grossd(8)grossd(8)NAMEgrossd - Greylisting of Suspicious Sources - the Server
SYNOPSISgrossd [-dCDhnrV] [-f config] [{-p|-P} pidfile]
DESCRIPTIONgrossd is a greylisting server, and more. It's blazingly fast and
amazingly resource efficient. It can be configured to query DNSBL
databases, and enforce greylisting only for hosts that are found on
those databases. It can block hosts that match multiple databases. It
can be replicated and run parallel on two servers. It supports Sun
Java System Messaging Server, Postfix and Exim. Sendmail Milter
implementation needs testing.
Theory of operation
Gross consists of grossd, the greylisting daemon, and a client library
for SJSMS. The server also implements Postfix content filtering
protocol.
Upon receiving a request from a client, grossd first validates it. The
request includes a triplet (`smtp-client-ip', `sender-address',
`recipient-address'). A hash is then calculated and matched against
the Bloom filters. If a match is found, and test result does not
exceed block_threshold value, grossd sends an OK (STATUS_TRUST)
message.
If the triplet is not in the Bloom filters (has not been seen
recently,) grossd then runs configured checks against the client
information. Based on check results grossd returns the client a
result. Possible results are STATUS_TRUST, STATUS_BLOCK and
STATUS_GREY. The final response is query protocol specific.
The Bloom filters are updated according the update configuration
option. A Bloom filter is a very efficient way to store data. It's a
probabilistic data structure, which means that there is a possibility
of error when querying the database. False positives are possible, but
false negatives are not. This means that there is a possibility that
grossd will falsely give an STATUS_TRUST response when a connection
should be greylisted. By sizing the bloom filters, you can control the
error possibility to meet your needs. The right bloom filter size
depends on the number of entries in the database, that is, the
retention time versus the number of handled connections.
OPTIONS-C Create the statefile and exit. The statefile configuration option
must be specified in the configuration file.
-D Make debugging output more verbose. It can be set twice for
maximum verbosity.
-d Run grossd on foreground without daemonizing the process. grossd
will output to terminal instead of using syslog.
-f config
Specifies the name of the configuration file. The default is
/etc/etc/grossd.conf
-h Output short usage information and exit.
-n Enable dry-run.
-P pidfile
Bail out if the pidfile already exists. Create pidfile after the
check.
-p pidfile
Create the pidfile. Overwrite if it already exists.
-r Disable replication.
-V Output version information and exit.
FILES
/etc/grossd.conf
SECURITY CONSIDERATIONS
Run grossd under some unprivileged user id. If started as root grossd
will setuid() itself to nobody's user id. There are no known security
flaws but you must not expose grossd to the Internet. It could be used
for a DoS against a domain's DNS servers by an attacker as there is no
authentication in grossd.
DIAGNOSTICSgrossd daemon exits 0 if success, and >0 if an error occurs.
SEE ALSO
Regarding the configuration both the daemon and MTA's, refer to
grossd.conf(5)
Gross project site: <http://code.google.com/p/gross/>
Bloom filters: <http://en.wikipedia.org/wiki/Bloom_filter>
DNS queries are done asynchronously using c-ares library
<http://daniel.haxx.se/projects/c-ares/>.
AUTHORS
Eino Tuominen and Antti Siira
2008-05-04 grossd(8)
