7 files changed, 173 insertions, 97 deletions

diff --git a/Documentation/networking/dccp.txt b/Documentation/networking/dccp.txt
index 74563b38ffd9..a8142a81038a 100644
--- a/Documentation/networking/dccp.txt
+++ b/Documentation/networking/dccp.txt
@@ -47,6 +47,22 @@ the socket will fall back to 0 (which means that no meaningful service code
 is present). Connecting sockets set at most one service option; for
 listening sockets, multiple service codes can be specified.
 
+DCCP_SOCKOPT_SEND_CSCOV and DCCP_SOCKOPT_RECV_CSCOV are used for setting the
+partial checksum coverage (RFC 4340, sec. 9.2). The default is that checksums
+always cover the entire packet and that only fully covered application data is
+accepted by the receiver. Hence, when using this feature on the sender, it must
+be enabled at the receiver, too with suitable choice of CsCov.
+
+DCCP_SOCKOPT_SEND_CSCOV sets the sender checksum coverage. Values in the
+        range 0..15 are acceptable. The default setting is 0 (full coverage),
+        values between 1..15 indicate partial coverage.
+DCCP_SOCKOPT_SEND_CSCOV is for the receiver and has a different meaning: it
+        sets a threshold, where again values 0..15 are acceptable. The default
+        of 0 means that all packets with a partial coverage will be discarded.
+        Values in the range 1..15 indicate that packets with minimally such a
+        coverage value are also acceptable. The higher the number, the more
+        restrictive this setting (see [RFC 4340, sec. 9.2.1]).
+
 Notes
 =====
 
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;
diff --git a/net/dccp/dccp.h b/net/dccp/dccp.h
index 2990bfb12587..d5c414bf7819 100644
--- a/net/dccp/dccp.h
+++ b/net/dccp/dccp.h
@@ -129,6 +129,30 @@ DECLARE_SNMP_STAT(struct dccp_mib, dccp_statistics);
 #define DCCP_ADD_STATS_USER(field, val) \
                         SNMP_ADD_STATS_USER(dccp_statistics, field, val)
 
+/*
+ *      Checksumming routines
+ */
+static inline int dccp_csum_coverage(const struct sk_buff *skb)
+{
+        const struct dccp_hdr* dh = dccp_hdr(skb);
+
+        if (dh->dccph_cscov == 0)
+                return skb->len;
+        return (dh->dccph_doff + dh->dccph_cscov - 1) * sizeof(u32);
+}
+
+static inline void dccp_csum_outgoing(struct sk_buff *skb)
+{
+        int cov = dccp_csum_coverage(skb);
+
+        if (cov >= skb->len)
+                dccp_hdr(skb)->dccph_cscov = 0;
+
+        skb->csum = skb_checksum(skb, 0, (cov > skb->len)? skb->len : cov, 0);
+}
+
+extern void dccp_v4_send_check(struct sock *sk, int len, struct sk_buff *skb);
+
 extern int  dccp_retransmit_skb(struct sock *sk, struct sk_buff *skb);
 
 extern void dccp_send_ack(struct sock *sk);
@@ -214,14 +238,9 @@ extern void	   dccp_shutdown(struct sock *sk, int how);
 extern int         inet_dccp_listen(struct socket *sock, int backlog);
 extern unsigned int dccp_poll(struct file *file, struct socket *sock,
                              poll_table *wait);
-extern void        dccp_v4_send_check(struct sock *sk, int len,
-                                      struct sk_buff *skb);
 extern int         dccp_v4_connect(struct sock *sk, struct sockaddr *uaddr,
                                    int addr_len);
 
-extern int         dccp_v4_checksum(const struct sk_buff *skb,
-                                    const __be32 saddr, const __be32 daddr);
-
 extern int         dccp_send_reset(struct sock *sk, enum dccp_reset_codes code);
 extern void        dccp_send_close(struct sock *sk, const int active);
 extern int         dccp_invalid_packet(struct sk_buff *skb);
diff --git a/net/dccp/ipv4.c b/net/dccp/ipv4.c
index 91bffaa761a6..496112080f3d 100644
--- a/net/dccp/ipv4.c
+++ b/net/dccp/ipv4.c
@@ -349,13 +349,19 @@ out:
         sock_put(sk);
 }
 
-/* This routine computes an IPv4 DCCP checksum. */
-void dccp_v4_send_check(struct sock *sk, int len, struct sk_buff *skb)
+static inline u16 dccp_v4_csum_finish(struct sk_buff *skb,
+                                      __be32 src, __be32 dst)
+{
+        return csum_tcpudp_magic(src, dst, skb->len, IPPROTO_DCCP, skb->csum);
+}
+
+void dccp_v4_send_check(struct sock *sk, int unused, struct sk_buff *skb)
 {
         const struct inet_sock *inet = inet_sk(sk);
         struct dccp_hdr *dh = dccp_hdr(skb);
 
