R-fx Networks

Archive for April, 2011

LMD 1.4: Little Something For Everyone!

by on Apr.20, 2011, under Development

The much awaited for 1.4 release of Linux Malware Detect is here! In this release there is quite literally something for everyone, from massive performance gains to FreeBSD support and everything in between :). For those who wish to dive straight into it, you can run the -d or –update-ver option to update your install to the latest build and check out the change log for full details.

I will try cover some of the highlights of this release for those with the appetite for it, here goes…

One of the more exciting changes is that Clam Anti-Virus is now supported as an optional scanner engine. When LMD detects that ClamAV is installed on the local system, through detection of the clamscan binary, it will default to using clamscan as the default scanner engine. The use of clamscan as the scanner engine leverages LMD in a couple of ways. First, it allows for ClamAV’s threat database to be used in detecting threats, over 900k strong, in addition to the LMD signatures which are ClamAV compatible. Secondly and more importantly, it improves scan performance greatly, over five times faster. Finally, it also improves the accuracy of threat detection as ClamAV is more efficient at doing hex payload analysis of files using LMD’s hex pattern match signatures. To enable this all you need to do is have ClamAV installed and LMD will detect it all on its own, if you wish to override the detection/usage of clamscan then you can set clamav_scan=0 in conf.maldet.

Another change that I am excited to announce, is that LMD 1.4 is now compatible with FreeBSD, less the inotify real-time monitoring as it is a Linux specific feature that requires me to design a new monitoring subsystem around FreeBSD’s inotify equivalent, kqueue. That said, allot of testing went into ensuring FreeBSD compatibility but it did not end there, I also went to great pains to improve Linux compatibility both with RH variants and non-RH variants alike, the officially supported set of distributions is as follows:
– RHEL/CentOS 5.6
– RHEL 6
– Fedora Core 14
– OpenSuse 11.4
– Suse Linux Enterprise Server 11 SP1
– Ubuntu Desktop/Server 10.10
– Debian 6.0.1a

This supported list is not meant as an exclusive list, it is simply a “test” set of distributions that I work with that give LMD the best expectation of working on an even wider set of Linux distributions. This improved compatibility will open up LMD to a larger community of users and there-in allow the project to grow and prosper in new and exciting ways.

The way LMD updates itself has now been improved, traditionally the daily signature updates only updated the core hex and md5 signature files but that proved to create some gaps in ensuring that all dynamic components for detecting threats are current. As such, now the update feature also pulls down the most current set of cleaner rules and LMD signatures in ClamAV format. In addition, the update process has seen an improvement in error checking; the signature files are now validated for length and missing files, if either validation checks fail then all signatures are forcibly updated.

The hex scanner (internally known as stage2 scanner) has been improved in that it now makes use of a named pipe (FIFO – first in first out) for processing file hex payload data, this allows for greater depth penetration into files and at a much lower cost in overhead. This means more accurate threat detection, fewer false positives and improved scan speeds; although it still pales in comparison to when clamscan is used as the scanner engine but nevertheless it is an improvement and an important one at that.

Further adding to the threat detection capabilities of LMD, is a new statistical analysis component that will see allot of expansion in later releases. The first feature in the statistical analysis component is called the string length test. The string length test is used to identify threats based on the length of the longest uninterrupted string within a file. This is useful as obfuscated code is often stored using encoding methods that produce very long strings without spaces (e.g: base64, gzip etc.. encoded files). This feature is presented in conf.maldet through the string_length variables, it is disabled by default as it can in some situations have a relatively high false-positive rate, especially on .js files. Future releases will see extension and file type based filtering specifically wrapped around the statistical analysis components to reduce false positives, however it is still a very powerful feature in detecting obfuscated/encoded malware.

There is a number of usage changes that have been made, the most notable and important being in ignore files, specifically the ignore_inotify and ignore_file_ext files.

The first, ignore_inotify is a specific file designed for ignoring paths from inotify real time monitoring, previous to LMD 1.4 this file only accepted absolute directory/file paths which was very limiting and created headaches for many people. The ignore_inotify file now fully supports posix extended regular expressions, meaning you can ignore absolute paths still or create regular expressions to cover specific file types or dynamic path/directory structures. An example of this is that temporary sql files may write out to /var/tmp in the format of /var/tmp/#sql_12384_4949.MYD, previously you would have to ignore /var/tmp completely which exposed the system more than it helped. Now, you can add an entry to ignore_inotify such as ^/var/tmp/#sql_.*\.MYD$ and it will properly ignore the temporary SQL files while retaining full monitoring of /var/tmp.

