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Date: Wed, 6 Nov 2013 12:02:32 -0600
From: Serge Hallyn <serge.hallyn@ubuntu.com>
To: Oleg Nesterov <oleg@redhat.com>, Christian Seiler <christian@iwakd.de>
Cc: lkml <linux-kernel@vger.kernel.org>, Andy Whitcroft <apw@canonical.com>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Lxc development list <lxc-devel@lists.sourceforge.net>
Subject: CLONE_PARENT after setns(CLONE_NEWPID)
Message-ID: <20131106180232.GA8980@ac100>
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Hi Oleg,

commit 40a0d32d1eaffe6aac7324ca92604b6b3977eb0e :
"fork: unify and tighten up CLONE_NEWUSER/CLONE_NEWPID checks"
breaks lxc-attach in 3.12.  That code forks a child which does
setns() and then does a clone(CLONE_PARENT).  That way the
grandchild can be in the right namespaces (which the child was
not) and be a child of the original task, which is the monitor.

lxc-attach in 3.11 was working fine with no side effects that I
could see.  Is there a real danger in allowing CLONE_PARENT
when current->nsproxy->pidns_for_children is not our pidns,
or was this done out of an "over-abundance of caution"?  Can we
safely revert that new extra check?

thanks,
-serge