// SPDX-License-Identifier: GPL-2.0
  /* Copyright (c) 2019 Facebook  */
  
  #include <linux/types.h>
  #include <linux/bpf_verifier.h>
  #include <linux/bpf.h>
  #include <linux/btf.h>
  #include <linux/filter.h>
  #include <net/tcp.h>

  #include <net/bpf_sk_storage.h>

  
  static u32 optional_ops[] = {
  	offsetof(struct tcp_congestion_ops, init),
  	offsetof(struct tcp_congestion_ops, release),
  	offsetof(struct tcp_congestion_ops, set_state),
  	offsetof(struct tcp_congestion_ops, cwnd_event),
  	offsetof(struct tcp_congestion_ops, in_ack_event),
  	offsetof(struct tcp_congestion_ops, pkts_acked),
  	offsetof(struct tcp_congestion_ops, min_tso_segs),
  	offsetof(struct tcp_congestion_ops, sndbuf_expand),
  	offsetof(struct tcp_congestion_ops, cong_control),
  };
  
  static u32 unsupported_ops[] = {
  	offsetof(struct tcp_congestion_ops, get_info),
  };
  
  static const struct btf_type *tcp_sock_type;
  static u32 tcp_sock_id, sock_id;
  
  static int bpf_tcp_ca_init(struct btf *btf)
  {
  	s32 type_id;
  
  	type_id = btf_find_by_name_kind(btf, "sock", BTF_KIND_STRUCT);
  	if (type_id < 0)
  		return -EINVAL;
  	sock_id = type_id;
  
  	type_id = btf_find_by_name_kind(btf, "tcp_sock", BTF_KIND_STRUCT);
  	if (type_id < 0)
  		return -EINVAL;
  	tcp_sock_id = type_id;
  	tcp_sock_type = btf_type_by_id(btf, tcp_sock_id);
  
  	return 0;
  }
  
  static bool is_optional(u32 member_offset)
  {
  	unsigned int i;
  
  	for (i = 0; i < ARRAY_SIZE(optional_ops); i++) {
  		if (member_offset == optional_ops[i])
  			return true;
  	}
  
  	return false;
  }
  
  static bool is_unsupported(u32 member_offset)
  {
  	unsigned int i;
  
  	for (i = 0; i < ARRAY_SIZE(unsupported_ops); i++) {
  		if (member_offset == unsupported_ops[i])
  			return true;
  	}
  
  	return false;
  }
  
  extern struct btf *btf_vmlinux;
  
  static bool bpf_tcp_ca_is_valid_access(int off, int size,
  				       enum bpf_access_type type,
  				       const struct bpf_prog *prog,
  				       struct bpf_insn_access_aux *info)
  {
  	if (off < 0 || off >= sizeof(__u64) * MAX_BPF_FUNC_ARGS)
  		return false;
  	if (type != BPF_READ)
  		return false;
  	if (off % size != 0)
  		return false;
  
  	if (!btf_ctx_access(off, size, type, prog, info))
  		return false;
  
  	if (info->reg_type == PTR_TO_BTF_ID && info->btf_id == sock_id)
  		/* promote it to tcp_sock */
  		info->btf_id = tcp_sock_id;
  
  	return true;
  }
  
  static int bpf_tcp_ca_btf_struct_access(struct bpf_verifier_log *log,
  					const struct btf_type *t, int off,
  					int size, enum bpf_access_type atype,
  					u32 *next_btf_id)
  {
  	size_t end;
  
  	if (atype == BPF_READ)
  		return btf_struct_access(log, t, off, size, atype, next_btf_id);
  
  	if (t != tcp_sock_type) {
  		bpf_log(log, "only read is supported
  ");
  		return -EACCES;
  	}
  
  	switch (off) {
  	case bpf_ctx_range(struct inet_connection_sock, icsk_ca_priv):
  		end = offsetofend(struct inet_connection_sock, icsk_ca_priv);
  		break;
  	case offsetof(struct inet_connection_sock, icsk_ack.pending):
  		end = offsetofend(struct inet_connection_sock,
  				  icsk_ack.pending);
  		break;
  	case offsetof(struct tcp_sock, snd_cwnd):
  		end = offsetofend(struct tcp_sock, snd_cwnd);
  		break;
  	case offsetof(struct tcp_sock, snd_cwnd_cnt):
  		end = offsetofend(struct tcp_sock, snd_cwnd_cnt);
  		break;
  	case offsetof(struct tcp_sock, snd_ssthresh):
  		end = offsetofend(struct tcp_sock, snd_ssthresh);
  		break;
  	case offsetof(struct tcp_sock, ecn_flags):
  		end = offsetofend(struct tcp_sock, ecn_flags);
  		break;
  	default:
  		bpf_log(log, "no write support to tcp_sock at off %d
  ", off);
  		return -EACCES;
  	}
  
