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When conntracks change during a dialog, SDP messages may be sent from different conntracks to establish expects with identical tuples. In this case expects conflict may be detected for the 2nd SDP message and end up with a process failure. The fixing here is to reuse an existing expect who has the same tuple for a different conntrack if any. Here are two scenarios for the case. 1) SERVER CPE | INVITE SDP | 5060 |<----------------------|5060 | 100 Trying | 5060 |---------------------->|5060 | 183 SDP | 5060 |---------------------->|5060 ===> Conntrack 1 | PRACK | 50601 |<----------------------|5060 | 200 OK (PRACK) | 50601 |---------------------->|5060 | 200 OK (INVITE) | 5060 |---------------------->|5060 | ACK | 50601 |<----------------------|5060 | | |<--- RTP stream ------>| | | | INVITE SDP (t38) | 50601 |---------------------->|5060 ===> Conntrack 2 With a certain configuration in the CPE, SIP messages "183 with SDP" and "re-INVITE with SDP t38" will go through the sip helper to create expects for RTP and RTCP. It is okay to create RTP and RTCP expects for "183", whose master connection source port is 5060, and destination port is 5060. In the "183" message, port in Contact header changes to 50601 (from the original 5060). So the following requests e.g. PRACK and ACK are sent to port 50601. It is a different conntrack (let call Conntrack 2) from the original INVITE (let call Conntrack 1) due to the port difference. In this example, after the call is established, there is RTP stream but no RTCP stream for Conntrack 1, so the RTP expect created upon "183" is cleared, and RTCP expect created for Conntrack 1 retains. When "re-INVITE with SDP t38" arrives to create RTP&RTCP expects, current ALG implementation will call nf_ct_expect_related() for RTP and RTCP. The expects tuples are identical to those for Conntrack 1. RTP expect for Conntrack 2 succeeds in creation as the one for Conntrack 1 has been removed. RTCP expect for Conntrack 2 fails in creation because it has idential tuples and 'conflict' with the one retained for Conntrack 1. And then result in a failure in processing of the re-INVITE. 2) SERVER A CPE | REGISTER | 5060 |<------------------| 5060 ==> CT1 | 200 | 5060 |------------------>| 5060 | | | INVITE SDP(1) | 5060 |<------------------| 5060 | 300(multi choice) | 5060 |------------------>| 5060 SERVER B | ACK | 5060 |<------------------| 5060 | INVITE SDP(2) | 5060 |-------------------->| 5060 ==> CT2 | 100 | 5060 |<--------------------| 5060 | 200(contact changes)| 5060 |<--------------------| 5060 | ACK | 5060 |-------------------->| 50601 ==> CT3 | | |<--- RTP stream ---->| | | | BYE | 5060 |<--------------------| 50601 | 200 | 5060 |-------------------->| 50601 | INVITE SDP(3) | 5060 |<------------------| 5060 ==> CT1 CPE sends an INVITE request(1) to Server A, and creates a RTP&RTCP expect pair for this Conntrack 1 (CT1). Server A responds 300 to redirect to Server B. The RTP&RTCP expect pairs created on CT1 are removed upon 300 response. CPE sends the INVITE request(2) to Server B, and creates an expect pair for the new conntrack (due to destination address difference), let call CT2. Server B changes the port to 50601 in 200 OK response, and the following requests ACK and BYE from CPE are sent to 50601. The call is established. There is RTP stream and no RTCP stream. So RTP expect is removed and RTCP expect for CT2 retains. As BYE request is sent from port 50601, it is another conntrack, let call CT3, different from CT2 due to the port difference. So the BYE request will not remove the RTCP expect for CT2. Then another outgoing call is made, with the same RTP port being used (not definitely but possibly). CPE firstly sends the INVITE request(3) to Server A, and tries to create a RTP&RTCP expect pairs for this CT1. In current ALG implementation, the RTCP expect for CT1 fails in creation because it 'conflicts' with the residual one for CT2. As a result the INVITE request fails to send. Signed-off-by: xiao ruizhu <katrina.xiaorz@gmail.com> Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
92 lines
2.5 KiB
C
92 lines
2.5 KiB
C
// SPDX-License-Identifier: GPL-2.0-or-later
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/* Amanda extension for TCP NAT alteration.
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* (C) 2002 by Brian J. Murrell <netfilter@interlinx.bc.ca>
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* based on a copy of HW's ip_nat_irc.c as well as other modules
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* (C) 2006-2012 Patrick McHardy <kaber@trash.net>
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*/
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#include <linux/kernel.h>
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#include <linux/module.h>
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#include <linux/skbuff.h>
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#include <linux/udp.h>
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#include <net/netfilter/nf_conntrack_helper.h>
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#include <net/netfilter/nf_conntrack_expect.h>
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#include <net/netfilter/nf_nat_helper.h>
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#include <linux/netfilter/nf_conntrack_amanda.h>
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#define NAT_HELPER_NAME "amanda"
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MODULE_AUTHOR("Brian J. Murrell <netfilter@interlinx.bc.ca>");
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MODULE_DESCRIPTION("Amanda NAT helper");
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MODULE_LICENSE("GPL");
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MODULE_ALIAS_NF_NAT_HELPER(NAT_HELPER_NAME);
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static struct nf_conntrack_nat_helper nat_helper_amanda =
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NF_CT_NAT_HELPER_INIT(NAT_HELPER_NAME);
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static unsigned int help(struct sk_buff *skb,
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enum ip_conntrack_info ctinfo,
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unsigned int protoff,
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unsigned int matchoff,
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unsigned int matchlen,
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struct nf_conntrack_expect *exp)
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{
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char buffer[sizeof("65535")];
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u_int16_t port;
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/* Connection comes from client. */
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exp->saved_proto.tcp.port = exp->tuple.dst.u.tcp.port;
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exp->dir = IP_CT_DIR_ORIGINAL;
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/* When you see the packet, we need to NAT it the same as the
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* this one (ie. same IP: it will be TCP and master is UDP). */
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exp->expectfn = nf_nat_follow_master;
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/* Try to get same port: if not, try to change it. */
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for (port = ntohs(exp->saved_proto.tcp.port); port != 0; port++) {
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int res;
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exp->tuple.dst.u.tcp.port = htons(port);
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res = nf_ct_expect_related(exp, 0);
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if (res == 0)
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break;
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else if (res != -EBUSY) {
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port = 0;
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break;
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}
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}
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if (port == 0) {
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nf_ct_helper_log(skb, exp->master, "all ports in use");
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return NF_DROP;
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}
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sprintf(buffer, "%u", port);
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if (!nf_nat_mangle_udp_packet(skb, exp->master, ctinfo,
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protoff, matchoff, matchlen,
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buffer, strlen(buffer))) {
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nf_ct_helper_log(skb, exp->master, "cannot mangle packet");
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nf_ct_unexpect_related(exp);
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return NF_DROP;
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}
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return NF_ACCEPT;
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}
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static void __exit nf_nat_amanda_fini(void)
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{
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nf_nat_helper_unregister(&nat_helper_amanda);
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RCU_INIT_POINTER(nf_nat_amanda_hook, NULL);
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synchronize_rcu();
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}
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static int __init nf_nat_amanda_init(void)
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{
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BUG_ON(nf_nat_amanda_hook != NULL);
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nf_nat_helper_register(&nat_helper_amanda);
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RCU_INIT_POINTER(nf_nat_amanda_hook, help);
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return 0;
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}
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module_init(nf_nat_amanda_init);
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module_exit(nf_nat_amanda_fini);
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