[PATCH bpf-next v7 2/5] bpf: Add bpf_list_add_impl to insert node after a given list node
From: Chengkaitao
Date: Sun Mar 08 2026 - 09:47:07 EST
From: Kaitao Cheng <chengkaitao@xxxxxxxxxx>
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@xxxxxxxxxx>
---
kernel/bpf/helpers.c | 56 ++++++++++++++++++++++++++++++-------------
kernel/bpf/verifier.c | 13 ++++++++--
2 files changed, 50 insertions(+), 19 deletions(-)
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 01b74c4ac00d..407520fde668 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -2379,11 +2379,12 @@ __bpf_kfunc void *bpf_refcount_acquire_impl(void *p__refcounted_kptr, void *meta
return (void *)p__refcounted_kptr;
}
-static int __bpf_list_add(struct bpf_list_node_kern *node,
- struct bpf_list_head *head,
- bool tail, struct btf_record *rec, u64 off)
+static int __bpf_list_add(struct bpf_list_head *head,
+ struct bpf_list_node_kern *new,
+ struct list_head *prev,
+ struct btf_record *rec, u64 off)
{
- struct list_head *n = &node->list_head, *h = (void *)head;
+ struct list_head *n = &new->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
@@ -2391,39 +2392,59 @@ static int __bpf_list_add(struct bpf_list_node_kern *node,
if (unlikely(!h->next))
INIT_LIST_HEAD(h);
- /* node->owner != NULL implies !list_empty(n), no need to separately
+ /* When prev is not the list head, it must be a node in this list. */
+ if (prev != h && WARN_ON_ONCE(READ_ONCE(container_of(
+ prev, struct bpf_list_node_kern, list_head)->owner) != head))
+ goto fail;
+
+ /* new->owner != NULL implies !list_empty(n), no need to separately
* check the latter
*/
- if (cmpxchg(&node->owner, NULL, BPF_PTR_POISON)) {
- /* Only called from BPF prog, no need to migrate_disable */
- __bpf_obj_drop_impl((void *)n - off, rec, false);
- return -EINVAL;
- }
-
- tail ? list_add_tail(n, h) : list_add(n, h);
- WRITE_ONCE(node->owner, head);
+ if (cmpxchg(&new->owner, NULL, BPF_PTR_POISON))
+ goto fail;
+ list_add(n, prev);
+ WRITE_ONCE(new->owner, head);
return 0;
+
+fail:
+ /* Only called from BPF prog, no need to migrate_disable */
+ __bpf_obj_drop_impl((void *)n - off, rec, false);
+ return -EINVAL;
}
__bpf_kfunc int bpf_list_push_front_impl(struct bpf_list_head *head,
struct bpf_list_node *node,
void *meta__ign, u64 off)
{
- struct bpf_list_node_kern *n = (void *)node;
+ struct bpf_list_node_kern *new = (void *)node;
struct btf_struct_meta *meta = meta__ign;
+ struct list_head *h = (void *)head;
- return __bpf_list_add(n, head, false, meta ? meta->record : NULL, off);
+ return __bpf_list_add(head, new, h, meta ? meta->record : NULL, off);
}
__bpf_kfunc int bpf_list_push_back_impl(struct bpf_list_head *head,
struct bpf_list_node *node,
void *meta__ign, u64 off)
{
- struct bpf_list_node_kern *n = (void *)node;
+ struct bpf_list_node_kern *new = (void *)node;
+ struct btf_struct_meta *meta = meta__ign;
+ struct list_head *h = (void *)head;
+
+ return __bpf_list_add(head, new, 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;
- return __bpf_list_add(n, head, true, meta ? meta->record : NULL, off);
+ return __bpf_list_add(head, kn, &kp->list_head,
+ meta ? meta->record : NULL, off);
}
static struct bpf_list_node *__bpf_list_del(struct bpf_list_head *head,
@@ -4563,6 +4584,7 @@ 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 c9557d3fb8dd..5f55b68ed935 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -12459,6 +12459,7 @@ 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,
@@ -12520,6 +12521,7 @@ 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)
@@ -12996,6 +12998,7 @@ static bool is_bpf_list_api_kfunc(u32 btf_id)
{
return btf_id == special_kfunc_list[KF_bpf_list_push_front_impl] ||
btf_id == special_kfunc_list[KF_bpf_list_push_back_impl] ||
+ btf_id == special_kfunc_list[KF_bpf_list_add_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] ||
@@ -13122,6 +13125,7 @@ static bool check_kfunc_is_graph_node_api(struct bpf_verifier_env *env,
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_add_impl] ||
kfunc_btf_id == special_kfunc_list[KF_bpf_list_del]);
break;
case BPF_RB_NODE:
@@ -14264,6 +14268,7 @@ 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].off;
@@ -23230,13 +23235,17 @@ 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)