[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, 7 insertions, 0 deletions

diff --git a/include/linux/dccp.h b/include/linux/dccp.h
index 90d04ffddae8..0502dfa7f32c 100644
--- a/include/linux/dccp.h
+++ b/include/linux/dccp.h
@@ -183,6 +183,7 @@ enum {
         DCCPF_ACK_RATIO = 5,
         DCCPF_SEND_ACK_VECTOR = 6,
         DCCPF_SEND_NDP_COUNT = 7,
+        DCCPF_MIN_CSUM_COVER = 8,
         /* 10-127 reserved */
         DCCPF_MIN_CCID_SPECIFIC = 128,
         DCCPF_MAX_CCID_SPECIFIC = 255,
@@ -200,6 +201,8 @@ struct dccp_so_feat {
 #define DCCP_SOCKOPT_SERVICE            2
 #define DCCP_SOCKOPT_CHANGE_L           3
 #define DCCP_SOCKOPT_CHANGE_R           4
+#define DCCP_SOCKOPT_SEND_CSCOV         10
+#define DCCP_SOCKOPT_RECV_CSCOV         11
 #define DCCP_SOCKOPT_CCID_RX_INFO       128
 #define DCCP_SOCKOPT_CCID_TX_INFO       192
 
@@ -450,6 +453,8 @@ struct dccp_ackvec;
  * @dccps_timestamp_echo - latest timestamp received on a TIMESTAMP option
  * @dccps_packet_size - Set thru setsockopt
  * @dccps_role - Role of this sock, one of %dccp_role
+ * @dccps_pcslen - sender   partial checksum coverage (via sockopt)
+ * @dccps_pcrlen - receiver partial checksum coverage (via sockopt)
  * @dccps_ndp_count - number of Non Data Packets since last data packet
  * @dccps_hc_rx_ackvec - rx half connection ack vector
  * @dccps_xmit_timer - timer for when CCID is not ready to send
@@ -474,6 +479,8 @@ struct dccp_sock {
         __u32                           dccps_packet_size;
         __u16                           dccps_l_ack_ratio;
         __u16                           dccps_r_ack_ratio;
+        __u16                           dccps_pcslen;
+        __u16                           dccps_pcrlen;
         unsigned long                   dccps_ndp_count;
         __u32                           dccps_mss_cache;
         struct dccp_minisock            dccps_minisock;