-        dh->dccph_checksum = dccp_v4_checksum(skb, inet->saddr, inet->daddr);
+        dccp_csum_outgoing(skb);
+        dh->dccph_checksum = dccp_v4_csum_finish(skb, inet->saddr, inet->daddr);
 }
 
 EXPORT_SYMBOL_GPL(dccp_v4_send_check);
@@ -454,47 +460,6 @@ static struct sock *dccp_v4_hnd_req(struct sock *sk, struct sk_buff *skb)
         return sk;
 }
 
-int dccp_v4_checksum(const struct sk_buff *skb, const __be32 saddr,
-                     const __be32 daddr)
-{
-        const struct dccp_hdr* dh = dccp_hdr(skb);
-        int checksum_len;
-        u32 tmp;
-
-        if (dh->dccph_cscov == 0)
-                checksum_len = skb->len;
-        else {
-                checksum_len = (dh->dccph_cscov + dh->dccph_x) * sizeof(u32);
-                checksum_len = checksum_len < skb->len ? checksum_len :
-                                                         skb->len;
-        }
-
-        tmp = csum_partial((unsigned char *)dh, checksum_len, 0);
-        return csum_tcpudp_magic(saddr, daddr, checksum_len,
-                                 IPPROTO_DCCP, tmp);
-}
-
-EXPORT_SYMBOL_GPL(dccp_v4_checksum);
-
-static int dccp_v4_verify_checksum(struct sk_buff *skb,
-                                   const __be32 saddr, const __be32 daddr)
-{
-        struct dccp_hdr *dh = dccp_hdr(skb);
-        int checksum_len;
-        u32 tmp;
-
-        if (dh->dccph_cscov == 0)
-                checksum_len = skb->len;
-        else {
-                checksum_len = (dh->dccph_cscov + dh->dccph_x) * sizeof(u32);
-                checksum_len = checksum_len < skb->len ? checksum_len :
-                                                         skb->len;
-        }
-        tmp = csum_partial((unsigned char *)dh, checksum_len, 0);
-        return csum_tcpudp_magic(saddr, daddr, checksum_len,
-                                 IPPROTO_DCCP, tmp) == 0 ? 0 : -1;
-}
-
 static struct dst_entry* dccp_v4_route_skb(struct sock *sk,
                                            struct sk_buff *skb)
 {
@@ -536,8 +501,8 @@ static int dccp_v4_send_response(struct sock *sk, struct request_sock *req,
                 const struct inet_request_sock *ireq = inet_rsk(req);
                 struct dccp_hdr *dh = dccp_hdr(skb);
 
-                dh->dccph_checksum = dccp_v4_checksum(skb, ireq->loc_addr,
-                                                      ireq->rmt_addr);
+                dh->dccph_checksum = dccp_v4_csum_finish(skb, ireq->loc_addr,
+                                                              ireq->rmt_addr);
                 memset(&(IPCB(skb)->opt), 0, sizeof(IPCB(skb)->opt));
                 err = ip_build_and_send_pkt(skb, sk, ireq->loc_addr,
                                             ireq->rmt_addr,
@@ -602,8 +567,9 @@ static void dccp_v4_ctl_send_reset(struct sk_buff *rxskb)
         dccp_hdr_set_ack(dccp_hdr_ack_bits(skb),
                          DCCP_SKB_CB(rxskb)->dccpd_seq);
 
-        dh->dccph_checksum = dccp_v4_checksum(skb, rxskb->nh.iph->saddr,
-                                              rxskb->nh.iph->daddr);
+        dccp_csum_outgoing(skb);
+        dh->dccph_checksum = dccp_v4_csum_finish(skb, rxskb->nh.iph->saddr,
+                                                      rxskb->nh.iph->daddr);
 
         bh_lock_sock(dccp_v4_ctl_socket->sk);
         err = ip_build_and_send_pkt(skb, dccp_v4_ctl_socket->sk,
@@ -779,6 +745,7 @@ EXPORT_SYMBOL_GPL(dccp_v4_do_rcv);
 int dccp_invalid_packet(struct sk_buff *skb)
 {
         const struct dccp_hdr *dh;
+        unsigned int cscov;
 
         if (skb->pkt_type != PACKET_HOST)
                 return 1;
@@ -830,6 +797,22 @@ int dccp_invalid_packet(struct sk_buff *skb)
                 return 1;
         }
 
