[PATCH bpf-next v7 1/5] bpf: Introduce the bpf_list_del kfunc.

[Chengkaitao]

From: Kaitao Cheng <chengkaitao@xxxxxxxxxx>

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 <chengkaitao@xxxxxxxxxx>
---
 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;
@@ -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] ||
-- 
2.50.1 (Apple Git-155)