Commit 70a217f1 authored by Martin KaFai Lau's avatar Martin KaFai Lau Committed by Alexei Starovoitov
Browse files

tcp: Use a struct to represent a saved_syn 



The TCP_SAVE_SYN has both the network header and tcp header.
The total length of the saved syn packet is currently stored in
the first 4 bytes (u32) of an array and the actual packet data is
stored after that.

A later patch will add a bpf helper that allows to get the tcp header
alone from the saved syn without the network header.  It will be more
convenient to have a direct offset to a specific header instead of
re-parsing it.  This requires to separately store the network hdrlen.
The total header length (i.e. network + tcp) is still needed for the
current usage in getsockopt.  Although this total length can be obtained
by looking into the tcphdr and then get the (th->doff << 2), this patch
chooses to directly store the tcp hdrlen in the second four bytes of
this newly created "struct saved_syn".  By using a new struct, it can
give a readable name to each individual header length.

Signed-off-by: default avatarMartin KaFai Lau <kafai@fb.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Reviewed-by: default avatarEric Dumazet <edumazet@google.com>
Acked-by: default avatarJohn Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20200820190014.2883694-1-kafai@fb.com
parent 9c0f8cbd

include/linux/tcp.h

+6 −1
Original line number Diff line number Diff line
@@ -406,7 +406,7 @@ struct tcp_sock { 
	 * socket. Used to retransmit SYNACKs etc.

	 */

	struct request_sock __rcu *fastopen_rsk;

	u32	*saved_syn;

	struct saved_syn *saved_syn;

};



enum tsq_enum {
@@ -484,6 +484,11 @@ static inline void tcp_saved_syn_free(struct tcp_sock *tp) 
	tp->saved_syn = NULL;

}



static inline u32 tcp_saved_syn_len(const struct saved_syn *saved_syn)

{

	return saved_syn->network_hdrlen + saved_syn->tcp_hdrlen;

}



struct sk_buff *tcp_get_timestamping_opt_stats(const struct sock *sk,

					       const struct sk_buff *orig_skb);

include/net/request_sock.h

+7 −1
Original line number Diff line number Diff line
@@ -41,6 +41,12 @@ struct request_sock_ops { 


int inet_rtx_syn_ack(const struct sock *parent, struct request_sock *req);



struct saved_syn {

	u32 network_hdrlen;

	u32 tcp_hdrlen;

	u8 data[];

};



/* struct request_sock - mini sock to represent a connection request

 */

struct request_sock {
@@ -60,7 +66,7 @@ struct request_sock { 
	struct timer_list		rsk_timer;

	const struct request_sock_ops	*rsk_ops;

	struct sock			*sk;

	u32				*saved_syn;

	struct saved_syn		*saved_syn;

	u32				secid;

	u32				peer_secid;

};

net/core/filter.c

+2 −2
Original line number Diff line number Diff line
@@ -4550,9 +4550,9 @@ static int _bpf_getsockopt(struct sock *sk, int level, int optname, 
			tp = tcp_sk(sk);



			if (optlen <= 0 || !tp->saved_syn ||

			    optlen > tp->saved_syn[0])

			    optlen > tcp_saved_syn_len(tp->saved_syn))

				goto err_clear;

			memcpy(optval, tp->saved_syn + 1, optlen);

			memcpy(optval, tp->saved_syn->data, optlen);

			break;

		default:

			goto err_clear;

net/ipv4/tcp.c

+5 −4
Original line number Diff line number Diff line
@@ -3788,20 +3788,21 @@ static int do_tcp_getsockopt(struct sock *sk, int level, 


		lock_sock(sk);

		if (tp->saved_syn) {

			if (len < tp->saved_syn[0]) {

				if (put_user(tp->saved_syn[0], optlen)) {

			if (len < tcp_saved_syn_len(tp->saved_syn)) {

				if (put_user(tcp_saved_syn_len(tp->saved_syn),

					     optlen)) {

					release_sock(sk);

					return -EFAULT;

				}

				release_sock(sk);

				return -EINVAL;

			}

			len = tp->saved_syn[0];

			len = tcp_saved_syn_len(tp->saved_syn);

			if (put_user(len, optlen)) {

				release_sock(sk);

				return -EFAULT;

			}

			if (copy_to_user(optval, tp->saved_syn + 1, len)) {

			if (copy_to_user(optval, tp->saved_syn->data, len)) {

				release_sock(sk);

				return -EFAULT;

			}

net/ipv4/tcp_input.c

+9 −7
Original line number Diff line number Diff line
@@ -6599,13 +6599,15 @@ static void tcp_reqsk_record_syn(const struct sock *sk, 
{

	if (tcp_sk(sk)->save_syn) {

		u32 len = skb_network_header_len(skb) + tcp_hdrlen(skb);

		u32 *copy;



		copy = kmalloc(len + sizeof(u32), GFP_ATOMIC);

		if (copy) {

			copy[0] = len;

			memcpy(&copy[1], skb_network_header(skb), len);

			req->saved_syn = copy;

		struct saved_syn *saved_syn;



		saved_syn = kmalloc(struct_size(saved_syn, data, len),

				    GFP_ATOMIC);

		if (saved_syn) {

			saved_syn->network_hdrlen = skb_network_header_len(skb);

			saved_syn->tcp_hdrlen = tcp_hdrlen(skb);

			memcpy(saved_syn->data, skb_network_header(skb), len);

			req->saved_syn = saved_syn;

		}

	}

}

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