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 1.44 2019/02/20 02:35:27 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 = CAST(const unsigned char *, 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 (mime == MAGIC_MIME_ENCODING) 82 return 1; 83 84 if (file_printf(ms, "%s", mime ? "application/x-tar" : 85 tartype[tar - 1]) == -1) 86 return -1; 87 88 return 1; 89 } 90 91 /* 92 * Return 93 * 0 if the checksum is bad (i.e., probably not a tar archive), 94 * 1 for old UNIX tar file, 95 * 2 for Unix Std (POSIX) tar file, 96 * 3 for GNU tar file. 97 */ 98 private int 99 is_tar(const unsigned char *buf, size_t nbytes) 100 { 101 const union record *header = RCAST(const union record *, 102 RCAST(const void *, buf)); 103 size_t i; 104 int sum, recsum; 105 const unsigned char *p, *ep; 106 107 if (nbytes < sizeof(*header)) 108 return 0; 109 110 recsum = from_oct(header->header.chksum, sizeof(header->header.chksum)); 111 112 sum = 0; 113 p = header->charptr; 114 ep = header->charptr + sizeof(*header); 115 while (p < ep) 116 sum += *p++; 117 118 /* Adjust checksum to count the "chksum" field as blanks. */ 119 for (i = 0; i < sizeof(header->header.chksum); i++) 120 sum -= header->header.chksum[i]; 121 sum += ' ' * sizeof(header->header.chksum); 122 123 if (sum != recsum) 124 return 0; /* Not a tar archive */ 125 126 if (strncmp(header->header.magic, GNUTMAGIC, 127 sizeof(header->header.magic)) == 0) 128 return 3; /* GNU Unix Standard tar archive */ 129 130 if (strncmp(header->header.magic, TMAGIC, 131 sizeof(header->header.magic)) == 0) 132 return 2; /* Unix Standard tar archive */ 133 134 return 1; /* Old fashioned tar archive */ 135 } 136 137 138 /* 139 * Quick and dirty octal conversion. 140 * 141 * Result is -1 if the field is invalid (all blank, or non-octal). 142 */ 143 private int 144 from_oct(const char *where, size_t digs) 145 { 146 int value; 147 148 if (digs == 0) 149 return -1; 150 151 while (isspace(CAST(unsigned char, *where))) { /* Skip spaces */ 152 where++; 153 if (digs-- == 0) 154 return -1; /* All blank field */ 155 } 156 value = 0; 157 while (digs > 0 && isodigit(*where)) { /* Scan til non-octal */ 158 value = (value << 3) | (*where++ - '0'); 159 digs--; 160 } 161 162 if (digs > 0 && *where && !isspace(CAST(unsigned char, *where))) 163 return -1; /* Ended on non-(space/NUL) */ 164 165 return value; 166 } 167