[PATCH bpf-next v10 5/8] bpf: Add bpf_list_add to insert node after a given list node

Kaitao cheng
2026-04-27T16:59:43Z

From: Kaitao Cheng <chengkaitao@kylinos.cn>

Add a new kfunc bpf_list_add(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, 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 | 11 +++++++++++
kernel/bpf/verifier.c | 12 +++++++++---
2 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 5388078f3171..2b8e8d4284a5 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -2570,6 +2570,16 @@ __bpf_kfunc int bpf_list_push_back_impl(struct bpf_list_head *head,
return bpf_list_push_back(head, node, meta__ign, off);
}

+__bpf_kfunc int bpf_list_add(struct bpf_list_head *head, struct bpf_list_node *new,
+ struct bpf_list_node *prev, struct btf_struct_meta *meta,
+ u64 off)
+{
+ struct bpf_list_node_kern *n = (void *)new, *p = (void *)prev;
+ struct list_head *prev_ptr = &p->list_head;
+
+ return __bpf_list_add(n, 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)
{
@@ -4748,6 +4758,7 @@ BTF_ID_FLAGS(func, bpf_list_push_front, KF_IMPLICIT_ARGS)
BTF_ID_FLAGS(func, bpf_list_push_front_impl)
BTF_ID_FLAGS(func, bpf_list_push_back, KF_IMPLICIT_ARGS)
BTF_ID_FLAGS(func, bpf_list_push_back_impl)
+BTF_ID_FLAGS(func, bpf_list_add, KF_IMPLICIT_ARGS)
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)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 3c0e0076bd69..50f8732aa065 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -10742,6 +10742,7 @@ enum special_kfunc_type {
KF_bpf_list_push_front,
KF_bpf_list_push_back_impl,
KF_bpf_list_push_back,
+ KF_bpf_list_add,
KF_bpf_list_pop_front,
KF_bpf_list_pop_back,
KF_bpf_list_del,
@@ -10811,6 +10812,7 @@ BTF_ID(func, bpf_list_push_front_impl)
BTF_ID(func, bpf_list_push_front)
BTF_ID(func, bpf_list_push_back_impl)
BTF_ID(func, bpf_list_push_back)
+BTF_ID(func, bpf_list_add)
BTF_ID(func, bpf_list_pop_front)
BTF_ID(func, bpf_list_pop_back)
BTF_ID(func, bpf_list_del)
@@ -10923,7 +10925,8 @@ static bool is_bpf_list_push_kfunc(u32 func_id)
return func_id == special_kfunc_list[KF_bpf_list_push_front] ||
func_id == special_kfunc_list[KF_bpf_list_push_front_impl] ||
func_id == special_kfunc_list[KF_bpf_list_push_back] ||
- func_id == special_kfunc_list[KF_bpf_list_push_back_impl];
+ func_id == special_kfunc_list[KF_bpf_list_push_back_impl] ||
+ func_id == special_kfunc_list[KF_bpf_list_add];
}

static bool is_bpf_rbtree_add_kfunc(u32 func_id)
@@ -19228,8 +19231,11 @@ int bpf_fixup_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
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 (is_bpf_rbtree_add_kfunc(desc->func_id)) {
+ /* list_add/rbtree_add have an extra arg (prev/less),
+ * so args-to-fixup are in diff regs.
+ */
+ if (desc->func_id == special_kfunc_list[KF_bpf_list_add] ||
+ is_bpf_rbtree_add_kfunc(desc->func_id)) {
struct_meta_reg = BPF_REG_4;
node_offset_reg = BPF_REG_5;
}
--
2.50.1 (Apple Git-155)