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-rw-r--r--Documentation/cgroup-v2.txt61
-rw-r--r--include/linux/cgroup-defs.h9
-rw-r--r--kernel/cgroup/cgroup.c88
3 files changed, 135 insertions, 23 deletions
diff --git a/Documentation/cgroup-v2.txt b/Documentation/cgroup-v2.txt
index 0260ed053efd..558c3a739baf 100644
--- a/Documentation/cgroup-v2.txt
+++ b/Documentation/cgroup-v2.txt
@@ -149,6 +149,16 @@ during boot, before manual intervention is possible. To make testing
and experimenting easier, the kernel parameter cgroup_no_v1= allows
disabling controllers in v1 and make them always available in v2.
+cgroup v2 currently supports the following mount options.
+
+ nsdelegate
+
+ Consider cgroup namespaces as delegation boundaries. This
+ option is system wide and can only be set on mount or modified
+ through remount from the init namespace. The mount option is
+ ignored on non-init namespace mounts. Please refer to the
+ Delegation section for details.
+
2-2. Organizing Processes
@@ -308,19 +318,27 @@ file.
2-5-1. Model of Delegation
-A cgroup can be delegated to a less privileged user by granting write
-access of the directory and its "cgroup.procs" and
-"cgroup.subtree_control" files to the user. Note that resource
-control interface files in a given directory control the distribution
-of the parent's resources and thus must not be delegated along with
-the directory.
-
-Once delegated, the user can build sub-hierarchy under the directory,
-organize processes as it sees fit and further distribute the resources
-it received from the parent. The limits and other settings of all
-resource controllers are hierarchical and regardless of what happens
-in the delegated sub-hierarchy, nothing can escape the resource
-restrictions imposed by the parent.
+A cgroup can be delegated in two ways. First, to a less privileged
+user by granting write access of the directory and its "cgroup.procs"
+and "cgroup.subtree_control" files to the user. Second, if the
+"nsdelegate" mount option is set, automatically to a cgroup namespace
+on namespace creation.
+
+Because the resource control interface files in a given directory
+control the distribution of the parent's resources, the delegatee
+shouldn't be allowed to write to them. For the first method, this is
+achieved by not granting access to these files. For the second, the
+kernel rejects writes to all files other than "cgroup.procs" and
+"cgroup.subtree_control" on a namespace root from inside the
+namespace.
+
+The end results are equivalent for both delegation types. Once
+delegated, the user can build sub-hierarchy under the directory,
+organize processes inside it as it sees fit and further distribute the
+resources it received from the parent. The limits and other settings
+of all resource controllers are hierarchical and regardless of what
+happens in the delegated sub-hierarchy, nothing can escape the
+resource restrictions imposed by the parent.
Currently, cgroup doesn't impose any restrictions on the number of
cgroups in or nesting depth of a delegated sub-hierarchy; however,
@@ -330,10 +348,12 @@ this may be limited explicitly in the future.
2-5-2. Delegation Containment
A delegated sub-hierarchy is contained in the sense that processes
-can't be moved into or out of the sub-hierarchy by the delegatee. For
-a process with a non-root euid to migrate a target process into a
-cgroup by writing its PID to the "cgroup.procs" file, the following
-conditions must be met.
+can't be moved into or out of the sub-hierarchy by the delegatee.
+
+For delegations to a less privileged user, this is achieved by
+requiring the following conditions for a process with a non-root euid
+to migrate a target process into a cgroup by writing its PID to the
+"cgroup.procs" file.
- The writer must have write access to the "cgroup.procs" file.
@@ -360,6 +380,11 @@ destination cgroup C00 is above the points of delegation and U0 would
not have write access to its "cgroup.procs" files and thus the write
will be denied with -EACCES.
+For delegations to namespaces, containment is achieved by requiring
+that both the source and destination cgroups are reachable from the
+namespace of the process which is attempting the migration. If either
+is not reachable, the migration is rejected with -ENOENT.
