[PATCH bpf-next v8 3/8] bpf: Introduce the bpf_list_del kfunc.

Chengkaitao
2026-03-16T11:29:17Z

From: Kaitao Cheng <chengkaitao@kylinos.cn>

If a user holds ownership of a node in the middle of a list, they
can directly remove it from the list without strictly adhering to
deletion rules from the head or tail.

We have added an additional parameter bpf_list_head *head to
bpf_list_del, as the verifier requires the head parameter to
check whether the lock is being held.

This is typically paired with bpf_refcount. After calling
bpf_list_del, it is generally necessary to drop the reference to
the list node twice to prevent reference count leaks.

Signed-off-by: Kaitao Cheng <chengkaitao@kylinos.cn>
---
kernel/bpf/helpers.c | 11 +++++++++++
kernel/bpf/verifier.c | 4 ++++
2 files changed, 15 insertions(+)

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index e87b263c5fe6..dac346eb1e2f 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -2437,6 +2437,8 @@ static struct bpf_list_node *__bpf_list_del(struct bpf_list_head *head,
*/
if (unlikely(!h->next))
INIT_LIST_HEAD(h);
+
+ /* verifier to guarantee n is a list node rather than the head */
if (list_empty(h))
return NULL;

@@ -2463,6 +2465,14 @@ __bpf_kfunc struct bpf_list_node *bpf_list_pop_back(struct bpf_list_head *head)
return __bpf_list_del(head, h->prev);
}

+__bpf_kfunc struct bpf_list_node *bpf_list_del(struct bpf_list_head *head,
+ struct bpf_list_node *node)
+{
+ struct bpf_list_node_kern *kn = (void *)node;
+
+ return __bpf_list_del(head, &kn->list_head);
+}
+
__bpf_kfunc struct bpf_list_node *bpf_list_front(struct bpf_list_head *head)
{
struct list_head *h = (struct list_head *)head;
@@ -4549,6 +4559,7 @@ BTF_ID_FLAGS(func, bpf_list_push_front_impl)
BTF_ID_FLAGS(func, bpf_list_push_back_impl)
BTF_ID_FLAGS(func, bpf_list_pop_front, KF_ACQUIRE | KF_RET_NULL)
BTF_ID_FLAGS(func, bpf_list_pop_back, KF_ACQUIRE | KF_RET_NULL)
+BTF_ID_FLAGS(func, bpf_list_del, KF_ACQUIRE | KF_RET_NULL)
BTF_ID_FLAGS(func, bpf_list_front, KF_RET_NULL)
BTF_ID_FLAGS(func, bpf_list_back, KF_RET_NULL)
BTF_ID_FLAGS(func, bpf_task_acquire, KF_ACQUIRE | KF_RCU | KF_RET_NULL)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 64c1f8343dfa..e928ad4290c7 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -12508,6 +12508,7 @@ enum special_kfunc_type {
KF_bpf_list_push_back_impl,
KF_bpf_list_pop_front,
KF_bpf_list_pop_back,
+ KF_bpf_list_del,
KF_bpf_list_front,
KF_bpf_list_back,
KF_bpf_cast_to_kern_ctx,
@@ -12568,6 +12569,7 @@ BTF_ID(func, bpf_list_push_front_impl)
BTF_ID(func, bpf_list_push_back_impl)
BTF_ID(func, bpf_list_pop_front)
BTF_ID(func, bpf_list_pop_back)
+BTF_ID(func, bpf_list_del)
BTF_ID(func, bpf_list_front)
BTF_ID(func, bpf_list_back)
BTF_ID(func, bpf_cast_to_kern_ctx)
@@ -12644,6 +12646,7 @@ static const enum special_kfunc_type bpf_list_api_kfuncs[] = {
KF_bpf_list_push_back_impl,
KF_bpf_list_pop_front,
KF_bpf_list_pop_back,
+ KF_bpf_list_del,
KF_bpf_list_front,
KF_bpf_list_back,
};
@@ -12652,6 +12655,7 @@ static const enum special_kfunc_type bpf_list_api_kfuncs[] = {
static const enum special_kfunc_type bpf_list_node_api_kfuncs[] = {
KF_bpf_list_push_front_impl,
KF_bpf_list_push_back_impl,
+ KF_bpf_list_del,
};

/* Kfuncs that take an rbtree node argument (bpf_rb_node *). */
--
2.50.1 (Apple Git-155)