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, 272 deletions

diff --git a/net/dccp/timer.c b/net/dccp/timer.c
deleted file mode 100644
index 232ac4ae0a73..000000000000
--- a/net/dccp/timer.c
+++ /dev/null
@@ -1,272 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0-or-later
-/*
- *  net/dccp/timer.c
- *
- *  An implementation of the DCCP protocol
- *  Arnaldo Carvalho de Melo <acme@conectiva.com.br>
- */
-
-#include <linux/dccp.h>
-#include <linux/skbuff.h>
-#include <linux/export.h>
-
-#include "dccp.h"
-
-/* sysctl variables governing numbers of retransmission attempts */
-int  sysctl_dccp_request_retries	__read_mostly = TCP_SYN_RETRIES;
-int  sysctl_dccp_retries1		__read_mostly = TCP_RETR1;
-int  sysctl_dccp_retries2		__read_mostly = TCP_RETR2;
-
-static void dccp_write_err(struct sock *sk)
-{
-	sk->sk_err = READ_ONCE(sk->sk_err_soft) ? : ETIMEDOUT;
-	sk_error_report(sk);
-
-	dccp_send_reset(sk, DCCP_RESET_CODE_ABORTED);
-	dccp_done(sk);
-	__DCCP_INC_STATS(DCCP_MIB_ABORTONTIMEOUT);
-}
-
-/* A write timeout has occurred. Process the after effects. */
-static int dccp_write_timeout(struct sock *sk)
-{
-	const struct inet_connection_sock *icsk = inet_csk(sk);
-	int retry_until;
-
-	if (sk->sk_state == DCCP_REQUESTING || sk->sk_state == DCCP_PARTOPEN) {
-		if (icsk->icsk_retransmits != 0)
-			dst_negative_advice(sk);
-		retry_until = icsk->icsk_syn_retries ?
-			    : sysctl_dccp_request_retries;
-	} else {
-		if (icsk->icsk_retransmits >= sysctl_dccp_retries1) {
-			/* NOTE. draft-ietf-tcpimpl-pmtud-01.txt requires pmtu
-			   black hole detection. :-(
-
-			   It is place to make it. It is not made. I do not want
-			   to make it. It is disguisting. It does not work in any
-			   case. Let me to cite the same draft, which requires for
-			   us to implement this:
-
-   "The one security concern raised by this memo is that ICMP black holes
-   are often caused by over-zealous security administrators who block
-   all ICMP messages.  It is vitally important that those who design and
-   deploy security systems understand the impact of strict filtering on
-   upper-layer protocols.  The safest web site in the world is worthless
-   if most TCP implementations cannot transfer data from it.  It would
-   be far nicer to have all of the black holes fixed rather than fixing
-   all of the TCP implementations."
-
-			   Golden words :-).
-		   */
-
-			dst_negative_advice(sk);
-		}
-
-		retry_until = sysctl_dccp_retries2;
-		/*
-		 * FIXME: see tcp_write_timout and tcp_out_of_resources
-		 */
-	}
-
-	if (icsk->icsk_retransmits >= retry_until) {
-		/* Has it gone just too far? */
-		dccp_write_err(sk);
-		return 1;
-	}
-	return 0;
-}
-
-/*
- *	The DCCP retransmit timer.
- */
-static void dccp_retransmit_timer(struct sock *sk)
-{
-	struct inet_connection_sock *icsk = inet_csk(sk);
-
-	/*
-	 * More than 4MSL (8 minutes) has passed, a RESET(aborted) was
-	 * sent, no need to retransmit, this sock is dead.
-	 */
-	if (dccp_write_timeout(sk))
-		return;
-
-	/*
-	 * We want to know the number of packets retransmitted, not the
-	 * total number of retransmissions of clones of original packets.
-	 */
-	if (icsk->icsk_retransmits == 0)
-		__DCCP_INC_STATS(DCCP_MIB_TIMEOUTS);
-
-	if (dccp_retransmit_skb(sk) != 0) {
-		/*
-		 * Retransmission failed because of local congestion,
-		 * do not backoff.