+
2-6. Guidelines
@@ -1414,7 +1439,7 @@ D. Deprecated v1 Core Features
- Multiple hierarchies including named ones are not supported.
-- All mount options and remounting are not supported.
+- All v1 mount options are not supported.
- The "tasks" file is removed and "cgroup.procs" is not sorted.
diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h
index 3bc4196bf217..09f4c7df1478 100644
--- a/include/linux/cgroup-defs.h
+++ b/include/linux/cgroup-defs.h
@@ -67,12 +67,21 @@ enum {
enum {
CGRP_ROOT_NOPREFIX = (1 << 1), /* mounted subsystems have no named prefix */
CGRP_ROOT_XATTR = (1 << 2), /* supports extended attributes */
+
+ /*
+ * Consider namespaces as delegation boundaries. If this flag is
+ * set, controller specific interface files in a namespace root
+ * aren't writeable from inside the namespace.
+ */
+ CGRP_ROOT_NS_DELEGATE = (1 << 3),
};
/* cftype->flags */
enum {
CFTYPE_ONLY_ON_ROOT = (1 << 0), /* only create on root cgrp */
CFTYPE_NOT_ON_ROOT = (1 << 1), /* don't create on root cgrp */
+ CFTYPE_NS_DELEGATABLE = (1 << 2), /* writeable beyond delegation boundaries */
+
CFTYPE_NO_PREFIX = (1 << 3), /* (DON'T USE FOR NEW FILES) no subsys prefix */
CFTYPE_WORLD_WRITABLE = (1 << 4), /* (DON'T USE FOR NEW FILES) S_IWUGO */
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index d48069ee84c2..620794a20a33 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -1547,10 +1547,56 @@ int cgroup_show_path(struct seq_file *sf, struct kernfs_node *kf_node,
return len;
}
+static int parse_cgroup_root_flags(char *data, unsigned int *root_flags)
+{
+ char *token;
+
+ *root_flags = 0;
+
+ if (!data)
+ return 0;
+
+ while ((token = strsep(&data, ",")) != NULL) {
+ if (!strcmp(token, "nsdelegate")) {
+ *root_flags |= CGRP_ROOT_NS_DELEGATE;
+ continue;
+ }
+
+ pr_err("cgroup2: unknown option \"%s\"\n", token);
+ return -EINVAL;
+ }
+
+ return 0;
+}
+
+static void apply_cgroup_root_flags(unsigned int root_flags)
+{
+ if (current->nsproxy->cgroup_ns == &init_cgroup_ns) {
+ if (root_flags & CGRP_ROOT_NS_DELEGATE)
+ cgrp_dfl_root.flags |= CGRP_ROOT_NS_DELEGATE;
+ else
+ cgrp_dfl_root.flags &= ~CGRP_ROOT_NS_DELEGATE;
+ }
+}
+
+static int cgroup_show_options(struct seq_file *seq, struct kernfs_root *kf_root)
+{
+ if (cgrp_dfl_root.flags & CGRP_ROOT_NS_DELEGATE)
+ seq_puts(seq, ",nsdelegate");
+ return 0;
+}
+
static int cgroup_remount(struct kernfs_root *kf_root, int *flags, char *data)
{
- pr_err("remount is not allowed\n");
- return -EINVAL;
+ unsigned int root_flags;
+ int ret;
+
+ ret = parse_cgroup_root_flags(data, &root_flags);
+ if (ret)
+ return ret;
+
+ apply_cgroup_root_flags(root_flags);
+ return 0;
}
/*
@@ -1790,6 +1836,7 @@ static struct dentry *cgroup_mount(struct file_system_type *fs_type,
{
struct cgroup_namespace *ns = current->nsproxy->cgroup_ns;
struct dentry *dentry;
+ int ret;
get_cgroup_ns(ns);
@@ -1807,16 +1854,21 @@ static struct dentry *cgroup_mount(struct file_system_type *fs_type,
cgroup_enable_task_cg_lists();
