Mark struct cgroup_subsys_state->cgroup as safe under RCU read lock. This
will enable accessing css->cgroup from a bpf css iterator.

Signed-off-by: Song Liu <song@kernel.org>
---
 kernel/bpf/verifier.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 279a64933262..e2f53dc8766a 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -7058,6 +7058,10 @@ BTF_TYPE_SAFE_RCU(struct css_set) {
 	struct cgroup *dfl_cgrp;
 };
 
+BTF_TYPE_SAFE_RCU(struct cgroup_subsys_state) {
+	struct cgroup *cgroup;
+};
+
 /* RCU trusted: these fields are trusted in RCU CS and can be NULL */
 BTF_TYPE_SAFE_RCU_OR_NULL(struct mm_struct) {
 	struct file __rcu *exe_file;
@@ -7108,6 +7112,7 @@ static bool type_is_rcu(struct bpf_verifier_env *env,
 	BTF_TYPE_EMIT(BTF_TYPE_SAFE_RCU(struct task_struct));
 	BTF_TYPE_EMIT(BTF_TYPE_SAFE_RCU(struct cgroup));
 	BTF_TYPE_EMIT(BTF_TYPE_SAFE_RCU(struct css_set));
+	BTF_TYPE_EMIT(BTF_TYPE_SAFE_RCU(struct cgroup_subsys_state));
 
 	return btf_nested_type_is_trusted(&env->log, reg, field_name, btf_id, "__safe_rcu");
 }
-- 
2.47.1

On Thu, Jun 19, 2025 at 03:01:12PM -0700, Song Liu wrote:
> Mark struct cgroup_subsys_state->cgroup as safe under RCU read lock. This
> will enable accessing css->cgroup from a bpf css iterator.
> 
> Signed-off-by: Song Liu <song@kernel.org>

Acked-by: Tejun Heo <tj@kernel.org>

Thanks.

-- 
tejun