ulogd, the Userspace logging daemon.
ulogd makes use of the Linux >= 2.4.x packet filter subsystem (iptables) and
the ULOG target for iptables.
I want to provide a flexible, almost universal logging daemon for my netfilter ULOG target. It is not optimized in any way, the goal is to keep as simple as possible. These are my thoughts about how the architecture which is most capable of doing that:
It should be possible to add plugins / runtime modules for new protocols, etc. For example the standard logging daemon provides source-ip, dest-ip, source-port, dest-port, etc. Logging for variuos other protocols (GRE, IPsec, ...) may be implemented as modules.
... describe how and where to put the information gained by logging plugins. The easiest way is to build a line per packet and fprint it to a file. Some people might want to log into a SQL database or want an output conforming to the intrusion detection systems communication draft from the IETF.
The major clue is providing a framework which is as flexible as possible. Nobody knows what strange network protocols are out there :) Flexibility depends on the communication between the output of the logging plugins and input of the output plugins.
Rusty advised me to use some kind of type-key-value triples, which is in fact what I implemented.
One issue is, of course, performance. Up to ulogd 0.3, ulogd did several linked list iterations and about 30 malloc() calls _per packet_. This changed with the new >= 0.9 revisions:
First you will need a recent 2.4.x kernel. If you have a kernel >= 2.4.18-pre8, it already has the kernel suport for ULOG (ipt_ULOG.o).
If you have an older kernel version (between 2.4.0 and 2.4.18-pre6), you can use the patch-o-matic system of netfilter/iptables, as described in the following section.
You only need to read this chapter if you have a 2.4.x kernel <= 2.4.18-pre6.
In order to put the ipt_ULOG module into your kernel source,you need the latest iptables package, or even better: the latest CVS snapshot. A description how to obtain this is provided on the netfilter homepage http://www.netfilter.org/.
To run patch-o-matic, just type
make patch-o-matic
Download the ulogd package from http://ftp.netfilter.org/pub/ulogd/ and untar it.
If you want to build ulogd with MySQL support, type './configure --with-mysql'. You may also have to specify the path of the mysql libraries using '--with-mysql=path'. To build ulogd without MySQL support, just use './configure'.
To compile and install the program, call 'make install'.
I also provide a SRPM, which should compile on almost any rpm-based distribution. It is available at http://ftp.netfilter.org/pub/ulogd/
Just download the package and do the usual 'rpm --rebuild <file>'.
Just add rules using the ULOG target to your firewalling chain. A very basic example:
iptables -A FORWARD -j ULOG --ulog-nlgroup 32 --ulog-prefix foo
To increase logging performance, try to use the
--ulog-qthreshold N
Of course you can combine the ULOG target with the different netfilter match modules. For a more detailed description, have a look at the netfilter HOWTO's, available on the netfilter homepage.
The number of the netlink multicast group to which ULOG'ed packets are sent. You will have to use the same group number in the ULOG target and ulogd in order to make logging work.
Copyrange. This works like the 'snaplen' paramter of tcpdump. You can specify a number of bytes up to which the packet is copied. If you say '40', you will receive the first fourty bytes of every packet. Leave it to '0'
Queue threshold. If a packet is matched by the iptables rule, and already N packets are in the queue, the queue is flushed to userspace. You can use this to implement a policy like: Use a big queue in order to gain high performance, but still have certain packets logged immediately to userspace.
A string that is associated with every packet logged by this rule. You can use this option to later tell from which rule the packet was logged.
The ipt_ULOG kernel module has a couple of module loadtime parameters which can (and should) be tuned to accomodate the needs of the application:
Netlink buffer size. A buffer of the specified size N is allocated for every netlink group that is used. Please note that due to restrictions of the kernel memory allocator, we cannot have a buffer size > 128kBytes. Larger buffer sizes increase the performance, since less kernel/userspace context switches are needed for the same amount of packets. The backside of this performance gain is a potentially larger delay. The default value is 4096 bytes, which is quite small.
The flushtimeout determines, after how many clock ticks (on alpha: 1ms, on x86 and most other platforms: 10ms time units) the buffer/queue is to be flushed, even if it is not full. This can be used to have the advantage of a large buffer, but still a finite maximum delay introduced. The default value is set to 10 seconds.
modprobe ipt_ULOG nlbufsiz=65535 flushtimeout=100
ulogd is what this is all about, so let's describe it's configuration...
All configurable parameters of ulogd are in the configfile, typically located at '/etc/ulogd.conf'.
The following configuration parameters are available:
The netlink multicast group, which ulgogd should bind to. This is the same as given with the '--ulog-nlgroup' option to iptables.
The main logfile, where ulogd reports any errors, warnings and other unexpected conditions. Apart from a regular filename, the following special values can be used; ``syslog'' to log via the unix syslog(3) mechanism. ``stdout'' to log to stdout.
This specifies, how verbose the logging to logfile is. Currently defined loglevels are: 1=debug information, 3=informational messages, 5=noticable exceptional conditions, 7=error conditions, 8=fatal errors, program abort.
This option is followed by a filename of a ulogd plugin, which ulogd shold load upon initialization. This option may appear more than once.
Size of the netlink socket receive memory. You should set this to at least the size of the kernel buffer (nlbufsiz parameter of the ipt_ULOG module). Please note that there is a maximum limit in /proc/sys/net/core/rmem_max which you cannot exceed by increasing the ``rmem'' parameter. You may need to raise the system-wide maximum limit before.
Size of the receive buffer. You should set this to at least the socket receive buffer (rmem).
Apart from the configfile, there are a couple of commandline options to ulogd:
Print a help message about the commandline options.
