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.


Cc: <>
Cc: Jess Frazelle <>
Signed-off-by: Aleksa Sarai <>
 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),

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