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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Alexander Kuznetsov <wwfq@yandex-team.ru>,
        Andrey Krasichkov <buglloc@yandex-team.ru>,
        Dmitry Yakunin <zeil@yandex-team.ru>, Tejun Heo <tj@kernel.org>
Subject: [PATCH 4.9 24/42] cgroup1: dont allow \n in renaming
Date:   Mon, 14 Jun 2021 12:27:15 +0200
Message-Id: <20210614102643.480406616@linuxfoundation.org>
In-Reply-To: <20210614102642.700712386@linuxfoundation.org>
References: <20210614102642.700712386@linuxfoundation.org>
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From: Alexander Kuznetsov <wwfq@yandex-team.ru>

commit b7e24eb1caa5f8da20d405d262dba67943aedc42 upstream.

cgroup_mkdir() have restriction on newline usage in names:
$ mkdir $'/sys/fs/cgroup/cpu/test\ntest2'
mkdir: cannot create directory
'/sys/fs/cgroup/cpu/test\ntest2': Invalid argument

But in cgroup1_rename() such check is missed.
This allows us to make /proc/<pid>/cgroup unparsable:
$ mkdir /sys/fs/cgroup/cpu/test
$ mv /sys/fs/cgroup/cpu/test $'/sys/fs/cgroup/cpu/test\ntest2'
$ echo $$ > $'/sys/fs/cgroup/cpu/test\ntest2'
$ cat /proc/self/cgroup
11:pids:/
10:freezer:/
9:hugetlb:/
8:cpuset:/
7:blkio:/user.slice
6:memory:/user.slice
5:net_cls,net_prio:/
4:perf_event:/
3:devices:/user.slice
2:cpu,cpuacct:/test
test2
1:name=systemd:/
0::/

Signed-off-by: Alexander Kuznetsov <wwfq@yandex-team.ru>
Reported-by: Andrey Krasichkov <buglloc@yandex-team.ru>
Acked-by: Dmitry Yakunin <zeil@yandex-team.ru>
Cc: stable@vger.kernel.org
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 kernel/cgroup.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -3598,6 +3598,10 @@ static int cgroup_rename(struct kernfs_n
 	struct cgroup *cgrp = kn->priv;
 	int ret;
 
+	/* do not accept '\n' to prevent making /proc/<pid>/cgroup unparsable */
+	if (strchr(new_name_str, '\n'))
+		return -EINVAL;
+
 	if (kernfs_type(kn) != KERNFS_DIR)
 		return -ENOTDIR;
 	if (kn->parent != new_parent)