From 8a7135a0ae559f4f4b2c7577c44075805fb71b4b Mon Sep 17 00:00:00 2001 From: "Eric W. Biederman" Date: Fri, 15 Jul 2016 06:36:44 -0500 Subject: [PATCH] cgroupns: Only allow creation of hierarchies in the initial cgroup namespace commit 726a4994b05ff5b6f83d64b5b43c3251217366ce upstream. Unprivileged users can't use hierarchies if they create them as they do not have privilieges to the root directory. Which means the only thing a hiearchy created by an unprivileged user is good for is expanding the number of cgroup links in every css_set, which is a DOS attack. We could allow hierarchies to be created in namespaces in the initial user namespace. Unfortunately there is only a single namespace for the names of heirarchies, so that is likely to create more confusion than not. So do the simple thing and restrict hiearchy creation to the initial cgroup namespace. Fixes: a79a908fd2b0 ("cgroup: introduce cgroup namespaces") Signed-off-by: "Eric W. Biederman" Signed-off-by: Tejun Heo Signed-off-by: Greg Kroah-Hartman --- kernel/cgroup.c | 8 ++------ 1 file changed, 2 insertions(+), 6 deletions(-) diff --git a/kernel/cgroup.c b/kernel/cgroup.c index e75efa819911a..e0be49fc382fc 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -2215,12 +2215,8 @@ static struct dentry *cgroup_mount(struct file_system_type *fs_type, goto out_unlock; } - /* - * We know this subsystem has not yet been bound. Users in a non-init - * user namespace may only mount hierarchies with no bound subsystems, - * i.e. 'none,name=user1' - */ - if (!opts.none && !capable(CAP_SYS_ADMIN)) { + /* Hierarchies may only be created in the initial cgroup namespace. */ + if (ns != &init_cgroup_ns) { ret = -EPERM; goto out_unlock; } -- 2.47.2