msdos/is_exec.c

   1 /* IS_EXEC.C
   2  *
   3  * Copyright (C) 1995 DJ Delorie
   4  * Copyright (C) 1994 Eli Zaretskii <eliz@is.elta.co.il>
   5  *
   6  * (See the README file in this directory for the copyright and license
   7  * history of this file.)
   8  *
   9  * This file is free software; you can redistribute it and/or modify
  10  * it under the terms of the GNU General Public License as published by
  11  * the Free Software Foundation; either version 2, or (at your option)
  12  * any later version.
  13  *
  14  * This file is distributed in the hope that it will be useful,
  15  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  16  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  17  * GNU General Public License for more details.
  18  *
  19  * You should have received a copy of the GNU General Public License
  20  * along with this file; see the file COPYING.  If not, write to
  21  * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  22  * Boston, MA 02110-1301, USA.
  23  *
  24  * Commentary:
  25  *
  26  * Given a filename or a file handle, and the extension of the file,
  27  * determine if the file is executable.
  28  * First, the file extension is checked in case it uniquely identifies
  29  * the file as either an executable or not.  Failing this, the first
  30  * two bytes of the file are tested for known signatures of executable
  31  * files.
  32  *
  33  */
  34
  35 #include <libc/stubs.h>
  36 #include <stdio.h>
  37 #include <string.h>
  38 #include <ctype.h>
  39 #include <errno.h>
  40 #include <dpmi.h>
  41 #include <go32.h>
  42 #include <io.h>
  43 #include <libc/farptrgs.h>
  44 #include <libc/dosio.h>
  45
  46 extern unsigned short _djstat_flags;
  47 unsigned short        _get_magic(const char *, int);
  48 int                   _is_executable(const char *, int, const char *);
  49
  50 /*
  51  * Read a MAGIC NUMBER from a given file.  These are the first
  52  * two bytes of the file, if we look at them as an unsigned short. */
  53
  54 #define _STAT_EXEC_EXT      2   /* get execute bits from file extension? */
  55 #define _STAT_EXEC_MAGIC    4   /* get execute bits from magic signature? */
  56
  57 unsigned short
  58 _get_magic(const char *s, int fh)
  59 {
  60   __dpmi_regs          regs;
  61   unsigned short       retval;
  62   unsigned short       fpos_high = 0, fpos_low = 0;
  63   int                  read_fail = 0;
  64
  65   /* If given a pathname, open the file. */
  66   if (s)
  67   {
  68     int handle;
  69     if((handle = _open(s,0)) == -1)
  70       return 0;
  71     regs.x.bx = handle;
  72   }
  73   /* Else file already open.  Remember its current file position
  74      and move to beginning of file. */
  75   else
  76   {
  77     regs.x.ax = 0x4201;         /* set pointer from current position */
  78     regs.x.bx = fh;
  79     regs.x.cx = regs.x.dx = 0;  /* move 0 bytes (i.e., stay put) */
  80     __dpmi_int(0x21, &regs);
  81     if (regs.x.flags & 1)
  82     {
  83       errno = __doserr_to_errno(regs.x.ax);
  84       return 0;
  85     }
  86     fpos_high = regs.x.dx;      /* got current position */
  87     fpos_low  = regs.x.ax;
  88
  89     regs.x.ax = 0x4200;         /* set pointer from the beginning of file */
  90     regs.x.cx = regs.x.dx = 0;  /* move to beginning of file */
  91     __dpmi_int(0x21, &regs);
  92     if (regs.x.flags & 1)
  93     {
  94       errno = __doserr_to_errno(regs.x.ax);
  95       return 0;
  96     }
  97   }
  98   regs.x.ds = __tb_segment;
  99   regs.x.dx = __tb_offset;
 100
 101   /* Read 2 bytes from the file. */
 102   regs.x.ax = 0x3f00;
 103   regs.x.cx = 2;
 104   __dpmi_int(0x21, &regs);
 105
 106   /* We can either (1) succeed, (2) read less than 2 bytes,
 107      or (3) fail to read at all.  */
 108   if (regs.x.ax != 2)
 109     read_fail = (regs.x.flags & 1) ? regs.x.ax : -1;
 110
 111   /* If called with filename, close the file. */
 112   if (s)
 113   {
 114     regs.x.ax = 0x3e00;
 115     __dpmi_int(0x21, &regs);
