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This patch simplifies the expectation filtering by looking up for the
master conntrack. If it does not exists, then we assume that we don't
want this expectation either.
This simplification also fixes the current broken expectation filtering,
since the master conntrack from expectations has neither reply tuple
nor state, however, the filtering code assumes the opposite.
This partially reverts (479a37a conntrackd: fix crash with IPv6 expectation
in the filtering code) since it was incorrectly setting the reply tuple
of the master conntrack.
Thanks to Bill Fink for providing feedback to resolve this issue.
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
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This patch adds support to synchronize expectations between
firewalls. This addition aims to re-use as much as possible
of the existing infrastructure for stability reasons. The
expectation support has been tested with the FTP helper.
This extension requires libnetfilter_conntrack 1.0.0.
If this is the first time you're playing with conntrackd,
I *strongly* recommend you to get working setup of conntrackd
without expectation support before as described in the
documentation. Then, enabling expectation support is rather
easy.
To know more about expectations, if you're not familiar with them,
I suggest you to read:
"Netfilter's Connection Tracking System"
http://people.netfilter.org/pablo/docs/login.pdf
Reprinted from ;login: The Magazine of USENIX, vol. 31, no. 3
(Berkeley, CA: USENIX Association, 2006, pp40-45.)
In short, expectations allow one Linux firewall to filter multi-flow
traffic like FTP, SIP and H.323.
In my testbed, there are two firewalls in a primary-backup configuration
running keepalived. The use a couple of floating cluster IP address
(192.168.0.100 and 192.168.1.100) that are used by the client. These
firewalls protect one FTP server (192.168.1.2) that will be accessed by
one client.
In ASCII art, it looks like this:
192.168.0.100 192.168.1.100
eth1 eth2
fw-1
/ \ FTP
-- client ------ ------ server --
192.168.0.2 \ / 192.168.1.2
fw-2
This is the rule-set for the firewalls:
-A POSTROUTING -t nat -s 192.168.0.2/32 -d 192.168.1.2/32 -j SNAT --to-source 192.168.1.100
-A INPUT -p tcp -m tcp --dport 22 -j ACCEPT
-A INPUT -m state --state INVALID -j DROP
-A FORWARD -m state --state RELATED -j ACCEPT
-A FORWARD -i eth2 -m state --state ESTABLISHED -j ACCEPT
-A FORWARD -i eth1 -p tcp -m tcp --dport 21 --tcp-flags FIN,SYN,RST,ACK SYN -m state --state NEW -j ACCEPT
-A FORWARD -i eth1 -p tcp -m state --state ESTABLISHED -j ACCEPT
-A FORWARD -m state --state INVALID -j LOG --log-prefix "invalid: "
The following steps detail how to check that the expectation support
works fine for conntrackd:
1) You have to enable the expectation support in the configuration
file with the following option:
Sync {
...
Options {
ExpectationSync {
ftp
sip
h323
}
}
}
This enables expectation synchronization for the FTP, SIP and H.323 helpers.
You can alternatively use:
Sync {
...
Options {
ExpectationSync On
}
}
To enable expectation synchronization for all helpers.
2) Make sure you have loaded the FTP helper in both firewalls.
root@fw1# modprobe nf_conntrack_ftp
root@fw2# modprobe nf_conntrack_ftp
3) Switch to the client. Start one FTP control connection to one
server that is protected by the firewalls, enter passive mode:
(term-1) user@client$ nc 192.168.1.2 21
220 dummy FTP server
USER anonymous
331 Please specify the password.
PASS nothing
230 Login successful.
PASV
227 Entering Passive Mode (192,168,1,2,163,11).
This means that port 163*256+11=41739 will be used for the data
traffic. Read this if you are not familiar with the FTP protocol:
http://www.freefire.org/articles/ftpexample.php
3) Switch to fw-1 (primary) to check that the expectation is in the
internal cache.