The second, ignore_file_ext was a feature added in the 1.3.x branch that was pulled back due to technical issues. The file speaks for itself, it allows you to ignore files from scan results based on file extensions, this has now been fixed and is working properly. The usage of the file is straight forward, simply add one extension per line to ignore_file_ext and it will be excluded from scan results (e.g: .tar.gz , .rpm , .html , .js etc…), there is no need to use an asterisk (*) in entries in the ignore file.

Further usage changes include that the -c|–checkout flags now supports directories instead of just absolute files, so you can upload threats to rfxn.com from an entire directory (please make sure all threats within the directory are actual malware, I would prefer not to sort through hundreds of html/web files). The -r|–scan-recent and -a|–scan-all flags now support single file scans, previously only directory paths were accepted. A background option has been added in the form of -b|–background that allows scans to be run in the background, the -b|–background option must come before the scan options, such as (see –help for more details):

maldet --background --scan-recent /home/?/public_html 7
maldet --background --scan-all /home/?/public_html
maldet -b -r /home/?/public_html 7
maldet -b -a /home/?/public_html

There have also been a couple of changes to the -e|–report flags allowing for the listing of available reports and emailing of previous scan reports. The usage of these changes is straight forward and is as follows:

maldet --report list
maldet --report SCANID user@domain.com

That about covers things, there have been a number of smaller changes and fixes in LMD 1.4 which are detailed in the change log. To ensure you are running the latest build please run the -d or –update-ver option to have LMD auto-update or visit the project home page and download the latest build.

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ATA Over Ethernet: As an Alternative

by on Apr.04, 2011, under HowTo, My Blog

New technologies, new toys — Oh how I love getting my hands dirty with them. Today I am going to have a look at ATA Over Ethernet (AoE) as an alternative solution to NFS in the role of a NAS/SAN implementation. We will look at both the server side vblade setup and the client side AoE kernel module along with a practical deployment setup which includes a convenience script I developed to make vbladed slightly less of a nuisance to maintain.

First things first though, what exactly is ATA Over Ethernet? Straight off the wikipedia page, here are the important parts that describe AoE best:

"ATA over Ethernet (AoE) is a network protocol developed by the Brantley Coile Company, designed for simple, high-performance access of SATA storage devices over Ethernet networks. It is used to build storage area networks (SANs) with low-cost, standard technologies.
AoE runs on layer 2 Ethernet, it does not use internet protocol (IP), so it cannot be accessed over the Internet or other IP networks. In this regard it is more comparable to Fibre Channel over Ethernet.
SATA (and older PATA) hard drives use the Advanced Technology Attachment (ATA) protocol to issue commands, such as read, write, and status. AoE encapsulates those commands inside Ethernet frames and lets them travel over an Ethernet network instead of a SATA or 40-pin ribbon cable. By using an AoE driver, the host operating system is able to access a remote disk as if it were directly attached."

OK, of note here is that AoE is an ATA implementation over Ethernet, being layer 2 it is a dumb protocol with no knowledge of the TCP/IP stack, as such it can only communicate in the simplest of ways inside a switched network (its packets cant be routed between multiple networks). As such, AoE is ideal when used on a private network or better yet a network dedicated to SAN (Storage Area Network), it can however be used on a public facing network as so long as the hosts in the AoE network are all within the same switched segment of the network (More info here on routable AoE).

That all said, what makes AoE a viable alternative to NFS? Well in the role of storage access in its simplest capacity, NFS is just bloated and adds a significant amount of overhead and complexity to something that deserves to be simple. Further, NFS is woefully inadequate at maintaining the level of reliability required when you are, for example, exporting an entire file system to another device for the purpose of high-availability usage such as a /home extension or MySQL file system. Personally, I am slightly biased as I hate NFS; I use it, but only for a lack of often anything better to meet the role in exporting file systems and directory trees across networks. Although it does what its supposed to just fine, more often than not you can get woken up at 4AM with the most mysterious and sudden of NFS issues that are notorious for being mind numbing to resolve. It is for this simple reason — NFS’s lack of reliability, that sent me searching for a simple, scalable and reliable alternative. AoE has managed to meet two of these three points — simple and reliable, while coming up short on the scalable side, more on that in a bit.

There are two components of an AoE setup, the server side storage device that will run vblade and the client side that will access the exported storage using the AoE kernel module under Linux. I should note that although the vblade server package is for Linux, the client side drivers are available for Windows, OS X, FreeBSD and more; in Linux the AoE kernel module is part of the mainline kernel.

