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>

5 files changed, 2 insertions, 70 deletions

diff --git a/security/lsm_audit.c b/security/lsm_audit.c
index 1b942b4908a2..7d623b00495c 100644
--- a/security/lsm_audit.c
+++ b/security/lsm_audit.c
@@ -24,7 +24,6 @@
 #include <net/ipv6.h>
 #include <linux/tcp.h>
 #include <linux/udp.h>
-#include <linux/dccp.h>
 #include <linux/sctp.h>
 #include <linux/lsm_audit.h>
 #include <linux/security.h>
@@ -68,13 +67,6 @@ int ipv4_skb_to_auditdata(struct sk_buff *skb,
 		ad->u.net->dport = uh->dest;
 		break;
 	}
-	case IPPROTO_DCCP: {
-		struct dccp_hdr *dh = dccp_hdr(skb);
-
-		ad->u.net->sport = dh->dccph_sport;
-		ad->u.net->dport = dh->dccph_dport;
-		break;
-	}
 	case IPPROTO_SCTP: {
 		struct sctphdr *sh = sctp_hdr(skb);
 
@@ -140,17 +132,6 @@ int ipv6_skb_to_auditdata(struct sk_buff *skb,
 		ad->u.net->dport = uh->dest;
 		break;
 	}
-	case IPPROTO_DCCP: {
-		struct dccp_hdr _dccph, *dh;
-
-		dh = skb_header_pointer(skb, offset, sizeof(_dccph), &_dccph);
-		if (dh == NULL)
-			break;
-
-		ad->u.net->sport = dh->dccph_sport;
-		ad->u.net->dport = dh->dccph_dport;
-		break;
-	}
 	case IPPROTO_SCTP: {
 		struct sctphdr _sctph, *sh;
 
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index e7a7dcab81db..b2695785610a 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -65,7 +65,6 @@
 #include <net/netlink.h>
 #include <linux/tcp.h>
 #include <linux/udp.h>
-#include <linux/dccp.h>
 #include <linux/sctp.h>
 #include <net/sctp/structs.h>
 #include <linux/quota.h>
@@ -1191,8 +1190,6 @@ static inline u16 socket_type_to_security_class(int family, int type, int protoc
 				return SECCLASS_ICMP_SOCKET;
 			else
 				return SECCLASS_RAWIP_SOCKET;
-		case SOCK_DCCP:
-			return SECCLASS_DCCP_SOCKET;
 		default:
 			return SECCLASS_RAWIP_SOCKET;
 		}
@@ -4392,22 +4389,6 @@ static int selinux_parse_skb_ipv4(struct sk_buff *skb,
 		break;
 	}
 
-	case IPPROTO_DCCP: {
-		struct dccp_hdr _dccph, *dh;
-
-		if (ntohs(ih->frag_off) & IP_OFFSET)
-			break;
-
-		offset += ihlen;
-		dh = skb_header_pointer(skb, offset, sizeof(_dccph), &_dccph);
-		if (dh == NULL)
-			break;
-
-		ad->u.net->sport = dh->dccph_sport;
-		ad->u.net->dport = dh->dccph_dport;
-		break;
-	}
-
 #if IS_ENABLED(CONFIG_IP_SCTP)
 	case IPPROTO_SCTP: {
 		struct sctphdr _sctph, *sh;
@@ -4486,18 +4467,6 @@ static int selinux_parse_skb_ipv6(struct sk_buff *skb,
 		break;
 	}
 
-	case IPPROTO_DCCP: {
-		struct dccp_hdr _dccph, *dh;
-
-		dh = skb_header_pointer(skb, offset, sizeof(_dccph), &_dccph);
-		if (dh == NULL)
-			break;
-
-		ad->u.net->sport = dh->dccph_sport;
-		ad->u.net->dport = dh->dccph_dport;
-		break;
-	}
-
 #if IS_ENABLED(CONFIG_IP_SCTP)
 	case IPPROTO_SCTP: {
 		struct sctphdr _sctph, *sh;
@@ -4849,10 +4818,6 @@ static int selinux_socket_bind(struct socket *sock, struct sockaddr *address, in
 			node_perm = UDP_SOCKET__NODE_BIND;
 			break;
 
-		case SECCLASS_DCCP_SOCKET:
-			node_perm = DCCP_SOCKET__NODE_BIND;
-			break;
-
 		case SECCLASS_SCTP_SOCKET:
 			node_perm = SCTP_SOCKET__NODE_BIND;
 			break;
@@ -4908,11 +4873,10 @@ static int selinux_socket_connect_helper(struct socket *sock,
 		return 0;
 
