linux-kernel - [RFC next 1/5] user_namespace: add children list node

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Message-Id: <20250509065417.147515-2-chenridong@huaweicloud.com>
Date: Fri,  9 May 2025 06:54:07 +0000
From: Chen Ridong <chenridong@...weicloud.com>
To: akpm@...ux-foundation.org,
	paulmck@...nel.org,
	bigeasy@...utronix.de,
	legion@...nel.org,
	roman.gushchin@...ux.dev,
	brauner@...nel.org,
	tglx@...utronix.de,
	frederic@...nel.org,
	peterz@...radead.org,
	oleg@...hat.com,
	joel.granados@...nel.org,
	viro@...iv.linux.org.uk,
	lorenzo.stoakes@...cle.com,
	avagin@...gle.com,
	mengensun@...cent.com,
	linux@...ssschuh.net,
	jlayton@...nel.org,
	ruanjinjie@...wei.com,
	kees@...nel.org
Cc: linux-kernel@...r.kernel.org,
	lujialin4@...wei.com,
	chenridong@...weicloud.com
Subject: [RFC next 1/5] user_namespace: add children list node

From: Chen Ridong <chenridong@...wei.com>

Add the 'children' and 'ns_node' fields to the user_namespace structure.
This addition enables the user_namespace to locate all of its nested
child namespaces efficiently.

Signed-off-by: Chen Ridong <chenridong@...wei.com>
---
 include/linux/user_namespace.h | 2 ++
 kernel/user.c                  | 2 ++
 kernel/user_namespace.c        | 4 ++++
 3 files changed, 8 insertions(+)

diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index a0bb6d012137..7b1e180227c8 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -78,6 +78,8 @@ struct user_namespace {
 	struct uid_gid_map	gid_map;
 	struct uid_gid_map	projid_map;
 	struct user_namespace	*parent;
+	struct list_head	ns_node;
+	struct list_head	children;
 	int			level;
 	kuid_t			owner;
 	kgid_t			group;
diff --git a/kernel/user.c b/kernel/user.c
index f46b1d41163b..3a712a6894fd 100644
--- a/kernel/user.c
+++ b/kernel/user.c
@@ -65,6 +65,8 @@ struct user_namespace init_user_ns = {
 			.nr_extents = 1,
 		},
 	},
+	.ns_node = LIST_HEAD_INIT(init_user_ns.ns_node),
+	.children = LIST_HEAD_INIT(init_user_ns.children),
 	.ns.count = REFCOUNT_INIT(3),
 	.owner = GLOBAL_ROOT_UID,
 	.group = GLOBAL_ROOT_GID,
diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index 682f40d5632d..b570536934cc 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -135,6 +135,9 @@ int create_user_ns(struct cred *new)
 	ns->level = parent_ns->level + 1;
 	ns->owner = owner;
 	ns->group = group;
+	INIT_LIST_HEAD(&ns->children);
+	INIT_LIST_HEAD(&ns->ns_node);
+	list_add_tail_rcu(&ns->ns_node, &parent_ns->children);
 	INIT_WORK(&ns->work, free_user_ns);
 	for (i = 0; i < UCOUNT_COUNTS; i++) {
 		ns->ucount_max[i] = INT_MAX;
@@ -217,6 +220,7 @@ static void free_user_ns(struct work_struct *work)
 		kfree(ns->binfmt_misc);
 #endif
 		retire_userns_sysctls(ns);
+		list_del_rcu(&ns->ns_node);
 		key_free_user_ns(ns);
 		ns_free_inum(&ns->ns);
 		kmem_cache_free(user_ns_cachep, ns);
-- 
2.34.1