Re: [kernel-hardening] [RFC] [PATCH 4/5] invoke path_chroot() LSM hook on mntns_install()

[Jann Horn <jann@thejh.net>]

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On Fri, Jul 29, 2016 at 10:34:39AM +0300, Elena Reshetova wrote:
> This adds an additional invocation of the
> security_path_chroot LSM hook inside mntns_install().
> Currently only capabilities are checked at this point,
> while process root actually changes.

Are you aware that unprivileged user namespace creation doesn't work in
a chrooted process? See the invocation of current_chrooted() in
create_user_ns(). This means that for this new LSM hook to make any
sense, a namespace admin has to attempt to sandbox himself with chroot().

If the current namespace is the init namespace, the process has
CAP_SYS_ADMIN in the init namespace, meaning that filesystem sandboxing
is probably useless.

If the current namespace is not the init namespace, the process probably
used namespaces to sandbox itself, in which case it wouldn't be using
chroot in the first place, or it is running in a container with admin
privileges. In the latter case, this mitigation miiight make a
difference, I'm not sure exactly how powerful the APIs for namespace
admins are - but a mitigation that only makes a difference inside
containers would be weird anyway.

So: What is your specific usecase here?

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