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| author | Gerrit Renker <gerrit@erg.abdn.ac.uk> | 2007-09-26 07:41:56 +0200 |
|---|---|---|
| committer | David S. Miller <davem@sunset.davemloft.net> | 2007-10-11 01:52:37 +0200 |
| commit | e155d7692290f7bc539ccb8ebc3450ec964e53fd (patch) | |
| tree | ceca4fe0902c5efc8fb0936ec40d9482907d5d3a /net/dccp/input.c | |
| parent | [DCCP]: Shorten variable names in dccp_check_seqno (diff) | |
| download | linux-e155d7692290f7bc539ccb8ebc3450ec964e53fd.tar.xz linux-e155d7692290f7bc539ccb8ebc3450ec964e53fd.zip | |
[DCCP]: Fix Reset/Sync-Flood Bug
This updates sequence number checking with regard to RFC 4340, 7.5.4.
Missing in the code was an exception for sequence-invalid Reset packets,
which get a Sync acknowledging GSR, instead of (as usual) P.seqno.
This can lead to an oscillating ping-pong flood of Reset packets.
In fact, it has been observed on the wire as follows:
1. client establishes connection to server;
2. before server can write to client, client crashes without notifying
the server (NB: now no longer possible due to ABORT function);
3. server sends DCCP-Data packet (has no ackno);
4. client generates Reset "No Connection", seqno=0, increments seqno;
5. server replies with Sync, using ackno = P.seqno;
6. client generates Reset "No Connection" with seqno = ackno + 1;
7. goto (5).
The difference is that now in (5) the server uses GSR. This causes the
Reset sent by the client in (6) to become sequence-valid, so that in (7)
the vicious circle is broken; the Reset is then enqueued and causes the
socket to enter TIMEWAIT state.
Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: Ian McDonald <ian.mcdonald@jandi.co.nz>
Signed-off-by: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/dccp/input.c')
| -rw-r--r-- | net/dccp/input.c | 14 |
1 files changed, 11 insertions, 3 deletions
diff --git a/net/dccp/input.c b/net/dccp/input.c index 6276b23fc204..cde0e704dfce 100644 --- a/net/dccp/input.c +++ b/net/dccp/input.c @@ -102,9 +102,6 @@ static int dccp_check_seqno(struct sock *sk, struct sk_buff *skb) * Update S.GSR, S.SWL, S.SWH * If P.type != Sync, * Update S.GAR - * Otherwise, - * Send Sync packet acknowledging P.seqno - * Drop packet and return */ lswl = dp->dccps_swl; lawl = dp->dccps_awl; @@ -135,6 +132,17 @@ static int dccp_check_seqno(struct sock *sk, struct sk_buff *skb) : "exists", (unsigned long long) lawl, (unsigned long long) ackno, (unsigned long long) dp->dccps_awh); + /* + * Step 6: Check sequence numbers + * Otherwise, + * If P.type == Reset, + * Send Sync packet acknowledging S.GSR + * Otherwise, + * Send Sync packet acknowledging P.seqno + * Drop packet and return + */ + if (dh->dccph_type == DCCP_PKT_RESET) + seqno = dp->dccps_gsr; dccp_send_sync(sk, seqno, DCCP_PKT_SYNC); return -1; } |