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| author | Gerrit Renker <gerrit@erg.abdn.ac.uk> | 2007-09-26 11:31:49 -0300 |
|---|---|---|
| committer | David S. Miller <davem@sunset.davemloft.net> | 2007-10-10 16:52:43 -0700 |
| commit | a94f0f970549e63e54c80c4509db299c514d8c11 (patch) | |
| tree | 3b9421fc70e00c16ed57ef4330b24504b04ae309 /net/dccp/sysctl.c | |
| parent | ee1a15922d356aff0e31bf9bb9088ab346b8033a (diff) | |
| download | linux-a94f0f970549e63e54c80c4509db299c514d8c11.tar.bz2 | |
[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 <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>
Diffstat (limited to 'net/dccp/sysctl.c')
| -rw-r--r-- | net/dccp/sysctl.c | 10 |
1 files changed, 10 insertions, 0 deletions
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, } }; |