157 lines
4.6 KiB
C
157 lines
4.6 KiB
C
/*
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* Copyright (c) Ian F. Darwin 1986-1995.
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* Software written by Ian F. Darwin and others;
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* maintained 1995-present by Christos Zoulas and others.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice immediately at the beginning of the file, without modification,
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* this list of conditions, and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE FOR
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* ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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/*
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* is_tar() -- figure out whether file is a tar archive.
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*
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* Stolen (by the author!) from the public domain tar program:
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* Public Domain version written 26 Aug 1985 John Gilmore (ihnp4!hoptoad!gnu).
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*
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* @(#)list.c 1.18 9/23/86 Public Domain - gnu
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*
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* Comments changed and some code/comments reformatted
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* for file command by Ian Darwin.
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*/
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#include "file.h"
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#include "magic.h"
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#include <string.h>
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#include <ctype.h>
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#include <sys/types.h>
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#include "tar.h"
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#ifndef lint
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FILE_RCSID("@(#)$File: is_tar.c,v 1.27 2007/01/12 17:38:28 christos Exp $")
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#endif
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#define isodigit(c) ( ((c) >= '0') && ((c) <= '7') )
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private int is_tar(const unsigned char *, size_t);
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private int from_oct(int, const char *); /* Decode octal number */
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protected int
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file_is_tar(struct magic_set *ms, const unsigned char *buf, size_t nbytes)
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{
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/*
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* Do the tar test first, because if the first file in the tar
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* archive starts with a dot, we can confuse it with an nroff file.
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*/
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switch (is_tar(buf, nbytes)) {
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case 1:
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if (file_printf(ms, (ms->flags & MAGIC_MIME) ?
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"application/x-tar" : "tar archive") == -1)
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return -1;
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return 1;
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case 2:
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if (file_printf(ms, (ms->flags & MAGIC_MIME) ?
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"application/x-tar, POSIX" : "POSIX tar archive") == -1)
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return -1;
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return 1;
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case 3:
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if (file_printf(ms, (ms->flags & MAGIC_MIME) ?
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"application/x-tar, POSIX (GNU)" :
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"POSIX tar archive (GNU)") == -1)
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return -1;
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return 1;
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default:
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return 0;
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}
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}
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/*
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* Return
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* 0 if the checksum is bad (i.e., probably not a tar archive),
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* 1 for old UNIX tar file,
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* 2 for Unix Std (POSIX) tar file.
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*/
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private int
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is_tar(const unsigned char *buf, size_t nbytes)
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{
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const union record *header = (const union record *)(const void *)buf;
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int i;
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int sum, recsum;
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const char *p;
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if (nbytes < sizeof(union record))
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return 0;
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recsum = from_oct(8, header->header.chksum);
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sum = 0;
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p = header->charptr;
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for (i = sizeof(union record); --i >= 0;) {
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/*
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* We cannot use unsigned char here because of old compilers,
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* e.g. V7.
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*/
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sum += 0xFF & *p++;
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}
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/* Adjust checksum to count the "chksum" field as blanks. */
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for (i = sizeof(header->header.chksum); --i >= 0;)
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sum -= 0xFF & header->header.chksum[i];
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sum += ' '* sizeof header->header.chksum;
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if (sum != recsum)
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return 0; /* Not a tar archive */
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if (strcmp(header->header.magic, GNUTMAGIC) == 0)
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return 3; /* GNU Unix Standard tar archive */
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if (strcmp(header->header.magic, TMAGIC) == 0)
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return 2; /* Unix Standard tar archive */
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return 1; /* Old fashioned tar archive */
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}
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/*
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* Quick and dirty octal conversion.
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*
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* Result is -1 if the field is invalid (all blank, or nonoctal).
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*/
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private int
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from_oct(int digs, const char *where)
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{
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int value;
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while (isspace((unsigned char)*where)) { /* Skip spaces */
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where++;
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if (--digs <= 0)
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return -1; /* All blank field */
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}
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value = 0;
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while (digs > 0 && isodigit(*where)) { /* Scan til nonoctal */
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value = (value << 3) | (*where++ - '0');
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--digs;
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}
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if (digs > 0 && *where && !isspace((unsigned char)*where))
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return -1; /* Ended on non-space/nul */
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return value;
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}
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