From: Aditya Kali <adityakali@xxxxxxxxxx>
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.
In order to support this, a new kernfs api is added to lookup the
dentry for the cgroupns-root.
Signed-off-by: Aditya Kali <adityakali@xxxxxxxxxx>
Acked-by: Serge E. Hallyn <serge.hallyn@xxxxxxxxxx>
---
fs/kernfs/mount.c | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
include/linux/kernfs.h | 2 ++
kernel/cgroup.c | 32 +++++++++++++++++++++++++++++++-
3 files changed, 81 insertions(+), 1 deletion(-)
diff --git a/fs/kernfs/mount.c b/fs/kernfs/mount.c
index 8eaf417..64613864 100644
--- a/fs/kernfs/mount.c
+++ b/fs/kernfs/mount.c
@@ -62,6 +62,54 @@ struct kernfs_root *kernfs_root_from_sb(struct super_block *sb)
return NULL;
}
+/**
+ * kernfs_obtain_root - get a dentry for the given kernfs_node
+ * @sb: the kernfs super_block
+ * @kn: kernfs_node for which a dentry is needed
+ *
+ * This can used used by callers which want to mount only a part of the kernfs
+ * as root of the filesystem.
+ */
+struct dentry *kernfs_obtain_root(struct super_block *sb,
+ struct kernfs_node *kn)
+{
+ struct dentry *dentry;
+ struct inode *inode;
+
+ BUG_ON(sb->s_op != &kernfs_sops);
+
+ /* inode for the given kernfs_node should already exist. */
+ inode = ilookup(sb, kn->ino);
+ if (!inode) {
+ pr_debug("kernfs: could not get inode for '");
+ pr_cont_kernfs_path(kn);
+ pr_cont("'.\n");
+ return ERR_PTR(-EINVAL);
+ }
+
+ /* instantiate and link root dentry */
+ dentry = d_obtain_root(inode);
+ if (!dentry) {
+ pr_debug("kernfs: could not get dentry for '");
+ pr_cont_kernfs_path(kn);
+ pr_cont("'.\n");
+ return ERR_PTR(-ENOMEM);
+ }
+
+ /* If this is a new dentry, set it up. We need kernfs_mutex because this
+ * may be called by callers other than kernfs_fill_super. */
+ mutex_lock(&kernfs_mutex);
+ if (!dentry->d_fsdata) {
+ kernfs_get(kn);
+ dentry->d_fsdata = kn;
+ } else {
+ WARN_ON(dentry->d_fsdata != kn);
+ }
+ mutex_unlock(&kernfs_mutex);
+
+ return dentry;
+}
+
static int kernfs_fill_super(struct super_block *sb, unsigned long magic)
{
struct kernfs_super_info *info = kernfs_info(sb);
diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h
index d025ebd..1903777 100644
--- a/include/linux/kernfs.h
+++ b/include/linux/kernfs.h
@@ -284,6 +284,8 @@ struct kernfs_node *kernfs_node_from_dentry(struct dentry *dentry);
struct kernfs_root *kernfs_root_from_sb(struct super_block *sb);
struct inode *kernfs_get_inode(struct super_block *sb, struct kernfs_node *kn);
+struct dentry *kernfs_obtain_root(struct super_block *sb,
+ struct kernfs_node *kn);
struct kernfs_root *kernfs_create_root(struct kernfs_syscall_ops *scops,
unsigned int flags, void *priv);
void kernfs_destroy_root(struct kernfs_root *root);
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 1d696de..0a3e893 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1980,6 +1980,14 @@ static struct dentry *cgroup_mount(struct file_system_type *fs_type,
int ret;
int i;
bool new_sb;
+ struct cgroup_namespace *ns =
+ get_cgroup_ns(current->nsproxy->cgroup_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
@@ -2112,11 +2120,31 @@ out_free:
kfree(opts.release_agent);
kfree(opts.name);
- if (ret)
+ if (ret) {
+ put_cgroup_ns(ns);
return ERR_PTR(ret);
+ }
dentry = kernfs_mount(fs_type, flags, root->kf_root,
CGROUP_SUPER_MAGIC, &new_sb);
+
+ if (!IS_ERR(dentry)) {
+ /* In non-init cgroup namespace, instead of root cgroup's
+ * dentry, we return the dentry corresponding to the
+ * cgroupns->root_cgrp.
+ */
+ if (ns != &init_cgroup_ns) {
+ struct dentry *nsdentry;
+ struct cgroup *cgrp;
+
+ cgrp = cset_cgroup_from_root(ns->root_cgrps, root);
+ nsdentry = kernfs_obtain_root(dentry->d_sb,
+ cgrp->kn);
+ dput(dentry);
+ dentry = nsdentry;
+ }
+ }
+
if (IS_ERR(dentry) || !new_sb)
cgroup_put(&root->cgrp);
@@ -2129,6 +2157,7 @@ out_free:
deactivate_super(pinned_sb);
}
+ put_cgroup_ns(ns);
return dentry;
}
@@ -2157,6 +2186,7 @@ static struct file_system_type cgroup_fs_type = {
.name = "cgroup",
.mount = cgroup_mount,
.kill_sb = cgroup_kill_sb,
+ .fs_flags = FS_USERNS_MOUNT,
};
char * __must_check cgroup_path_ns(struct cgroup_namespace *ns,
--
1.7.9.5
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