The server you choose to run vblade can be any device that you want to export files or devices on, there is little in the way of requirements as vblade is a pretty slim package and doesn’t consume much in the way of resources other than CPU. For a modest environment where you plan to export to no more than 10-15 clients, a dual core system with 2GB RAM is more than sufficient for the vblade server. For my deployment, I run vblade on a quad core Xeon 3.0Ghz, 6GB RAM and 9TB Raid5 array that exports to 54 client servers. More on my setup later when we review scalability but for now lets jump right into the vblade setup and usage.

Lets go ahead and grab the vblade package, compile and install it:

# wget http://iweb.dl.sourceforge.net/project/aoetools/vblade/20/vblade-20.tgz
# tar xvfz vblade-20.tgz
# cd vblade-20
# make && make install
install vblade /usr/sbin/
install vbladed /usr/sbin/
install vblade.8 /usr/share/man/man8/

There is no compile time configure script or any other real configuration required, vblade installs straight into /usr/sbin and is an overall painless process. The simplicity of the vblade package comes at a cost, in that there is no support for a configuration file to control multiple vblade instances, making things slightly tedious. This should not detract from the use of vblade, it is a mature and reliable package but one with a very simple approach that does little in the way other than what it is supposed to do.

To make life easier for myself, I created a wrapper of the sorts to add support for a configuration file along with limited error checking and some command line conveniences — we’ll grab the wrapper and default config template as follows:

# wget http://rfxn.com/downloads/vbladed.conf
# wget http://rfxn.com/downloads/vbladectl
# mv vbladed.conf /etc/
# mv vbladectl /usr/sbin
# chmod 640 /etc/vbladed.conf
# chmod 750 /usr/sbin/vbladectl
# ln -s /usr/sbin/vbladectl /etc/init.d/vbladed
# chkconfig --level 2345 on

You will note, that we enabled vblade to start on boot through init, although the wrapper is not technically an init script, it does support being called from init and managed through chkconfig for convenience. Lets look at the configuration file /etc/vbladed.conf then we’ll review the vbladectl usage after that:

# vbladed export configuration file

# unique shelf identifier for this vblade server
SHELF="0"     # must be numeric 0-254, default 0

# 0 /data/server.img FF:FF:FF:FF:FF:FF eth1 server

The configuration file is pretty straight forward, the SHELF variable only matters if you intend to run multiple vblade servers on the same network, if that is the case then this value must be unique to each vblade server or you will run into client side conflicts of being unable to distinguish between vblade servers. The export definitions follow in the format of “AOESLOT FILE MAC IFACE ALIAS” which the below breaks down further:
AOESLOT is a per-client identifier for EACH exported file or device to the SAME client; in other words if you configure multiple exports to the same client server then this value needs to be unique for each.
FILE is the full path to a device or file you want to export, this can be an unformatted raw device such as /dev/sdb, a preformatted partition such as /dev/sdb5 or a loopback image such as /data/server.img.
MAC is the MAC address of the client-side interface that is attached to the network you intend AoE traffic to move over; more appropriately, it is the interface connected to your private network on the client server
IFACE is the server-side interface that can reach the client-side interface you defined the MAC address for; more appropriately, it is the interface connected to your private network on the vblade server
ALIAS is a reference alias for each configuration entry, this must be unique to each vbladed.conf definition

For the purpose of this article, we will go ahead and create a loopback image, format it and export it for a client server called apollo, then we will review how to import the file system onto the apollo server using the AoE kernel module. First, lets create our image:

# dd if=/dev/zero of=/home/apollo.img bs=1 count=0 seek=10G
# yes | mkfs.ext3 /home/apollo.img

This will create a sparse, zero filled file, meaning it will be 0bytes on disk and allocate space, up to 10G, as data is stored to it. There is a slight performance hit to this as the image file must grow itself as data is written, this however is made up for in improved efficiency of space usage. To create an image that preallocates space on the disk you would run ‘# dd if=/dev/zero of=/home/apollo.img bs=1M count=10000‘, be patient as this will take some time to complete, then format it as described above.

Now that we have the image/device we want to export, we need to add the definition for it into the vbladed.conf file, to do so we need to note the MAC address of the interface on apollo that will communicate with the vblade server, in our case this is a private interface eth1 but in your setup it can be a public facing interface if needed — just make sure its within the same subnet as the vblade server.

[root@apollo ~]# ifconfig eth1
eth1      Link encap:Ethernet  HWaddr 00:16:E6:D3:ED:E5
          inet addr:  Bcast:  Mask:
    ... truncated ...

