linux-kernel - [RFC PATCH 3/4] namespacefs: Couple namespacefs to the PID namespace

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Date:   Thu, 18 Nov 2021 20:12:09 +0200
From:   "Yordan Karadzhov (VMware)" <y.karadz@...il.com>
To:     linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Cc:     viro@...iv.linux.org.uk, ebiederm@...ssion.com,
        rostedt@...dmis.org, mingo@...hat.com, hagen@...u.net,
        rppt@...nel.org, James.Bottomley@...senPartnership.com,
        akpm@...ux-foundation.org, vvs@...tuozzo.com, shakeelb@...gle.com,
        christian.brauner@...ntu.com, mkoutny@...e.com,
        "Yordan Karadzhov (VMware)" <y.karadz@...il.com>
Subject: [RFC PATCH 3/4] namespacefs: Couple namespacefs to the PID namespace

When the PID namespace gets initialized, a directory called 'pid' is
added to 'namespacesfs'. This directory represents the main PID namespace
and also serves as a trunk (parent) of all child PID namespaces. Every
time when a new PID namespace is created a corresponding directory is
added to 'namespacefs/pid/parent/hierarchy/'. The 'inum' of the new
namespace gives the name of its directory. When the PID namespace is
destroyed the corresponding directory is removed.

Signed-off-by: Yordan Karadzhov (VMware) <y.karadz@...il.com>
---
 fs/namespacefs/inode.c | 21 +++++++++++++++++++++
 kernel/pid_namespace.c |  9 +++++++++
 2 files changed, 30 insertions(+)

diff --git a/fs/namespacefs/inode.c b/fs/namespacefs/inode.c
index 012c1c43b44d..55d71733164c 100644
--- a/fs/namespacefs/inode.c
+++ b/fs/namespacefs/inode.c
@@ -11,7 +11,9 @@
 #include <linux/fsnotify.h>
 #include <linux/magic.h>
 #include <linux/idr.h>
+#include <linux/proc_ns.h>
 #include <linux/seq_file.h>
+#include <linux/pid_namespace.h>
 
 static struct vfsmount *namespacefs_mount;
 static int namespacefs_mount_count;
@@ -307,6 +309,19 @@ void namespacefs_remove_pid_ns_dir(struct pid_namespace *ns)
 	namespacefs_remove_dir(ns->ns.dentry);
 }
 
+static int add_ns_dentry(struct ns_common *ns)
+{
+	struct dentry *dentry =
+		namespacefs_create_dir(ns->ops->name, NULL, &init_user_ns);
+
+	if (IS_ERR(dentry))
+		return PTR_ERR(dentry);
+
+	ns->dentry = dentry;
+
+	return 0;
+}
+
 #define _NS_MOUNT_DIR	"namespaces"
 
 static int __init namespacefs_init(void)
@@ -321,8 +336,14 @@ static int __init namespacefs_init(void)
 	if (err)
 		goto rm_mount;
 
+	err = add_ns_dentry(&init_pid_ns.ns);
+	if (err)
+		goto unreg;
+
 	return 0;
 
+ unreg:
+	unregister_filesystem(&namespacefs_fs_type);
  rm_mount:
 	sysfs_remove_mount_point(fs_kobj, _NS_MOUNT_DIR);
  fail:
diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
index a46a3723bc66..1690b2c87661 100644
--- a/kernel/pid_namespace.c
+++ b/kernel/pid_namespace.c
@@ -12,6 +12,7 @@
 #include <linux/pid.h>
 #include <linux/pid_namespace.h>
 #include <linux/user_namespace.h>
+#include <linux/namespacefs.h>
 #include <linux/syscalls.h>
 #include <linux/cred.h>
 #include <linux/err.h>
@@ -101,6 +102,7 @@ static struct pid_namespace *create_pid_namespace(struct user_namespace *user_ns
 	err = ns_alloc_inum(&ns->ns);
 	if (err)
 		goto out_free_idr;
+
 	ns->ns.ops = &pidns_operations;
 
 	refcount_set(&ns->ns.count, 1);
@@ -110,8 +112,14 @@ static struct pid_namespace *create_pid_namespace(struct user_namespace *user_ns
 	ns->ucounts = ucounts;
 	ns->pid_allocated = PIDNS_ADDING;
 
+	err = namespacefs_create_pid_ns_dir(ns);
+	if (err)
+		goto out_free_inum;
+
 	return ns;
 
+out_free_inum:
+	ns_free_inum(&ns->ns);
 out_free_idr:
 	idr_destroy(&ns->idr);
 	kmem_cache_free(pid_ns_cachep, ns);
@@ -133,6 +141,7 @@ static void delayed_free_pidns(struct rcu_head *p)
 
 static void destroy_pid_namespace(struct pid_namespace *ns)
 {
+	namespacefs_remove_pid_ns_dir(ns);
 	ns_free_inum(&ns->ns);
 
 	idr_destroy(&ns->idr);
-- 
2.33.1