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 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 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 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