[DCCP]: Factor out common code for generating Resets

This factors code common to dccp_v{4,6}_ctl_send_reset into a separate function,
and adds support for filling in the Data 1 ... Data 3 fields from RFC 4340, 5.6.

It is useful to have this separate, since the following Reset codes will always
be generated from the control socket rather than via dccp_send_reset:
 * Code 3, "No Connection", cf. 8.3.1;
 * Code 4, "Packet Error" (identification for Data 1 added);
 * Code 5, "Option Error" (identification for Data 1..3 added, will be used later);
 * Code 6, "Mandatory Error" (same as Option Error);
 * Code 7, "Connection Refused" (what on Earth is the difference to "No Connection"?);
 * Code 8, "Bad Service Code";
 * Code 9, "Too Busy";
 * Code 10, "Bad Init Cookie" (not used).

Code 0 is not recommended by the RFC, the following codes would be used in
dccp_send_reset() instead, since they all relate to an established DCCP connection:
 * Code 1, "Closed";
 * Code 2, "Aborted";
 * Code 11, "Aggression Penalty" (12.3).

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>

1 files changed, 52 insertions, 0 deletions

diff --git a/net/dccp/output.c b/net/dccp/output.c
index f4bde2056204..6a334ed5e9d6 100644
--- a/net/dccp/output.c
+++ b/net/dccp/output.c
@@ -327,6 +327,58 @@ struct sk_buff *dccp_make_response(struct sock *sk, struct dst_entry *dst,
 
 EXPORT_SYMBOL_GPL(dccp_make_response);
 
+/* answer offending packet in @rcv_skb with Reset from control socket @ctl */
+struct sk_buff *dccp_ctl_make_reset(struct socket *ctl, struct sk_buff *rcv_skb)
+{
+        struct dccp_hdr *rxdh = dccp_hdr(rcv_skb), *dh;
+        struct dccp_skb_cb *dcb = DCCP_SKB_CB(rcv_skb);
+        const u32 dccp_hdr_reset_len = sizeof(struct dccp_hdr) +
+                                       sizeof(struct dccp_hdr_ext) +
+                                       sizeof(struct dccp_hdr_reset);
+        struct dccp_hdr_reset *dhr;
+        struct sk_buff *skb;
+
+        skb = alloc_skb(ctl->sk->sk_prot->max_header, GFP_ATOMIC);
+        if (skb == NULL)
+                return NULL;
+
+        skb_reserve(skb, ctl->sk->sk_prot->max_header);
+
+        /* Swap the send and the receive. */
+        dh = dccp_zeroed_hdr(skb, dccp_hdr_reset_len);
+        dh->dccph_type  = DCCP_PKT_RESET;
+        dh->dccph_sport = rxdh->dccph_dport;
+        dh->dccph_dport = rxdh->dccph_sport;
+        dh->dccph_doff  = dccp_hdr_reset_len / 4;
+        dh->dccph_x     = 1;
+
+        dhr = dccp_hdr_reset(skb);
+        dhr->dccph_reset_code = dcb->dccpd_reset_code;
+
+        switch (dcb->dccpd_reset_code) {
+        case DCCP_RESET_CODE_PACKET_ERROR:
+                dhr->dccph_reset_data[0] = rxdh->dccph_type;
+                break;
+        case DCCP_RESET_CODE_OPTION_ERROR:      /* fall through */
+        case DCCP_RESET_CODE_MANDATORY_ERROR:
+                memcpy(dhr->dccph_reset_data, dcb->dccpd_reset_data, 3);
+                break;
+        }
+        /*
+         * From RFC 4340, 8.3.1:
+         *   If P.ackno exists, set R.seqno := P.ackno + 1.
+         *   Else set R.seqno := 0.
+         */
+        if (dcb->dccpd_ack_seq != DCCP_PKT_WITHOUT_ACK_SEQ)
+                dccp_hdr_set_seq(dh, ADD48(dcb->dccpd_ack_seq, 1));
+        dccp_hdr_set_ack(dccp_hdr_ack_bits(skb), dcb->dccpd_seq);
+
+        dccp_csum_outgoing(skb);
+        return skb;
+}
+
+EXPORT_SYMBOL_GPL(dccp_ctl_make_reset);
+
 /* send Reset on established socket, to close or abort the connection */
 int dccp_send_reset(struct sock *sk, enum dccp_reset_codes code)
 {