Print version information about ulogd.
For off into daemon mode. Unless you are debugging, you will want to use this most of the time.
Using this commandline option, an alternate config file can be used. This is important if multiple instances of ulogd are to be run on a single machine.
It is important to understand that ulogd without plugins does nothing. It will receive packets, and do nothing with them.
There are two kinds of plugins, interpreter and output plugins. Interpreter plugins parse the packet, output plugin write the interpreted information to some logfile/database/...
ulogd comes with the following interpreter plugins:
Basic interpreter plugin for nfmark, timestamp, mac address, ip header, tcp header, udp header, icmp header, ah/esp header... Most people will want to load this very important plugin.
Example interpreter plugin to log plaintext passwords as used with FTP and POP3. Don't blame me for writing this plugin! The protocols are inherently insecure, and there are a lot of other tools for sniffing passwords... it's just an example.
This is a 'virtual interpreter'. It doesn't really return any information on the packet itself, rather the local system time and hostname. Please note that the time is the time at the time of logging, not the packets receive time.
ulogd comes with the following output plugins:
A very simple output module, dumping all packets in the format
===>PACKET BOUNDARY
key=value
key=value
...
===>PACKET BOUNDARY
...
The module defines the following configuration directives:
The filename where it should log to. The default is
/var/log/ulogd.pktlog
An output module which tries to emulate the old syslog-based LOG targed as far as possible. Logging is done to a seperate textfile instead of syslog, though.
The module defines the following configuration directives:
The filename where it should log to. The default is
/var/log/ulogd.syslogemu
Set this to 1 if you want to have your logfile written
synchronously. This may reduce performance, but makes your log-lines appear
immediately. The default is 0
An output plugin for logging into a mysql database. This is only compiled if you have the mysql libraries installed, and the configure script was able to detect them. (that is: --with-mysql was specified for ./configure)
The plugin automagically inserts the data into the configured table; It connects to mysql during the startup phase of ulogd and obtains a list of the columns in the table. Then it tries to resolve the column names against keys of interpreter plugins. This way you can easly select which information you want to log - just by the layout of the table.
If, for example, your table contains a field called 'ip_saddr', ulogd will resolve this against the key 'ip.saddr' and put the ip address as 32bit unsigned integer into the table.
You may want to have a look at the file 'doc/mysql.table' as an
example table including fields to log all keys from ulogd_BASE.so. Just delete
the fields you are not interested in, and create the table.
The module defines the following configuration directives:
Name of the table to which ulogd should log
Name of the mysql database
Name of the mysql database host
TCP port number of mysql database server
Name of the mysql user
Password for mysql
An output plugin for logging into a postgresql database. This is only compiled if you have the mysql libraries installed, and the configure script was able to detect them. (that is: --with-pgsql was specified for ./configure)
The plugin automagically inserts the data into the configured table; It connects to pgsql during the startup phase of ulogd and obtains a list of the columns in the table. Then it tries to resolve the column names against keys of interpreter plugins. This way you can easly select which information you want to log - just by the layout of the table.
If, for example, your table contains a field called 'ip_saddr', ulogd will resolve this against the key 'ip.saddr' and put the ip address as 32bit unsigned integer into the table.
You may want to have a look at the file 'doc/mysql.table' as an
example table including fields to log all keys from ulogd_BASE.so. Just delete
the fields you are not interested in, and create the table.
The module defines the following configuration directives:
Name of the table to which ulogd should log
Name of the database
Name of the mysql database host
TCP port number of database server
Name of the sql user
Password for sql user
An output plugin that can be used to generate libpcap-style packet logfiles. This can be useful for later analysing the packet log with tools like tcpdump or ethereal.
The module defines the following configuration directives:
The filename where it should log to. The default is:
/var/log/ulogd.pcap
Set this to 1 if you want to have your pcap logfile written
synchronously. This may reduce performance, but makes your packets appear
immediately in the file on disk. The default is 0
An output plugin for logging into a SQLITE v3 database. This is only compiled if you have the sqlite libraries installed, and the configure script was able to detect them. (that is: --with-sqlite3 was specified for ./configure)
The plugin automagically inserts the data into the configured table; It opens the sqlite db during the startup phase of ulogd and obtains a list of the columns in the table. Then it tries to resolve the column names against keys of interpreter plugins. This way you can easly select which information you want to log - just by the layout of the table.
If, for example, your table contains a field called 'ip_saddr', ulogd will resolve this against the key 'ip.saddr' and put the ip address as 32bit unsigned integer into the table.
You may want to have a look at the file 'doc/sqlite3.table' as an
example table including fields to log all keys from ulogd_BASE.so. Just delete
the fields you are not interested in, and create the table.
The module defines the following configuration directives:
Name of the table to which ulogd should log
Name of the database
Size of the sqlite buffer
An output plugin that really logs via syslogd. Lines will look exactly like printed with traditional LOG target.
The module defines the following configuration directives:
The syslog facility (LOG_DAEMON, LOG_KERN, LOG_LOCAL0 .. LOG_LOCAL7, LOG_USER)
The syslog level (LOG_EMERG, LOG_ALERT, LOG_CRIT, LOG_ERR, LOG_WARNING, LOG_NOTICE, LOG_INFO, LOG_DEBUG)
All comments / questions / ... are appreciated.
Just drop me a note to laforge@gnumonks.org
Please note also that there is now a mailinglist, ulogd@lists.gnumonks.org. You can subscribe at http://lists.gnumonks.org/mailman/listinfo/ulogd/
The preferred method for reporting bugs is the netfilter bugzilla system, available at http://bugzilla.netfilter.org/.