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-rw-r--r--net/dccp/dccp.h20
1 files changed, 20 insertions, 0 deletions
diff --git a/net/dccp/dccp.h b/net/dccp/dccp.h
index f9ed0cbd1bf..e4d6e76ced4 100644
--- a/net/dccp/dccp.h
+++ b/net/dccp/dccp.h
@@ -415,6 +415,23 @@ 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);
}
@@ -425,6 +442,9 @@ 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;
}