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 --- include/linux/dccp.h | 2 ++ 1 file changed, 2 insertions(+) (limited to 'include') diff --git a/include/linux/dccp.h b/include/linux/dccp.h index 20e0717aa8e..4ed82e2c9f6 100644 --- a/include/linux/dccp.h +++ b/include/linux/dccp.h @@ -470,6 +470,7 @@ struct dccp_ackvec; * @dccps_pcrlen - receiver partial checksum coverage (via sockopt) * @dccps_ndp_count - number of Non Data Packets since last data packet * @dccps_mss_cache - current value of MSS (path MTU minus header sizes) + * @dccps_rate_last - timestamp for rate-limiting DCCP-Sync (RFC 4340, 7.5.4) * @dccps_minisock - associated minisock (accessed via dccp_msk) * @dccps_hc_rx_ackvec - rx half connection ack vector * @dccps_hc_rx_ccid - CCID used for the receiver (or receiving half-connection) @@ -505,6 +506,7 @@ struct dccp_sock { __u16 dccps_pcrlen; unsigned long dccps_ndp_count; __u32 dccps_mss_cache; + unsigned long dccps_rate_last; struct dccp_minisock dccps_minisock; struct dccp_ackvec *dccps_hc_rx_ackvec; struct ccid *dccps_hc_rx_ccid; -- cgit v1.2.3-70-g09d2