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4e1567acff
62c2915build: supply `-Wl,--high-entropy-va` (Wladimir J. van der Laan)9a75d29devtools: Check for high-entropy ASLR in 64-bit PE executables (Wladimir J. van der Laan)
217 lines
8.0 KiB
Python
Executable File
217 lines
8.0 KiB
Python
Executable File
#!/usr/bin/env python
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# Copyright (c) 2015-2016 The Bitcoin Core developers
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# Distributed under the MIT software license, see the accompanying
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# file COPYING or http://www.opensource.org/licenses/mit-license.php.
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'''
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Perform basic ELF security checks on a series of executables.
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Exit status will be 0 if successful, and the program will be silent.
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Otherwise the exit status will be 1 and it will log which executables failed which checks.
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Needs `readelf` (for ELF) and `objdump` (for PE).
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'''
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from __future__ import division,print_function,unicode_literals
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import subprocess
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import sys
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import os
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READELF_CMD = os.getenv('READELF', '/usr/bin/readelf')
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OBJDUMP_CMD = os.getenv('OBJDUMP', '/usr/bin/objdump')
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NONFATAL = {'HIGH_ENTROPY_VA'} # checks which are non-fatal for now but only generate a warning
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def check_ELF_PIE(executable):
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'''
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Check for position independent executable (PIE), allowing for address space randomization.
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'''
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p = subprocess.Popen([READELF_CMD, '-h', '-W', executable], stdout=subprocess.PIPE, stderr=subprocess.PIPE, stdin=subprocess.PIPE)
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(stdout, stderr) = p.communicate()
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if p.returncode:
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raise IOError('Error opening file')
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ok = False
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for line in stdout.split(b'\n'):
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line = line.split()
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if len(line)>=2 and line[0] == b'Type:' and line[1] == b'DYN':
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ok = True
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return ok
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def get_ELF_program_headers(executable):
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'''Return type and flags for ELF program headers'''
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p = subprocess.Popen([READELF_CMD, '-l', '-W', executable], stdout=subprocess.PIPE, stderr=subprocess.PIPE, stdin=subprocess.PIPE)
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(stdout, stderr) = p.communicate()
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if p.returncode:
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raise IOError('Error opening file')
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in_headers = False
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count = 0
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headers = []
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for line in stdout.split(b'\n'):
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if line.startswith(b'Program Headers:'):
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in_headers = True
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if line == b'':
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in_headers = False
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if in_headers:
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if count == 1: # header line
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ofs_typ = line.find(b'Type')
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ofs_offset = line.find(b'Offset')
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ofs_flags = line.find(b'Flg')
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ofs_align = line.find(b'Align')
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if ofs_typ == -1 or ofs_offset == -1 or ofs_flags == -1 or ofs_align == -1:
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raise ValueError('Cannot parse elfread -lW output')
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elif count > 1:
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typ = line[ofs_typ:ofs_offset].rstrip()
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flags = line[ofs_flags:ofs_align].rstrip()
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headers.append((typ, flags))
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count += 1
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return headers
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def check_ELF_NX(executable):
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'''
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Check that no sections are writable and executable (including the stack)
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'''
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have_wx = False
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have_gnu_stack = False
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for (typ, flags) in get_ELF_program_headers(executable):
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if typ == b'GNU_STACK':
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have_gnu_stack = True
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if b'W' in flags and b'E' in flags: # section is both writable and executable
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have_wx = True
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return have_gnu_stack and not have_wx
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def check_ELF_RELRO(executable):
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'''
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Check for read-only relocations.
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GNU_RELRO program header must exist
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Dynamic section must have BIND_NOW flag
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'''
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have_gnu_relro = False
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for (typ, flags) in get_ELF_program_headers(executable):
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# Note: not checking flags == 'R': here as linkers set the permission differently
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# This does not affect security: the permission flags of the GNU_RELRO program header are ignored, the PT_LOAD header determines the effective permissions.
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# However, the dynamic linker need to write to this area so these are RW.
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# Glibc itself takes care of mprotecting this area R after relocations are finished.
