net: Retire DCCP socket.

DCCP was orphaned in 2021 by commit 054c4610bd05 ("MAINTAINERS: dccp:
move Gerrit Renker to CREDITS"), which noted that the last maintainer
had been inactive for five years.

In recent years, it has become a playground for syzbot, and most changes
to DCCP have been odd bug fixes triggered by syzbot.  Apart from that,
the only changes have been driven by treewide or networking API updates
or adjustments related to TCP.

Thus, in 2023, we announced we would remove DCCP in 2025 via commit
b144fcaf46d4 ("dccp: Print deprecation notice.").

Since then, only one individual has contacted the netdev mailing list. [0]

There is ongoing research for Multipath DCCP.  The repository is hosted
on GitHub [1], and development is not taking place through the upstream
community.  While the repository is published under the GPLv2 license,
the scheduling part remains proprietary, with a LICENSE file [2] stating:

  "This is not Open Source software."

The researcher mentioned a plan to address the licensing issue, upstream
the patches, and step up as a maintainer, but there has been no further
communication since then.

Maintaining DCCP for a decade without any real users has become a burden.

Therefore, it's time to remove it.

Removing DCCP will also provide significant benefits to TCP.  It allows
us to freely reorganize the layout of struct inet_connection_sock, which
is currently shared with DCCP, and optimize it to reduce the number of
cachelines accessed in the TCP fast path.

Note that we keep DCCP netfilter modules as requested.  [3]

Link: https://lore.kernel.org/netdev/20230710182253.81446-1-kuniyu@amazon.com/T/#u #[0]
Link: https://github.com/telekom/mp-dccp #[1]
Link: https://github.com/telekom/mp-dccp/blob/mpdccp_v03_k5.10/net/dccp/non_gpl_scheduler/LICENSE #[2]
Link: https://lore.kernel.org/netdev/Z_VQ0KlCRkqYWXa-@calendula/ #[3]
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Acked-by: Paul Moore <paul@paul-moore.com> (LSM and SELinux)
Acked-by: Casey Schaufler <casey@schaufler-ca.com>
Link: https://patch.msgid.link/20250410023921.11307-3-kuniyu@amazon.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 0 insertions, 266 deletions

