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|
"""
Fetch a LIBC binary based on some heuristics.
"""
from __future__ import absolute_import
from __future__ import division
import os
import six
import tempfile
from pwnlib.context import context
from pwnlib.elf import ELF
from pwnlib.log import getLogger
from pwnlib.tubes.process import process
from pwnlib.util.fiddling import enhex
from pwnlib.util.misc import read
from pwnlib.util.misc import which
from pwnlib.util.misc import write
from pwnlib.util.web import wget
log = getLogger(__name__)
HASHES = ['build_id', 'sha1', 'sha256', 'md5']
DEBUGINFOD_SERVERS = [
'https://debuginfod.elfutils.org/',
]
if 'DEBUGINFOD_URLS' in os.environ:
urls = os.environ['DEBUGINFOD_URLS'].split(' ')
DEBUGINFOD_SERVERS = urls + DEBUGINFOD_SERVERS
# https://gitlab.com/libcdb/libcdb wasn't updated after 2019,
# but still is a massive database of older libc binaries.
def provider_libcdb(hex_encoded_id, hash_type):
# Deferred import because it's slow
import requests
from six.moves import urllib
# Build the URL using the requested hash type
url_base = "https://gitlab.com/libcdb/libcdb/raw/master/hashes/%s/" % hash_type
url = urllib.parse.urljoin(url_base, hex_encoded_id)
data = b""
log.debug("Downloading data from LibcDB: %s", url)
try:
while not data.startswith(b'\x7fELF'):
data = wget(url, timeout=20)
if not data:
log.warn_once("Could not fetch libc for %s %s from libcdb", hash_type, hex_encoded_id)
break
# GitLab serves up symlinks with
if data.startswith(b'..'):
url = os.path.dirname(url) + '/'
url = urllib.parse.urljoin(url.encode('utf-8'), data)
except requests.RequestException as e:
log.warn_once("Failed to fetch libc for %s %s from libcdb: %s", hash_type, hex_encoded_id, e)
return data
def query_libc_rip(params):
# Deferred import because it's slow
import requests
url = "https://libc.rip/api/find"
try:
result = requests.post(url, json=params, timeout=20)
result.raise_for_status()
if result.status_code != 200:
log.debug("Error: %s", result.text)
return None
return result.json()
except requests.RequestException as e:
log.warn_once("Failed to fetch libc info from libc.rip: %s", e)
return None
# https://libc.rip/
def provider_libc_rip(hex_encoded_id, hash_type):
# Build the request for the hash type
# https://github.com/niklasb/libc-database/blob/master/searchengine/api.yml
if hash_type == 'build_id':
hash_type = 'buildid'
params = {hash_type: hex_encoded_id}
libc_match = query_libc_rip(params)
if not libc_match:
log.warn_once("Could not find libc info for %s %s on libc.rip", hash_type, hex_encoded_id)
return None
if len(libc_match) > 1:
log.debug("Received multiple matches. Choosing the first match and discarding the others.")
log.debug("%r", libc_match)
url = libc_match[0]['download_url']
log.debug("Downloading data from libc.rip: %s", url)
data = wget(url, timeout=20)
if not data:
log.warn_once("Could not fetch libc binary for %s %s from libc.rip", hash_type, hex_encoded_id)
return None
return data
PROVIDERS = [provider_libcdb, provider_libc_rip]
def search_by_hash(hex_encoded_id, hash_type='build_id', unstrip=True):
assert hash_type in HASHES, hash_type
# Ensure that the libcdb cache directory exists
cache, cache_valid = _check_elf_cache('libcdb', hex_encoded_id, hash_type)
if cache_valid:
return cache
# Run through all available libc database providers to see if we have a match.
for provider in PROVIDERS:
data = provider(hex_encoded_id, hash_type)
if data and data.startswith(b'\x7FELF'):
break
if not data:
log.warn_once("Could not find libc for %s %s anywhere", hash_type, hex_encoded_id)
# Save whatever we got to the cache
write(cache, data or b'')
# Return ``None`` if we did not get a valid ELF file
if not data or not data.startswith(b'\x7FELF'):
