[PATCH v1] shebang: restrict python interactive prompt/interpreter

[Matt Brown]

On 6/9/17 12:43 PM, Jason Zaman wrote:
> On Fri, Jun 09, 2017 at 12:37:50PM -0400, Matt Brown wrote:
>> On 6/9/17 11:41 AM, Tetsuo Handa wrote:
>>> Matt Brown wrote:
>>>>> What about execution via ld-linux ?
>>>>>
>>>>>    $ /lib64/ld-linux-x86-64.so.2 /usr/bin/python2
>>>>>
>>>>
>>>> Just tested this and you are correct, this allows you to bypass the
>>>> protection.
>>>>
>>>> I was able to fix this bypass by including /lib64/ld-linux-x86-64.so.2
>>>> in the list of interpreters.
>>>
>>> And there is also PYTHONINSPECT environment variable. ;-)
>>>
>>> # echo '#!/usr/bin/python2' > run-python
>>> # chmod 755 run-python
>>> # ./run-python
>>> # PYTHONINSPECT=yes ./run-python
>>>>>> print "hello"
>>> hello
>>>>>>
>>
>> While this bypass works against this LSM alone, when combined with
>> Trusted Path Execution this is prevented for non-root/untrusted user.
>> This is why I feel like this is such a great feature to combine with TPE
>> as I said here:
>>
>> http://www.openwall.com/lists/kernel-hardening/2017/06/09/13
>>
>> Results from my test:
>>
>> $ PYTHONINSPECT=yes ./run-python
>>
>>
>> -bash: ./run-python: /usr/bin/python2: bad interpreter: Operation not
>> permitted
>>
>> and in the dmesg log:
>> TPE: Denied exec of /home/test/run-python Reason: file in non-root-owned
>> directory
> 
> What if you just use any existing python script on the system?
> 
> jason at meriadoc ~ $ PYTHONINSPECT=yes /usr/bin/emerge
> emerge: command-line interface to the Portage system
> Usage:
>    emerge [ options ] [ action ] [ ebuild | tbz2 | file | @set | atom ] [ ... ]
>    emerge [ options ] [ action ] < @system | @world >
>    emerge < --sync | --metadata | --info >
>    emerge --resume [ --pretend | --ask | --skipfirst ]
>    emerge --help
> Options: -[abBcCdDefgGhjkKlnNoOpPqrsStuvVw]
>           [ --color < y | n >            ] [ --columns    ]
>           [ --complete-graph             ] [ --deep       ]
>           [ --jobs JOBS ] [ --keep-going ] [ --load-average LOAD            ]
>           [ --newrepo   ] [ --newuse     ] [ --noconfmem  ] [ --nospinner   ]
>           [ --oneshot   ] [ --onlydeps   ] [ --quiet-build [ y | n ]        ]
>           [ --reinstall changed-use      ] [ --with-bdeps < y | n >         ]
> Actions:  [ --depclean | --list-sets | --search | --sync | --version        ]
> 
>    For more help consult the man page.
> Traceback (most recent call last):
>   File "/usr/lib/python-exec/python3.4/emerge", line 79, in <module>
>     sys.exit(retval)
> SystemExit: 1
>>>>
> 
> -- Jason
> 

crap you're right. This does work.

what does everyone thing about a envp_blacklist option that is a list of
environmental variables that will be stripped from exec calls. This can
be done in the LSM hook bprm_check_security.

Is there any reason on a hardened system why you would need the
PYTHONINSPECT environmental variable?

Matt
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