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

[Eric W. Biederman]

Aleksa Sarai <asarai@xxxxxxxx> writes:

> 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>

Acked-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>

> ---
>  fs/proc/base.c              | 3 ++-
>  include/linux/sched/debug.h | 4 +++-
>  kernel/sched/debug.c        | 5 +++--
>  3 files changed, 8 insertions(+), 4 deletions(-)
>
> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index 719c2e943ea1..98fd8f6df851 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -1408,12 +1408,13 @@ static const struct file_operations proc_fail_nth_operations = {
>  static int sched_show(struct seq_file *m, void *v)
>  {
>  	struct inode *inode = m->private;
> +	struct pid_namespace *ns = inode->i_sb->s_fs_info;
>  	struct task_struct *p;
>  
>  	p = get_proc_task(inode);
>  	if (!p)
>  		return -ESRCH;
> -	proc_sched_show_task(p, m);
> +	proc_sched_show_task(p, ns, m);
>  
>  	put_task_struct(p);
>  
> diff --git a/include/linux/sched/debug.h b/include/linux/sched/debug.h
> index e0eaee54c5a4..5d58d49e9f87 100644
> --- a/include/linux/sched/debug.h
> +++ b/include/linux/sched/debug.h
> @@ -6,6 +6,7 @@
>   */
>  
>  struct task_struct;
> +struct pid_namespace;
>  
>  extern void dump_cpu_task(int cpu);
>  
> @@ -34,7 +35,8 @@ extern void sched_show_task(struct task_struct *p);
>  
>  #ifdef CONFIG_SCHED_DEBUG
>  struct seq_file;
> -extern void proc_sched_show_task(struct task_struct *p, struct seq_file *m);
> +extern void proc_sched_show_task(struct task_struct *p,
> +				 struct pid_namespace *ns, struct seq_file *m);
>  extern void proc_sched_set_task(struct task_struct *p);
>  #endif
>  
> diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
> index 4fa66de52bd6..ac345115877b 100644
> --- a/kernel/sched/debug.c
> +++ b/kernel/sched/debug.c
> @@ -872,11 +872,12 @@ static void sched_show_numa(struct task_struct *p, struct seq_file *m)
>  #endif
>  }
>  
> -void proc_sched_show_task(struct task_struct *p, struct seq_file *m)
> +void proc_sched_show_task(struct task_struct *p, struct pid_namespace *ns,
> +						  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_nr_ns(p, ns),
>  						get_nr_threads(p));
>  	SEQ_printf(m,
>  		"---------------------------------------------------------"