[PATCH bpf-next v9 6/9] bpf: Add bpf_list_add_impl to insert node after a given list node

[Chengkaitao <pilgrimtao@gmail.com>]

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 | 12 ++++++++++--
 2 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 669e380746a6..68c83a009275 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -2447,6 +2447,19 @@ __bpf_kfunc int bpf_list_push_back_impl(struct bpf_list_head *head,
 	return __bpf_list_add(n, 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 *n = (void *)new, *p = (void *)prev;
+	struct btf_struct_meta *meta = meta__ign;
+	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)
 {
@@ -4585,6 +4598,7 @@ 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 ae8d1f2e32de..69dcf0105973 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -12478,6 +12478,7 @@ 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,
@@ -12539,6 +12540,7 @@ 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)
@@ -12617,6 +12619,7 @@ 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,
@@ -12628,6 +12631,7 @@ 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,
 };
 
@@ -12681,6 +12685,7 @@ static const enum special_kfunc_type bpf_stream_api_kfuncs[] = {
 static const enum special_kfunc_type bpf_collection_insert_kfuncs[] = {
 	KF_bpf_list_push_front_impl,
 	KF_bpf_list_push_back_impl,
+	KF_bpf_list_add_impl,
 	KF_bpf_rbtree_add_impl,
 };
 
@@ -23354,8 +23359,11 @@ static int 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 (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)