return None
# Try to find debug info for this libc.
if unstrip:
unstrip_libc(cache)
return cache
def _search_debuginfo_by_hash(base_url, hex_encoded_id):
# Deferred import because it's slow
import requests
from six.moves import urllib
# Check if we tried this buildid before.
cache, cache_valid = _check_elf_cache('libcdb_dbg', hex_encoded_id, 'build_id')
if cache_valid:
return cache
# Try to find separate debuginfo.
url = '/buildid/{}/debuginfo'.format(hex_encoded_id)
url = urllib.parse.urljoin(base_url, url)
data = b""
log.debug("Downloading data from debuginfod: %s", url)
try:
data = wget(url, timeout=20)
except requests.RequestException as e:
log.warn_once("Failed to fetch libc debuginfo for build_id %s from %s: %s", hex_encoded_id, base_url, e)
# Save whatever we got to the cache
write(cache, data or b'')
# Return ``None`` if we did not get a valid ELF file
if not data or not data.startswith(b'\x7FELF'):
log.warn_once("Could not fetch libc debuginfo for build_id %s from %s", hex_encoded_id, base_url)
return None
return cache
def _check_elf_cache(cache_type, hex_encoded_id, hash_type):
"""
Check if there already is an ELF file for this hash in the cache.
>>> cache, _ = _check_elf_cache('libcdb', '2d1c5e0b85cb06ff47fa6fa088ec22cb6e06074e', 'build_id')
>>> os.unlink(cache) if os.path.exists(cache)
>>> filename = search_by_hash('2d1c5e0b85cb06ff47fa6fa088ec22cb6e06074e', 'build_id', unstrip=False)
>>> hex(ELF(filename).symbols.read)
'0xe56c0'
>>> filename == cache
True
"""
# Ensure that the cache directory exists
cache_dir = os.path.join(context.cache_dir, cache_type, hash_type)
if not os.path.isdir(cache_dir):
os.makedirs(cache_dir)
# If we already downloaded the file, and it looks even passingly like
# a valid ELF file, return it.
cache = os.path.join(cache_dir, hex_encoded_id)
if not os.path.exists(cache):
return cache, False
log.debug("Found existing cached ELF at %r", cache)
data = read(cache)
if not data.startswith(b'\x7FELF'):
log.info_once("Skipping unavailable ELF %s", hex_encoded_id)
return cache, False
log.info_once("Using cached data from %r", cache)
return cache, True
def unstrip_libc(filename):
"""
Given a path to a libc binary, attempt to download matching debug info
and add them back to the given binary.
This modifies the given file.
Arguments:
filename(str):
Path to the libc binary to unstrip.
Returns:
:const:`True` if binary was unstripped, :const:`False` otherwise.
Examples:
>>> filename = search_by_build_id('69389d485a9793dbe873f0ea2c93e02efaa9aa3d', unstrip=False)
>>> libc = ELF(filename)
>>> 'main_arena' in libc.symbols
False
>>> unstrip_libc(filename)
True
>>> libc = ELF(filename)
>>> hex(libc.symbols.main_arena)
'0x219c80'
>>> unstrip_libc(pwnlib.data.elf.get('test-x86'))
False
>>> filename = search_by_build_id('d1704d25fbbb72fa95d517b883131828c0883fe9', unstrip=True)
>>> 'main_arena' in ELF(filename).symbols
True
"""
if not which('eu-unstrip'):
log.warn_once('Couldn\'t find "eu-unstrip" in PATH. Install elfutils first.')
return False
libc = ELF(filename, checksec=False)
if not libc.buildid:
log.warn_once('Given libc does not have a buildid. Cannot look for debuginfo to unstrip.')
return False
log.debug('Trying debuginfod servers: %r', DEBUGINFOD_SERVERS)
for server_url in DEBUGINFOD_SERVERS:
libc_dbg = _search_debuginfo_by_hash(server_url, enhex(libc.buildid))
if libc_dbg:
break
else:
log.warn_once('Couldn\'t find debug info for libc with build_id %s on any debuginfod server.', enhex(libc.buildid))
return False
# Add debug info to given libc binary inplace.
p = process(['eu-unstrip', '-o', filename, filename, libc_dbg])
output = p.recvall()
p.close()
if output:
log.error('Failed to unstrip libc binary: %r', output)
return False
return True
def _extract_tarfile(cache_dir, data_filename, tarball):
