[DCCP]: calling dccp_v{4,6}_reqsk_send_ack is a BUG

This patch removes two functions, the send_ack functions of request_sock,
which are not called/used by the DCCP code. It is correct that these
functions are not called, below is a justification why calling these
functions (on a passive socket in the LISTEN/RESPOND state) would mean
a DCCP protocol violation.

A) Background: using request_sock in TCP:

net/dccp/dccp.h

@@ -131,6 +131,8 @@ extern int  dccp_retransmit_skb(struct sock *sk, struct sk_buff *skb);
 
 extern void dccp_send_ack(struct sock *sk);
 extern void dccp_send_delayed_ack(struct sock *sk);
+extern void dccp_reqsk_send_ack(struct sk_buff *sk, struct request_sock *rsk);
+
 extern void dccp_send_sync(struct sock *sk, const u64 seq,
 			   const enum dccp_pkt_type pkt_type);
 

net/dccp/ipv4.c

@@ -193,52 +193,6 @@ static inline void dccp_do_pmtu_discovery(struct sock *sk,
 	} /* else let the usual retransmit timer handle it */
 }
 
-static void dccp_v4_reqsk_send_ack(struct sk_buff *rxskb,
-				   struct request_sock *req)
-{
-	int err;
-	struct dccp_hdr *rxdh = dccp_hdr(rxskb), *dh;
-	const u32 dccp_hdr_ack_len = sizeof(struct dccp_hdr) +
-				     sizeof(struct dccp_hdr_ext) +
-				     sizeof(struct dccp_hdr_ack_bits);
-	struct sk_buff *skb;
-
-	if (((struct rtable *)rxskb->dst)->rt_type != RTN_LOCAL)
-		return;
-
-	skb = alloc_skb(dccp_v4_ctl_socket->sk->sk_prot->max_header, GFP_ATOMIC);
-	if (skb == NULL)
-		return;
-
-	/* Reserve space for headers. */
-	skb_reserve(skb, dccp_v4_ctl_socket->sk->sk_prot->max_header);
-	skb->dst = dst_clone(rxskb->dst);
-
-	dh = dccp_zeroed_hdr(skb, dccp_hdr_ack_len);
-
-	/* Build DCCP header and checksum it. */
-	dh->dccph_type	   = DCCP_PKT_ACK;
-	dh->dccph_sport	   = rxdh->dccph_dport;
-	dh->dccph_dport	   = rxdh->dccph_sport;
-	dh->dccph_doff	   = dccp_hdr_ack_len / 4;
-	dh->dccph_x	   = 1;
-
-	dccp_hdr_set_seq(dh, DCCP_SKB_CB(rxskb)->dccpd_ack_seq);
-	dccp_hdr_set_ack(dccp_hdr_ack_bits(skb),
-			 DCCP_SKB_CB(rxskb)->dccpd_seq);
-
-	bh_lock_sock(dccp_v4_ctl_socket->sk);
-	err = ip_build_and_send_pkt(skb, dccp_v4_ctl_socket->sk,
-				    rxskb->nh.iph->daddr,
-				    rxskb->nh.iph->saddr, NULL);
-	bh_unlock_sock(dccp_v4_ctl_socket->sk);
-
-	if (err == NET_XMIT_CN || err == 0) {
-		DCCP_INC_STATS_BH(DCCP_MIB_OUTSEGS);
-		DCCP_INC_STATS_BH(DCCP_MIB_OUTRSTS);
-	}
-}
-
 static int dccp_v4_send_response(struct sock *sk, struct request_sock *req,
 				 struct dst_entry *dst)
 {
@@ -1014,7 +968,7 @@ static struct request_sock_ops dccp_request_sock_ops __read_mostly = {
 	.family		= PF_INET,
 	.obj_size	= sizeof(struct dccp_request_sock),
 	.rtx_syn_ack	= dccp_v4_send_response,
-	.send_ack	= dccp_v4_reqsk_send_ack,
+	.send_ack	= dccp_reqsk_send_ack,
 	.destructor	= dccp_v4_reqsk_destructor,
 	.send_reset	= dccp_v4_ctl_send_reset,
 };

net/dccp/ipv6.c

@@ -37,8 +37,6 @@
 static struct socket *dccp_v6_ctl_socket;
 
 static void dccp_v6_ctl_send_reset(struct sk_buff *skb);
-static void dccp_v6_reqsk_send_ack(struct sk_buff *skb,
-				   struct request_sock *req);
 static void dccp_v6_send_check(struct sock *sk, int len, struct sk_buff *skb);
 
