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

[jason@perfinion.com (Jason Zaman)]

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
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