On Wed, 4 Mar 2026 at 15:50, Chengkaitao <[email protected]> wrote:
>
> From: Kaitao Cheng <[email protected]>
>
> 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 <[email protected]>
> ---
> kernel/bpf/helpers.c | 27 +++++++++++++++++++++++++++
> kernel/bpf/verifier.c | 6 +++++-
> 2 files changed, 32 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> index 6eb6c82ed2ee..cc1a096a1f64 100644
> --- a/kernel/bpf/helpers.c
> +++ b/kernel/bpf/helpers.c
> @@ -2459,6 +2459,32 @@ __bpf_kfunc struct bpf_list_node
> *bpf_list_pop_back(struct bpf_list_head *head)
> return __bpf_list_del(head, true);
> }
>
> +__bpf_kfunc struct bpf_list_node *bpf_list_del(struct bpf_list_head *head,
> + struct bpf_list_node *node)
> +{
> + struct bpf_list_node_kern *knode = (struct bpf_list_node_kern *)node;
> + struct list_head *h = (void *)head;
> +
> + /* If list_head was 0-initialized by map, bpf_obj_init_field wasn't
> + * called on its fields, so init here
> + */
> + if (unlikely(!h->next)) {
> + INIT_LIST_HEAD(h);
> + return NULL;
> + }
nit: I would avoid doing this here, just for symmetry.
If we are part of the list after the owner checks, this should be
initialized correctly anyway.
> +
> + if (unlikely(!knode))
> + return NULL;
nit: It seems like node can't (shouldn't) be NULL, so we can lose this check.
> +
> + if (WARN_ON_ONCE(READ_ONCE(knode->owner) != head))
> + return NULL;
> +
> + list_del_init(&knode->list_head);
> + WRITE_ONCE(knode->owner, NULL);
> +
> + return node;
> +}
> +
> __bpf_kfunc struct bpf_list_node *bpf_list_front(struct bpf_list_head *head)
> {
> struct list_head *h = (struct list_head *)head;
> @@ -4545,6 +4571,7 @@ 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 67c09b43a497..c9557d3fb8dd 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -12461,6 +12461,7 @@ 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,
> @@ -12521,6 +12522,7 @@ 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)
> @@ -12996,6 +12998,7 @@ static bool is_bpf_list_api_kfunc(u32 btf_id)
> btf_id == special_kfunc_list[KF_bpf_list_push_back_impl] ||
> btf_id == special_kfunc_list[KF_bpf_list_pop_front] ||
> btf_id == special_kfunc_list[KF_bpf_list_pop_back] ||
> + btf_id == special_kfunc_list[KF_bpf_list_del] ||
> btf_id == special_kfunc_list[KF_bpf_list_front] ||
> btf_id == special_kfunc_list[KF_bpf_list_back];
> }
> @@ -13118,7 +13121,8 @@ static bool check_kfunc_is_graph_node_api(struct
> bpf_verifier_env *env,
> switch (node_field_type) {
> case BPF_LIST_NODE:
> ret = (kfunc_btf_id ==
> special_kfunc_list[KF_bpf_list_push_front_impl] ||
> - kfunc_btf_id ==
> special_kfunc_list[KF_bpf_list_push_back_impl]);
> + kfunc_btf_id ==
> special_kfunc_list[KF_bpf_list_push_back_impl] ||
> + kfunc_btf_id == special_kfunc_list[KF_bpf_list_del]);
> break;
> case BPF_RB_NODE:
> ret = (kfunc_btf_id ==
> special_kfunc_list[KF_bpf_rbtree_remove] ||
> --
> 2.50.1 (Apple Git-155)
>
>
