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 1.38 2015/04/09 20:01:41 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(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 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|MAGIC_EXTENSION)) != 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 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 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