root@fw1# conntrackd -i exp
proto=6 src=192.168.0.2 dst=192.168.1.2 sport=0 dport=41739 mask-src=255.255.255.255 mask-dst=255.255.255.255 sport=0 dport=65535 master-src=192.168.0.2 master-dst=192.168.1.2 sport=36390 dport=21 [active since 5s]
4) Switch to fw-2 (backup) to check that the expectation has been successfully
replicated.
root@fw2# conntrackd -e exp
proto=6 src=192.168.0.2 dst=192.168.1.2 sport=0 dport=41739 mask-src=255.255.255.255 mask-dst=255.255.255.255 sport=0 dport=65535 master-src=192.168.0.2 master-dst=192.168.1.2 sport=36390 dport=21 [active since 8s]
5) Make the primary firewall fw-1 fail. Now fw-2 becomes primary.
6) Switch to fw-2 (primary) to commit the external cache into the kernel.
root@fw2# conntrackd -c exp
The logs should display that the commit was successful:
root@fw2# tail -100f /var/log/conntrackd.log
[Wed Dec 7 22:16:31 2011] (pid=19195) [notice] committing external cache: expectations
[Wed Dec 7 22:16:31 2011] (pid=19195) [notice] Committed 1 new entries
[Wed Dec 7 22:16:31 2011] (pid=19195) [notice] commit has taken 0.000366 seconds
7) Switch to the client. Open a new terminal and connect to the port that
has been announced by the server:
(term-2) user@client$ nc -vvv 192.168.1.2 41739
(UNKNOWN) [192.168.1.2] 41739 (?) open
8) Switch to term-1 and ask for the file listing:
[...]
227 Entering Passive Mode (192,168,1,2,163,11).
LIST
9) Switch to term-2, it should display the listing. That means
everything has worked fine.
You may want to try disabling the expectation support and
repeating the steps to check that *it does not work* without
the state-synchronization.
You can also display expectation statistics by means of:
root@fwX# conntrackd -s exp
This update requires no changes in the primary-backup.sh script
that is used by the HA manager to interact with conntrackd. Thus,
we provide a backward compatible command line interface.
Regarding the Filter clause and expectations, we use the master
conntrack to filter expectation events. The filtering is performed
in user-space. No kernel-space filtering support for expectations
yet (this support should go in libnetfilter_conntrack at some
point).
This patch also includes support to disable caching and to allow
direct injection of expectations.
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
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The ct object that is passed as parameter is not modified,
make it constant.
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
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Currently, the caching system is implemented in a two layer
architecture: hashtable (inner layer) and cache (upper layer).
This patch reworks the hash-cache infrastructure to solve some
initial design problems to make it more flexible, the main strong
points of this patch are:
* Memory handling is done in the cache layer, not in the inner
hashtable layer. This removes one of the main dependencies between
the hashtable and the cache classes.
* Remove excessive encapsulation: the former cache used to hide a
lot of details of the inner hashtable implementation.
* Fix over-hashing of some operations: lookup-delete-add required
three hash calculations. Similarly, the update-or-add operation
required two hash calculations. Now, we calculate the hash once
and re-use the value how many times as we need.
This patch simplifies the caching system. As a result, we save ~130
lines of code. Small code means and less complexity means less
chance to have bugs.
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
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This patch is a cleanup. It moves the callbacks from netlink.c to
run.c where they are actually invoked. This is better for code
readability as I usually have to switch from run.c to netlink.c
to remember what the callbacks actually do.
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
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This patch adds CIDR-based filtering support. The current
implementation is O(n).
This patch also introduces the vector data type which is
used to store the IP address and the network mask.
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
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This patch reworks the user-space filtering. Although we have
kernel-space filtering since Linux kernel >= 2.6.26, we keep userspace
filtering to ensure backward compatibility. Moreover, this patch
prepares the implementation of the kernel-space filtering via
libnetfilter_conntrack's high-level berkeley socket filter API.
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
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