[Bug 1452115] Re: Python interpreter binary is not compiled as PIE

[Jeff Dileo]

Thanks @Giovanni Pellerano for bumping this again. I can confirm that
this is an issue in python3.9 (3.9.7, "3.9.7-2build1") and python3.10
(3.10.0, "3.10.0-2") on 21.10 (amd64). I imagine if nothing is done, the
upcoming 22.04 LTS will have the issue in its default python(3), which I
imagine will be some version of 3.10.

# python3 --version
Python 3.9.7
# ./checksec --file=/usr/bin/python3
RELRO           STACK CANARY      NX            PIE             RPATH      RUNPATH	Symbols		FORTIFY	Fortified	Fortifiable	FILE
Partial RELRO   Canary found      NX enabled    No PIE          No RPATH   No RUNPATH   No Symbols	  Yes	14		39		/usr/bin/python3

# python3.10 --version
Python 3.10.0
# ./checksec --file=/usr/bin/python3.10
RELRO           STACK CANARY      NX            PIE             RPATH      RUNPATH	Symbols		FORTIFY	Fortified	Fortifiable	FILE
Partial RELRO   Canary found      NX enabled    No PIE          No RPATH   No RUNPATH   No Symbols	  Yes	14		39		/usr/bin/python3.10

Alternatively, via `hardening-check` from the devscripts package:

# hardening-check /usr/bin/python3
/usr/bin/python3:
 Position Independent Executable: no, normal executable!
 Stack protected: yes
 Fortify Source functions: yes (some protected functions found)
 Read-only relocations: yes
 Immediate binding: no, not found!
 Stack clash protection: unknown, no -fstack-clash-protection instructions found
 Control flow integrity: yes
# hardening-check /usr/bin/python3.10
/usr/bin/python3.10:
 Position Independent Executable: no, normal executable!
 Stack protected: yes
 Fortify Source functions: yes (some protected functions found)
 Read-only relocations: yes
 Immediate binding: no, not found!
 Stack clash protection: unknown, no -fstack-clash-protection instructions found
 Control flow integrity: yes

** Also affects: python3.9 (Ubuntu)
   Importance: Undecided
       Status: New

** Also affects: python3.10 (Ubuntu)
   Importance: Undecided
       Status: New

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https://bugs.launchpad.net/bugs/1452115

Title:
  Python interpreter binary is not compiled as PIE

Status in Python:
  New
Status in python2.7 package in Ubuntu:
  Fix Released
Status in python3.10 package in Ubuntu:
  New
Status in python3.4 package in Ubuntu:
  Fix Released
Status in python3.6 package in Ubuntu:
  Confirmed
Status in python3.7 package in Ubuntu:
  Confirmed
Status in python3.8 package in Ubuntu:
  Confirmed
Status in python3.9 package in Ubuntu:
  New
Status in python3.7 package in Debian:
  New
Status in python3.8 package in Debian:
  New

Bug description:
  The python2.7 binary (installed at /usr/bin/python2.7; package version
  2.7.6-8) is not compiled as a position independent executable (PIE).
  It appears that the python compilation process is somewhat arcane and
  the hardening wrapper probably doesn't do the trick for it.

  This is incredibly dangerous as it means that any vulnerability within
  a native module (e.g. ctypes-based), or within python itself will
  expose an incredibly large amount of known memory contents at known
  addresses (including a large number of dangerous instruction
  groupings). This enables ROP-based
  (https://en.wikipedia.org/wiki/Return-oriented_programming) to abuse
  the interpreter itself to bypass non-executable page protections.

  I have put together an example vulnerable C shared object (with a buffer overflow) accessed via python through the ctypes interface as an example. This uses a single ROP "gadget" on top of using the known PLT location for system(3) (https://en.wikipedia.org/wiki/Return-to-libc_attack) to call "id". The example code is accessible at:
  - https://gist.github.com/ChaosData/ae6076cb1c3cc7b0a367

  I'm not exactly familiar enough with the python build process to say
  where exactly an -fPIE needs to be injected into a script/makefile,
  but I feel that given the perceived general preference for ctypes-
  based modules over python written ones, as the native code
  implementations tend to be more performant, this feels like a large
  security hole within the system. Given the nature of this "issue," I'm
  not 100% sure of where it is best reported, but from what I can tell,
  this conflicts with the Ubuntu hardening features and is definitely
  exploitable should a native module contain a sufficiently exploitable
  vulnerability that allows for control of the instruction register.

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