2 files changed, 18 insertions, 2 deletions

diff --git a/net/dccp/dccp.h b/net/dccp/dccp.h
index 08a569ff02d1..d6bc47363b1c 100644
--- a/net/dccp/dccp.h
+++ b/net/dccp/dccp.h
@@ -63,11 +63,14 @@ extern void dccp_time_wait(struct sock *sk, int state, int timeo);
  *    - DCCP-Reset    with ACK Subheader and 4 bytes of Reset Code fields
  *  Hence a safe upper bound for the maximum option length is 1020-28 = 992
  */
-#define MAX_DCCP_SPECIFIC_HEADER (255 * sizeof(int))
+#define MAX_DCCP_SPECIFIC_HEADER (255 * sizeof(uint32_t))
 #define DCCP_MAX_PACKET_HDR 28
 #define DCCP_MAX_OPT_LEN (MAX_DCCP_SPECIFIC_HEADER - DCCP_MAX_PACKET_HDR)
 #define MAX_DCCP_HEADER (MAX_DCCP_SPECIFIC_HEADER + MAX_HEADER)
 
+/* Upper bound for initial feature-negotiation overhead (padded to 32 bits) */
+#define DCCP_FEATNEG_OVERHEAD    (32 * sizeof(uint32_t))
+
 #define DCCP_TIMEWAIT_LEN (60 * HZ) /* how long to wait to destroy TIME-WAIT
                                      * state, about 60 seconds */
 
diff --git a/net/dccp/output.c b/net/dccp/output.c
index 27c79bcc6a1e..36bcc00654d3 100644
--- a/net/dccp/output.c
+++ b/net/dccp/output.c
@@ -276,7 +276,20 @@ void dccp_write_xmit(struct sock *sk, int block)
                         const int len = skb->len;
 
                         if (sk->sk_state == DCCP_PARTOPEN) {
-                                /* See 8.1.5.  Handshake Completion */
+                                const u32 cur_mps = dp->dccps_mss_cache - DCCP_FEATNEG_OVERHEAD;
+                                /*
+                                 * See 8.1.5 - Handshake Completion.
+                                 *
+                                 * For robustness we resend Confirm options until the client has
+                                 * entered OPEN. During the initial feature negotiation, the MPS
+                                 * is smaller than usual, reduced by the Change/Confirm options.
+                                 */
+                                if (!list_empty(&dp->dccps_featneg) && len > cur_mps) {
+                                        DCCP_WARN("Payload too large (%d) for featneg.\n", len);
+                                        dccp_send_ack(sk);
+                                        dccp_feat_list_purge(&dp->dccps_featneg);
+                                }
+
                                 inet_csk_schedule_ack(sk);
                                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
                                                   inet_csk(sk)->icsk_rto,