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 46extern unsigned short _djstat_flags; 47unsigned short _get_magic(const char *, int); 48int _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 57unsigned 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, ®s); 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, ®s); 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, ®s); 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, ®s); 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, ®s); 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. */ 151static 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. */ 158static 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 182int 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) */ 243