2690d97ade
Commit5901b6be88attempted to introduce IPv6 support into IRC NAT helper. By doing so, the following code seemed to be removed by accident: ip = ntohl(exp->master->tuplehash[IP_CT_DIR_REPLY].tuple.dst.u3.ip); sprintf(buffer, "%u %u", ip, port); pr_debug("nf_nat_irc: inserting '%s' == %pI4, port %u\n", buffer, &ip, port); This leads to the fact that buffer[] was left uninitialized and contained some stack value. When we call nf_nat_mangle_tcp_packet(), we call strlen(buffer) on excatly this uninitialized buffer. If we are unlucky and the skb has enough tailroom, we overwrite resp. leak contents with values that sit on our stack into the packet and send that out to the receiver. Since the rather informal DCC spec [1] does not seem to specify IPv6 support right now, we log such occurences so that admins can act accordingly, and drop the packet. I've looked into XChat source, and IPv6 is not supported there: addresses are in u32 and print via %u format string. Therefore, restore old behaviour as in IPv4, use snprintf(). The IRC helper does not support IPv6 by now. By this, we can safely use strlen(buffer) in nf_nat_mangle_tcp_packet() and prevent a buffer overflow. Also simplify some code as we now have ct variable anyway. [1] http://www.irchelp.org/irchelp/rfc/ctcpspec.html Fixes:5901b6be88("netfilter: nf_nat: support IPv6 in IRC NAT helper") Signed-off-by: Daniel Borkmann <dborkman@redhat.com> Cc: Harald Welte <laforge@gnumonks.org> Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
120 lines
3.4 KiB
C
120 lines
3.4 KiB
C
/* IRC extension for TCP NAT alteration.
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*
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* (C) 2000-2001 by Harald Welte <laforge@gnumonks.org>
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* (C) 2004 Rusty Russell <rusty@rustcorp.com.au> IBM Corporation
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* based on a copy of RR's ip_nat_ftp.c
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version
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* 2 of the License, or (at your option) any later version.
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*/
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#include <linux/module.h>
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#include <linux/moduleparam.h>
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#include <linux/tcp.h>
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#include <linux/kernel.h>
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#include <net/netfilter/nf_nat.h>
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#include <net/netfilter/nf_nat_helper.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 <linux/netfilter/nf_conntrack_irc.h>
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MODULE_AUTHOR("Harald Welte <laforge@gnumonks.org>");
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MODULE_DESCRIPTION("IRC (DCC) NAT helper");
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MODULE_LICENSE("GPL");
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MODULE_ALIAS("ip_nat_irc");
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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("4294967296 65635")];
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struct nf_conn *ct = exp->master;
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union nf_inet_addr newaddr;
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u_int16_t port;
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unsigned int ret;
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/* Reply comes from server. */
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newaddr = ct->tuplehash[IP_CT_DIR_REPLY].tuple.dst.u3;
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exp->saved_proto.tcp.port = exp->tuple.dst.u.tcp.port;
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exp->dir = IP_CT_DIR_REPLY;
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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 ret;
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exp->tuple.dst.u.tcp.port = htons(port);
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ret = nf_ct_expect_related(exp);
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if (ret == 0)
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break;
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else if (ret != -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, ct, "all ports in use");
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return NF_DROP;
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}
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/* strlen("\1DCC CHAT chat AAAAAAAA P\1\n")=27
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* strlen("\1DCC SCHAT chat AAAAAAAA P\1\n")=28
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* strlen("\1DCC SEND F AAAAAAAA P S\1\n")=26
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* strlen("\1DCC MOVE F AAAAAAAA P S\1\n")=26
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* strlen("\1DCC TSEND F AAAAAAAA P S\1\n")=27
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*
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* AAAAAAAAA: bound addr (1.0.0.0==16777216, min 8 digits,
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* 255.255.255.255==4294967296, 10 digits)
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* P: bound port (min 1 d, max 5d (65635))
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* F: filename (min 1 d )
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* S: size (min 1 d )
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* 0x01, \n: terminators
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*/
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/* AAA = "us", ie. where server normally talks to. */
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snprintf(buffer, sizeof(buffer), "%u %u", ntohl(newaddr.ip), port);
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pr_debug("nf_nat_irc: inserting '%s' == %pI4, port %u\n",
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buffer, &newaddr.ip, port);
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ret = nf_nat_mangle_tcp_packet(skb, ct, ctinfo, protoff, matchoff,
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matchlen, buffer, strlen(buffer));
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if (ret != NF_ACCEPT) {
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nf_ct_helper_log(skb, ct, "cannot mangle packet");
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nf_ct_unexpect_related(exp);
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}
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return ret;
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}
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static void __exit nf_nat_irc_fini(void)
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{
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RCU_INIT_POINTER(nf_nat_irc_hook, NULL);
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synchronize_rcu();
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}
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static int __init nf_nat_irc_init(void)
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{
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BUG_ON(nf_nat_irc_hook != NULL);
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RCU_INIT_POINTER(nf_nat_irc_hook, help);
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return 0;
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}
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/* Prior to 2.6.11, we had a ports param. No longer, but don't break users. */
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static int warn_set(const char *val, struct kernel_param *kp)
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{
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printk(KERN_INFO KBUILD_MODNAME
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": kernel >= 2.6.10 only uses 'ports' for conntrack modules\n");
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return 0;
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}
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module_param_call(ports, warn_set, NULL, NULL, 0);
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module_init(nf_nat_irc_init);
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module_exit(nf_nat_irc_fini);
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