 	/*
-	 * If a TCP, DCCP or SCTP socket, check name_connect permission
+	 * If a TCP or SCTP socket, check name_connect permission
 	 * for the port.
 	 */
 	if (sksec->sclass == SECCLASS_TCP_SOCKET ||
-	    sksec->sclass == SECCLASS_DCCP_SOCKET ||
 	    sksec->sclass == SECCLASS_SCTP_SOCKET) {
 		struct common_audit_data ad;
 		struct lsm_network_audit net = {0,};
@@ -4957,9 +4921,6 @@ static int selinux_socket_connect_helper(struct socket *sock,
 		case SECCLASS_TCP_SOCKET:
 			perm = TCP_SOCKET__NAME_CONNECT;
 			break;
-		case SECCLASS_DCCP_SOCKET:
-			perm = DCCP_SOCKET__NAME_CONNECT;
-			break;
 		case SECCLASS_SCTP_SOCKET:
 			perm = SCTP_SOCKET__NAME_CONNECT;
 			break;
diff --git a/security/selinux/include/classmap.h b/security/selinux/include/classmap.h
index 04a9b480885e..5665aa5e7853 100644
--- a/security/selinux/include/classmap.h
+++ b/security/selinux/include/classmap.h
@@ -127,8 +127,6 @@ const struct security_class_mapping secclass_map[] = {
 	{ "key",
 	  { "view", "read", "write", "search", "link", "setattr", "create",
 	    NULL } },
-	{ "dccp_socket",
-	  { COMMON_SOCK_PERMS, "node_bind", "name_connect", NULL } },
 	{ "memprotect", { "mmap_zero", NULL } },
 	{ "peer", { "recv", NULL } },
 	{ "capability2", { COMMON_CAP2_PERMS, NULL } },
diff --git a/security/selinux/nlmsgtab.c b/security/selinux/nlmsgtab.c
index 3a95986b134f..2c0b07f9fbbd 100644
--- a/security/selinux/nlmsgtab.c
+++ b/security/selinux/nlmsgtab.c
@@ -98,7 +98,6 @@ static const struct nlmsg_perm nlmsg_route_perms[] = {
 
 static const struct nlmsg_perm nlmsg_tcpdiag_perms[] = {
 	{ TCPDIAG_GETSOCK, NETLINK_TCPDIAG_SOCKET__NLMSG_READ },
-	{ DCCPDIAG_GETSOCK, NETLINK_TCPDIAG_SOCKET__NLMSG_READ },
 	{ SOCK_DIAG_BY_FAMILY, NETLINK_TCPDIAG_SOCKET__NLMSG_READ },
 	{ SOCK_DESTROY, NETLINK_TCPDIAG_SOCKET__NLMSG_WRITE },
 };
diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index 99833168604e..fc340a6f0dde 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -24,7 +24,6 @@
 #include <linux/ip.h>
 #include <linux/tcp.h>
 #include <linux/udp.h>
-#include <linux/dccp.h>
 #include <linux/icmpv6.h>
 #include <linux/slab.h>
 #include <linux/mutex.h>
@@ -4061,7 +4060,6 @@ static int smk_skb_to_addr_ipv6(struct sk_buff *skb, struct sockaddr_in6 *sip)
 	__be16 frag_off;
 	struct tcphdr _tcph, *th;
 	struct udphdr _udph, *uh;
-	struct dccp_hdr _dccph, *dh;
 
 	sip->sin6_port = 0;
 
@@ -4090,11 +4088,6 @@ static int smk_skb_to_addr_ipv6(struct sk_buff *skb, struct sockaddr_in6 *sip)
 		if (uh != NULL)
 			sip->sin6_port = uh->source;
 		break;
-	case IPPROTO_DCCP:
-		dh = skb_header_pointer(skb, offset, sizeof(_dccph), &_dccph);
-		if (dh != NULL)
-			sip->sin6_port = dh->dccph_sport;
-		break;
 	}
 	return proto;
 }
@@ -4216,7 +4209,7 @@ static int smack_socket_sock_rcv_skb(struct sock *sk, struct sk_buff *skb)
 	case PF_INET6:
 		proto = smk_skb_to_addr_ipv6(skb, &sadd);
 		if (proto != IPPROTO_UDP && proto != IPPROTO_UDPLITE &&
-		    proto != IPPROTO_TCP && proto != IPPROTO_DCCP)
+		    proto != IPPROTO_TCP)
 			break;
 #ifdef SMACK_IPV6_SECMARK_LABELING
 		skp = smack_from_skb(skb);