bpf: Add helper bpf_tcp_udpate_seq to synchronize tcp seq/ack

Offering: HULK
hulk inclusion
category: feature
bugzilla: N/A

--------------------------------

In order to process TCP packet with BPF/XDP, it's necessary to
synchronize seq and ack between kernel network stack and bpf prog.
This patch introduces a sample helper to do the sync.

Note that, it's only used for samples, retransmission and congestion
control are not supported.
Signed-off-by: NHe Fengqing <hefengqing@huawei.com>
Signed-off-by: NXu Kuohai <xukuohai@huawei.com>
Signed-off-by: NYang Jihong <yangjihong@huawei.com>

include/uapi/linux/bpf.h

@@ -4050,6 +4050,12 @@ union bpf_attr {
  *		**-ENOENT** if symbol is not found.
  *
  *		**-EPERM** if caller does not have permission to obtain kernel address.
+ *
+ * int bpf_update_tcp_seq(struct xdp_buff *ctx, struct bpf_sock_tuple *tuple, u32 len, u32 netns_id, u64 flags)
+ *     Description
+ *             Update tcp seq
+ *     Return
+ *             0 on success, or a negative error in case of failure.
  */
 #define __BPF_FUNC_MAPPER(FN)		\
 	FN(unspec),			\
@@ -4235,6 +4241,7 @@ union bpf_attr {
 	FN(btf_find_by_name_kind),	\
 	FN(sys_close),			\
 	FN(kallsyms_lookup_name),	\
+	FN(update_tcp_seq),		\
 	/* */
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper
@@ -4583,6 +4590,10 @@ struct bpf_sock_tuple {
 			__be16 dport;
 		} ipv6;
 	};
+
+	__be32 seq;
+	__be32 delta;
+	__be32 ack_seq;
 };
 
 struct bpf_xdp_sock {

net/core/filter.c

@@ -6239,6 +6239,54 @@ static const struct bpf_func_proto bpf_xdp_sk_lookup_tcp_proto = {
 	.arg5_type      = ARG_ANYTHING,
 };
 
+/* If we update tp->rcv_nxt, also update tp->bytes_received */
+static void tcp_rcv_nxt_update(struct tcp_sock *tp, u32 seq)
+{
+	u32 delta = seq - tp->rcv_nxt;
+
+	sock_owned_by_me((struct sock *)tp);
+	tp->bytes_received += delta;
+	WRITE_ONCE(tp->rcv_nxt, seq);
+}
+
+BPF_CALL_5(bpf_xdp_update_tcp_seq, struct xdp_buff *, ctx,
+	   struct bpf_sock_tuple *, tuple, u32, len, u32, netns_id, u64, flags)
+{
+	struct net *caller_net = dev_net(ctx->rxq->dev);
+	int ifindex = ctx->rxq->dev->ifindex;
+	struct sock *sk;
+	struct tcp_sock *tp;
+
+	sk = __bpf_sk_lookup(NULL, tuple, len, caller_net,
+			     ifindex, IPPROTO_TCP, netns_id,
+			     flags);
+	if (!sk)
+		return -1;
+
+	tp = tcp_sk(sk);
+	tcp_rcv_nxt_update(tp, tuple->seq + tuple->delta);
+
+	WRITE_ONCE(tp->snd_nxt, tuple->ack_seq);
+	WRITE_ONCE(tp->copied_seq, tp->rcv_nxt);
+	WRITE_ONCE(tp->bytes_sent, tuple->ack_seq);
+	WRITE_ONCE(tp->bytes_acked, tuple->ack_seq);
+	WRITE_ONCE(tp->write_seq, tuple->ack_seq);
+
+	return 0;
+}
+
+static const struct bpf_func_proto bpf_xdp_update_tcp_seq_proto = {
+	.func           = bpf_xdp_update_tcp_seq,
+	.gpl_only       = false,
+	.pkt_access     = true,
+	.ret_type       = RET_INTEGER,
+	.arg1_type      = ARG_PTR_TO_CTX,
+	.arg2_type      = ARG_PTR_TO_MEM,
+	.arg3_type      = ARG_CONST_SIZE,
+	.arg4_type      = ARG_ANYTHING,
+	.arg5_type      = ARG_ANYTHING,
+};
+
 BPF_CALL_5(bpf_sock_addr_skc_lookup_tcp, struct bpf_sock_addr_kern *, ctx,
 	   struct bpf_sock_tuple *, tuple, u32, len, u64, netns_id, u64, flags)
 {
@@ -7317,6 +7365,8 @@ xdp_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 		return &bpf_xdp_sk_lookup_udp_proto;
 	case BPF_FUNC_sk_lookup_tcp:
 		return &bpf_xdp_sk_lookup_tcp_proto;
+	case BPF_FUNC_update_tcp_seq:
+		return &bpf_xdp_update_tcp_seq_proto;
 	case BPF_FUNC_sk_release:
 		return &bpf_sk_release_proto;
 	case BPF_FUNC_skc_lookup_tcp:

tools/include/uapi/linux/bpf.h

@@ -4760,6 +4760,12 @@ union bpf_attr {
  *		**-ENOENT** if symbol is not found.
  *
  *		**-EPERM** if caller does not have permission to obtain kernel address.
+ *
+ * int bpf_update_tcp_seq(struct xdp_buff *ctx, struct bpf_sock_tuple *tuple, u32 len, u32 netns_id, u64 flags)
+ *     Description
+ *             Update tcp seq
+ *     Return
+ *             0 on success, or a negative error in case of failure.
  */
 #define __BPF_FUNC_MAPPER(FN)		\
 	FN(unspec),			\
@@ -4945,6 +4951,7 @@ union bpf_attr {
 	FN(btf_find_by_name_kind),	\
 	FN(sys_close),			\
 	FN(kallsyms_lookup_name),	\
+	FN(update_tcp_seq),		\
 	/* */
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper
@@ -5292,6 +5299,10 @@ struct bpf_sock_tuple {
 			__be16 dport;
 		} ipv6;
 	};
+
+	__be32 seq;
+	__be32 delta;
+	__be32 ack_seq;
 };
 
 struct bpf_xdp_sock {