[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, 22 insertions, 4 deletions

diff --git a/net/dccp/proto.c b/net/dccp/proto.c
index 047d170a363a..db54e557eff1 100644
--- a/net/dccp/proto.c
+++ b/net/dccp/proto.c
@@ -472,7 +472,6 @@ static int do_dccp_setsockopt(struct sock *sk, int level, int optname,
         case DCCP_SOCKOPT_PACKET_SIZE:
                 dp->dccps_packet_size = val;
                 break;
-
         case DCCP_SOCKOPT_CHANGE_L:
                 if (optlen != sizeof(struct dccp_so_feat))
                         err = -EINVAL;
@@ -481,7 +480,6 @@ static int do_dccp_setsockopt(struct sock *sk, int level, int optname,
                                                      (struct dccp_so_feat __user *)
                                                      optval);
                 break;
-
         case DCCP_SOCKOPT_CHANGE_R:
                 if (optlen != sizeof(struct dccp_so_feat))
                         err = -EINVAL;
@@ -490,12 +488,26 @@ static int do_dccp_setsockopt(struct sock *sk, int level, int optname,
                                                      (struct dccp_so_feat __user *)
                                                      optval);
                 break;
-
+        case DCCP_SOCKOPT_SEND_CSCOV:   /* sender side, RFC 4340, sec. 9.2 */
+                if (val < 0 || val > 15)
+                        err = -EINVAL;
+                else
+                        dp->dccps_pcslen = val;
+                break;
+        case DCCP_SOCKOPT_RECV_CSCOV:   /* receiver side, RFC 4340 sec. 9.2.1 */
+                if (val < 0 || val > 15)
+                        err = -EINVAL;
+                else {
+                        dp->dccps_pcrlen = val;
+                        /* FIXME: add feature negotiation,
+                         * ChangeL(MinimumChecksumCoverage, val) */
+                }
+                break;
         default:
                 err = -ENOPROTOOPT;
                 break;
         }
-        
+
         release_sock(sk);
         return err;
 }
@@ -575,6 +587,12 @@ static int do_dccp_getsockopt(struct sock *sk, int level, int optname,
         case DCCP_SOCKOPT_SERVICE:
                 return dccp_getsockopt_service(sk, len,
                                                (__be32 __user *)optval, optlen);
+        case DCCP_SOCKOPT_SEND_CSCOV:
+                val = dp->dccps_pcslen;
+                break;
+        case DCCP_SOCKOPT_RECV_CSCOV:
+                val = dp->dccps_pcrlen;
+                break;
         case 128 ... 191:
                 return ccid_hc_rx_getsockopt(dp->dccps_hc_rx_ccid, sk, optname,
                                              len, (u32 __user *)optval, optlen);