1 files changed, 36 insertions, 8 deletions

diff --git a/net/dccp/dccp.h b/net/dccp/dccp.h
index 019d6ffee354..3eb264b60823 100644
--- a/net/dccp/dccp.h
+++ b/net/dccp/dccp.h
@@ -153,18 +153,27 @@ static inline u64 max48(const u64 seq1, const u64 seq2)
 }
 
 /**
- * dccp_loss_free  -  Evaluates condition for data loss from RFC 4340, 7.7.1
- * @s1:  start sequence number
- * @s2:  end sequence number
+ * dccp_loss_count - Approximate the number of lost data packets in a burst loss
+ * @s1:  last known sequence number before the loss ('hole')
+ * @s2:  first sequence number seen after the 'hole'
  * @ndp: NDP count on packet with sequence number @s2
- * Returns true if the sequence range s1...s2 has no data loss.
  */
-static inline bool dccp_loss_free(const u64 s1, const u64 s2, const u64 ndp)
+static inline u64 dccp_loss_count(const u64 s1, const u64 s2, const u64 ndp)
 {
         s64 delta = dccp_delta_seqno(s1, s2);
 
         WARN_ON(delta < 0);
-        return (u64)delta <= ndp + 1;
+        delta -= ndp + 1;
+
+        return delta > 0 ? delta : 0;
+}
+
+/**
+ * dccp_loss_free - Evaluate condition for data loss from RFC 4340, 7.7.1
+ */
+static inline bool dccp_loss_free(const u64 s1, const u64 s2, const u64 ndp)
+{
+        return dccp_loss_count(s1, s2, ndp) == 0;
 }
 
 enum {
@@ -414,6 +423,23 @@ static inline void dccp_update_gsr(struct sock *sk, u64 seq)
         dp->dccps_gsr = seq;
         /* Sequence validity window depends on remote Sequence Window (7.5.1) */
         dp->dccps_swl = SUB48(ADD48(dp->dccps_gsr, 1), dp->dccps_r_seq_win / 4);
+        /*
+         * Adjust SWL so that it is not below ISR. In contrast to RFC 4340,
+         * 7.5.1 we perform this check beyond the initial handshake: W/W' are
+         * always > 32, so for the first W/W' packets in the lifetime of a
+         * connection we always have to adjust SWL.
+         * A second reason why we are doing this is that the window depends on
+         * the feature-remote value of Sequence Window: nothing stops the peer
+         * from updating this value while we are busy adjusting SWL for the
+         * first W packets (we would have to count from scratch again then).
+         * Therefore it is safer to always make sure that the Sequence Window
+         * is not artificially extended by a peer who grows SWL downwards by
+         * continually updating the feature-remote Sequence-Window.
+         * If sequence numbers wrap it is bad luck. But that will take a while
+         * (48 bit), and this measure prevents Sequence-number attacks.
+         */
+        if (before48(dp->dccps_swl, dp->dccps_isr))
+                dp->dccps_swl = dp->dccps_isr;
         dp->dccps_swh = ADD48(dp->dccps_gsr, (3 * dp->dccps_r_seq_win) / 4);
 }
 
@@ -424,14 +450,16 @@ static inline void dccp_update_gss(struct sock *sk, u64 seq)
         dp->dccps_gss = seq;
         /* Ack validity window depends on local Sequence Window value (7.5.1) */
         dp->dccps_awl = SUB48(ADD48(dp->dccps_gss, 1), dp->dccps_l_seq_win);
+        /* Adjust AWL so that it is not below ISS - see comment above for SWL */
+        if (before48(dp->dccps_awl, dp->dccps_iss))
+                dp->dccps_awl = dp->dccps_iss;
         dp->dccps_awh = dp->dccps_gss;
 }
 
 static inline int dccp_ack_pending(const struct sock *sk)
 {
         const struct dccp_sock *dp = dccp_sk(sk);
-        return dp->dccps_timestamp_echo != 0 ||
-               (dp->dccps_hc_rx_ackvec != NULL &&
+        return (dp->dccps_hc_rx_ackvec != NULL &&
                 dccp_ackvec_pending(dp->dccps_hc_rx_ackvec)) ||
                inet_csk_ack_scheduled(sk);
 }