[DCCP]: Support for partial checksums (RFC 4340, sec. 9.2)

This patch does the following:
  a) introduces variable-length checksums as specified in [RFC 4340, sec. 9.2]
  b) provides necessary socket options and documentation as to how to use them
  c) basic support and infrastructure for the Minimum Checksum Coverage feature
     [RFC 4340, sec. 9.2.1]: acceptability tests, user notification and user
     interface

In addition, it

 (1) fixes two bugs in the DCCPv4 checksum computation:
 	* pseudo-header used checksum_len instead of skb->len
	* incorrect checksum coverage calculation based on dccph_x
 (2) removes dccp_v4_verify_checksum() since it reduplicates code of the
     checksum computation; code calling this function is updated accordingly.
 (3) now uses skb_checksum(), which is safer than checksum_partial() if the
     sk_buff has is a non-linear buffer (has pages attached to it).
 (4) fixes an outstanding TODO item:
        * If P.CsCov is too large for the packet size, drop packet and return.

The code has been tested with applications, the latest version of tcpdump now
comes with support for partial DCCP checksums.

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

1 files changed, 5 insertions, 8 deletions

diff --git a/net/dccp/output.c b/net/dccp/output.c
index 51654975e8ea..992caedd7725 100644
--- a/net/dccp/output.c
+++ b/net/dccp/output.c
@@ -96,6 +96,7 @@ static int dccp_transmit_skb(struct sock *sk, struct sk_buff *skb)
                 dh->dccph_dport = inet->dport;
                 dh->dccph_doff  = (dccp_header_size + dcb->dccpd_opt_len) / 4;
                 dh->dccph_ccval = dcb->dccpd_ccval;
+                dh->dccph_cscov = dp->dccps_pcslen;
                 /* XXX For now we're using only 48 bits sequence numbers */
                 dh->dccph_x     = 1;
 
@@ -115,7 +116,7 @@ static int dccp_transmit_skb(struct sock *sk, struct sk_buff *skb)
                         break;
                 }
 
-                icsk->icsk_af_ops->send_check(sk, skb->len, skb);
+                icsk->icsk_af_ops->send_check(sk, 0, skb);
 
                 if (set_ack)
                         dccp_event_ack_sent(sk);
@@ -329,7 +330,6 @@ struct sk_buff *dccp_make_response(struct sock *sk, struct dst_entry *dst,
         skb_reserve(skb, sk->sk_prot->max_header);
 
         skb->dst = dst_clone(dst);
-        skb->csum = 0;
 
         dreq = dccp_rsk(req);
         DCCP_SKB_CB(skb)->dccpd_type = DCCP_PKT_RESPONSE;
@@ -352,6 +352,8 @@ struct sk_buff *dccp_make_response(struct sock *sk, struct dst_entry *dst,
         dccp_hdr_set_ack(dccp_hdr_ack_bits(skb), dreq->dreq_isr);
         dccp_hdr_response(skb)->dccph_resp_service = dreq->dreq_service;
 
+        dccp_csum_outgoing(skb);
+
         DCCP_INC_STATS(DCCP_MIB_OUTSEGS);
         return skb;
 }
@@ -376,7 +378,6 @@ static struct sk_buff *dccp_make_reset(struct sock *sk, struct dst_entry *dst,
         skb_reserve(skb, sk->sk_prot->max_header);
 
         skb->dst = dst_clone(dst);
-        skb->csum = 0;
 
         dccp_inc_seqno(&dp->dccps_gss);
 
@@ -401,7 +402,7 @@ static struct sk_buff *dccp_make_reset(struct sock *sk, struct dst_entry *dst,
         dccp_hdr_set_ack(dccp_hdr_ack_bits(skb), dp->dccps_gsr);
 
         dccp_hdr_reset(skb)->dccph_reset_code = code;
-        inet_csk(sk)->icsk_af_ops->send_check(sk, skb->len, skb);
+        inet_csk(sk)->icsk_af_ops->send_check(sk, 0, skb);
 
         DCCP_INC_STATS(DCCP_MIB_OUTSEGS);
         return skb;
@@ -475,7 +476,6 @@ int dccp_connect(struct sock *sk)
         skb_reserve(skb, sk->sk_prot->max_header);
 
         DCCP_SKB_CB(skb)->dccpd_type = DCCP_PKT_REQUEST;
-        skb->csum = 0;
 
         dccp_skb_entail(sk, skb);
         dccp_transmit_skb(sk, skb_clone(skb, GFP_KERNEL));
@@ -507,7 +507,6 @@ void dccp_send_ack(struct sock *sk)
 
                 /* Reserve space for headers */
                 skb_reserve(skb, sk->sk_prot->max_header);
-                skb->csum = 0;
                 DCCP_SKB_CB(skb)->dccpd_type = DCCP_PKT_ACK;
                 dccp_transmit_skb(sk, skb);
         }
@@ -561,7 +560,6 @@ void dccp_send_sync(struct sock *sk, const u64 seq,
 
         /* Reserve space for headers and prepare control bits. */
         skb_reserve(skb, sk->sk_prot->max_header);
-        skb->csum = 0;
         DCCP_SKB_CB(skb)->dccpd_type = pkt_type;
         DCCP_SKB_CB(skb)->dccpd_seq = seq;
 
@@ -587,7 +585,6 @@ void dccp_send_close(struct sock *sk, const int active)
 
         /* Reserve space for headers and prepare control bits. */
         skb_reserve(skb, sk->sk_prot->max_header);
-        skb->csum = 0;
         DCCP_SKB_CB(skb)->dccpd_type = dp->dccps_role == DCCP_ROLE_CLIENT ?
                                         DCCP_PKT_CLOSE : DCCP_PKT_CLOSEREQ;