From e155d7692290f7bc539ccb8ebc3450ec964e53fd Mon Sep 17 00:00:00 2001 From: Gerrit Renker Date: Tue, 25 Sep 2007 22:41:56 -0700 Subject: [PATCH] [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 Signed-off-by: Ian McDonald Signed-off-by: Arnaldo Carvalho de Melo Signed-off-by: David S. Miller --- net/dccp/input.c | 14 +++++++++++--- 1 file 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; } -- 2.20.1