linux-kernel - [PATCH] cgroup: update some statememt about delegation

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Message-ID: <20240815024118.3137952-1-chenridong@huawei.com>
Date: Thu, 15 Aug 2024 02:41:18 +0000
From: Chen Ridong <chenridong@...wei.com>
To: <tj@...nel.org>, <lizefan.x@...edance.com>, <hannes@...xchg.org>,
	<longman@...hat.com>, <mkoutny@...e.com>
CC: <cgroups@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: [PATCH] cgroup: update some statememt about delegation

The comment in cgroup_file_write is missing some interfaces, such as
'cgroup.threads'. All delegatable files are listed in
'/sys/kernel/cgroup/delegate', so update the comment in cgroup_file_write.
Besides, add a statement that files outside the namespace shouldn't be
visible from inside the delegated namespace.

Signed-off-by: Chen Ridong <chenridong@...wei.com>
---
 Documentation/admin-guide/cgroup-v2.rst | 10 ++++++----
 kernel/cgroup/cgroup.c                  |  4 ++--
 2 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
index f2d1ec7d6aba..2665d08159fb 100644
--- a/Documentation/admin-guide/cgroup-v2.rst
+++ b/Documentation/admin-guide/cgroup-v2.rst
@@ -533,10 +533,12 @@ cgroup namespace on namespace creation.
 Because the resource control interface files in a given directory
 control the distribution of the parent's resources, the delegatee
 shouldn't be allowed to write to them.  For the first method, this is
-achieved by not granting access to these files.  For the second, the
-kernel rejects writes to all files other than "cgroup.procs" and
-"cgroup.subtree_control" on a namespace root from inside the
-namespace.
+achieved by not granting access to these files.  For the second, files
+outside the namespace shouldn't be visible from within the delegated
+namespace, and the kernel rejects writes to all files on a namespace
+root from inside the namespace, except for those files listed in
+"/sys/kernel/cgroup/delegate" (including "cgroup.procs", "cgroup.threads",
+"cgroup.subtree_control", etc.).
 
 The end results are equivalent for both delegation types.  Once
 delegated, the user can build sub-hierarchy under the directory,
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index a3fa645f8433..9758686f0332 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -4130,8 +4130,8 @@ static ssize_t cgroup_file_write(struct kernfs_open_file *of, char *buf,
 	/*
 	 * If namespaces are delegation boundaries, disallow writes to
 	 * files in an non-init namespace root from inside the namespace
-	 * except for the files explicitly marked delegatable -
-	 * cgroup.procs and cgroup.subtree_control.
+	 * except for the set delegatable files shown in /sys/kernel/cgroup/delegate,
+	 * including cgroup.procs, cgroup.threads and cgroup.subtree_control, etc.
 	 */
 	if ((cgrp->root->flags & CGRP_ROOT_NS_DELEGATE) &&
 	    !(cft->flags & CFTYPE_NS_DELEGATABLE) &&
-- 
2.34.1