[PATCH bpf-next v7 2/5] 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  | 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)