from six import BytesIO
import tarfile
# Handle zstandard compression, since tarfile only supports gz, bz2, and xz.
if data_filename.endswith('.zst') or data_filename.endswith('.zstd'):
import zstandard
dctx = zstandard.ZstdDecompressor()
decompressed_tar = BytesIO()
dctx.copy_stream(tarball, decompressed_tar)
decompressed_tar.seek(0)
tarball.close()
tarball = decompressed_tar
if six.PY2 and data_filename.endswith('.xz'):
# Python 2's tarfile doesn't support xz, so we need to decompress it first.
# Shell out to xz, since the Python 2 pylzma module is broken.
# (https://github.com/fancycode/pylzma/issues/67)
if not which('xz'):
log.error('Couldn\'t find "xz" in PATH. Please install xz first.')
import subprocess
try:
uncompressed_tarball = subprocess.check_output(['xz', '--decompress', '--stdout', tarball.name])
tarball = BytesIO(uncompressed_tarball)
except subprocess.CalledProcessError:
log.error('Failed to decompress xz archive.')
with tarfile.open(fileobj=tarball) as tar_file:
# Find the library folder in the archive (e.g. /lib/x86_64-linux-gnu/)
lib_dir = None
libc_name = None
for member in tar_file.getmembers():
if not member.isfile():
continue
libc_name = os.path.basename(member.name)
if libc_name == 'libc.so.6' or (libc_name.startswith('libc') and libc_name.endswith('.so')):
lib_dir = os.path.dirname(member.name)
break
else:
log.error('Couldn\'t find library folder containing the libc in the archive.')
# Extract everything in the library folder
for member in tar_file.getmembers():
if os.path.dirname(member.name) != lib_dir:
continue
if not member.isfile() and not member.issym():
continue
# Extract while keeping file permissions
tar_file.extract(member, cache_dir)
# Move the files up to the cache root
target_dir = os.path.join(cache_dir, lib_dir)
for file in os.listdir(target_dir):
os.rename(os.path.join(target_dir, file), os.path.join(cache_dir, file))
os.removedirs(target_dir)
return os.path.join(cache_dir, libc_name)
def _extract_debfile(cache_dir, package_filename, package):
# Extract data.tar in the .deb archive.
if six.PY2:
if not which('ar'):
log.error('Missing command line tool "ar" to extract .deb archive. Please install "ar" first.')
import atexit
import shutil
import subprocess
# Use mkdtemp instead of TemporaryDirectory because the latter is not available in Python 2.
tempdir = tempfile.mkdtemp(prefix=".pwntools-tmp")
atexit.register(shutil.rmtree, tempdir)
with tempfile.NamedTemporaryFile(mode='wb', dir=tempdir) as debfile:
debfile.write(package)
debfile.flush()
try:
files_in_deb = subprocess.check_output(['ar', 't', debfile.name]).split(b'\n')
except subprocess.CalledProcessError:
log.error('Failed to list files in .deb archive.')
[data_filename] = filter(lambda f: f.startswith(b'data.tar'), files_in_deb)
try:
subprocess.check_call(['ar', 'x', debfile.name, data_filename], cwd=tempdir)
except subprocess.CalledProcessError:
log.error('Failed to extract data.tar from .deb archive.')
with open(os.path.join(tempdir, data_filename), 'rb') as tarball:
return _extract_tarfile(cache_dir, data_filename, tarball)
else:
import unix_ar
from six import BytesIO
ar_file = unix_ar.open(BytesIO(package))
try:
data_filename = next(filter(lambda f: f.name.startswith(b'data.tar'), ar_file.infolist())).name.decode()
tarball = ar_file.open(data_filename)
return _extract_tarfile(cache_dir, data_filename, tarball)
finally:
ar_file.close()
def _extract_pkgfile(cache_dir, package_filename, package):
from six import BytesIO
return _extract_tarfile(cache_dir, package_filename, BytesIO(package))
def _find_libc_package_lib_url(libc):
# Check https://libc.rip for the libc package
libc_match = query_libc_rip({'buildid': enhex(libc.buildid)})
if libc_match is not None:
for match in libc_match:
yield match['libs_url']
# Check launchpad.net if it's an Ubuntu libc
# GNU C Library (Ubuntu GLIBC 2.36-0ubuntu4)
import re
version = re.search(br'GNU C Library \(Ubuntu E?GLIBC ([^\)]+)\)', libc.data)
if version is not None:
libc_version = version.group(1).decode()
yield 'https://launchpad.net/ubuntu/+archive/primary/+files/libc6_{}_{}.deb'.format(libc_version, libc.arch)
def download_libraries(libc_path, unstrip=True):
"""download_libraries(str, bool) -> str
Download the matching libraries for the given libc binary and cache
them in a local directory. The libraries are looked up using `libc.rip <https://libc.rip>`_
and fetched from the official package repositories if available.