  	if (off + size > end) {
  		bpf_log(log,
  			"write access at off %d with size %d beyond the member of tcp_sock ended at %zu
  ",
  			off, size, end);
  		return -EACCES;
  	}
  
  	return NOT_INIT;
  }

  BPF_CALL_2(bpf_tcp_send_ack, struct tcp_sock *, tp, u32, rcv_nxt)
  {
  	/* bpf_tcp_ca prog cannot have NULL tp */
  	__tcp_send_ack((struct sock *)tp, rcv_nxt);
  	return 0;
  }
  
  static const struct bpf_func_proto bpf_tcp_send_ack_proto = {
  	.func		= bpf_tcp_send_ack,
  	.gpl_only	= false,
  	/* In case we want to report error later */
  	.ret_type	= RET_INTEGER,
  	.arg1_type	= ARG_PTR_TO_BTF_ID,

  	.arg1_btf_id	= &tcp_sock_id,

  	.arg2_type	= ARG_ANYTHING,

  };

  static const struct bpf_func_proto *
  bpf_tcp_ca_get_func_proto(enum bpf_func_id func_id,
  			  const struct bpf_prog *prog)
  {

  	switch (func_id) {
  	case BPF_FUNC_tcp_send_ack:
  		return &bpf_tcp_send_ack_proto;

  	case BPF_FUNC_sk_storage_get:

  		return &bpf_sk_storage_get_proto;

  	case BPF_FUNC_sk_storage_delete:

  		return &bpf_sk_storage_delete_proto;

  	default:
  		return bpf_base_func_proto(func_id);
  	}

  }
  
  static const struct bpf_verifier_ops bpf_tcp_ca_verifier_ops = {
  	.get_func_proto		= bpf_tcp_ca_get_func_proto,
  	.is_valid_access	= bpf_tcp_ca_is_valid_access,
  	.btf_struct_access	= bpf_tcp_ca_btf_struct_access,
  };
  
  static int bpf_tcp_ca_init_member(const struct btf_type *t,
  				  const struct btf_member *member,
  				  void *kdata, const void *udata)
  {
  	const struct tcp_congestion_ops *utcp_ca;
  	struct tcp_congestion_ops *tcp_ca;

  	int prog_fd;
  	u32 moff;
  
  	utcp_ca = (const struct tcp_congestion_ops *)udata;
  	tcp_ca = (struct tcp_congestion_ops *)kdata;
  
  	moff = btf_member_bit_offset(t, member) / 8;
  	switch (moff) {
  	case offsetof(struct tcp_congestion_ops, flags):
  		if (utcp_ca->flags & ~TCP_CONG_MASK)
  			return -EINVAL;
  		tcp_ca->flags = utcp_ca->flags;
  		return 1;
  	case offsetof(struct tcp_congestion_ops, name):

  		if (bpf_obj_name_cpy(tcp_ca->name, utcp_ca->name,
  				     sizeof(tcp_ca->name)) <= 0)

  			return -EINVAL;
  		if (tcp_ca_find(utcp_ca->name))
  			return -EEXIST;

  		return 1;
  	}
  
  	if (!btf_type_resolve_func_ptr(btf_vmlinux, member->type, NULL))
  		return 0;
  
  	/* Ensure bpf_prog is provided for compulsory func ptr */
  	prog_fd = (int)(*(unsigned long *)(udata + moff));
  	if (!prog_fd && !is_optional(moff) && !is_unsupported(moff))
  		return -EINVAL;
  
  	return 0;
  }
  
  static int bpf_tcp_ca_check_member(const struct btf_type *t,
  				   const struct btf_member *member)
  {
  	if (is_unsupported(btf_member_bit_offset(t, member) / 8))
  		return -ENOTSUPP;
  	return 0;
  }
  
  static int bpf_tcp_ca_reg(void *kdata)
  {
  	return tcp_register_congestion_control(kdata);
  }
  
  static void bpf_tcp_ca_unreg(void *kdata)
  {
  	tcp_unregister_congestion_control(kdata);
  }
  
  /* Avoid sparse warning.  It is only used in bpf_struct_ops.c. */
  extern struct bpf_struct_ops bpf_tcp_congestion_ops;
  
  struct bpf_struct_ops bpf_tcp_congestion_ops = {
  	.verifier_ops = &bpf_tcp_ca_verifier_ops,
  	.reg = bpf_tcp_ca_reg,
  	.unreg = bpf_tcp_ca_unreg,
  	.check_member = bpf_tcp_ca_check_member,
  	.init_member = bpf_tcp_ca_init_member,
  	.init = bpf_tcp_ca_init,
  	.name = "tcp_congestion_ops",
  };