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 1.47 2022/09/13 18:46:07 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 static const char gpkg_match[] = "/gpkg-1"; 102 103 const union record *header = RCAST(const union record *, 104 RCAST(const void *, buf)); 105 size_t i; 106 int sum, recsum; 107 const unsigned char *p, *ep; 108 const char *nulp; 109 110 if (nbytes < sizeof(*header)) 111 return 0; 112 113 /* If the file looks like Gentoo GLEP 78 binary package (GPKG), 114 * don't waste time on further checks and fall back to magic rules. 115 */ 116 nulp = CAST(const char *, 117 memchr(header->header.name, 0, sizeof(header->header.name))); 118 if (nulp != NULL && nulp >= header->header.name + sizeof(gpkg_match) && 119 memcmp(nulp - sizeof(gpkg_match) + 1, gpkg_match, 120 sizeof(gpkg_match)) == 0) 121 return 0; 122 123 recsum = from_oct(header->header.chksum, sizeof(header->header.chksum)); 124 125 sum = 0; 126 p = header->charptr; 127 ep = header->charptr + sizeof(*header); 128 while (p < ep) 129 sum += *p++; 130 131 /* Adjust checksum to count the "chksum" field as blanks. */ 132 for (i = 0; i < sizeof(header->header.chksum); i++) 133 sum -= header->header.chksum[i]; 134 sum += ' ' * sizeof(header->header.chksum); 135 136 if (sum != recsum) 137 return 0; /* Not a tar archive */ 138 139 if (strncmp(header->header.magic, GNUTMAGIC, 140 sizeof(header->header.magic)) == 0) 141 return 3; /* GNU Unix Standard tar archive */ 142 143 if (strncmp(header->header.magic, TMAGIC, 144 sizeof(header->header.magic)) == 0) 145 return 2; /* Unix Standard tar archive */ 146 147 return 1; /* Old fashioned tar archive */ 148 } 149 150 151 /* 152 * Quick and dirty octal conversion. 153 * 154 * Result is -1 if the field is invalid (all blank, or non-octal). 155 */ 156 private int 157 from_oct(const char *where, size_t digs) 158 { 159 int value; 160 161 if (digs == 0) 162 return -1; 163 164 while (isspace(CAST(unsigned char, *where))) { /* Skip spaces */ 165 where++; 166 if (digs-- == 0) 167 return -1; /* All blank field */ 168 } 169 value = 0; 170 while (digs > 0 && isodigit(*where)) { /* Scan til non-octal */ 171 value = (value << 3) | (*where++ - '0'); 172 digs--; 173 } 174 175 if (digs > 0 && *where && !isspace(CAST(unsigned char, *where))) 176 return -1; /* Ended on non-(space/NUL) */ 177 178 return value; 179 } 180