From e250d91d65750a0c0c62483ac4f9f357e7317617 Mon Sep 17 00:00:00 2001
From: Ondrej Mosnacek <omosnace@redhat.com>
Date: Thu, 13 Dec 2018 15:17:37 +0100
Subject: [PATCH] cgroup: fix parsing empty mount option string
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Git-commit: e250d91d65750a0c0c62483ac4f9f357e7317617
Patch-mainline: v5.0-rc1
References: bsc#1133094

This fixes the case where all mount options specified are consumed by an
LSM and all that's left is an empty string. In this case cgroupfs should
accept the string and not fail.

How to reproduce (with SELinux enabled):

    # umount /sys/fs/cgroup/unified
    # mount -o context=system_u:object_r:cgroup_t:s0 -t cgroup2 cgroup2 /sys/fs/cgroup/unified
    mount: /sys/fs/cgroup/unified: wrong fs type, bad option, bad superblock on cgroup2, missing codepage or helper program, or other error.
    # dmesg | tail -n 1
    [   31.575952] cgroup: cgroup2: unknown option ""

Fixes: 67e9c74b8a87 ("cgroup: replace __DEVEL__sane_behavior with cgroup2 fs type")
[NOTE: should apply on top of commit 5136f6365ce3 ("cgroup: implement "nsdelegate" mount option"), older versions need manual rebase]
Suggested-by: Stephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
[mkoutny: adjusted for missing "nsdelegate" option]
Signed-off-by: Michal Koutný <mkoutny@suse.com>
---
 kernel/cgroup/cgroup.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -1801,7 +1801,7 @@ static struct dentry *cgroup_mount(struc
 		cgroup_enable_task_cg_lists();
 
 	if (fs_type == &cgroup2_fs_type) {
-		if (data) {
+		if (data && *(char *)data != '\0') {
 			pr_err("cgroup2: unknown option \"%s\"\n", (char *)data);
 			put_cgroup_ns(ns);
 			return ERR_PTR(-EINVAL);