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cgroup: mount cgroupns-root when inside non-init cgroupns

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This patch enables cgroup mounting inside userns when a process
as appropriate privileges. The cgroup filesystem mounted is
rooted at the cgroupns-root. Thus, in a container-setup, only
the hierarchy under the cgroupns-root is exposed inside the container.
This allows container management tools to run inside the containers
without depending on any global state.

Signed-off-by: Serge Hallyn <serge.hallyn@canonical.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Serge Hallyn 2016-01-29 02:54:09 -06:00 committed by Tejun Heo
parent fb3c831565
commit ed82571b1a
1 changed files with 47 additions and 1 deletions
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48
kernel/cgroup.c
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@ -1994,6 +1994,7 @@ static struct dentry *cgroup_mount(struct file_system_type *fs_type,
{
bool is_v2 = fs_type == &cgroup2_fs_type;
struct super_block *pinned_sb = NULL;
struct cgroup_namespace *ns = current->nsproxy->cgroup_ns;
struct cgroup_subsys *ss;
struct cgroup_root *root;
struct cgroup_sb_opts opts;
@ -2002,6 +2003,14 @@ static struct dentry *cgroup_mount(struct file_system_type *fs_type,
int i;
bool new_sb;
get_cgroup_ns(ns);
/* Check if the caller has permission to mount. */
if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN)) {
put_cgroup_ns(ns);
return ERR_PTR(-EPERM);
}
/*
* The first time anyone tries to mount a cgroup, enable the list
* linking each css_set to its tasks and fix up all existing tasks.
@ -2012,6 +2021,7 @@ static struct dentry *cgroup_mount(struct file_system_type *fs_type,
if (is_v2) {
if (data) {
pr_err("cgroup2: unknown option \"%s\"\n", (char *)data);
put_cgroup_ns(ns);
return ERR_PTR(-EINVAL);
}
cgrp_dfl_root_visible = true;
@ -2117,6 +2127,16 @@ 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)) {
ret = -EPERM;
goto out_unlock;
}
root = kzalloc(sizeof(*root), GFP_KERNEL);
if (!root) {
ret = -ENOMEM;
@ -2135,12 +2155,37 @@ out_free:
kfree(opts.release_agent);
kfree(opts.name);
if (ret)
if (ret) {
put_cgroup_ns(ns);
return ERR_PTR(ret);
}
out_mount:
dentry = kernfs_mount(fs_type, flags, root->kf_root,
is_v2 ? CGROUP2_SUPER_MAGIC : CGROUP_SUPER_MAGIC,
&new_sb);
/*
* In non-init cgroup namespace, instead of root cgroup's
* dentry, we return the dentry corresponding to the
* cgroupns->root_cgrp.
*/
if (!IS_ERR(dentry) && ns != &init_cgroup_ns) {
struct dentry *nsdentry;
struct cgroup *cgrp;
mutex_lock(&cgroup_mutex);
spin_lock_bh(&css_set_lock);
cgrp = cset_cgroup_from_root(ns->root_cset, root);
spin_unlock_bh(&css_set_lock);
mutex_unlock(&cgroup_mutex);
nsdentry = kernfs_node_dentry(cgrp->kn, dentry->d_sb);
dput(dentry);
dentry = nsdentry;
}
if (IS_ERR(dentry) || !new_sb)
cgroup_put(&root->cgrp);
@ -2153,6 +2198,7 @@ out_mount:
deactivate_super(pinned_sb);
}
put_cgroup_ns(ns);
return dentry;
}