 116     if (regs.x.flags & 1)
 117       errno = __doserr_to_errno(regs.x.ax);
 118   }
 119   /* Else leave file pointer where we found it. */
 120   else
 121   {
 122     regs.x.ax = 0x4200;         /* set pointer from the beginning of file */
 123     regs.x.bx = fh;
 124     regs.x.cx = fpos_high;
 125     regs.x.dx = fpos_low;
 126     __dpmi_int(0x21, &regs);
 127     if (regs.x.flags & 1)
 128     {
 129       errno = __doserr_to_errno(regs.x.ax);
 130       return 0;
 131     }
 132   }
 133
 134   if (read_fail == 0)
 135     retval = _farpeekw(_dos_ds, __tb);
 136   else
 137   {
 138     /* The file couldn't be read: assume non-executable.  If the file
 139        *is* executable, but was passed as a file-handle, and the user
 140        opened it in write-only mode, they lose...  */
 141     retval = 0;
 142     if (read_fail != -1)
 143       errno = __doserr_to_errno(read_fail);
 144   }
 145
 146   return retval;
 147 }
 148
 149 /* A list of extensions which designate executable files.  These
 150    are NOT tested for the magic number.  */
 151 static char executables[] = "|EXE|COM|BAT|BTM|DLL|VXD|";
 152
 153 /* A list of extensions which belong to files known to NEVER be
 154    executables.  These exist to minimize read()'ing files while
 155    detecting executables by magic number.  You are welcome to
 156    add to this list, but remember: only extensions which could
 157    NEVER be present in executables should go here.  */
 158 static char non_executables[] = "\
 159 |A|A01|A02|A03|A04|A05|ADL|ARC|ARJ|ASC|ASM|AUX|AWK\
 160 |BAS|BIB|BGI|BMP\
 161 |C|CC|CFG|CGZ|CH3|CHR|CI|CLP|CMF|CPI|CPP|CXX\
 162 |DAT|DBF|DIZ|DOC|DVI\
 163 |E|EL|ELC\
 164 |F77|FN3\
 165 |GIF|GZ\
 166 |H|HLP|HPP|HXX\
 167 |ICO|IN|INC|INF|INI\
 168 |JPG\
 169 |L|LEX|LF|LIB|LOG|LST|LZH\
 170 |M|MAK|MAP|MF|MID|MPG\
 171 |O|OBJ\
 172 |PAK|PAS|PBM|PCD|PCX|PDS|PIC|PIF|PN3|PRJ|PS\
 173 |RAS|RGB|RLE\
 174 |S|SND|SY3\
 175 |TAR|TAZ|TEX|TGA|TGZ|TIF|TXH|TXI|TXT\
 176 |VOC\
 177 |WAV|WK1|WK3|WKB|WQ1|WQ3|WQ4|WQ5|WQ6|WQ!\
 178 |XBM\
 179 |Y\
 180 |ZIP|ZOO|";
 181
 182 int
 183 _is_executable(const char *filename, int fhandle, const char *extension)
 184 {
 185   if (!extension && filename)
 186   {
 187     const char *cp, *ep=0;
 188     for (cp=filename; *cp; cp++)
 189     {
 190       if (*cp == '.')
 191         ep = cp;
 192       if (*cp == '/' || *cp == '\\' || *cp == ':')
 193         ep = 0;
 194     }
 195     extension = ep;
 196   }
 197   if ((_djstat_flags & _STAT_EXEC_EXT) == 0
 198       && extension
 199       && *extension
 200       && strlen(extension) <= ((extension[0]=='.') ? 4 : 3))
 201     {
 202       /* Search the list of extensions in executables[]. */
 203       char tmp_buf[6], *tp = tmp_buf;
 204
 205       *tp++ = '|';
 206       if (*extension == '.')
 207         extension++;
 208       while (*extension)
 209         *tp++ = toupper (*extension++);
 210       *tp++ = '|';
 211       *tp = '\0';
 212       if (strstr(non_executables, tmp_buf))
 213         return 0;
 214       else if (strstr(executables, tmp_buf))
 215         return 1;
 216     }
 217
 218   /* No extension, or extension doesn't define execute
 219      bits unambiguously.  We are in for some dirty work.
 220      Read the first two bytes of the file and see if they
 221      are any of the known magic numbers which designate
 222      executable files.
 223      Unix-like shells, which have executable shell scripts
 224      without extensions and DON'T have "#!" as their FIRST
 225      TWO CHARACTERS, lose here.  Sorry, folks.  */
 226   if ( (_djstat_flags & _STAT_EXEC_MAGIC) == 0 )
 227     {
 228       switch (_get_magic(filename, fhandle))
 229         {
 230           case 0x5a4d:      /* "MZ" */
 231           case 0x010b:
 232           case 0x014c:
 233           case 0x2123:      /* "#!" */
 234               return 1;
 235         }
 236     }
 237
 238   return 0;
 239 }
 240
 241 /* arch-tag: b0965811-8c3e-4bc4-8d81-4447a3594785
 242    (do not change this comment) */