We now have the client side MAC address (00:16:E6:D3:ED:E5) and we have the device/file we want to export (/home/apollo.img), and we also know the private network interface on our vblade server is eth1 as well, so we can create the vbladed.conf definition:

0 /home/apollo.img 00:16:E6:D3:ED:E51 eth1 apollo

That should be appended into the bottom of /etc/vbladed.conf, then we are ready to start the vblade instance for the configuration we’ve added. The vbladectl wrapper includes start, stop and restart flags which also accept an optional alias for performing actions against only a specific vblade instance, run vbladectl with no options for usage help. Time to start the vblade instance for apollo as follows:

# /usr/sbin/vbladectl start apollo
started vbladed for apollo (pid:16320 file:/home/apollo.img iface:eth1 mac:00:16:E6:D3:ED:E51)
( you could also just pass the start option without an alias to start instances for all entries in vbladectl.conf )

The default behavior for vblade also sends log data to the kernel log, typically /var/log/messages on most systems, so tailing the log will produce the following logs if all is normal:

# tail /var/log/messages
Apr  3 16:49:25 backup5 vbladed: started vbladed for apollo (pid:16320 file:/home/apollo.img iface:eth1 mac:00:16:E6:D3:ED:E51)
Apr  3 16:49:24 backup5 vbladed: pid 16320: e0.0, 419430400 sectors O_RDWR

The important part there is the ‘vbladed: pid 16320: e0.0, 419430400 sectors O_RDWR’ entry in the log as this comes from vblade itself, the other log entry comes from the wrapper. This log entry tells us that vbladed forked off successfully and that it has exported our data for the defined server as e0.0 (etherdrive shelf 0 slot 0), you’ll see the significance of this shortly.

We are now ready to move over to our client server, apollo, and import our new AoE file system. This is an easy task and if you are running a current Fedora / RHEL (CentOS) based distribution, you’ll find the AoE kernel module already included. The module is also part of the mainline kernel so if you are using a custom kernel, please be sure to enable the corresponding config option (CONFIG_ATA_OVER_ETH).

There is really no right way to load a kernel module, you can either use modprobe which I recommend or you can use insmod on the modules full path, which is a matter of preference. Let’s first verify the module exists, which modprobe does for us but for the sake of this article and familiarity, we will check (remember you’re running this on the client server, i.e apollo):

# find /lib/modules/$(uname -r)/ -name "aoe.ko"

There we have it, the module returned fine, listing the full path to it. If you did not get anything back this may be that you are running a custom kernel by your own choosing, and need to configure the CONFIG_ATA_OVER_ETH option. It may also be that your data center provider or a software vendor installed a custom kernel without this feature and you should contact them requesting it. As an alternative, you could download the etherdrive sources for the AoE kernel module on the coraid website and compile it against your kernel, this requires your kernel build sources or on RHEL based systems the kernel-headers package.

That said, we will now load the module using modprobe, the preferred method:

# /sbin/modprobe aoe
( or you can run /sbin/insmod MODULE-PATH )

If everything went OK, then modprobe will generate no output and you can verify the module is loaded as follows:

# lsmod | grep aoe
aoe                    60385  1

When the AoE module is loaded it will start listening for broadcast traffic from AoE on all available interfaces, a very passive process. If you have done everything correct then the module will quickly detect the exported device/file from the vblade server and inform you in the kernel log along with creating the appropriate /dev/etherd/ device file. Let’s verify this by checking the log and then checking the /dev/etherd path:

# tail /var/log/messages
Apr  4 17:13:02 apollo kernel: aoe: aoe_init: AoE v22i initialised.
Apr  4 17:13:02 apollo kernel: aoe: 003048761643 e0.0 v4014 has 419430400 sectors
Apr  4 17:13:02 apollo kernel:  etherd/e0.0: unknown partition table
# ls /dev/etherd/

If for some reason you do not see the log entries described above along with no e0.0 device file under /dev/ethered, this may be a misconfiguration on the vblade server, perhaps you got the interface or mac address in vbladed.conf wrong? Double check all values. If you opted to try run things over a public facing interface, the issue may be that your network VLAN’s each server (which is fairly common), in that case you may need to request that all your hardware be part of the same VLAN or the provisioning of a private switch and private links for your hardware.

Assuming that things went good, that you see the appropriate log entries and the e0.0 device file under /dev/etherd/, we are ready to mount the file system, we will mount it as /mnt/aoe for the purpose of this article:

# mkdir /mnt/aoe
# mount /dev/etherd/e0.0 /mnt/aoe
# df -h /mnt/aoe
Filesystem            Size  Used Avail Use% Mounted on
/dev/etherd/e0.0      5G   36M  4.9G  0% /mnt/aoe

You may run into an issue of unrecognized file system on the device, though the file system we created on it, on the vblade server, should show through. If it does not, simply run an ‘mkfs.ext3 /dev/etherd/e0.0’ on it and you will be all set. There is no hard set rule on creating the file system on the vblade server, you could just export raw images and devices then partition/format file systems on them on a per-client basis as you require it.

