1 files changed, 80 insertions, 0 deletions
diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
index c24029937431..80676fc00d81 100644
--- a/kernel/bpf/cgroup.c
+++ b/kernel/bpf/cgroup.c
@@ -500,6 +500,86 @@ cleanup:
 	return err;
 }
 
+/* Swap updated BPF program for given link in effective program arrays across
+ * all descendant cgroups. This function is guaranteed to succeed.
+ */
+static void replace_effective_prog(struct cgroup *cgrp,
+				   enum bpf_attach_type type,
+				   struct bpf_cgroup_link *link)
+{
+	struct bpf_prog_array_item *item;
+	struct cgroup_subsys_state *css;
+	struct bpf_prog_array *progs;
+	struct bpf_prog_list *pl;
+	struct list_head *head;
+	struct cgroup *cg;
+	int pos;
+
+	css_for_each_descendant_pre(css, &cgrp->self) {
+		struct cgroup *desc = container_of(css, struct cgroup, self);
+
+		if (percpu_ref_is_zero(&desc->bpf.refcnt))
+			continue;
+
+		/* find position of link in effective progs array */
+		for (pos = 0, cg = desc; cg; cg = cgroup_parent(cg)) {
+			if (pos && !(cg->bpf.flags[type] & BPF_F_ALLOW_MULTI))
+				continue;
+
+			head = &cg->bpf.progs[type];
+			list_for_each_entry(pl, head, node) {
+				if (!prog_list_prog(pl))
+					continue;
+				if (pl->link == link)
+					goto found;
+				pos++;
+			}
+		}
+found:
+		BUG_ON(!cg);
+		progs = rcu_dereference_protected(
+				desc->bpf.effective[type],
+				lockdep_is_held(&cgroup_mutex));
+		item = &progs->items[pos];
+		WRITE_ONCE(item->prog, link->link.prog);
+	}
+}
+
+/**
+ * __cgroup_bpf_replace() - Replace link's program and propagate the change
+ *                          to descendants
+ * @cgrp: The cgroup which descendants to traverse
+ * @link: A link for which to replace BPF program
+ * @type: Type of attach operation
+ *
+ * Must be called with cgroup_mutex held.
+ */
+int __cgroup_bpf_replace(struct cgroup *cgrp, struct bpf_cgroup_link *link,
+			 struct bpf_prog *new_prog)
+{
+	struct list_head *progs = &cgrp->bpf.progs[link->type];
+	struct bpf_prog *old_prog;
+	struct bpf_prog_list *pl;
+	bool found = false;
+
+	if (link->link.prog->type != new_prog->type)
+		return -EINVAL;
+
+	list_for_each_entry(pl, progs, node) {
+		if (pl->link == link) {
+			found = true;
+			break;
+		}
+	}
+	if (!found)
+		return -ENOENT;
+
+	old_prog = xchg(&link->link.prog, new_prog);
+	replace_effective_prog(cgrp, link->type, link);
+	bpf_prog_put(old_prog);
+	return 0;
+}
+
 static struct bpf_prog_list *find_detach_entry(struct list_head *progs,
 					       struct bpf_prog *prog,
 					       struct bpf_cgroup_link *link,