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![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>
87 lines
2.3 KiB
C
87 lines
2.3 KiB
C
#ifndef __LINUX_IP_NETFILTER_H
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#define __LINUX_IP_NETFILTER_H
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/* IPv4-specific defines for netfilter.
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* (C)1998 Rusty Russell -- This code is GPL.
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*/
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#include <linux/netfilter.h>
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/* only for userspace compatibility */
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#ifndef __KERNEL__
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#include <limits.h> /* for INT_MIN, INT_MAX */
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/* IP Cache bits. */
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/* Src IP address. */
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#define NFC_IP_SRC 0x0001
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/* Dest IP address. */
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#define NFC_IP_DST 0x0002
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/* Input device. */
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#define NFC_IP_IF_IN 0x0004
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/* Output device. */
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#define NFC_IP_IF_OUT 0x0008
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/* TOS. */
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#define NFC_IP_TOS 0x0010
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/* Protocol. */
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#define NFC_IP_PROTO 0x0020
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/* IP options. */
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#define NFC_IP_OPTIONS 0x0040
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/* Frag & flags. */
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#define NFC_IP_FRAG 0x0080
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/* Per-protocol information: only matters if proto match. */
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/* TCP flags. */
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#define NFC_IP_TCPFLAGS 0x0100
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/* Source port. */
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#define NFC_IP_SRC_PT 0x0200
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/* Dest port. */
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#define NFC_IP_DST_PT 0x0400
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/* Something else about the proto */
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#define NFC_IP_PROTO_UNKNOWN 0x2000
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/* IP Hooks */
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/* After promisc drops, checksum checks. */
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#define NF_IP_PRE_ROUTING 0
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/* If the packet is destined for this box. */
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#define NF_IP_LOCAL_IN 1
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/* If the packet is destined for another interface. */
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#define NF_IP_FORWARD 2
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/* Packets coming from a local process. */
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#define NF_IP_LOCAL_OUT 3
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/* Packets about to hit the wire. */
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#define NF_IP_POST_ROUTING 4
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#define NF_IP_NUMHOOKS 5
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#endif /* ! __KERNEL__ */
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enum nf_ip_hook_priorities {
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NF_IP_PRI_FIRST = INT_MIN,
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NF_IP_PRI_CONNTRACK_DEFRAG = -400,
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NF_IP_PRI_RAW = -300,
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NF_IP_PRI_SELINUX_FIRST = -225,
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NF_IP_PRI_CONNTRACK = -200,
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NF_IP_PRI_MANGLE = -150,
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NF_IP_PRI_NAT_DST = -100,
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NF_IP_PRI_FILTER = 0,
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NF_IP_PRI_SECURITY = 50,
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NF_IP_PRI_NAT_SRC = 100,
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NF_IP_PRI_SELINUX_LAST = 225,
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NF_IP_PRI_CONNTRACK_HELPER = 300,
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NF_IP_PRI_CONNTRACK_CONFIRM = INT_MAX,
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NF_IP_PRI_LAST = INT_MAX,
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};
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/* Arguments for setsockopt SOL_IP: */
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/* 2.0 firewalling went from 64 through 71 (and +256, +512, etc). */
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/* 2.2 firewalling (+ masq) went from 64 through 76 */
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/* 2.4 firewalling went 64 through 67. */
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#define SO_ORIGINAL_DST 80
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#ifdef __KERNEL__
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extern int ip_route_me_harder(struct sk_buff *skb, unsigned addr_type);
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extern int ip_xfrm_me_harder(struct sk_buff *skb);
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extern __sum16 nf_ip_checksum(struct sk_buff *skb, unsigned int hook,
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unsigned int dataoff, u_int8_t protocol);
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#endif /*__KERNEL__*/
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#endif /*__LINUX_IP_NETFILTER_H*/
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