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authorGerrit Renker <gerrit@erg.abdn.ac.uk>2008-06-11 11:19:09 +0100
committerGerrit Renker <gerrit@erg.abdn.ac.uk>2008-06-11 11:19:09 +0100
commit3294f202dc1acd82223e83ef59f272bd87bb06b2 (patch)
treeb3841a093322afbc7cd608ccc6ae60debe8c015a
parent513fd370e6832f81ab717df4645f5ce679e44f14 (diff)
dccp ccid-3: Bug-Fix - Zero RTT is possible
In commit $(825de27d9e40b3117b29a79d412b7a4b78c5d815) (from 27th May, commit message `dccp ccid-3: Fix "t_ipi explosion" bug'), the CCID-3 window counter computation was fixed to cope with RTTs < 4 microseconds. Such RTTs can be found e.g. when running CCID-3 over loopback. The fix removed a check against RTT < 4, but introduced a divide-by-zero bug. All steady-state RTTs in DCCP are filtered using dccp_sample_rtt(), which ensures non-zero samples. However, a zero RTT is possible on initialisation, when there is no RTT sample from the Request/Response exchange. The fix is to use the fallback-RTT from RFC 4340, 3.4. This is also better than just fixing update_win_count() since it allows other parts of the code to always assume that the RTT is non-zero during the time that the CCID is used. Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
-rw-r--r--net/dccp/ccids/ccid3.c10
1 files changed, 8 insertions, 2 deletions
diff --git a/net/dccp/ccids/ccid3.c b/net/dccp/ccids/ccid3.c
index f813077234b..0474f4c5707 100644
--- a/net/dccp/ccids/ccid3.c
+++ b/net/dccp/ccids/ccid3.c
@@ -329,8 +329,14 @@ static int ccid3_hc_tx_send_packet(struct sock *sk, struct sk_buff *skb)
hctx->ccid3hctx_x = rfc3390_initial_rate(sk);
hctx->ccid3hctx_t_ld = now;
} else {
- /* Sender does not have RTT sample: X_pps = 1 pkt/sec */
- hctx->ccid3hctx_x = hctx->ccid3hctx_s;
+ /*
+ * Sender does not have RTT sample:
+ * - set fallback RTT (RFC 4340, 3.4) since a RTT value
+ * is needed in several parts (e.g. window counter);
+ * - set sending rate X_pps = 1pps as per RFC 3448, 4.2.
+ */
+ hctx->ccid3hctx_rtt = DCCP_FALLBACK_RTT;
+ hctx->ccid3hctx_x = hctx->ccid3hctx_s;
hctx->ccid3hctx_x <<= 6;
}
ccid3_update_send_interval(hctx);