cgroup/bpf: only cgroup v2 can be attached by bpf programs

[ Upstream commit 2190df6 ]

Only cgroup v2 can be attached by bpf programs, so this patch introduces
that cgroup_bpf_inherit and cgroup_bpf_offline can only be called in
cgroup v2, and this can fix the memleak mentioned by commit 04f8ef5
("cgroup: Fix memory leak caused by missing cgroup_bpf_offline"), which
has been reverted.

Fixes: 2b0d3d3 ("percpu_ref: reduce memory footprint of percpu_ref in fast path")
Fixes: 4bfc0bb ("bpf: decouple the lifetime of cgroup_bpf from cgroup itself")
Link: https://lore.kernel.org/cgroups/aka2hk5jsel5zomucpwlxsej6iwnfw4qu5jkrmjhyfhesjlfdw@46zxhg5bdnr7/
Signed-off-by: Chen Ridong <chenridong@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: Chen Ridong

kernel/cgroup/cgroup.c

@@ -2140,8 +2140,10 @@ int cgroup_setup_root(struct cgroup_root *root, u16 ss_mask)
 	if (ret)
 		goto exit_stats;
 
-	ret = cgroup_bpf_inherit(root_cgrp);
-	WARN_ON_ONCE(ret);
+	if (root == &cgrp_dfl_root) {
+		ret = cgroup_bpf_inherit(root_cgrp);
+		WARN_ON_ONCE(ret);
+	}
 
 	trace_cgroup_setup_root(root);
 
@@ -5708,9 +5710,11 @@ static struct cgroup *cgroup_create(struct cgroup *parent, const char *name,
 	if (ret)
 		goto out_kernfs_remove;
 
-	ret = cgroup_bpf_inherit(cgrp);
-	if (ret)
-		goto out_psi_free;
+	if (cgrp->root == &cgrp_dfl_root) {
+		ret = cgroup_bpf_inherit(cgrp);
+		if (ret)
+			goto out_psi_free;
+	}
 
 	/*
 	 * New cgroup inherits effective freeze counter, and
@@ -6024,7 +6028,8 @@ static int cgroup_destroy_locked(struct cgroup *cgrp)
 
 	cgroup1_check_for_release(parent);
 
-	cgroup_bpf_offline(cgrp);
+	if (cgrp->root == &cgrp_dfl_root)
+		cgroup_bpf_offline(cgrp);
 
 	/* put the base reference */
 	percpu_ref_kill(&cgrp->self.refcnt);