[DCCP]: Twice the wrong reset code in receiving connection-Requests

This fixes two bugs in processing of connection-Requests in
v{4,6}_conn_request:

 1. Due to using the variable `reset_code', the Reset code generated
    internally by dccp_parse_options() is overwritten with the
    initialised value ("Too Busy") of reset_code, which is not what is
    intended.

 2. When receiving a connection-Request on a multicast or broadcast
    address, no Reset should be generated, to avoid storms of such
    packets. Instead of jumping to the `drop' label, the
    v{4,6}_conn_request functions now return 0. Below is why in my
    understanding this is correct:

    When the conn_request function returns < 0, then the caller,
    dccp_rcv_state_process(), returns 1. In all instances where
    dccp_rcv_state_process is called (dccp_v4_do_rcv, dccp_v6_do_rcv,
    and dccp_child_process), a return value of != 0 from
    dccp_rcv_state_process() means that a Reset is generated.

    If on the other hand the conn_request function returns 0, the
    packet is discarded and no Reset is generated.

Note: There may be a related problem when sending the Response, due to
the following.

	if (dccp_v6_send_response(sk, req, NULL))
		goto drop_and_free;
	/* ... */
	drop_and_free:
		return -1;

In this case, if send_response fails due to transmission errors, the
next thing that is generated is a Reset with a code "Too Busy". I
haven't been able to conjure up such a condition, but it might be good
to change the behaviour here also (not done by this patch).
Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: Ian McDonald <ian.mcdonald@jandi.co.nz>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/dccp/ipv4.c

@@ -568,17 +568,14 @@ int dccp_v4_conn_request(struct sock *sk, struct sk_buff *skb)
 	struct dccp_request_sock *dreq;
 	const __be32 service = dccp_hdr_request(skb)->dccph_req_service;
 	struct dccp_skb_cb *dcb = DCCP_SKB_CB(skb);
-	__u8 reset_code = DCCP_RESET_CODE_TOO_BUSY;
 
 	/* Never answer to DCCP_PKT_REQUESTs send to broadcast or multicast */
 	if (((struct rtable *)skb->dst)->rt_flags &
-	    (RTCF_BROADCAST | RTCF_MULTICAST)) {
-		reset_code = DCCP_RESET_CODE_NO_CONNECTION;
-		goto drop;
-	}
+	    (RTCF_BROADCAST | RTCF_MULTICAST))
+		return 0;	/* discard, don't send a reset here */
 
 	if (dccp_bad_service_code(sk, service)) {
-		reset_code = DCCP_RESET_CODE_BAD_SERVICE_CODE;
+		dcb->dccpd_reset_code = DCCP_RESET_CODE_BAD_SERVICE_CODE;
 		goto drop;
 	}
 	/*
@@ -586,6 +583,7 @@ int dccp_v4_conn_request(struct sock *sk, struct sk_buff *skb)
 	 * limitations, they conserve resources and peer is
 	 * evidently real one.
 	 */
+	dcb->dccpd_reset_code = DCCP_RESET_CODE_TOO_BUSY;
 	if (inet_csk_reqsk_queue_is_full(sk))
 		goto drop;
 
@@ -638,7 +636,6 @@ drop_and_free:
 	reqsk_free(req);
 drop:
 	DCCP_INC_STATS_BH(DCCP_MIB_ATTEMPTFAILS);
-	dcb->dccpd_reset_code = reset_code;
 	return -1;
 }
 

net/dccp/ipv6.c

@@ -390,21 +390,21 @@ static int dccp_v6_conn_request(struct sock *sk, struct sk_buff *skb)
 	struct ipv6_pinfo *np = inet6_sk(sk);
 	const __be32 service = dccp_hdr_request(skb)->dccph_req_service;
 	struct dccp_skb_cb *dcb = DCCP_SKB_CB(skb);
-	__u8 reset_code = DCCP_RESET_CODE_TOO_BUSY;
 
 	if (skb->protocol == htons(ETH_P_IP))
 		return dccp_v4_conn_request(sk, skb);
 
 	if (!ipv6_unicast_destination(skb))
-		goto drop;
+		return 0;	/* discard, don't send a reset here */
 
 	if (dccp_bad_service_code(sk, service)) {
-		reset_code = DCCP_RESET_CODE_BAD_SERVICE_CODE;
+		dcb->dccpd_reset_code = DCCP_RESET_CODE_BAD_SERVICE_CODE;
 		goto drop;
 	}
 	/*
 	 * There are no SYN attacks on IPv6, yet...
 	 */
+	dcb->dccpd_reset_code = DCCP_RESET_CODE_TOO_BUSY;
 	if (inet_csk_reqsk_queue_is_full(sk))
 		goto drop;
 
@@ -464,7 +464,6 @@ drop_and_free:
 	reqsk_free(req);
 drop:
 	DCCP_INC_STATS_BH(DCCP_MIB_ATTEMPTFAILS);
-	dcb->dccpd_reset_code = reset_code;
 	return -1;
 }