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authorGerrit Renker <gerrit@erg.abdn.ac.uk>2010-10-11 20:35:40 +0200
committerGerrit Renker <gerrit@erg.abdn.ac.uk>2010-10-12 06:57:40 +0200
commit0b53d4604ac2b4f2faa9a62a04ea9b383ad2efe0 (patch)
tree70ed0d136ef719f33655f78b31650d1c88cd3e00 /net/dccp
parent0ed8ddf4045fcfcac36bad753dc4046118c603ec (diff)
downloadvexpress-lsk-0b53d4604ac2b4f2faa9a62a04ea9b383ad2efe0.tar.gz
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>
Diffstat (limited to 'net/dccp')
-rw-r--r--net/dccp/dccp.h20
-rw-r--r--net/dccp/input.c18
-rw-r--r--net/dccp/minisocks.c30
3 files changed, 35 insertions, 33 deletions
diff --git a/net/dccp/dccp.h b/net/dccp/dccp.h
index 019d6ffee35..e051c774ef5 100644
--- a/net/dccp/dccp.h
+++ b/net/dccp/dccp.h
@@ -414,6 +414,23 @@ 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);
}
@@ -424,6 +441,9 @@ 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;
}
diff --git a/net/dccp/input.c b/net/dccp/input.c
index 10c957a88f4..aecc8c7443c 100644
--- a/net/dccp/input.c
+++ b/net/dccp/input.c
@@ -441,20 +441,14 @@ static int dccp_rcv_request_sent_state_process(struct sock *sk,
kfree_skb(sk->sk_send_head);
sk->sk_send_head = NULL;
- dp->dccps_isr = DCCP_SKB_CB(skb)->dccpd_seq;
- dccp_update_gsr(sk, dp->dccps_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.
- *
- * AWL was adjusted in dccp_v4_connect -acme
+ * Set ISR, GSR from packet. ISS was set in dccp_v{4,6}_connect
+ * and GSS in dccp_transmit_skb(). Setting AWL/AWH and SWL/SWH
+ * is done as part of activating the feature values below, since
+ * these settings depend on the local/remote Sequence Window
+ * features, which were undefined or not confirmed until now.
*/
- dccp_set_seqno(&dp->dccps_swl,
- max48(dp->dccps_swl, dp->dccps_isr));
+ dp->dccps_gsr = dp->dccps_isr = DCCP_SKB_CB(skb)->dccpd_seq;
dccp_sync_mss(sk, icsk->icsk_pmtu_cookie);
diff --git a/net/dccp/minisocks.c b/net/dccp/minisocks.c
index 128b089d3ae..d7041a0963a 100644
--- a/net/dccp/minisocks.c
+++ b/net/dccp/minisocks.c
@@ -121,30 +121,18 @@ struct sock *dccp_create_openreq_child(struct sock *sk,
*
* 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
- */
- 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);
-
- /*
- * 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.
+ * 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).
*/
- 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));
+ newdp->dccps_gss = newdp->dccps_iss = dreq->dreq_iss;
+ newdp->dccps_gar = newdp->dccps_iss;
+ newdp->dccps_gsr = newdp->dccps_isr = dreq->dreq_isr;
/*
- * 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