2 files changed, 36 insertions, 0 deletions

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index a20320c666fd..984f73b719a9 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -87,6 +87,7 @@ struct cgroup_subsys_state *css_tryget_online_from_dir(struct dentry *dentry,
                                                        struct cgroup_subsys *ss);
 
 struct cgroup *cgroup_get_from_path(const char *path);
+struct cgroup *cgroup_get_from_fd(int fd);
 
 int cgroup_attach_task_all(struct task_struct *from, struct task_struct *);
 int cgroup_transfer_tasks(struct cgroup *to, struct cgroup *from);
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 75c0ff00aca6..50787cd61da2 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -62,6 +62,7 @@
 #include <linux/proc_ns.h>
 #include <linux/nsproxy.h>
 #include <linux/proc_ns.h>
+#include <linux/file.h>
 #include <net/sock.h>
 
 /*
@@ -6209,6 +6210,40 @@ struct cgroup *cgroup_get_from_path(const char *path)
 }
 EXPORT_SYMBOL_GPL(cgroup_get_from_path);
 
+/**
+ * cgroup_get_from_fd - get a cgroup pointer from a fd
+ * @fd: fd obtained by open(cgroup2_dir)
+ *
+ * Find the cgroup from a fd which should be obtained
+ * by opening a cgroup directory.  Returns a pointer to the
+ * cgroup on success. ERR_PTR is returned if the cgroup
+ * cannot be found.
+ */
+struct cgroup *cgroup_get_from_fd(int fd)
+{
+        struct cgroup_subsys_state *css;
+        struct cgroup *cgrp;
+        struct file *f;
+
+        f = fget_raw(fd);
+        if (!f)
+                return ERR_PTR(-EBADF);
+
+        css = css_tryget_online_from_dir(f->f_path.dentry, NULL);
+        fput(f);
+        if (IS_ERR(css))
+                return ERR_CAST(css);
+
+        cgrp = css->cgroup;
+        if (!cgroup_on_dfl(cgrp)) {
+                cgroup_put(cgrp);
+                return ERR_PTR(-EBADF);
+        }
+
+        return cgrp;
+}
+EXPORT_SYMBOL_GPL(cgroup_get_from_fd);
+
 /*
  * sock->sk_cgrp_data handling.  For more info, see sock_cgroup_data
  * definition in cgroup-defs.h.