This commonly includes the ``ld-linux-x86-64.so.2`` and ``libpthread.so.0`` binaries
which can be used to execute the program locally when the given libc is
incompatible with the local dynamic loader.
Note: Only .deb and .pkg.tar.* packages are currently supported (Debian/Ubuntu, Arch).
Arguments:
libc_path(str):
The path the libc binary.
unstrip(bool):
Try to fetch debug info for the libc and apply it to the downloaded file.
Returns:
The path to the cached directory containing the downloaded libraries.
Example:
>>> libc_path = ELF(which('ls'), checksec=False).libc.path
>>> lib_path = download_libraries(libc_path)
>>> lib_path is not None
True
>>> os.path.exists(os.path.join(lib_path, 'libc.so.6'))
True
>>> os.path.exists(os.path.join(lib_path, 'ld-linux-x86-64.so.2'))
True
"""
libc = ELF(libc_path, checksec=False)
if not libc.buildid:
log.warn_once('Given libc does not have a buildid.')
return None
# Handle caching and don't redownload if it already exists.
cache_dir = os.path.join(context.cache_dir, 'libcdb_libs')
if not os.path.isdir(cache_dir):
os.makedirs(cache_dir)
cache_dir = os.path.join(cache_dir, enhex(libc.buildid))
if os.path.exists(cache_dir):
return cache_dir
for package_url in _find_libc_package_lib_url(libc):
extension_handlers = {
'.deb': _extract_debfile,
'.pkg.tar.xz': _extract_pkgfile,
'.pkg.tar.zst': _extract_pkgfile,
}
package_filename = os.path.basename(package_url)
for extension, handler in extension_handlers.items():
if package_filename.endswith(extension):
break
else:
log.failure('Cannot handle %s (%s)', package_filename, package_url)
continue
# Download the package
package = wget(package_url, timeout=20)
if not package:
continue
# Create target cache directory to extract files into
if not os.path.isdir(cache_dir):
os.makedirs(cache_dir)
try:
# Extract the archive
libc_path = handler(cache_dir, package_filename, package)
except Exception as e:
os.removedirs(cache_dir)
log.failure('Failed to extract %s: %s', package_filename, e)
continue
# Unstrip the libc binary
try:
if unstrip:
unstrip_libc(libc_path)
except Exception:
pass
return cache_dir
log.warn_once('Failed to find matching libraries for provided libc.')
return None
def _handle_multiple_matching_libcs(matching_libcs):
from pwnlib.term import text
from pwnlib.ui import options
log.info('Multiple matching libc libraries for requested symbols:')
for idx, libc in enumerate(matching_libcs):
log.info('%d. %s', idx+1, text.red(libc['id']))
log.indented('\t%-20s %s', text.green('BuildID:'), libc['buildid'])
log.indented('\t%-20s %s', text.green('MD5:'), libc['md5'])
log.indented('\t%-20s %s', text.green('SHA1:'), libc['sha1'])
log.indented('\t%-20s %s', text.green('SHA256:'), libc['sha256'])
log.indented('\t%s', text.green('Symbols:'))
for symbol, address in libc['symbols'].items():
log.indented('\t%25s = %s', symbol, address)
selected_index = options("Select the libc version to use:", [libc['id'] for libc in matching_libcs])
return matching_libcs[selected_index]
def search_by_symbol_offsets(symbols, select_index=None, unstrip=True, return_as_list=False):
"""
Lookup possible matching libc versions based on leaked function addresses.