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# See also http://permalink.gmane.org/gmane.comp.gnu.binutils/71347
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if typ == b'GNU_RELRO':
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have_gnu_relro = True
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have_bindnow = False
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p = subprocess.Popen([READELF_CMD, '-d', '-W', executable], stdout=subprocess.PIPE, stderr=subprocess.PIPE, stdin=subprocess.PIPE)
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(stdout, stderr) = p.communicate()
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if p.returncode:
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raise IOError('Error opening file')
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for line in stdout.split(b'\n'):
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tokens = line.split()
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if len(tokens)>1 and tokens[1] == b'(BIND_NOW)' or (len(tokens)>2 and tokens[1] == b'(FLAGS)' and b'BIND_NOW' in tokens[2]):
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have_bindnow = True
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return have_gnu_relro and have_bindnow
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def check_ELF_Canary(executable):
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'''
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Check for use of stack canary
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'''
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p = subprocess.Popen([READELF_CMD, '--dyn-syms', '-W', executable], stdout=subprocess.PIPE, stderr=subprocess.PIPE, stdin=subprocess.PIPE)
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(stdout, stderr) = p.communicate()
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if p.returncode:
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raise IOError('Error opening file')
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ok = False
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for line in stdout.split(b'\n'):
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if b'__stack_chk_fail' in line:
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ok = True
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return ok
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def get_PE_dll_characteristics(executable):
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'''
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Get PE DllCharacteristics bits.
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Returns a tuple (arch,bits) where arch is 'i386:x86-64' or 'i386'
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and bits is the DllCharacteristics value.
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'''
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p = subprocess.Popen([OBJDUMP_CMD, '-x', executable], stdout=subprocess.PIPE, stderr=subprocess.PIPE, stdin=subprocess.PIPE)
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(stdout, stderr) = p.communicate()
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if p.returncode:
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raise IOError('Error opening file')
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arch = ''
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bits = 0
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for line in stdout.split('\n'):
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tokens = line.split()
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if len(tokens)>=2 and tokens[0] == 'architecture:':
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arch = tokens[1].rstrip(',')
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if len(tokens)>=2 and tokens[0] == 'DllCharacteristics':
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bits = int(tokens[1],16)
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return (arch,bits)
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IMAGE_DLL_CHARACTERISTICS_HIGH_ENTROPY_VA = 0x0020
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IMAGE_DLL_CHARACTERISTICS_DYNAMIC_BASE = 0x0040
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IMAGE_DLL_CHARACTERISTICS_NX_COMPAT = 0x0100
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def check_PE_DYNAMIC_BASE(executable):
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'''PIE: DllCharacteristics bit 0x40 signifies dynamicbase (ASLR)'''
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(arch,bits) = get_PE_dll_characteristics(executable)
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reqbits = IMAGE_DLL_CHARACTERISTICS_DYNAMIC_BASE
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return (bits & reqbits) == reqbits
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# On 64 bit, must support high-entropy 64-bit address space layout randomization in addition to DYNAMIC_BASE
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# to have secure ASLR.
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def check_PE_HIGH_ENTROPY_VA(executable):
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'''PIE: DllCharacteristics bit 0x20 signifies high-entropy ASLR'''
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(arch,bits) = get_PE_dll_characteristics(executable)
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if arch == 'i386:x86-64':
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reqbits = IMAGE_DLL_CHARACTERISTICS_HIGH_ENTROPY_VA
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else: # Unnecessary on 32-bit
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assert(arch == 'i386')
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reqbits = 0
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return (bits & reqbits) == reqbits
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def check_PE_NX(executable):
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'''NX: DllCharacteristics bit 0x100 signifies nxcompat (DEP)'''
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(arch,bits) = get_PE_dll_characteristics(executable)
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return (bits & IMAGE_DLL_CHARACTERISTICS_NX_COMPAT) == IMAGE_DLL_CHARACTERISTICS_NX_COMPAT
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CHECKS = {
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'ELF': [
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('PIE', check_ELF_PIE),
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('NX', check_ELF_NX),
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('RELRO', check_ELF_RELRO),
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('Canary', check_ELF_Canary)
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],
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'PE': [
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('DYNAMIC_BASE', check_PE_DYNAMIC_BASE),
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('HIGH_ENTROPY_VA', check_PE_HIGH_ENTROPY_VA),
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('NX', check_PE_NX)
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]
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}
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def identify_executable(executable):
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with open(filename, 'rb') as f:
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magic = f.read(4)
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if magic.startswith(b'MZ'):
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return 'PE'
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elif magic.startswith(b'\x7fELF'):
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return 'ELF'
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return None
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if __name__ == '__main__':
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retval = 0
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for filename in sys.argv[1:]:
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try:
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etype = identify_executable(filename)
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if etype is None:
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print('%s: unknown format' % filename)
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retval = 1
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continue
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failed = []
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warning = []
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for (name, func) in CHECKS[etype]:
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if not func(filename):
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if name in NONFATAL:
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warning.append(name)
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else:
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failed.append(name)
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if failed:
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print('%s: failed %s' % (filename, ' '.join(failed)))
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retval = 1
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if warning:
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print('%s: warning %s' % (filename, ' '.join(warning)))
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except IOError:
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print('%s: cannot open' % filename)
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retval = 1
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exit(retval)
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