The only thing that is left is to set our new file system on apollo to load at boot time, the simplest way to do this is to append a couple of lines to /etc/rc.local as follows:

/sbin/modprobe aoe
sleep 5 ; mount /dev/etherd/e0.0 /mnt/aoe -onoatime

The rc.local script is run at boot time after all other services have started, so if you are loading a file system used for mysql, user home data or similar you will probably want to also add a line after the mount to restart said services. You’ll also notice two things about the entries we added to rc.local; The first is the sleep delay before the mount, this allows the aoe kernel module to complete its discovery process for AoE file systems before we try to mount it. Then, we are using the noatime option on the mount command, which disables the updating of the last access time on files during read/write operations. This is important because traditionally whenever a file is read from disk, it causes a write operation back to disk to update the atime attribute on the file, so disabling atime usage can greatly reduce i/o calls (effectively in half for reads), which is especially significant for networked file systems.

I have had an overall good experience with AoE so far, it is incredibly simple and very reliable as an implementation. The only issue I have seen is the scalability of it and I attribute this more to the vblade server package than AoE as a protocol. There appears to be a degradation in I/O throughput performance for exported file systems that is in-line with the number of (instances) file systems you export on the same physical server. The best usage example of this is that in my environment I run vblade on one server with exports to 54 servers, the throughput when there is 1-10 instances running averages about 51MB/s (408Mbit), as that increases though to 54 instances, the throughput per client server drops drastically to an average of 14MB/s (112Mbit). This is a very sharp decrease in performance, one that makes the viability of vblade in much larger of a setup questionable.

I do need to caution that this issue may be environment specific as speaking to other vblade users has produced mixed feedback, some do not experience this kind of performance loss while others do. I will also note that I run vblade on a second storage device, on the same private network as the 54 instance vblade server, and this second storage device has only 4 instances running with an average throughput of 71MB/s (568Mbit). So the conclusion you draw from this is up to you, at the end of the day I am more than happy with the implementation as a whole and can accept the loss of performance for the larger implementation in the name of reliability and simplicity.

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LMD 1.3.9r1: Hexdepth Bug

by on Apr.03, 2011, under Development, My Blog

I have put up a revision to the 1.3.9 release of LMD that fixes a hexdepth bug in which malware greater than 65Kbytes would cause an error in the internal hexstring.pl script and be considered clean on the stage2 hex scanning of malware. This would mean that unless malware had a MD5 signature for it to be caught on stage1 scan, it would not be picked up by a corresponding HEX rule in stage2 scan if its file size was greater than 65Kbyte, due to the bug.

In addition, I have made the decision in this revision to enable release update checks in the default cron.daily entry installed by LMD, this can be found at /etc/cron.daily/maldet line 9 (after update) if you wish to comment it out. I would however encourage users to leave this option enabled as it will greatly improve receiving timely updates for future bugs fixes and release updates. In the past, the decision was made to not enable automatic release updates for many reasons but mostly in the interest of the software still maturing and being in early development, thereby not wanting to rock any boats with large and sweeping release updates to a version they may have got working the way they prefer. Now though, LMD has come a long way, the installer imports most options and ignore files and there are no drastically sweeping changes planned that will cause a great deal of headaches — so it seemed fitting time to enable automatic updates.

You can update your installation using the ‘maldet -d|–update-ver’ flags or download the current build for new installations.

This release update also coincides with passing 7k signatures….. We now sit at 7,106 signatures or +146 signatures added today. This is no small feat, I remember when we had just a couple hundred signatures not so long ago and I thought that was a big deal! The LMD submissions repository stays very active, it is now the source of almost 60% of the weekly signature additions and has contributed greatly to creating a vastly more accurate signature set that is representative of the threats you, the users, face day-to-day.

That said, month ending March stats recorded +1,464 installations of LMD bringing the install count to 7,157 — which puts LMD now ahead of APF in month-to-month new installation growth. Although, APF still beat LMD on raw downloads last month (3,091 vs 2,583), it is reasonable to predict that LMD will soon take the number one spot for downloads as well. It however still has a long way to go for total active installations, which APF sits at a comfortable 24,791 currently.

Till next time, happy malware hunting 🙂

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