linux-kernel - Re: [PATCH v2] sched: debug: use task_pid_nr

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Message-ID: <20170807084451.rdtsjws6hwtdy6ki@hirez.programming.kicks-ass.net>
Date:   Mon, 7 Aug 2017 10:44:51 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Aleksa Sarai <asarai@...e.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>, cyphar@...har.com,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Jess Frazelle <acidburn@...gle.com>
Subject: Re: [PATCH v2] sched: debug: use task_pid_nr_ns in /proc/$pid/sched

On Sun, Aug 06, 2017 at 02:41:41PM +1000, Aleksa Sarai wrote:
> It appears as though the addition of the PID namespace did not update
> the output code for /proc/*/sched, which resulted in it providing PIDs
> that were not self-consistent with the /proc mount. This additionally
> made it trivial to detect whether a process was inside &init_pid_ns from
> userspace (making container detection trivial[1]). This lead to
> situations such as:
> 
>   % unshare -pmf
>   % mount -t proc proc /proc
>   % head -n1 /proc/1/sched
>   head (10047, #threads: 1)
> 
> Fix this by just using task_pid_nr_ns for the output of /proc/*/sched.
> All of the other uses of task_pid_nr in kernel/sched/debug.c are from a
> sysctl context and thus don't need to be namespaced.
> 
> [1]: https://github.com/jessfraz/amicontained
> 
> Cc: <stable@...r.kernel.org>
> Cc: Jess Frazelle <acidburn@...gle.com>
> Signed-off-by: Aleksa Sarai <asarai@...e.com>

Thanks!