Commit 825de27d9e40b3117b29a79d412b7a4b78c5d815 fixed the CCID-3 window counter
computation for RTTs < 4 microseconds (as happens on loopback).
Since it uses the term "1/RTT", it needs to be protected against divide-by-zero,
done in established state using dccp_sample_rtt().
But there was an oversight, as a zero RTT can happen on sender 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 a (fallback) RTT value is available.
Signed-off-by: Gerrit Renker <gerrit@xxxxxxxxxxxxxx>
---
net/dccp/ccids/ccid3.c | 10 ++++++++--
1 files changed, 8 insertions(+), 2 deletions(-)
--- 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);
--
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