linux-kernel - Re: [PATCH] sched: debug: use task_pid

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Date:   Sun, 06 Aug 2017 03:58:27 +1000
From:   Aleksa Sarai <asarai@...e.de>
To:     Aleksa Sarai <ASarai@...e.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Aleksa Sarai <cyphar@...har.com>,
        Jess Frazelle <acidburn@...gle.com>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        "Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [PATCH] sched: debug: use task_pid_vnr in /proc/$pid/sched

On 2017-08-06 02:52, Aleksa Sarai wrote:
> It appears as though the addition of the PID namespace did not update
> the output code for /proc/$pid/sched, which made it trivial to figure
> out whether a process was inside &init_pid_ns from userspace (making
> container detection trivial[1]). This lead to situations such as:
> 
>   % unshare -pf head -n1 /proc/self/sched
>   head (10047, #threads: 1)
> 
> Fix this by just using task_pid_vnr for the output of /proc/$pid/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>
> ---
>  kernel/sched/debug.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
> index 4fa66de52bd6..a06acbe33e16 100644
> --- a/kernel/sched/debug.c
> +++ b/kernel/sched/debug.c
> @@ -876,7 +876,7 @@ void proc_sched_show_task(struct task_struct *p,
> struct seq_file *m)
>  {
>  	unsigned long nr_switches;
> 
> -	SEQ_printf(m, "%s (%d, #threads: %d)\n", p->comm, task_pid_nr(p),
> +	SEQ_printf(m, "%s (%d, #threads: %d)\n", p->comm, task_pid_vnr(p),
>  						get_nr_threads(p));
>  	SEQ_printf(m,
>  		"---------------------------------------------------------"

Added Eric to Cc.

-- 
Aleksa Sarai
Software Engineer (Containers)
SUSE Linux GmbH
https://www.cyphar.com/