![Pablo Neira Ayuso](/assets/img/avatar_default.png)
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>
56 lines
1.1 KiB
C
56 lines
1.1 KiB
C
#ifndef _NFNL_CTHELPER_H_
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#define _NFNL_CTHELPER_H_
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#define NFCT_HELPER_STATUS_DISABLED 0
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#define NFCT_HELPER_STATUS_ENABLED 1
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enum nfnl_acct_msg_types {
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NFNL_MSG_CTHELPER_NEW,
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NFNL_MSG_CTHELPER_GET,
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NFNL_MSG_CTHELPER_DEL,
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NFNL_MSG_CTHELPER_MAX
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};
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enum nfnl_cthelper_type {
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NFCTH_UNSPEC,
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NFCTH_NAME,
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NFCTH_TUPLE,
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NFCTH_QUEUE_NUM,
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NFCTH_POLICY,
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NFCTH_PRIV_DATA_LEN,
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NFCTH_STATUS,
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__NFCTH_MAX
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};
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#define NFCTH_MAX (__NFCTH_MAX - 1)
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enum nfnl_cthelper_policy_type {
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NFCTH_POLICY_SET_UNSPEC,
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NFCTH_POLICY_SET_NUM,
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NFCTH_POLICY_SET,
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NFCTH_POLICY_SET1 = NFCTH_POLICY_SET,
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NFCTH_POLICY_SET2,
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NFCTH_POLICY_SET3,
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NFCTH_POLICY_SET4,
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__NFCTH_POLICY_SET_MAX
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};
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#define NFCTH_POLICY_SET_MAX (__NFCTH_POLICY_SET_MAX - 1)
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enum nfnl_cthelper_pol_type {
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NFCTH_POLICY_UNSPEC,
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NFCTH_POLICY_NAME,
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NFCTH_POLICY_EXPECT_MAX,
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NFCTH_POLICY_EXPECT_TIMEOUT,
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__NFCTH_POLICY_MAX
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};
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#define NFCTH_POLICY_MAX (__NFCTH_POLICY_MAX - 1)
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enum nfnl_cthelper_tuple_type {
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NFCTH_TUPLE_UNSPEC,
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NFCTH_TUPLE_L3PROTONUM,
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NFCTH_TUPLE_L4PROTONUM,
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__NFCTH_TUPLE_MAX,
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};
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#define NFCTH_TUPLE_MAX (__NFCTH_TUPLE_MAX - 1)
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#endif /* _NFNL_CTHELPER_H */
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