On 8/3/26 21:46, Chengkaitao 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 | 30 +++++++++++++++++++++++-------
> kernel/bpf/verifier.c | 6 +++++-
> 2 files changed, 28 insertions(+), 8 deletions(-)
>
> diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> index 6eb6c82ed2ee..01b74c4ac00d 100644
> --- a/kernel/bpf/helpers.c
> +++ b/kernel/bpf/helpers.c
> @@ -2426,20 +2426,23 @@ __bpf_kfunc int bpf_list_push_back_impl(struct
> bpf_list_head *head,
> return __bpf_list_add(n, head, true, meta ? meta->record : NULL, off);
> }
>
> -static struct bpf_list_node *__bpf_list_del(struct bpf_list_head *head, bool
> tail)
> +static struct bpf_list_node *__bpf_list_del(struct bpf_list_head *head,
> + struct list_head *n)
> {
> - struct list_head *n, *h = (void *)head;
> + struct list_head *h = (void *)head;
> struct bpf_list_node_kern *node;
>
> /* 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))
> + if (unlikely(!h->next)) {
> INIT_LIST_HEAD(h);
> - if (list_empty(h))
> + return NULL;
> + }
> +
> + if (n == h)
> return NULL;
>
> - n = tail ? h->prev : h->next;
> node = container_of(n, struct bpf_list_node_kern, list_head);
> if (WARN_ON_ONCE(READ_ONCE(node->owner) != head))
> return NULL;
This refactoring is worth, because the "struct list_head *n" seems
better than "bool tail".
But, such refactoring should be a preparatory patch. Importantly,
refactoring should not introduce functional changes.
Thanks,
Leon
> @@ -2451,12 +2454,24 @@ static struct bpf_list_node *__bpf_list_del(struct
> bpf_list_head *head, bool tai
>
> __bpf_kfunc struct bpf_list_node *bpf_list_pop_front(struct bpf_list_head
> *head)
> {
> - return __bpf_list_del(head, false);
> + struct list_head *h = (void *)head;
> +
> + return __bpf_list_del(head, h->next);
> }
>
> __bpf_kfunc struct bpf_list_node *bpf_list_pop_back(struct bpf_list_head
> *head)
> {
> - return __bpf_list_del(head, true);
> + struct list_head *h = (void *)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)
> @@ -4545,6 +4560,7 @@ 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]
> ||
