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authorGerrit Renker <gerrit@erg.abdn.ac.uk>2008-06-11 06:19:09 -0400
committerGerrit Renker <gerrit@erg.abdn.ac.uk>2008-06-11 06:19:09 -0400
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 f813077234b7..0474f4c5707a 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)
329 hctx->ccid3hctx_x = rfc3390_initial_rate(sk); 329 hctx->ccid3hctx_x = rfc3390_initial_rate(sk);
330 hctx->ccid3hctx_t_ld = now; 330 hctx->ccid3hctx_t_ld = now;
331 } else { 331 } else {
332 /* Sender does not have RTT sample: X_pps = 1 pkt/sec */ 332 /*
333 hctx->ccid3hctx_x = hctx->ccid3hctx_s; 333 * Sender does not have RTT sample:
334 * - set fallback RTT (RFC 4340, 3.4) since a RTT value
335 * is needed in several parts (e.g. window counter);
336 * - set sending rate X_pps = 1pps as per RFC 3448, 4.2.
337 */
338 hctx->ccid3hctx_rtt = DCCP_FALLBACK_RTT;
339 hctx->ccid3hctx_x = hctx->ccid3hctx_s;
334 hctx->ccid3hctx_x <<= 6; 340 hctx->ccid3hctx_x <<= 6;
335 } 341 }
336 ccid3_update_send_interval(hctx); 342 ccid3_update_send_interval(hctx);