dccp: fix the adjustments to AWL and SWL
This fixes a problem and a potential loophole with regard to seqno/ackno
validity: currently the initial adjustments to AWL/SWL are only performed
once at the begin of the connection, during the handshake.
Since the Sequence Window feature is always greater than Wmin=32 (7.5.2),
it is however necessary to perform these adjustments at least for the first
W/W' (variables as per 7.5.1) packets in the lifetime of a connection.
This requirement is complicated by the fact that W/W' can change at any time
during the lifetime of a connection.
Therefore it is better to perform that safety check each time SWL/AWL are
updated, as implemented by the patch.
A second problem solved by this patch is that the remote/local Sequence Window
feature values (which set the bounds for AWL/SWL/SWH) are undefined until the
feature negotiation has completed.
During the initial handshake we have more stringent sequence number protection;
the changes added by this patch effect that {A,S}W{L,H} are within the correct
bounds at the instant that feature negotiation completes (since the SeqWin
feature activation handlers call dccp_update_gsr/gss()).
Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
diff --git a/net/dccp/minisocks.c b/net/dccp/minisocks.c
index 128b089..d7041a0 100644
--- a/net/dccp/minisocks.c
+++ b/net/dccp/minisocks.c
@@ -121,30 +121,18 @@
*
* Choose S.ISS (initial seqno) or set from Init Cookies
* Initialize S.GAR := S.ISS
- * Set S.ISR, S.GSR, S.SWL, S.SWH from packet or Init Cookies
+ * Set S.ISR, S.GSR from packet (or Init Cookies)
+ *
+ * Setting AWL/AWH and SWL/SWH happens as part of the feature
+ * activation below, as these windows all depend on the local
+ * and remote Sequence Window feature values (7.5.2).
*/
- newdp->dccps_gar = newdp->dccps_iss = dreq->dreq_iss;
- dccp_update_gss(newsk, dreq->dreq_iss);
-
- newdp->dccps_isr = dreq->dreq_isr;
- dccp_update_gsr(newsk, dreq->dreq_isr);
+ newdp->dccps_gss = newdp->dccps_iss = dreq->dreq_iss;
+ newdp->dccps_gar = newdp->dccps_iss;
+ newdp->dccps_gsr = newdp->dccps_isr = dreq->dreq_isr;
/*
- * SWL and AWL are initially adjusted so that they are not less than
- * the initial Sequence Numbers received and sent, respectively:
- * SWL := max(GSR + 1 - floor(W/4), ISR),
- * AWL := max(GSS - W' + 1, ISS).
- * These adjustments MUST be applied only at the beginning of the
- * connection.
- */
- dccp_set_seqno(&newdp->dccps_swl,
- max48(newdp->dccps_swl, newdp->dccps_isr));
- dccp_set_seqno(&newdp->dccps_awl,
- max48(newdp->dccps_awl, newdp->dccps_iss));
-
- /*
- * Activate features after initialising the sequence numbers,
- * since CCID initialisation may depend on GSS, ISR, ISS etc.
+ * Activate features: initialise CCIDs, sequence windows etc.
*/
if (dccp_feat_activate_values(newsk, &dreq->dreq_featneg)) {
/* It is still raw copy of parent, so invalidate