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authorGerrit Renker <gerrit@erg.abdn.ac.uk>2007-09-26 09:41:56 +0400
committerDavid S. Miller <davem@sunset.davemloft.net>2007-10-11 03:52:37 +0400
commite155d7692290f7bc539ccb8ebc3450ec964e53fd (patch)
treececa4fe0902c5efc8fb0936ec40d9482907d5d3a /net/dccp/input.c
parentcbe1f5f88af454303a9c1a0624209269430d49fe (diff)
downloadlinux-e155d7692290f7bc539ccb8ebc3450ec964e53fd.tar.xz
[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.c14
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;
}