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, 85 deletions

diff --git a/net/dccp/diag.c b/net/dccp/diag.c
deleted file mode 100644
index f5019d95c3ae..000000000000
--- a/net/dccp/diag.c
+++ /dev/null
@@ -1,85 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0-only
-/*
- *  net/dccp/diag.c
- *
- *  An implementation of the DCCP protocol
- *  Arnaldo Carvalho de Melo <acme@mandriva.com>
- */
-
-
-#include <linux/module.h>
-#include <linux/inet_diag.h>
-
-#include "ccid.h"
-#include "dccp.h"
-
-static void dccp_get_info(struct sock *sk, struct tcp_info *info)
-{
-	struct dccp_sock *dp = dccp_sk(sk);
-	const struct inet_connection_sock *icsk = inet_csk(sk);
-
-	memset(info, 0, sizeof(*info));
-
-	info->tcpi_state	= sk->sk_state;
-	info->tcpi_retransmits	= icsk->icsk_retransmits;
-	info->tcpi_probes	= icsk->icsk_probes_out;
-	info->tcpi_backoff	= icsk->icsk_backoff;
-	info->tcpi_pmtu		= icsk->icsk_pmtu_cookie;
-
-	if (dp->dccps_hc_rx_ackvec != NULL)
-		info->tcpi_options |= TCPI_OPT_SACK;
-
-	if (dp->dccps_hc_rx_ccid != NULL)
-		ccid_hc_rx_get_info(dp->dccps_hc_rx_ccid, sk, info);
-
-	if (dp->dccps_hc_tx_ccid != NULL)
-		ccid_hc_tx_get_info(dp->dccps_hc_tx_ccid, sk, info);
-}
-
-static void dccp_diag_get_info(struct sock *sk, struct inet_diag_msg *r,
-			       void *_info)
-{
-	r->idiag_rqueue = r->idiag_wqueue = 0;
-
-	if (_info != NULL)
-		dccp_get_info(sk, _info);
-}
-
-static void dccp_diag_dump(struct sk_buff *skb, struct netlink_callback *cb,
-			   const struct inet_diag_req_v2 *r)
-{
-	inet_diag_dump_icsk(&dccp_hashinfo, skb, cb, r);
-}
-
-static int dccp_diag_dump_one(struct netlink_callback *cb,
-			      const struct inet_diag_req_v2 *req)
-{
-	return inet_diag_dump_one_icsk(&dccp_hashinfo, cb, req);
-}
-
-static const struct inet_diag_handler dccp_diag_handler = {
-	.owner		 = THIS_MODULE,
-	.dump		 = dccp_diag_dump,
-	.dump_one	 = dccp_diag_dump_one,
-	.idiag_get_info	 = dccp_diag_get_info,
-	.idiag_type	 = IPPROTO_DCCP,
-	.idiag_info_size = sizeof(struct tcp_info),
-};
-
-static int __init dccp_diag_init(void)
-{
-	return inet_diag_register(&dccp_diag_handler);
-}
-
-static void __exit dccp_diag_fini(void)
-{
-	inet_diag_unregister(&dccp_diag_handler);
-}
-
-module_init(dccp_diag_init);
-module_exit(dccp_diag_fini);
-
-MODULE_LICENSE("GPL");
-MODULE_AUTHOR("Arnaldo Carvalho de Melo <acme@mandriva.com>");
-MODULE_DESCRIPTION("DCCP inet_diag handler");
-MODULE_ALIAS_NET_PF_PROTO_TYPE(PF_NETLINK, NETLINK_SOCK_DIAG, 2-33 /* AF_INET - IPPROTO_DCCP */);