 static int dccp_v6_do_rcv(struct sock *sk, struct sk_buff *skb);
@@ -493,7 +491,7 @@ static struct request_sock_ops dccp6_request_sock_ops = {
 	.family		= AF_INET6,
 	.obj_size	= sizeof(struct dccp6_request_sock),
 	.rtx_syn_ack	= dccp_v6_send_response,
-	.send_ack	= dccp_v6_reqsk_send_ack,
+	.send_ack	= dccp_reqsk_send_ack,
 	.destructor	= dccp_v6_reqsk_destructor,
 	.send_reset	= dccp_v6_ctl_send_reset,
 };
@@ -582,59 +580,6 @@ static void dccp_v6_ctl_send_reset(struct sk_buff *rxskb)
 	kfree_skb(skb);
 }
 
-static void dccp_v6_reqsk_send_ack(struct sk_buff *rxskb,
-				   struct request_sock *req)
-{
-	struct flowi fl;
-	struct dccp_hdr *rxdh = dccp_hdr(rxskb), *dh;
-	const u32 dccp_hdr_ack_len = sizeof(struct dccp_hdr) +
-				     sizeof(struct dccp_hdr_ext) +
-				     sizeof(struct dccp_hdr_ack_bits);
-	struct sk_buff *skb;
-
-	skb = alloc_skb(dccp_v6_ctl_socket->sk->sk_prot->max_header,
-			GFP_ATOMIC);
-	if (skb == NULL)
-		return;
-
-	skb_reserve(skb, dccp_v6_ctl_socket->sk->sk_prot->max_header);
-
-	dh = dccp_zeroed_hdr(skb, dccp_hdr_ack_len);
-
-	/* Build DCCP header and checksum it. */
-	dh->dccph_type	= DCCP_PKT_ACK;
-	dh->dccph_sport = rxdh->dccph_dport;
-	dh->dccph_dport = rxdh->dccph_sport;
-	dh->dccph_doff	= dccp_hdr_ack_len / 4;
-	dh->dccph_x	= 1;
-
-	dccp_hdr_set_seq(dh, DCCP_SKB_CB(rxskb)->dccpd_ack_seq);
-	dccp_hdr_set_ack(dccp_hdr_ack_bits(skb),
-			 DCCP_SKB_CB(rxskb)->dccpd_seq);
-
-	memset(&fl, 0, sizeof(fl));
-	ipv6_addr_copy(&fl.fl6_dst, &rxskb->nh.ipv6h->saddr);
-	ipv6_addr_copy(&fl.fl6_src, &rxskb->nh.ipv6h->daddr);
-
-	/* FIXME: calculate checksum, IPv4 also should... */
-
-	fl.proto = IPPROTO_DCCP;
-	fl.oif = inet6_iif(rxskb);
-	fl.fl_ip_dport = dh->dccph_dport;
-	fl.fl_ip_sport = dh->dccph_sport;
-	security_req_classify_flow(req, &fl);
-
-	if (!ip6_dst_lookup(NULL, &skb->dst, &fl)) {
-		if (xfrm_lookup(&skb->dst, &fl, NULL, 0) >= 0) {
-			ip6_xmit(dccp_v6_ctl_socket->sk, skb, &fl, NULL, 0);
-			DCCP_INC_STATS_BH(DCCP_MIB_OUTSEGS);
-			return;
-		}
-	}
-
-	kfree_skb(skb);
-}
-
 static struct sock *dccp_v6_hnd_req(struct sock *sk,struct sk_buff *skb)
 {
 	const struct dccp_hdr *dh = dccp_hdr(skb);

net/dccp/minisocks.c

@@ -11,6 +11,7 @@
  */
 
 #include <linux/dccp.h>
+#include <linux/kernel.h>
 #include <linux/skbuff.h>
 #include <linux/timer.h>
 
@@ -283,3 +284,12 @@ int dccp_child_process(struct sock *parent, struct sock *child,
 }
 
 EXPORT_SYMBOL_GPL(dccp_child_process);
+
+void dccp_reqsk_send_ack(struct sk_buff *skb, struct request_sock *rsk)
+{
+	pr_info(KERN_WARNING "DCCP: ACK packets are never sent in "
+			     "LISTEN/RESPOND state\n");
+	dump_stack();
+}
+
+EXPORT_SYMBOL_GPL(dccp_reqsk_send_ack);