-		 */
-		if (--icsk->icsk_retransmits == 0)
-			icsk->icsk_retransmits = 1;
-		inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
-					  min(icsk->icsk_rto,
-					      TCP_RESOURCE_PROBE_INTERVAL),
-					  DCCP_RTO_MAX);
-		return;
-	}
-
-	icsk->icsk_backoff++;
-
-	icsk->icsk_rto = min(icsk->icsk_rto << 1, DCCP_RTO_MAX);
-	inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, icsk->icsk_rto,
-				  DCCP_RTO_MAX);
-	if (icsk->icsk_retransmits > sysctl_dccp_retries1)
-		__sk_dst_reset(sk);
-}
-
-static void dccp_write_timer(struct timer_list *t)
-{
-	struct inet_connection_sock *icsk =
-			from_timer(icsk, t, icsk_retransmit_timer);
-	struct sock *sk = &icsk->icsk_inet.sk;
-	int event = 0;
-
-	bh_lock_sock(sk);
-	if (sock_owned_by_user(sk)) {
-		/* Try again later */
-		sk_reset_timer(sk, &icsk->icsk_retransmit_timer,
-			       jiffies + (HZ / 20));
-		goto out;
-	}
-
-	if (sk->sk_state == DCCP_CLOSED || !icsk->icsk_pending)
-		goto out;
-
-	if (time_after(icsk_timeout(icsk), jiffies)) {
-		sk_reset_timer(sk, &icsk->icsk_retransmit_timer,
-			       icsk_timeout(icsk));
-		goto out;
-	}
-
-	event = icsk->icsk_pending;
-	icsk->icsk_pending = 0;
-
-	switch (event) {
-	case ICSK_TIME_RETRANS:
-		dccp_retransmit_timer(sk);
-		break;
-	}
-out:
-	bh_unlock_sock(sk);
-	sock_put(sk);
-}
-
-static void dccp_keepalive_timer(struct timer_list *t)
-{
-	struct sock *sk = from_timer(sk, t, sk_timer);
-
-	pr_err("dccp should not use a keepalive timer !\n");
-	sock_put(sk);
-}
-
-/* This is the same as tcp_delack_timer, sans prequeue & mem_reclaim stuff */
-static void dccp_delack_timer(struct timer_list *t)
-{
-	struct inet_connection_sock *icsk =
-			from_timer(icsk, t, icsk_delack_timer);
-	struct sock *sk = &icsk->icsk_inet.sk;
-
-	bh_lock_sock(sk);
-	if (sock_owned_by_user(sk)) {
-		/* Try again later. */
-		__NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKLOCKED);
-		sk_reset_timer(sk, &icsk->icsk_delack_timer,
-			       jiffies + TCP_DELACK_MIN);
-		goto out;
-	}
-
-	if (sk->sk_state == DCCP_CLOSED ||
-	    !(icsk->icsk_ack.pending & ICSK_ACK_TIMER))
-		goto out;
-	if (time_after(icsk_delack_timeout(icsk), jiffies)) {
-		sk_reset_timer(sk, &icsk->icsk_delack_timer,
-			       icsk_delack_timeout(icsk));
-		goto out;
-	}
-
-	icsk->icsk_ack.pending &= ~ICSK_ACK_TIMER;
-
-	if (inet_csk_ack_scheduled(sk)) {
-		if (!inet_csk_in_pingpong_mode(sk)) {
-			/* Delayed ACK missed: inflate ATO. */
-			icsk->icsk_ack.ato = min_t(u32, icsk->icsk_ack.ato << 1,
-						   icsk->icsk_rto);
-		} else {
-			/* Delayed ACK missed: leave pingpong mode and
-			 * deflate ATO.
-			 */
-			inet_csk_exit_pingpong_mode(sk);
-			icsk->icsk_ack.ato = TCP_ATO_MIN;
-		}
-		dccp_send_ack(sk);
-		__NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKS);
-	}
-out:
-	bh_unlock_sock(sk);
-	sock_put(sk);
-}
-
-/**
- * dccp_write_xmitlet  -  Workhorse for CCID packet dequeueing interface
- * @t: pointer to the tasklet associated with this handler
- *
- * See the comments above %ccid_dequeueing_decision for supported modes.
- */
-static void dccp_write_xmitlet(struct tasklet_struct *t)
-{
-	struct dccp_sock *dp = from_tasklet(dp, t, dccps_xmitlet);
-	struct sock *sk = &dp->dccps_inet_connection.icsk_inet.sk;
-
-	bh_lock_sock(sk);
-	if (sock_owned_by_user(sk))
-		sk_reset_timer(sk, &dccp_sk(sk)->dccps_xmit_timer, jiffies + 1);
-	else
-		dccp_write_xmit(sk);
-	bh_unlock_sock(sk);
-	sock_put(sk);
-}
-
-static void dccp_write_xmit_timer(struct timer_list *t)
-{
-	struct dccp_sock *dp = from_timer(dp, t, dccps_xmit_timer);
-
-	dccp_write_xmitlet(&dp->dccps_xmitlet);
-}
-
-void dccp_init_xmit_timers(struct sock *sk)
-{
-	struct dccp_sock *dp = dccp_sk(sk);
-
-	tasklet_setup(&dp->dccps_xmitlet, dccp_write_xmitlet);
-	timer_setup(&dp->dccps_xmit_timer, dccp_write_xmit_timer, 0);
-	inet_csk_init_xmit_timers(sk, &dccp_write_timer, &dccp_delack_timer,
-				  &dccp_keepalive_timer);
-}
-
-static ktime_t dccp_timestamp_seed;
-/**
- * dccp_timestamp  -  10s of microseconds time source
- * Returns the number of 10s of microseconds since loading DCCP. This is native
- * DCCP time difference format (RFC 4340, sec. 13).
- * Please note: This will wrap around about circa every 11.9 hours.
- */
-u32 dccp_timestamp(void)
-{
-	u64 delta = (u64)ktime_us_delta(ktime_get_real(), dccp_timestamp_seed);
-
-	do_div(delta, 10);
-	return delta;
-}
-EXPORT_SYMBOL_GPL(dccp_timestamp);
-
-void __init dccp_timestamping_init(void)
-{
-	dccp_timestamp_seed = ktime_get_real();
-}