1 files changed, 57 insertions, 2 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 470f6536b9e8..a57b7c86871c 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2663,6 +2663,45 @@ static int cgroup_attach_task(struct cgroup *dst_cgrp,
 	return ret;
 }
 
+int subsys_cgroup_allow_attach(struct cgroup_taskset *tset)
+{
+	const struct cred *cred = current_cred(), *tcred;
+	struct task_struct *task;
+	struct cgroup_subsys_state *css;
+
+	if (capable(CAP_SYS_NICE))
+		return 0;
+
+	cgroup_taskset_for_each(task, css, tset) {
+		tcred = __task_cred(task);
+
+		if (current != task && !uid_eq(cred->euid, tcred->uid) &&
+		    !uid_eq(cred->euid, tcred->suid))
+			return -EACCES;
+	}
+
+	return 0;
+}
+
+static int cgroup_allow_attach(struct cgroup *cgrp, struct cgroup_taskset *tset)
+{
+	struct cgroup_subsys_state *css;
+	int i;
+	int ret;
+
+	for_each_css(css, i, cgrp) {
+		if (css->ss->allow_attach) {
+			ret = css->ss->allow_attach(tset);
+			if (ret)
+				return ret;
+		} else {
+			return -EACCES;
+		}
+	}
+
+	return 0;
+}
+
 static int cgroup_procs_write_permission(struct task_struct *task,
 					 struct cgroup *dst_cgrp,
 					 struct kernfs_open_file *of)
@@ -2677,8 +2716,24 @@ static int cgroup_procs_write_permission(struct task_struct *task,
 	 */
 	if (!uid_eq(cred->euid, GLOBAL_ROOT_UID) &&
 	    !uid_eq(cred->euid, tcred->uid) &&
-	    !uid_eq(cred->euid, tcred->suid))
-		ret = -EACCES;
+	    !uid_eq(cred->euid, tcred->suid)) {
+		/*
+		 * if the default permission check fails, give each
+		 * cgroup a chance to extend the permission check
+		 */
+		struct cgroup_taskset tset = {
+			.src_csets = LIST_HEAD_INIT(tset.src_csets),
+			.dst_csets = LIST_HEAD_INIT(tset.dst_csets),
+			.csets = &tset.src_csets,
+		};
+		struct css_set *cset;
+		cset = task_css_set(task);
+		list_add(&cset->mg_node, &tset.src_csets);
+		ret = cgroup_allow_attach(dst_cgrp, &tset);
+		list_del(&tset.src_csets);
+		if (ret)
+			ret = -EACCES;
+	}
 
 	if (!ret && cgroup_on_dfl(dst_cgrp)) {
 		struct super_block *sb = of->file->f_path.dentry->d_sb;