Follow @Openwall on Twitter for new release announcements and other news
[<prev] [next>] [thread-next>] [day] [month] [year] [list]
Date: Sun, 11 Jun 2017 13:44:22 +0200
From: Mickaël Salaün <>
To: Tetsuo Handa <>,,
        Daniel Micay <>,
        kernel-hardening <>,
        LKML <>
Subject: Re: [PATCH v1] shebang: restrict python interactive

On 10/06/2017 07:27, Tetsuo Handa wrote:
> Kees Cook wrote:
>> On Fri, Jun 9, 2017 at 10:23 AM, Matt Brown <> wrote:
>>> 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?
>> As part of shebang, it likely makes sense to whitelist (rather than
>> blacklist) the env of the restricted interpreters. Though this is
>> starting to get complex. :P
> Blacklisting environment variables is dangerous. I think that
> administrators can afford whitelisting environment variable names.
> I think that implementing whitelist of environment variable names
> as an independent LSM module would be fine.
> While it is true that things starts getting complex if we check environment
> variables, shebang will already become complex if it starts worrying about
> updating inode number list in order to close the race window between doing
> creat()+write()+close()+chmod()+rename() by the package manager and teaching
> the kernel the new inode number determined by creat(). We will need an
> interface for allowing the package manager to teach the kernel the new inode
> number and modification of the package manager, for the kernel side is doing
> inode number based blacklisting while user side can execute it before rename().
> --
> To unsubscribe from this list: send the line "unsubscribe linux-security-module" in
> the body of a message to
> More majordomo info at

Using filesystem xattr seems like a good idea for this kind of
exceptions and instead of a hardcoded interpreter path. Something like
"security.tpe.interpreter=1|2" (bitmask for interpreter-only and/or CLI)
and "security.tpe.environment=HOME,LOGNAME" would be quite flexible to
configure a security policy for some binaries. This could also be
protected by IMA/EVM, if needed.

This kind of xattr should be writable by the owner of the file. The TPE
LSM [1] could then take these xattr into account according to the TPE

The "security.tpe.environment" could also be set on a script file to be
part of the union with the interpreter's environment whitelist. This may
be needed to be able to use environment variables as configuration in a

In the future, a "security.tpe.memory" could contain a set of flags as
PaX uses for mprotect-like exceptions (user.pax.flags).

Userland daemons such as paxctld or paxrat could be used (with some
tweaks) to keep a consistent TPE policy over time.



Download attachment "signature.asc" of type "application/pgp-signature" (489 bytes)

Powered by blists - more mailing lists

Confused about mailing lists and their use? Read about mailing lists on Wikipedia and check out these guidelines on proper formatting of your messages.