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| author | Gerrit Renker <gerrit@erg.abdn.ac.uk> | 2008-06-11 14:19:09 +0400 |
|---|---|---|
| committer | Gerrit Renker <gerrit@erg.abdn.ac.uk> | 2008-06-11 14:19:09 +0400 |
| commit | 3294f202dc1acd82223e83ef59f272bd87bb06b2 (patch) | |
| tree | b3841a093322afbc7cd608ccc6ae60debe8c015a /net/dccp | |
| parent | 513fd370e6832f81ab717df4645f5ce679e44f14 (diff) | |
| download | linux-3294f202dc1acd82223e83ef59f272bd87bb06b2.tar.xz | |
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>
Diffstat (limited to 'net/dccp')
| -rw-r--r-- | net/dccp/ccids/ccid3.c | 10 |
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) 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); |