The leaked function addresses have to be provided as a dict mapping the
function name to the leaked value. Only the lower 3 nibbles are relevant
for the lookup.
If there are multiple matches you are presented with a list to select one
interactively, unless the ``select_index`` or ``return_as_list`` arguments
are used.
Arguments:
symbols(dict):
Dictionary mapping symbol names to their addresses.
select_index(int):
The libc to select if there are multiple matches (starting at 1).
unstrip(bool):
Try to fetch debug info for the libc and apply it to the downloaded file.
return_as_list(bool):
Return a list of build ids of all matching libc versions
instead of a path to a downloaded file.
Returns:
Path to the downloaded library on disk, or :const:`None`.
If the ``return_as_list`` argument is :const:`True`, a list of build ids
is returned instead.
Examples:
>>> filename = search_by_symbol_offsets({'puts': 0x420, 'printf': 0xc90}, select_index=1)
>>> libc = ELF(filename)
>>> libc.sym.system == 0x52290
True
>>> matched_libcs = search_by_symbol_offsets({'__libc_start_main_ret': '7f89ad926550'}, return_as_list=True)
>>> len(matched_libcs) > 1
True
>>> for buildid in matched_libcs: # doctest +SKIP
... libc = ELF(search_by_build_id(buildid)) # doctest +SKIP
"""
for symbol, address in symbols.items():
if isinstance(address, int):
symbols[symbol] = hex(address)
params = {'symbols': symbols}
log.debug('Request: %s', params)
matching_libcs = query_libc_rip(params)
log.debug('Result: %s', matching_libcs)
if matching_libcs is None or len(matching_libcs) == 0:
log.warn_once("No matching libc for symbols %r on libc.rip", symbols)
return None
if return_as_list:
return [libc['buildid'] for libc in matching_libcs]
if len(matching_libcs) == 1:
return search_by_build_id(matching_libcs[0]['buildid'], unstrip=unstrip)
if select_index is not None:
if select_index > 0 and select_index <= len(matching_libcs):
return search_by_build_id(matching_libcs[select_index - 1]['buildid'], unstrip=unstrip)
else:
log.error('Invalid selected libc index. %d is not in the range of 1-%d.', select_index, len(matching_libcs))
return None
selected_libc = _handle_multiple_matching_libcs(matching_libcs)
return search_by_build_id(selected_libc['buildid'], unstrip=unstrip)
def search_by_build_id(hex_encoded_id, unstrip=True):
"""
Given a hex-encoded Build ID, attempt to download a matching libc from libcdb.
Arguments:
hex_encoded_id(str):
Hex-encoded Build ID (e.g. 'ABCDEF...') of the library
unstrip(bool):
Try to fetch debug info for the libc and apply it to the downloaded file.
Returns:
Path to the downloaded library on disk, or :const:`None`.
Examples:
>>> filename = search_by_build_id('fe136e485814fee2268cf19e5c124ed0f73f4400')
>>> hex(ELF(filename).symbols.read)
'0xda260'
>>> None == search_by_build_id('XX')
True
>>> filename = search_by_build_id('a5a3c3f65fd94f4c7f323a175707c3a79cbbd614')
>>> hex(ELF(filename).symbols.read)
'0xeef40'
"""
return search_by_hash(hex_encoded_id, 'build_id', unstrip)
def search_by_md5(hex_encoded_id, unstrip=True):
"""
Given a hex-encoded md5sum, attempt to download a matching libc from libcdb.
Arguments:
hex_encoded_id(str):
Hex-encoded md5sum (e.g. 'ABCDEF...') of the library
unstrip(bool):
Try to fetch debug info for the libc and apply it to the downloaded file.
Returns:
Path to the downloaded library on disk, or :const:`None`.
Examples:
>>> filename = search_by_md5('7a71dafb87606f360043dcd638e411bd')
>>> hex(ELF(filename).symbols.read)
'0xda260'
>>> None == search_by_md5('XX')
True
>>> filename = search_by_md5('74f2d3062180572fc8bcd964b587eeae')
>>> hex(ELF(filename).symbols.read)
'0xeef40'
"""
return search_by_hash(hex_encoded_id, 'md5', unstrip)
def search_by_sha1(hex_encoded_id, unstrip=True):
"""
Given a hex-encoded sha1, attempt to download a matching libc from libcdb.