diff --git a/net/dccp/minisocks.c b/net/dccp/minisocks.c
deleted file mode 100644
index fecc8190064f..000000000000
--- a/net/dccp/minisocks.c
+++ /dev/null
@@ -1,266 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0-or-later
-/*
- *  net/dccp/minisocks.c
- *
- *  An implementation of the DCCP protocol
- *  Arnaldo Carvalho de Melo <acme@conectiva.com.br>
- */
-
-#include <linux/dccp.h>
-#include <linux/gfp.h>
-#include <linux/kernel.h>
-#include <linux/skbuff.h>
-#include <linux/timer.h>
-
-#include <net/sock.h>
-#include <net/xfrm.h>
-#include <net/inet_timewait_sock.h>
-#include <net/rstreason.h>
-
-#include "ackvec.h"
-#include "ccid.h"
-#include "dccp.h"
-#include "feat.h"
-
-struct inet_timewait_death_row dccp_death_row = {
-	.tw_refcount = REFCOUNT_INIT(1),
-	.sysctl_max_tw_buckets = NR_FILE * 2,
-	.hashinfo	= &dccp_hashinfo,
-};
-
-EXPORT_SYMBOL_GPL(dccp_death_row);
-
-void dccp_time_wait(struct sock *sk, int state, int timeo)
-{
-	struct inet_timewait_sock *tw;
-
-	tw = inet_twsk_alloc(sk, &dccp_death_row, state);
-
-	if (tw != NULL) {
-		const struct inet_connection_sock *icsk = inet_csk(sk);
-		const int rto = (icsk->icsk_rto << 2) - (icsk->icsk_rto >> 1);
-#if IS_ENABLED(CONFIG_IPV6)
-		if (tw->tw_family == PF_INET6) {
-			tw->tw_v6_daddr = sk->sk_v6_daddr;
-			tw->tw_v6_rcv_saddr = sk->sk_v6_rcv_saddr;
-			tw->tw_ipv6only = sk->sk_ipv6only;
-		}
-#endif
-
-		/* Get the TIME_WAIT timeout firing. */
-		if (timeo < rto)
-			timeo = rto;
-
-		if (state == DCCP_TIME_WAIT)
-			timeo = DCCP_TIMEWAIT_LEN;
-
-		/* Linkage updates.
-		 * Note that access to tw after this point is illegal.
-		 */
-		inet_twsk_hashdance_schedule(tw, sk, &dccp_hashinfo, timeo);
-	} else {
-		/* Sorry, if we're out of memory, just CLOSE this
-		 * socket up.  We've got bigger problems than
-		 * non-graceful socket closings.
-		 */
-		DCCP_WARN("time wait bucket table overflow\n");
-	}
-
-	dccp_done(sk);
-}
-
-struct sock *dccp_create_openreq_child(const struct sock *sk,
-				       const struct request_sock *req,
-				       const struct sk_buff *skb)
-{
-	/*
-	 * Step 3: Process LISTEN state
-	 *
-	 *   (* Generate a new socket and switch to that socket *)
-	 *   Set S := new socket for this port pair
-	 */
-	struct sock *newsk = inet_csk_clone_lock(sk, req, GFP_ATOMIC);
-
-	if (newsk != NULL) {
-		struct dccp_request_sock *dreq = dccp_rsk(req);
-		struct inet_connection_sock *newicsk = inet_csk(newsk);
-		struct dccp_sock *newdp = dccp_sk(newsk);
-
-		newdp->dccps_role	    = DCCP_ROLE_SERVER;
-		newdp->dccps_hc_rx_ackvec   = NULL;
-		newdp->dccps_service_list   = NULL;
-		newdp->dccps_hc_rx_ccid     = NULL;
-		newdp->dccps_hc_tx_ccid     = NULL;
-		newdp->dccps_service	    = dreq->dreq_service;
-		newdp->dccps_timestamp_echo = dreq->dreq_timestamp_echo;
-		newdp->dccps_timestamp_time = dreq->dreq_timestamp_time;
-		newicsk->icsk_rto	    = DCCP_TIMEOUT_INIT;
-
-		INIT_LIST_HEAD(&newdp->dccps_featneg);
-		/*
-		 * Step 3: Process LISTEN state
-		 *
-		 *    Choose S.ISS (initial seqno) or set from Init Cookies
-		 *    Initialize S.GAR := S.ISS
-		 *    Set S.ISR, S.GSR from packet (or Init Cookies)
-		 *
-		 *    Setting AWL/AWH and SWL/SWH happens as part of the feature
-		 *    activation below, as these windows all depend on the local
-		 *    and remote Sequence Window feature values (7.5.2).
-		 */
-		newdp->dccps_iss = dreq->dreq_iss;
-		newdp->dccps_gss = dreq->dreq_gss;
-		newdp->dccps_gar = newdp->dccps_iss;
-		newdp->dccps_isr = dreq->dreq_isr;
-		newdp->dccps_gsr = dreq->dreq_gsr;
-
-		/*
-		 * Activate features: initialise CCIDs, sequence windows etc.
-		 */
-		if (dccp_feat_activate_values(newsk, &dreq->dreq_featneg)) {
-			sk_free_unlock_clone(newsk);
-			return NULL;
-		}
-		dccp_init_xmit_timers(newsk);
-
-		__DCCP_INC_STATS(DCCP_MIB_PASSIVEOPENS);
-	}
-	return newsk;
-}
-
-EXPORT_SYMBOL_GPL(dccp_create_openreq_child);
-
-/*
