Re: [PATCH v2] sched: debug: use task_pid_nr_ns in /proc/$pid/sched

From: Peter Zijlstra
Date: Mon Aug 07 2017 - 04:45:00 EST

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]:
> Cc: <stable@xxxxxxxxxxxxxxx>
> Cc: Jess Frazelle <acidburn@xxxxxxxxxx>
> Signed-off-by: Aleksa Sarai <asarai@xxxxxxxx>