+        /*
+         * If P.CsCov is too large for the packet size, drop packet and return.
+         * This must come _before_ checksumming (not as RFC 4340 suggests).
+         */
+        cscov = dccp_csum_coverage(skb);
+        if (cscov > skb->len) {
+                LIMIT_NETDEBUG(KERN_WARNING
+                               "DCCP: P.CsCov %u exceeds packet length %d\n",
+                               dh->dccph_cscov, skb->len);
+                return 1;
+        }
+
+        /* If header checksum is incorrect, drop packet and return.
+         * (This step is completed in the AF-dependent functions.) */
+        skb->csum = skb_checksum(skb, 0, cscov, 0);
+
         return 0;
 }
 
@@ -840,16 +823,17 @@ static int dccp_v4_rcv(struct sk_buff *skb)
 {
         const struct dccp_hdr *dh;
         struct sock *sk;
+        int min_cov;
 
-        /* Step 1: Check header basics: */
+        /* Step 1: Check header basics */
 
         if (dccp_invalid_packet(skb))
                 goto discard_it;
 
-        /* If the header checksum is incorrect, drop packet and return */
-        if (dccp_v4_verify_checksum(skb, skb->nh.iph->saddr,
-                                    skb->nh.iph->daddr) < 0) {
-                LIMIT_NETDEBUG(KERN_WARNING "%s: incorrect header checksum\n",
+        /* Step 1: If header checksum is incorrect, drop packet and return */
+        if (dccp_v4_csum_finish(skb, skb->nh.iph->saddr, skb->nh.iph->daddr)) {
+                LIMIT_NETDEBUG(KERN_WARNING
+                               "%s: dropped packet with invalid checksum\n",
                                __FUNCTION__);
                 goto discard_it;
         }
@@ -905,6 +889,21 @@ static int dccp_v4_rcv(struct sk_buff *skb)
                 goto no_dccp_socket;
         }
 
+        /*
+         * RFC 4340, sec. 9.2.1: Minimum Checksum Coverage
+         *      o if MinCsCov = 0, only packets with CsCov = 0 are accepted
+         *      o if MinCsCov > 0, also accept packets with CsCov >= MinCsCov
+         */
+        min_cov = dccp_sk(sk)->dccps_pcrlen;
+        if (dh->dccph_cscov && (min_cov == 0 || dh->dccph_cscov < min_cov))  {
+                dccp_pr_debug("Packet CsCov %d does not satisfy MinCsCov %d\n",
+                              dh->dccph_cscov, min_cov);
+                /* FIXME: "Such packets SHOULD be reported using Data Dropped
+                 *         options (Section 11.7) with Drop Code 0, Protocol
+                 *         Constraints."                                     */
+                goto discard_and_relse;
+        }
+
         if (!xfrm4_policy_check(sk, XFRM_POLICY_IN, skb))
                 goto discard_and_relse;
         nf_reset(skb);
diff --git a/net/dccp/ipv6.c b/net/dccp/ipv6.c
index 201801e1532d..193b946fd039 100644
--- a/net/dccp/ipv6.c
+++ b/net/dccp/ipv6.c
@@ -58,12 +58,22 @@ static void dccp_v6_hash(struct sock *sk)
         }
 }
 
-static inline u16 dccp_v6_check(struct dccp_hdr *dh, int len,
-                                struct in6_addr *saddr,
-                                struct in6_addr *daddr,
-                                unsigned long base)
+/* add pseudo-header to DCCP checksum stored in skb->csum */
+static inline u16 dccp_v6_csum_finish(struct sk_buff *skb,
+                                      struct in6_addr *saddr,
+                                      struct in6_addr *daddr)
 {
-        return csum_ipv6_magic(saddr, daddr, len, IPPROTO_DCCP, base);
+        return csum_ipv6_magic(saddr, daddr, skb->len, IPPROTO_DCCP, skb->csum);
+}
+
+static inline void dccp_v6_send_check(struct sock *sk, int unused_value,
+                                      struct sk_buff *skb)
+{
+        struct ipv6_pinfo *np = inet6_sk(sk);
+        struct dccp_hdr *dh = dccp_hdr(skb);
+
+        dccp_csum_outgoing(skb);
+        dh->dccph_checksum = dccp_v6_csum_finish(skb, &np->saddr, &np->daddr);
 }
 
 static __u32 dccp_v6_init_sequence(struct sock *sk, struct sk_buff *skb)
@@ -280,12 +290,9 @@ static int dccp_v6_send_response(struct sock *sk, struct request_sock *req,
         if (skb != NULL) {
                 struct dccp_hdr *dh = dccp_hdr(skb);
 
