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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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This patch removes:
* nl_init_dump_handler()
* nl_init_request_handler()
* nl_init_resync_handler()
since they all look very similar.
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
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This patch moves the timeout mangling inside nl_*_conntrack().
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
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This function is a synonimous of nl_get_conntrack(), use the get
function instead.
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
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This patch is a cleanup. The overrun handler is actually a way to
resynchronize against the conntrack kernel table. The name overrun
was used because it was initially its purpose. The new naming shows
its genericity.
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
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This patch adds support for redundant dedicated links. You can add
a pool of dedicated links that can be used if the current active
fails.
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
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This patch fixes a race condition that triggers EILSEQ errors
(wrong sequence message). The problems is triggered when the child
process resets the timers at the same time that the parent process
requests a resync. Since both the child and the parent process use
the same descriptors, the sequence tracking code in libnfnetlink
gets confused as it considers that it is receiving out of sequence
netlink messages.
This patch introduces internal handlers to commit and reset timers
so that the parent and the child do not use the same descriptors
to operate with the kernel.
This patch changes the prototype of all nf_*_conntrack() functions.
Now, the nfct handler is passed as first parameter, this change is
required to fix this problem. The rest of the changes on the API
is done for consistency.
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
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This patch recovers the option -F for conntrackd. This will be
particularly useful to flush the kernel conntrack table without
getting the event notification of the conntrack deletions
(that will happen with Linux kernel >= 2.6.29).
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
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Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
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This patch constifies the first parameter, which is a conntrack
object, in all nl_*_conntrack() functions.
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
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This patch changes the behaviour of nl_create_conntrack() and
nl_update_conntrack() which now clone the conntrack object
received as parameter. This was not required as these functions
were called inside fork(), thus, they modified a copy of the
real conntrack objects in the child process.
However, this behaviour is broken following the try-again
logic in __do_commit_step. For example, if we try to update
an expected conntrack object that has vanished for whatever
reason, since nl_update_conntrack() modifies the object (unset
the master conntrack information), nl_create_conntrak() will
create an entry without the master conntrack information.
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 avoids a double filtering in user-space and kernel-space if
the kernel support BSF. Since we do not use BSF for dumps and resyncs,
we add a new parameter to ignore_conntrack to indicate if we have to
perform the filtering in user-space or not.
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
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Commit master entries before related ones to avoid ENOENT errors.
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
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This patch adds nl_get_conntrack and it changes the behaviour of
nl_exist_conntrack. Now, nl_get_conntrack requests the kernel for
a conntrack and updates the cached entry. On the other hand,
nl_exist_conntrack only inquiries for the existence of the
entry.
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
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