On 6/9/17 11:41 AM, Tetsuo Handa wrote:

Matt Brown wrote:

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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

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print "hello"

hello

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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

Matt
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