From a94f0f970549e63e54c80c4509db299c514d8c11 Mon Sep 17 00:00:00 2001 From: Gerrit Renker Date: Wed, 26 Sep 2007 11:31:49 -0300 Subject: [DCCP]: Rate-limit DCCP-Syncs This implements a SHOULD from RFC 4340, 7.5.4: "To protect against denial-of-service attacks, DCCP implementations SHOULD impose a rate limit on DCCP-Syncs sent in response to sequence-invalid packets, such as not more than eight DCCP-Syncs per second." The rate-limit is maintained on a per-socket basis. This is a more stringent policy than enforcing the rate-limit on a per-source-address basis and protects against attacks with forged source addresses. Moreover, the mechanism is deliberately kept simple. In contrast to xrlim_allow(), bursts of Sync packets in reply to sequence-invalid packets are not supported. This foils such attacks where the receipt of a Sync triggers further sequence-invalid packets. (I have tested this mechanism against xrlim_allow algorithm for Syncs, permitting bursts just increases the problems.) In order to keep flexibility, the timeout parameter can be set via sysctl; and the whole mechanism can even be disabled (which is however not recommended). The algorithm in this patch has been improved with regard to wrapping issues thanks to a suggestion by Arnaldo. Commiter note: Rate limited the step 6 DCCP_WARN too, as it says we're sending a sync. Signed-off-by: Gerrit Renker Signed-off-by: Ian McDonald Signed-off-by: Arnaldo Carvalho de Melo --- net/dccp/dccp.h | 1 + 1 file changed, 1 insertion(+) (limited to 'net/dccp/dccp.h') diff --git a/net/dccp/dccp.h b/net/dccp/dccp.h index e282201..a602d92 100644 --- a/net/dccp/dccp.h +++ b/net/dccp/dccp.h @@ -92,6 +92,7 @@ extern int sysctl_dccp_feat_ack_ratio; extern int sysctl_dccp_feat_send_ack_vector; extern int sysctl_dccp_feat_send_ndp_count; extern int sysctl_dccp_tx_qlen; +extern int sysctl_dccp_sync_ratelimit; /* * 48-bit sequence number arithmetic (signed and unsigned) -- cgit v1.1