- * Process an incoming packet for RESPOND sockets represented
- * as an request_sock.
- */
-struct sock *dccp_check_req(struct sock *sk, struct sk_buff *skb,
-			    struct request_sock *req)
-{
-	struct sock *child = NULL;
-	struct dccp_request_sock *dreq = dccp_rsk(req);
-	bool own_req;
-
-	/* TCP/DCCP listeners became lockless.
-	 * DCCP stores complex state in its request_sock, so we need
-	 * a protection for them, now this code runs without being protected
-	 * by the parent (listener) lock.
-	 */
-	spin_lock_bh(&dreq->dreq_lock);
-
-	/* Check for retransmitted REQUEST */
-	if (dccp_hdr(skb)->dccph_type == DCCP_PKT_REQUEST) {
-
-		if (after48(DCCP_SKB_CB(skb)->dccpd_seq, dreq->dreq_gsr)) {
-			dccp_pr_debug("Retransmitted REQUEST\n");
-			dreq->dreq_gsr = DCCP_SKB_CB(skb)->dccpd_seq;
-			/*
-			 * Send another RESPONSE packet
-			 * To protect against Request floods, increment retrans
-			 * counter (backoff, monitored by dccp_response_timer).
-			 */
-			inet_rtx_syn_ack(sk, req);
-		}
-		/* Network Duplicate, discard packet */
-		goto out;
-	}
-
-	DCCP_SKB_CB(skb)->dccpd_reset_code = DCCP_RESET_CODE_PACKET_ERROR;
-
-	if (dccp_hdr(skb)->dccph_type != DCCP_PKT_ACK &&
-	    dccp_hdr(skb)->dccph_type != DCCP_PKT_DATAACK)
-		goto drop;
-
-	/* Invalid ACK */
-	if (!between48(DCCP_SKB_CB(skb)->dccpd_ack_seq,
-				dreq->dreq_iss, dreq->dreq_gss)) {
-		dccp_pr_debug("Invalid ACK number: ack_seq=%llu, "
-			      "dreq_iss=%llu, dreq_gss=%llu\n",
-			      (unsigned long long)
-			      DCCP_SKB_CB(skb)->dccpd_ack_seq,
-			      (unsigned long long) dreq->dreq_iss,
-			      (unsigned long long) dreq->dreq_gss);
-		goto drop;
-	}
-
-	if (dccp_parse_options(sk, dreq, skb))
-		 goto drop;
-
-	child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL,
-							 req, &own_req);
-	if (child) {
-		child = inet_csk_complete_hashdance(sk, child, req, own_req);
-		goto out;
-	}
-
-	DCCP_SKB_CB(skb)->dccpd_reset_code = DCCP_RESET_CODE_TOO_BUSY;
-drop:
-	if (dccp_hdr(skb)->dccph_type != DCCP_PKT_RESET)
-		req->rsk_ops->send_reset(sk, skb, SK_RST_REASON_NOT_SPECIFIED);
-
-	inet_csk_reqsk_queue_drop(sk, req);
-out:
-	spin_unlock_bh(&dreq->dreq_lock);
-	return child;
-}
-
-EXPORT_SYMBOL_GPL(dccp_check_req);
-
-/*
- *  Queue segment on the new socket if the new socket is active,
- *  otherwise we just shortcircuit this and continue with
- *  the new socket.
- */
-int dccp_child_process(struct sock *parent, struct sock *child,
-		       struct sk_buff *skb)
-	__releases(child)
-{
-	int ret = 0;
-	const int state = child->sk_state;
-
-	if (!sock_owned_by_user(child)) {
-		ret = dccp_rcv_state_process(child, skb, dccp_hdr(skb),
-					     skb->len);
-
-		/* Wakeup parent, send SIGIO */
-		if (state == DCCP_RESPOND && child->sk_state != state)
-			parent->sk_data_ready(parent);
-	} else {
-		/* Alas, it is possible again, because we do lookup
-		 * in main socket hash table and lock on listening
-		 * socket does not protect us more.
-		 */
-		__sk_add_backlog(child, skb);
-	}
-
-	bh_unlock_sock(child);
-	sock_put(child);
-	return ret;
-}
-
-EXPORT_SYMBOL_GPL(dccp_child_process);
-
-void dccp_reqsk_send_ack(const struct sock *sk, struct sk_buff *skb,
-			 struct request_sock *rsk)
-{
-	DCCP_BUG("DCCP-ACK packets are never sent in LISTEN/RESPOND state");
-}
-
-EXPORT_SYMBOL_GPL(dccp_reqsk_send_ack);
-
-int dccp_reqsk_init(struct request_sock *req,
-		    struct dccp_sock const *dp, struct sk_buff const *skb)
-{
-	struct dccp_request_sock *dreq = dccp_rsk(req);
-
-	spin_lock_init(&dreq->dreq_lock);
-	inet_rsk(req)->ir_rmt_port = dccp_hdr(skb)->dccph_sport;
-	inet_rsk(req)->ir_num	   = ntohs(dccp_hdr(skb)->dccph_dport);
-	inet_rsk(req)->acked	   = 0;
-	dreq->dreq_timestamp_echo  = 0;
-
-	/* inherit feature negotiation options from listening socket */
-	return dccp_feat_clone_list(&dp->dccps_featneg, &dreq->dreq_featneg);
-}
-
-EXPORT_SYMBOL_GPL(dccp_reqsk_init);