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

[Peter Zijlstra]

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

Thanks!