diff options
author | Pablo Neira Ayuso <pablo@netfilter.org> | 2012-05-13 21:44:54 +0200 |
---|---|---|
committer | Pablo Neira Ayuso <pablo@netfilter.org> | 2012-06-16 15:40:02 +0200 |
commit | 12f7a505331e6b2754684b509f2ac8f0011ce644 (patch) | |
tree | da127aa83f0fdf0fc6be32c6386a304d5087c858 /net/netfilter/nf_conntrack_helper.c | |
parent | ae243bee397102c51fbf9db440eca3b077e0e702 (diff) | |
download | op-kernel-dev-12f7a505331e6b2754684b509f2ac8f0011ce644.zip op-kernel-dev-12f7a505331e6b2754684b509f2ac8f0011ce644.tar.gz |
netfilter: add user-space connection tracking helper infrastructure
There are good reasons to supports helpers in user-space instead:
* Rapid connection tracking helper development, as developing code
in user-space is usually faster.
* Reliability: A buggy helper does not crash the kernel. Moreover,
we can monitor the helper process and restart it in case of problems.
* Security: Avoid complex string matching and mangling in kernel-space
running in privileged mode. Going further, we can even think about
running user-space helpers as a non-root process.
* Extensibility: It allows the development of very specific helpers (most
likely non-standard proprietary protocols) that are very likely not to be
accepted for mainline inclusion in the form of kernel-space connection
tracking helpers.
This patch adds the infrastructure to allow the implementation of
user-space conntrack helpers by means of the new nfnetlink subsystem
`nfnetlink_cthelper' and the existing queueing infrastructure
(nfnetlink_queue).
I had to add the new hook NF_IP6_PRI_CONNTRACK_HELPER to register
ipv[4|6]_helper which results from splitting ipv[4|6]_confirm into
two pieces. This change is required not to break NAT sequence
adjustment and conntrack confirmation for traffic that is enqueued
to our user-space conntrack helpers.
Basic operation, in a few steps:
1) Register user-space helper by means of `nfct':
nfct helper add ftp inet tcp
[ It must be a valid existing helper supported by conntrack-tools ]
2) Add rules to enable the FTP user-space helper which is
used to track traffic going to TCP port 21.
For locally generated packets:
iptables -I OUTPUT -t raw -p tcp --dport 21 -j CT --helper ftp
For non-locally generated packets:
iptables -I PREROUTING -t raw -p tcp --dport 21 -j CT --helper ftp
3) Run the test conntrackd in helper mode (see example files under
doc/helper/conntrackd.conf
conntrackd
4) Generate FTP traffic going, if everything is OK, then conntrackd
should create expectations (you can check that with `conntrack':
conntrack -E expect
[NEW] 301 proto=6 src=192.168.1.136 dst=130.89.148.12 sport=0 dport=54037 mask-src=255.255.255.255 mask-dst=255.255.255.255 sport=0 dport=65535 master-src=192.168.1.136 master-dst=130.89.148.12 sport=57127 dport=21 class=0 helper=ftp
[DESTROY] 301 proto=6 src=192.168.1.136 dst=130.89.148.12 sport=0 dport=54037 mask-src=255.255.255.255 mask-dst=255.255.255.255 sport=0 dport=65535 master-src=192.168.1.136 master-dst=130.89.148.12 sport=57127 dport=21 class=0 helper=ftp
This confirms that our test helper is receiving packets including the
conntrack information, and adding expectations in kernel-space.
The user-space helper can also store its private tracking information
in the conntrack structure in the kernel via the CTA_HELP_INFO. The
kernel will consider this a binary blob whose layout is unknown. This
information will be included in the information that is transfered
to user-space via glue code that integrates nfnetlink_queue and
ctnetlink.
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Diffstat (limited to 'net/netfilter/nf_conntrack_helper.c')
-rw-r--r-- | net/netfilter/nf_conntrack_helper.c | 21 |
1 files changed, 17 insertions, 4 deletions
diff --git a/net/netfilter/nf_conntrack_helper.c b/net/netfilter/nf_conntrack_helper.c index 9c18ecb..2918ec2 100644 --- a/net/netfilter/nf_conntrack_helper.c +++ b/net/netfilter/nf_conntrack_helper.c @@ -30,8 +30,10 @@ #include <net/netfilter/nf_conntrack_extend.h> static DEFINE_MUTEX(nf_ct_helper_mutex); -static struct hlist_head *nf_ct_helper_hash __read_mostly; -static unsigned int nf_ct_helper_hsize __read_mostly; +struct hlist_head *nf_ct_helper_hash __read_mostly; +EXPORT_SYMBOL_GPL(nf_ct_helper_hash); +unsigned int nf_ct_helper_hsize __read_mostly; +EXPORT_SYMBOL_GPL(nf_ct_helper_hsize); static unsigned int nf_ct_helper_count __read_mostly; static bool nf_ct_auto_assign_helper __read_mostly = true; @@ -322,6 +324,9 @@ EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_symbol); int nf_conntrack_helper_register(struct nf_conntrack_helper *me) { + int ret = 0; + struct nf_conntrack_helper *cur; + struct hlist_node *n; unsigned int h = helper_hash(&me->tuple); BUG_ON(me->expect_policy == NULL); @@ -329,11 +334,19 @@ int nf_conntrack_helper_register(struct nf_conntrack_helper *me) BUG_ON(strlen(me->name) > NF_CT_HELPER_NAME_LEN - 1); mutex_lock(&nf_ct_helper_mutex); + hlist_for_each_entry(cur, n, &nf_ct_helper_hash[h], hnode) { + if (strncmp(cur->name, me->name, NF_CT_HELPER_NAME_LEN) == 0 && + cur->tuple.src.l3num == me->tuple.src.l3num && + cur->tuple.dst.protonum == me->tuple.dst.protonum) { + ret = -EEXIST; + goto out; + } + } hlist_add_head_rcu(&me->hnode, &nf_ct_helper_hash[h]); nf_ct_helper_count++; +out: mutex_unlock(&nf_ct_helper_mutex); - - return 0; + return ret; } EXPORT_SYMBOL_GPL(nf_conntrack_helper_register); |