From 726a4994b05ff5b6f83d64b5b43c3251217366ce 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 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. Cc: stable@vger.kernel.org Fixes: a79a908fd2b0 ("cgroup: introduce cgroup namespaces") Signed-off-by: "Eric W. Biederman" Signed-off-by: Tejun Heo --- kernel/cgroup.c | 8 ++------ 1 file changed, 2 insertions(+), 6 deletions(-) diff --git a/kernel/cgroup.c b/kernel/cgroup.c index e75efa819911..e0be49fc382f 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; } -- 2.45.2