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/sysctl.c | 10 ++++++++++ 1 file changed, 10 insertions(+) (limited to 'net/dccp/sysctl.c') diff --git a/net/dccp/sysctl.c b/net/dccp/sysctl.c index 1260aabac5e1..9364b2fb4dbd 100644 --- a/net/dccp/sysctl.c +++ b/net/dccp/sysctl.c @@ -18,6 +18,9 @@ #error This file should not be compiled without CONFIG_SYSCTL defined #endif +/* rate-limit for syncs in reply to sequence-invalid packets; RFC 4340, 7.5.4 */ +int sysctl_dccp_sync_ratelimit __read_mostly = HZ / 8; + static struct ctl_table dccp_default_table[] = { { .procname = "seq_window", @@ -89,6 +92,13 @@ static struct ctl_table dccp_default_table[] = { .mode = 0644, .proc_handler = proc_dointvec, }, + { + .procname = "sync_ratelimit", + .data = &sysctl_dccp_sync_ratelimit, + .maxlen = sizeof(sysctl_dccp_sync_ratelimit), + .mode = 0644, + .proc_handler = proc_dointvec_ms_jiffies, + }, { .ctl_name = 0, } }; -- cgit v1.2.3