-                dh->dccph_checksum = dccp_v6_check(dh, skb->len,
-                                                   &ireq6->loc_addr,
-                                                   &ireq6->rmt_addr,
-                                                   csum_partial((char *)dh,
-                                                                skb->len,
-                                                                skb->csum));
+                dh->dccph_checksum = dccp_v6_csum_finish(skb,
+                                                         &ireq6->loc_addr,
+                                                         &ireq6->rmt_addr);
                 ipv6_addr_copy(&fl.fl6_dst, &ireq6->rmt_addr);
                 err = ip6_xmit(sk, skb, &fl, opt, 0);
                 if (err == NET_XMIT_CN)
@@ -305,18 +312,6 @@ static void dccp_v6_reqsk_destructor(struct request_sock *req)
                 kfree_skb(inet6_rsk(req)->pktopts);
 }
 
-static void dccp_v6_send_check(struct sock *sk, int len, struct sk_buff *skb)
-{
-        struct ipv6_pinfo *np = inet6_sk(sk);
-        struct dccp_hdr *dh = dccp_hdr(skb);
-
-        dh->dccph_checksum = csum_ipv6_magic(&np->saddr, &np->daddr,
-                                             len, IPPROTO_DCCP,
-                                             csum_partial((char *)dh,
-                                                          dh->dccph_doff << 2,
-                                                          skb->csum));
-}
-
 static void dccp_v6_ctl_send_reset(struct sk_buff *rxskb)
 {
         struct dccp_hdr *rxdh = dccp_hdr(rxskb), *dh;
@@ -360,12 +355,14 @@ static void dccp_v6_ctl_send_reset(struct sk_buff *rxskb)
         dccp_hdr_set_ack(dccp_hdr_ack_bits(skb),
                          DCCP_SKB_CB(rxskb)->dccpd_seq);
 
+        dccp_csum_outgoing(skb);
+        dh->dccph_checksum = dccp_v6_csum_finish(skb, &rxskb->nh.ipv6h->saddr,
+                                                      &rxskb->nh.ipv6h->daddr);
+
         memset(&fl, 0, sizeof(fl));
         ipv6_addr_copy(&fl.fl6_dst, &rxskb->nh.ipv6h->saddr);
         ipv6_addr_copy(&fl.fl6_src, &rxskb->nh.ipv6h->daddr);
-        dh->dccph_checksum = csum_ipv6_magic(&fl.fl6_src, &fl.fl6_dst,
-                                             sizeof(*dh), IPPROTO_DCCP,
-                                             skb->csum);
+
         fl.proto = IPPROTO_DCCP;
         fl.oif = inet6_iif(rxskb);
         fl.fl_ip_dport = dh->dccph_dport;
@@ -825,12 +822,22 @@ static int dccp_v6_rcv(struct sk_buff **pskb)
         const struct dccp_hdr *dh;
         struct sk_buff *skb = *pskb;
         struct sock *sk;
+        int min_cov;
 
-        /* Step 1: Check header basics: */
+        /* Step 1: Check header basics */
 
         if (dccp_invalid_packet(skb))
                 goto discard_it;
 
+        /* Step 1: If header checksum is incorrect, drop packet and return. */
+        if (dccp_v6_csum_finish(skb, &skb->nh.ipv6h->saddr,
+                                     &skb->nh.ipv6h->daddr)) {
+                LIMIT_NETDEBUG(KERN_WARNING
+                               "%s: dropped packet with invalid checksum\n",
+                               __FUNCTION__);
+                goto discard_it;
+        }
+
         dh = dccp_hdr(skb);
 
         DCCP_SKB_CB(skb)->dccpd_seq  = dccp_hdr_seq(skb);
@@ -869,6 +876,19 @@ static int dccp_v6_rcv(struct sk_buff **pskb)
                 goto no_dccp_socket;
         }
 
+        /*
+         * RFC 4340, sec. 9.2.1: Minimum Checksum Coverage
+         *      o if MinCsCov = 0, only packets with CsCov = 0 are accepted
+         *      o if MinCsCov > 0, also accept packets with CsCov >= MinCsCov
+         */
+        min_cov = dccp_sk(sk)->dccps_pcrlen;
+        if (dh->dccph_cscov  &&  (min_cov == 0 || dh->dccph_cscov < min_cov))  {
+                dccp_pr_debug("Packet CsCov %d does not satisfy MinCsCov %d\n",
+                              dh->dccph_cscov, min_cov);
+                /* FIXME: send Data Dropped option (see also dccp_v4_rcv) */
+                goto discard_and_relse;
+        }
+
         if (!xfrm6_policy_check(sk, XFRM_POLICY_IN, skb))
                 goto discard_and_relse;
 
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;
 
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);