linux-kernel - Re: [PATCH] pidfd: show pids for nested pid namespaces in fdinfo

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Message-ID: <20191008135258.mzc7o2djiq5yydko@wittgenstein>
Date:   Tue, 8 Oct 2019 15:52:59 +0200
From:   Christian Brauner <christian.brauner@...ntu.com>
To:     Christian Kellner <ckellner@...hat.com>
Cc:     linux-kernel@...r.kernel.org,
        Christian Kellner <christian@...lner.me>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>, Michal Hocko <mhocko@...e.com>,
        Elena Reshetova <elena.reshetova@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Roman Gushchin <guro@...com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        "Dmitry V. Levin" <ldv@...linux.org>
Subject: Re: [PATCH] pidfd: show pids for nested pid namespaces in fdinfo

On Tue, Oct 08, 2019 at 03:36:37PM +0200, Christian Kellner wrote:
> From: Christian Kellner <christian@...lner.me>
> 
> The fdinfo file for a process file descriptor already contains the
> pid of the process in the callers namespaces. Additionally, if pid
> namespaces are configured, show the process ids of the process in
> all nested namespaces in the same format as in the procfs status
> file, i.e. "NSPid:\t%d\%d...". This allows the easy identification
> of the processes in nested namespaces.
> 
> Signed-off-by: Christian Kellner <christian@...lner.me>

Yeah, makes sense to me.
Note that if you send the pidfd to a sibling pid namespace NSpid won't
show you anything useful. But that's what I'd expect security wise. You
should only be able to snoop on descendant pid namespaces.

Please add a test for this to verify that this all works correctly and
then resend. The tests live in tools/testing/selftests/pidfd/ and should
already have most of the infrastructure there. The fdinfo parsing code
should be in samples/pidfd/ which

For the patch itself:

Reviewed-by: Christian Brauner <christian.brauner@...ntu.com>

You can resend with my Reviewed-by retained if you don't change
anything. Before I see tests I'll hold off on merging this. ;)

Thanks!
Christian