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update GridFTP analyzer to use connection thresholding instead

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of polling
This commit is contained in:
Johanna Amann 2015-04-17 07:15:53 -07:00
parent 86c54c3dbd
commit 024bb7206e
1 changed files with 32 additions and 33 deletions
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55
scripts/base/protocols/ftp/gridftp.bro
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@ -11,13 +11,13 @@
##! GridFTP data channels are identified by a heuristic that relies on
##! the fact that default settings for GridFTP clients typically
##! mutually authenticate the data channel with TLS/SSL and negotiate a
##! NULL bulk cipher (no encryption). Connections with those
##! attributes are then polled for two minutes with decreasing frequency
##! to check if the transfer sizes are large enough to indicate a
##! GridFTP data channel that would be undesirable to analyze further
##! (e.g. stop TCP reassembly). A side effect is that true connection
##! sizes are not logged, but at the benefit of saving CPU cycles that
##! would otherwise go to analyzing the large (and likely benign) connections.
##! NULL bulk cipher (no encryption). Connections with those attributes
##! are marked as GridFTP if the data transfer within the first two minites
##! is big enough to indicate a GripFTP data channel that would be
##! undesirable to analyze further (e.g. stop TCP reassembly). A side
##! effect is that true connection sizes are not logged, but at the benefit
##! of saving CPU cycles that would otherwise go to analyzing the large
##! (and likely benign) connections.
@load ./info
@load ./main
@ -32,23 +32,14 @@ export {
## GridFTP data channel.
const size_threshold = 1073741824 &redef;
## Max number of times to check whether a connection's size exceeds the
## Time dunring which we check whether a connection's size exceeds the
## :bro:see:`GridFTP::size_threshold`.
const max_poll_count = 15 &redef;
const max_time = 2 min &redef;
## Whether to skip further processing of the GridFTP data channel once
## detected, which may help performance.
const skip_data = T &redef;
## Base amount of time between checking whether a GridFTP data connection
## has transferred more than :bro:see:`GridFTP::size_threshold` bytes.
const poll_interval = 1sec &redef;
## The amount of time the base :bro:see:`GridFTP::poll_interval` is
## increased by each poll interval. Can be used to make more frequent
## checks at the start of a connection and gradually slow down.
const poll_interval_increase = 1sec &redef;
## Raised when a GridFTP data channel is detected.
##
## c: The connection pertaining to the GridFTP data channel.
@ -79,23 +70,27 @@ event ftp_request(c: connection, command: string, arg: string) &priority=4
c$ftp$last_auth_requested = arg;
}
function size_callback(c: connection, cnt: count): interval
{
if ( c$orig$size > size_threshold || c$resp$size > size_threshold )
event ConnThreshold::bytes_threshold_crossed(c: connection, threshold: count, is_orig: bool)
{
if ( threshold < size_threshold || c$duration > max_time )
return;
add c$service["gridftp-data"];
event GridFTP::data_channel_detected(c);
if ( skip_data )
skip_further_processing(c$id);
return -1sec;
}
if ( cnt >= max_poll_count )
return -1sec;
return poll_interval + poll_interval_increase * cnt;
event gridftp_possibility_timeout(c: connection)
{
# only remove if we did not already detect it and the connection
# is not yet at its end.
if ( "gridftp-data" !in c$service && ! c$conn?$service )
{
ConnThreshold::delete_bytes_threshold(c, size_threshold, T);
ConnThreshold::delete_bytes_threshold(c, size_threshold, F);
}
}
event ssl_established(c: connection) &priority=5
@ -118,5 +113,9 @@ event ssl_established(c: connection) &priority=-3
# By default GridFTP data channels do mutual authentication and
# negotiate a cipher suite with a NULL bulk cipher.
if ( data_channel_initial_criteria(c) )
ConnPolling::watch(c, size_callback, 0, 0secs);
{
ConnThreshold::set_bytes_threshold(c, size_threshold, T);
ConnThreshold::set_bytes_threshold(c, size_threshold, F);
schedule max_time { gridftp_possibility_timeout(c) };
}
}