;
84 }
85
86 if (digs > 0 && *where && !isspace((unsigned char)*where))
87 return -1; /* Ended on non-space/nul */
88
89 return value;
90 }
91