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Date:   Mon, 22 Nov 2021 18:15:52 +0200
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Subject: Re: [RFC PATCH 0/4] namespacefs: Proof-of-Concept
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To:     James Bottomley <James.Bottomley@HansenPartnership.com>,
        Steven Rostedt <rostedt@goodmis.org>
Cc:     linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        viro@zeniv.linux.org.uk, mingo@redhat.com, hagen@jauu.net,
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        mkoutny@suse.com, Linux Containers <containers@lists.linux.dev>,
        "Eric W. Biederman" <ebiederm@xmission.com>
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From:   Yordan Karadzhov <y.karadz@gmail.com>
In-Reply-To: <63f54c213253b80fcf3f8653766d5c6f5761034a.camel@HansenPartnership.com>
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On 22.11.21 г. 17:47 ч., James Bottomley wrote:
>> Hmm, Isn't that true only if somehow we know that (3) happened before
>> (4).
> This depends.  There are only two parented namespaces: pid and user.
> You said you were only interested in pid for now.  setns on the process
> only affects pid_for_children because you have to fork to enter the pid
> namespace, so in your scenario X has a new ns/pid_for_children but its
> own ns/pid never changed.  It's the ns/pid not the ns/pid_for_children
> which is the parent.  This makes me suspect that the specific thing
> you're trying to do: trace the pid parentage, can actually be done with
> the information we have now.

This is very good point indeed. Thank you very much!
Yordan

> 
> If you do this with the user_ns, then you have a problem because it's
> not fork on entry.  But, as I listed in the examples, there are a load
> of other problems with tracing the user_ns tree.