if (fs_type == &cgroup2_fs_type) {
- if (data) {
- pr_err("cgroup2: unknown option \"%s\"\n", (char *)data);
+ unsigned int root_flags;
+
+ ret = parse_cgroup_root_flags(data, &root_flags);
+ if (ret) {
put_cgroup_ns(ns);
- return ERR_PTR(-EINVAL);
+ return ERR_PTR(ret);
}
+
cgrp_dfl_visible = true;
cgroup_get_live(&cgrp_dfl_root.cgrp);
dentry = cgroup_do_mount(&cgroup2_fs_type, flags, &cgrp_dfl_root,
CGROUP2_SUPER_MAGIC, ns);
+ if (!IS_ERR(dentry))
+ apply_cgroup_root_flags(root_flags);
} else {
dentry = cgroup1_mount(&cgroup_fs_type, flags, data,
CGROUP_SUPER_MAGIC, ns);
@@ -2364,6 +2416,8 @@ static int cgroup_procs_write_permission(struct task_struct *task,
struct kernfs_open_file *of)
{
struct super_block *sb = of->file->f_path.dentry->d_sb;
+ struct cgroup_namespace *ns = current->nsproxy->cgroup_ns;
+ struct cgroup *root_cgrp = ns->root_cset->dfl_cgrp;
struct cgroup *src_cgrp, *com_cgrp;
struct inode *inode;
int ret;
@@ -2407,6 +2461,15 @@ static int cgroup_procs_write_permission(struct task_struct *task,
if (ret)
return ret;
+ /*
+ * If namespaces are delegation boundaries, %current must be able
+ * to see both source and destination cgroups from its namespace.
+ */
+ if ((cgrp_dfl_root.flags & CGRP_ROOT_NS_DELEGATE) &&
+ (!cgroup_is_descendant(src_cgrp, root_cgrp) ||
+ !cgroup_is_descendant(dst_cgrp, root_cgrp)))
+ return -ENOENT;
+
return 0;
}
@@ -2971,11 +3034,23 @@ static void cgroup_file_release(struct kernfs_open_file *of)
static ssize_t cgroup_file_write(struct kernfs_open_file *of, char *buf,
size_t nbytes, loff_t off)
{
+ struct cgroup_namespace *ns = current->nsproxy->cgroup_ns;
struct cgroup *cgrp = of->kn->parent->priv;
struct cftype *cft = of->kn->priv;
struct cgroup_subsys_state *css;
int ret;
+ /*
+ * If namespaces are delegation boundaries, disallow writes to
+ * files in an non-init namespace root from inside the namespace
+ * except for the files explicitly marked delegatable -
+ * cgroup.procs and cgroup.subtree_control.
+ */
+ if ((cgrp->root->flags & CGRP_ROOT_NS_DELEGATE) &&
+ !(cft->flags & CFTYPE_NS_DELEGATABLE) &&
+ ns != &init_cgroup_ns && ns->root_cset->dfl_cgrp == cgrp)
+ return -EPERM;
+
if (cft->write)
return cft->write(of, buf, nbytes, off);
@@ -3809,6 +3884,7 @@ static int cgroup_procs_show(struct seq_file *s, void *v)
static struct cftype cgroup_base_files[] = {
{
.name = "cgroup.procs",
+ .flags = CFTYPE_NS_DELEGATABLE,
.file_offset = offsetof(struct cgroup, procs_file),
.release = cgroup_procs_release,
.seq_start = cgroup_procs_start,
@@ -3822,6 +3898,7 @@ static struct cftype cgroup_base_files[] = {
},
{
.name = "cgroup.subtree_control",
+ .flags = CFTYPE_NS_DELEGATABLE,
.seq_show = cgroup_subtree_control_show,
.write = cgroup_subtree_control_write,
},
@@ -4410,6 +4487,7 @@ int cgroup_rmdir(struct kernfs_node *kn)
}
static struct kernfs_syscall_ops cgroup_kf_syscall_ops = {
+ .show_options = cgroup_show_options,
.remount_fs = cgroup_remount,
.mkdir = cgroup_mkdir,
.rmdir = cgroup_rmdir,