[PATCH bpf-next v8 5/8] bpf: Add bpf_list_add_impl to insert node after a given list node

Chengkaitao
2026-03-16T11:29:31Z

From: Kaitao Cheng <chengkaitao@kylinos.cn>

Add a new kfunc bpf_list_add_impl(head, new, prev, meta, off) that
inserts 'new' after 'prev' in the BPF linked list. Both must be in
the same list; 'prev' must already be in the list. The new node must
be an owning reference (e.g. from bpf_obj_new); the kfunc consumes
that reference and the node becomes non-owning once inserted.

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

Returns 0 on success, -EINVAL if 'prev' is not in a list or 'new'
is already in a list (or duplicate insertion). On failure, the
kernel drops the passed-in node.

Signed-off-by: Kaitao Cheng <chengkaitao@kylinos.cn>
---
kernel/bpf/helpers.c | 14 ++++++++++++++
kernel/bpf/verifier.c | 13 +++++++++++--
2 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index a9665f97b3bc..dc4f8b4eec01 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -2438,6 +2438,19 @@ __bpf_kfunc int bpf_list_push_back_impl(struct bpf_list_head *head,
return __bpf_list_add(new, head, &h->prev, meta ? meta->record : NULL, off);
}

+__bpf_kfunc int bpf_list_add_impl(struct bpf_list_head *head,
+ struct bpf_list_node *new,
+ struct bpf_list_node *prev,
+ void *meta__ign, u64 off)
+{
+ struct bpf_list_node_kern *kn = (void *)new, *kp = (void *)prev;
+ struct btf_struct_meta *meta = meta__ign;
+ struct list_head *prev_ptr = &kp->list_head;
+
+ return __bpf_list_add(kn, head, &prev_ptr,
+ meta ? meta->record : NULL, off);
+}
+
static struct bpf_list_node *__bpf_list_del(struct bpf_list_head *head,
struct list_head *n)
{
@@ -4574,6 +4587,7 @@ 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_list_add_impl)
BTF_ID_FLAGS(func, bpf_task_acquire, KF_ACQUIRE | KF_RCU | KF_RET_NULL)
BTF_ID_FLAGS(func, bpf_task_release, KF_RELEASE)
BTF_ID_FLAGS(func, bpf_rbtree_remove, KF_ACQUIRE | KF_RET_NULL)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index e928ad4290c7..98ddb370feb5 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -12506,6 +12506,7 @@ enum special_kfunc_type {
KF_bpf_refcount_acquire_impl,
KF_bpf_list_push_front_impl,
KF_bpf_list_push_back_impl,
+ KF_bpf_list_add_impl,
KF_bpf_list_pop_front,
KF_bpf_list_pop_back,
KF_bpf_list_del,
@@ -12567,6 +12568,7 @@ BTF_ID(func, bpf_obj_drop_impl)
BTF_ID(func, bpf_refcount_acquire_impl)
BTF_ID(func, bpf_list_push_front_impl)
BTF_ID(func, bpf_list_push_back_impl)
+BTF_ID(func, bpf_list_add_impl)
BTF_ID(func, bpf_list_pop_front)
BTF_ID(func, bpf_list_pop_back)
BTF_ID(func, bpf_list_del)
@@ -12644,6 +12646,7 @@ BTF_ID(func, bpf_stream_print_stack)
static const enum special_kfunc_type bpf_list_api_kfuncs[] = {
KF_bpf_list_push_front_impl,
KF_bpf_list_push_back_impl,
+ KF_bpf_list_add_impl,
KF_bpf_list_pop_front,
KF_bpf_list_pop_back,
KF_bpf_list_del,
@@ -12655,6 +12658,7 @@ 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_add_impl,
KF_bpf_list_del,
};

@@ -14345,6 +14349,7 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,

if (meta.func_id == special_kfunc_list[KF_bpf_list_push_front_impl] ||
meta.func_id == special_kfunc_list[KF_bpf_list_push_back_impl] ||
+ meta.func_id == special_kfunc_list[KF_bpf_list_add_impl] ||
meta.func_id == special_kfunc_list[KF_bpf_rbtree_add_impl]) {
release_ref_obj_id = regs[BPF_REG_2].ref_obj_id;
insn_aux->insert_off = regs[BPF_REG_2].var_off.value;
@@ -23357,13 +23362,17 @@ static int fixup_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
*cnt = 3;
} else if (desc->func_id == special_kfunc_list[KF_bpf_list_push_back_impl] ||
desc->func_id == special_kfunc_list[KF_bpf_list_push_front_impl] ||
+ desc->func_id == special_kfunc_list[KF_bpf_list_add_impl] ||
desc->func_id == special_kfunc_list[KF_bpf_rbtree_add_impl]) {
struct btf_struct_meta *kptr_struct_meta = env->insn_aux_data[insn_idx].kptr_struct_meta;
int struct_meta_reg = BPF_REG_3;
int node_offset_reg = BPF_REG_4;

- /* rbtree_add has extra 'less' arg, so args-to-fixup are in diff regs */
- if (desc->func_id == special_kfunc_list[KF_bpf_rbtree_add_impl]) {
+ /* list/rbtree_add_impl have an extra arg (prev/less),
+ * so args-to-fixup are in different regs.
+ */
+ if (desc->func_id == special_kfunc_list[KF_bpf_list_add_impl] ||
+ desc->func_id == special_kfunc_list[KF_bpf_rbtree_add_impl]) {
struct_meta_reg = BPF_REG_4;
node_offset_reg = BPF_REG_5;
}
--
2.50.1 (Apple Git-155)