[tip:sched/core] sched/debug: Use task_pid_nr_ns in /proc/$pid/sched

[tip-bot for Aleksa Sarai <tipbot@zytor.com>]

Commit-ID:  74dc3384fc7983b78cc46ebb1824968a3db85eb1
Gitweb:     http://git.kernel.org/tip/74dc3384fc7983b78cc46ebb1824968a3db85eb1
Author:     Aleksa Sarai <asarai@suse.com>
AuthorDate: Sun, 6 Aug 2017 14:41:41 +1000
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Thu, 10 Aug 2017 12:18:19 +0200

sched/debug: Use task_pid_nr_ns in /proc/$pid/sched

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:

   https://github.com/jessfraz/amicontained

This leads 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.

Signed-off-by: Aleksa Sarai <asarai@suse.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Eric W. Biederman <ebiederm@xmission.com>
Cc: Jess Frazelle <acidburn@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: cyphar@cyphar.com
Link: http://lkml.kernel.org/r/20170806044141.5093-1-asarai@suse.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 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 719c2e9..98fd8f6 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 e0eaee5..5d58d49 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 4fa66de..ac34511 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,
 		"---------------------------------------------------------"