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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 /include | |
| parent | ee1a15922d356aff0e31bf9bb9088ab346b8033a (diff) | |
| download | lwn-a94f0f970549e63e54c80c4509db299c514d8c11.tar.gz lwn-a94f0f970549e63e54c80c4509db299c514d8c11.zip | |
[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 'include')
| -rw-r--r-- | include/linux/dccp.h | 2 |
1 files changed, 2 insertions, 0 deletions
diff --git a/include/linux/dccp.h b/include/linux/dccp.h index 20e0717aa8e1..4ed82e2c9f65 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; |