Arguments:
hex_encoded_id(str):
Hex-encoded sha1sum (e.g. 'ABCDEF...') of the library
unstrip(bool):
Try to fetch debug info for the libc and apply it to the downloaded file.
Returns:
Path to the downloaded library on disk, or :const:`None`.
Examples:
>>> filename = search_by_sha1('34471e355a5e71400b9d65e78d2cd6ce7fc49de5')
>>> hex(ELF(filename).symbols.read)
'0xda260'
>>> None == search_by_sha1('XX')
True
>>> filename = search_by_sha1('0041d2f397bc2498f62aeb4134d522c5b2635e87')
>>> hex(ELF(filename).symbols.read)
'0xeef40'
"""
return search_by_hash(hex_encoded_id, 'sha1', unstrip)
def search_by_sha256(hex_encoded_id, unstrip=True):
"""
Given a hex-encoded sha256, attempt to download a matching libc from libcdb.
Arguments:
hex_encoded_id(str):
Hex-encoded sha256sum (e.g. 'ABCDEF...') of the library
unstrip(bool):
Try to fetch debug info for the libc and apply it to the downloaded file.
Returns:
Path to the downloaded library on disk, or :const:`None`.
Examples:
>>> filename = search_by_sha256('5e877a8272da934812d2d1f9ee94f73c77c790cbc5d8251f5322389fc9667f21')
>>> hex(ELF(filename).symbols.read)
'0xda260'
>>> None == search_by_sha256('XX')
True
>>> filename = search_by_sha256('5d78fc60054df18df20480c71f3379218790751090f452baffb62ac6b2aff7ee')
>>> hex(ELF(filename).symbols.read)
'0xeef40'
"""
return search_by_hash(hex_encoded_id, 'sha256', unstrip)
def get_build_id_offsets():
"""
Returns a list of file offsets where the Build ID should reside within
an ELF file of the currently selected architecture.
"""
# Given the corpus of almost all libc to have been released with
# RedHat, Fedora, Ubuntu, Debian, etc. over the past several years,
# we can say with 99% certainty that the GNU Build ID section will
# be at one of the specified addresses.
#
# The point here is to get an easy win by reading less DWORDs than would
# have otherwise been required to walk the section table and the string
# stable.
#
# function check_arch() {
# readelf -n $(file -L * | grep -i "$1" | cut -d ':' -f 1) \
# | grep -B3 BUILD_ID \
# | grep offset \
# | sort \
# | uniq -c
# }
return {
# $ check_arch 80386
# 181 Displaying notes found at file offset 0x00000174 with length 0x00000024:
'i386': [0x174, 0x1b4, 0x1d4],
# $ check_arch "ARM, EABI5"
# 69 Displaying notes found at file offset 0x00000174 with length 0x00000024:
'arm': [0x174],
'thumb': [0x174],
# $ check_arch "ARM aarch64"
# 1 Displaying notes found at file offset 0x00000238 with length 0x00000024:
'aarch64': [0x238],
# $ check_arch "x86-64"
# 6 Displaying notes found at file offset 0x00000174 with length 0x00000024:
# 82 Displaying notes found at file offset 0x00000270 with length 0x00000024:
'amd64': [0x270, 0x174, 0x2e0, 0x370],
# $ check_arch "PowerPC or cisco"
# 88 Displaying notes found at file offset 0x00000174 with length 0x00000024:
'powerpc': [0x174],
# $ check_arch "64-bit PowerPC"
# 30 Displaying notes found at file offset 0x00000238 with length 0x00000024:
'powerpc64': [0x238],
# $ check_arch "SPARC32"
# 32 Displaying notes found at file offset 0x00000174 with length 0x00000024:
'sparc': [0x174],
# $ check_arch "SPARC V9"
# 33 Displaying notes found at file offset 0x00000270 with length 0x00000024:
'sparc64': [0x270]
}.get(context.arch, [])
__all__ = ['get_build_id_offsets', 'search_by_build_id', 'search_by_sha1', 'search_by_sha256', 'search_by_md5', 'unstrip_libc', 'search_by_symbol_offsets', 'download_libraries']
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