devtools: Add security-check.py
Perform the following ELF security checks: - PIE: Check for position independent executable (PIE), allowing for address space randomization - NX: Check that no sections are writable and executable (including the stack) - RELRO: Check for read-only relocations, binding at startup - Canary: Check for use of stack canary Also add a check to symbol-check.py that checks that only the subset of allowed libraries is imported (to avoid incompatibilities).
This commit is contained in:
Wladimir J. van der Laan
parent
a1d623da3e
commit
579b863cd7
3 changed files with 268 additions and 3 deletions
181
contrib/devtools/security-check.py
Executable file
181
contrib/devtools/security-check.py
Executable file
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#!/usr/bin/python2
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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 succesful, 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
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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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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('\n'):
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line = line.split()
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if len(line)>=2 and line[0] == 'Type:' and line[1] == '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('\n'):
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if line.startswith('Program Headers:'):
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in_headers = True
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if line == '':
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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('Type')
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ofs_offset = line.find('Offset')
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ofs_flags = line.find('Flg')
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ofs_align = line.find('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 == 'GNU_STACK':
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have_gnu_stack = True
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if 'W' in flags and '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 == '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('\n'):
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tokens = line.split()
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if len(tokens)>1 and tokens[1] == '(BIND_NOW)':
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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('\n'):
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if '__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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'''
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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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for line in stdout.split('\n'):
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tokens = line.split()
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if len(tokens)>=2 and tokens[0] == 'DllCharacteristics':
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return int(tokens[1],16)
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return 0
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def check_PE_PIE(executable):
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'''PIE: DllCharacteristics bit 0x40 signifies dynamicbase (ASLR)'''
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return bool(get_PE_dll_characteristics(executable) & 0x40)
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def check_PE_NX(executable):
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'''NX: DllCharacteristics bit 0x100 signifies nxcompat (DEP)'''
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return bool(get_PE_dll_characteristics(executable) & 0x100)
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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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('PIE', check_PE_PIE),
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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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for (name, func) in CHECKS[etype]:
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if not func(filename):
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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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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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@ -1,4 +1,4 @@
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#!/usr/bin/python
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#!/usr/bin/python2
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# Copyright (c) 2014 Wladimir J. van der Laan
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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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@ -15,6 +15,7 @@ from __future__ import division, print_function
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import subprocess
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import re
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import sys
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import os
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# Debian 6.0.9 (Squeeze) has:
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#
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@ -45,8 +46,10 @@ MAX_VERSIONS = {
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IGNORE_EXPORTS = {
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'_edata', '_end', '_init', '__bss_start', '_fini'
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}
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READELF_CMD = '/usr/bin/readelf'
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CPPFILT_CMD = '/usr/bin/c++filt'
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READELF_CMD = os.getenv('READELF', '/usr/bin/readelf')
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CPPFILT_CMD = os.getenv('CPPFILT', '/usr/bin/c++filt')
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# Allowed NEEDED libraries
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ALLOWED_LIBRARIES = {'librt.so.1','libpthread.so.0','libanl.so.1','libm.so.6','libgcc_s.so.1','libc.so.6','ld-linux-x86-64.so.2'}
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class CPPFilt(object):
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'''
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@ -98,6 +101,22 @@ def check_version(max_versions, version):
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return False
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return ver <= max_versions[lib]
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def read_libraries(filename):
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p = subprocess.Popen([READELF_CMD, '-d', '-W', filename], 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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libraries = []
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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[1] == '(NEEDED)':
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match = re.match('^Shared library: \[(.*)\]$', ' '.join(tokens[2:]))
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if match:
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libraries.append(match.group(1))
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else:
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raise ValueError('Unparseable (NEEDED) specification')
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return libraries
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if __name__ == '__main__':
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cppfilt = CPPFilt()
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retval = 0
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@ -113,6 +132,11 @@ if __name__ == '__main__':
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continue
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print('%s: export of symbol %s not allowed' % (filename, cppfilt(sym)))
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retval = 1
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# Check dependency libraries
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for library_name in read_libraries(filename):
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if library_name not in ALLOWED_LIBRARIES:
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print('%s: NEEDED library %s is not allowed' % (filename, library_name))
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retval = 1
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exit(retval)
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60
contrib/devtools/test-security-check.py
Executable file
60
contrib/devtools/test-security-check.py
Executable file
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#!/usr/bin/python2
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'''
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Test script for security-check.py
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'''
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from __future__ import division,print_function
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import subprocess
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import sys
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import unittest
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def write_testcode(filename):
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with open(filename, 'w') as f:
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f.write('''
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#include <stdio.h>
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int main()
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{
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printf("the quick brown fox jumps over the lazy god\\n");
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return 0;
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}
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''')
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def call_security_check(cc, source, executable, options):
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subprocess.check_call([cc,source,'-o',executable] + options)
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p = subprocess.Popen(['./security-check.py',executable], stdout=subprocess.PIPE, stderr=subprocess.PIPE, stdin=subprocess.PIPE)
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(stdout, stderr) = p.communicate()
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return (p.returncode, stdout.rstrip())
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class TestSecurityChecks(unittest.TestCase):
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def test_ELF(self):
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source = 'test1.c'
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executable = 'test1'
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cc = 'gcc'
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write_testcode(source)
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self.assertEqual(call_security_check(cc, source, executable, ['-Wl,-zexecstack','-fno-stack-protector','-Wl,-znorelro']),
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(1, executable+': failed PIE NX RELRO Canary'))
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self.assertEqual(call_security_check(cc, source, executable, ['-Wl,-znoexecstack','-fno-stack-protector','-Wl,-znorelro']),
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(1, executable+': failed PIE RELRO Canary'))
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self.assertEqual(call_security_check(cc, source, executable, ['-Wl,-znoexecstack','-fstack-protector-all','-Wl,-znorelro']),
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(1, executable+': failed PIE RELRO'))
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self.assertEqual(call_security_check(cc, source, executable, ['-Wl,-znoexecstack','-fstack-protector-all','-Wl,-znorelro','-pie','-fPIE']),
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(1, executable+': failed RELRO'))
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self.assertEqual(call_security_check(cc, source, executable, ['-Wl,-znoexecstack','-fstack-protector-all','-Wl,-zrelro','-Wl,-z,now','-pie','-fPIE']),
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(0, ''))
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def test_PE(self):
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source = 'test1.c'
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executable = 'test1.exe'
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cc = 'i686-w64-mingw32-gcc'
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write_testcode(source)
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self.assertEqual(call_security_check(cc, source, executable, []),
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(1, executable+': failed PIE NX'))
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self.assertEqual(call_security_check(cc, source, executable, ['-Wl,--nxcompat']),
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(1, executable+': failed PIE'))
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self.assertEqual(call_security_check(cc, source, executable, ['-Wl,--nxcompat','-Wl,--dynamicbase']),
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(0, ''))
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if __name__ == '__main__':
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unittest.main()
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