[PATCH bpf-next v11 4/8] bpf: Introduce the bpf_list_del kfunc.

[Kaitao Cheng]

From: Kaitao Cheng <chengkaitao@xxxxxxxxxx>

Allow users to remove any node from a linked list.

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.

Signed-off-by: Kaitao Cheng <chengkaitao@xxxxxxxxxx>
Reviewed-by: Eduard Zingerman <eddyz87@xxxxxxxxx>
---
 kernel/bpf/helpers.c  | 10 ++++++++++
 kernel/bpf/verifier.c |  6 +++++-
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 59855b434f0b..804c201c28f3 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -2601,6 +2601,15 @@ __bpf_kfunc struct bpf_list_node *bpf_list_pop_back(struct bpf_list_head *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__nonown_allowed)
+{
+	struct bpf_list_node_kern *kn = (void *)node__nonown_allowed;
+
+	/* verifier guarantees node is a list node rather than list head */
+	return __bpf_list_del(head, &kn->list_head);
+}
+
 __bpf_kfunc struct bpf_list_node *bpf_list_front(struct bpf_list_head *head)
 {
 	struct list_head *h = (struct list_head *)head;
@@ -4733,6 +4742,7 @@ 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_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 f3cf8d85bea0..35eebb5e7769 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -10961,6 +10961,7 @@ enum special_kfunc_type {
 	KF_bpf_list_push_back,
 	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,
@@ -11029,6 +11030,7 @@ BTF_ID(func, bpf_list_push_back_impl)
 BTF_ID(func, bpf_list_push_back)
 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)
@@ -11549,6 +11551,7 @@ static bool is_bpf_list_api_kfunc(u32 btf_id)
 	return is_bpf_list_push_kfunc(btf_id) ||
 	       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];
 }
@@ -11671,7 +11674,8 @@ static bool check_kfunc_is_graph_node_api(struct bpf_verifier_env *env,
 
 	switch (node_field_type) {
 	case BPF_LIST_NODE:
-		ret = is_bpf_list_push_kfunc(kfunc_btf_id);
+		ret = is_bpf_list_push_kfunc(kfunc_btf_id) ||
+		      kfunc_btf_id == special_kfunc_list[KF_bpf_list_del];
 		break;
 	case BPF_RB_NODE:
 		ret = (is_bpf_rbtree_add_kfunc(kfunc_btf_id) ||
-- 
2.50.1 (Apple Git-155)