[PATCH 1/1] /proc/$PID/status : show list NSpid data based on current process namespace.

[Kuenhwan Kwak]

This patch helps creating a pid mapping data to parent processes.

Reading 'NSpid' field in '/proc/$PID/status' is currently a simple
way to getting child pid from parent pid in userspace. But this field
supplies only single direction mapping('parent pid' to 'child pid').
If parent process want to translate child pid to current namespace pid,
there is no way to get except full searching in current procfs.

This patch will helps in getting current namespace pid by reading child
procfs file without any side effects.

For example, Process id is 24771 in level 0, 435 in level 1.
a) The output of '/proc/24771/status' in level 0 namespace.
NSpid : 24771 435

b) The output of '/proc/435/status' in level 1 namespace.
NSpid : 435

c) Process in level 0 mount level1 proc to '/var/child/proc'
after setns(). The output of '/var/child/proc/435/status' is
NSpid : 24771 435

Signed-off-by: Kuenhwan Kwak <kh243.kwak@xxxxxxxxxxx>
---
 fs/proc/array.c |   12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/fs/proc/array.c b/fs/proc/array.c
index 3f57dac..b3f5efa 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -83,6 +83,7 @@
 #include <linux/tracehook.h>
 #include <linux/string_helpers.h>
 #include <linux/user_namespace.h>
+#include <linux/sched.h>
 
 #include <asm/pgtable.h>
 #include <asm/processor.h>
@@ -149,6 +150,9 @@ static inline void task_state(struct seq_file *m, struct pid_namespace *ns,
 	const struct cred *cred;
 	pid_t ppid, tpid = 0, tgid, ngid;
 	unsigned int max_fds = 0;
+#ifdef CONFIG_PID_NS
+	struct pid_namespace *current_pid_ns = task_active_pid_ns(current);
+#endif
 
 	rcu_read_lock();
 	ppid = pid_alive(p) ?
@@ -198,19 +202,19 @@ static inline void task_state(struct seq_file *m, struct pid_namespace *ns,
 
 #ifdef CONFIG_PID_NS
 	seq_puts(m, "\nNStgid:");
-	for (g = ns->level; g <= pid->level; g++)
+	for (g = current_pid_ns->level; g <= pid->level; g++)
 		seq_printf(m, "\t%d",
 			task_tgid_nr_ns(p, pid->numbers[g].ns));
 	seq_puts(m, "\nNSpid:");
-	for (g = ns->level; g <= pid->level; g++)
+	for (g = current_pid_ns->level; g <= pid->level; g++)
 		seq_printf(m, "\t%d",
 			task_pid_nr_ns(p, pid->numbers[g].ns));
 	seq_puts(m, "\nNSpgid:");
-	for (g = ns->level; g <= pid->level; g++)
+	for (g = current_pid_ns->level; g <= pid->level; g++)
 		seq_printf(m, "\t%d",
 			task_pgrp_nr_ns(p, pid->numbers[g].ns));
 	seq_puts(m, "\nNSsid:");
-	for (g = ns->level; g <= pid->level; g++)
+	for (g = current_pid_ns->level; g <= pid->level; g++)
 		seq_printf(m, "\t%d",
 			task_session_nr_ns(p, pid->numbers[g].ns));
 #endif
-- 
1.7.9.5

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