![Patrick McHardy](/assets/img/avatar_default.png)
Fix a crash in synproxy_send_tcp() when using the SYNPROXY target in the PREROUTING chain caused by missing routing information. Reported-by: Nicki P. <xastx@gmx.de> Signed-off-by: Patrick McHardy <kaber@trash.net> Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
483 lines
12 KiB
C
483 lines
12 KiB
C
/*
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* Copyright (c) 2013 Patrick McHardy <kaber@trash.net>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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*/
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#include <linux/module.h>
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#include <linux/skbuff.h>
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#include <net/tcp.h>
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#include <linux/netfilter_ipv4/ip_tables.h>
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#include <linux/netfilter/x_tables.h>
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#include <linux/netfilter/xt_SYNPROXY.h>
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#include <net/netfilter/nf_conntrack.h>
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#include <net/netfilter/nf_conntrack_seqadj.h>
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#include <net/netfilter/nf_conntrack_synproxy.h>
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static struct iphdr *
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synproxy_build_ip(struct sk_buff *skb, u32 saddr, u32 daddr)
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{
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struct iphdr *iph;
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skb_reset_network_header(skb);
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iph = (struct iphdr *)skb_put(skb, sizeof(*iph));
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iph->version = 4;
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iph->ihl = sizeof(*iph) / 4;
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iph->tos = 0;
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iph->id = 0;
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iph->frag_off = htons(IP_DF);
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iph->ttl = sysctl_ip_default_ttl;
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iph->protocol = IPPROTO_TCP;
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iph->check = 0;
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iph->saddr = saddr;
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iph->daddr = daddr;
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return iph;
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}
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static void
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synproxy_send_tcp(const struct sk_buff *skb, struct sk_buff *nskb,
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struct nf_conntrack *nfct, enum ip_conntrack_info ctinfo,
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struct iphdr *niph, struct tcphdr *nth,
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unsigned int tcp_hdr_size)
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{
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nth->check = ~tcp_v4_check(tcp_hdr_size, niph->saddr, niph->daddr, 0);
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nskb->ip_summed = CHECKSUM_PARTIAL;
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nskb->csum_start = (unsigned char *)nth - nskb->head;
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nskb->csum_offset = offsetof(struct tcphdr, check);
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skb_dst_set_noref(nskb, skb_dst(skb));
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nskb->protocol = htons(ETH_P_IP);
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if (ip_route_me_harder(nskb, RTN_UNSPEC))
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goto free_nskb;
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if (nfct) {
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nskb->nfct = nfct;
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nskb->nfctinfo = ctinfo;
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nf_conntrack_get(nfct);
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}
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ip_local_out(nskb);
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return;
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free_nskb:
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kfree_skb(nskb);
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}
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static void
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synproxy_send_client_synack(const struct sk_buff *skb, const struct tcphdr *th,
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const struct synproxy_options *opts)
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{
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struct sk_buff *nskb;
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struct iphdr *iph, *niph;
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struct tcphdr *nth;
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unsigned int tcp_hdr_size;
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u16 mss = opts->mss;
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iph = ip_hdr(skb);
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tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
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nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
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GFP_ATOMIC);
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if (nskb == NULL)
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return;
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skb_reserve(nskb, MAX_TCP_HEADER);
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niph = synproxy_build_ip(nskb, iph->daddr, iph->saddr);
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skb_reset_transport_header(nskb);
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nth = (struct tcphdr *)skb_put(nskb, tcp_hdr_size);
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nth->source = th->dest;
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nth->dest = th->source;
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nth->seq = htonl(__cookie_v4_init_sequence(iph, th, &mss));
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nth->ack_seq = htonl(ntohl(th->seq) + 1);
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tcp_flag_word(nth) = TCP_FLAG_SYN | TCP_FLAG_ACK;
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if (opts->options & XT_SYNPROXY_OPT_ECN)
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tcp_flag_word(nth) |= TCP_FLAG_ECE;
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nth->doff = tcp_hdr_size / 4;
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nth->window = 0;
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nth->check = 0;
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nth->urg_ptr = 0;
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synproxy_build_options(nth, opts);
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synproxy_send_tcp(skb, nskb, skb->nfct, IP_CT_ESTABLISHED_REPLY,
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niph, nth, tcp_hdr_size);
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}
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static void
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synproxy_send_server_syn(const struct synproxy_net *snet,
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const struct sk_buff *skb, const struct tcphdr *th,
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const struct synproxy_options *opts, u32 recv_seq)
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{
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struct sk_buff *nskb;
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struct iphdr *iph, *niph;
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struct tcphdr *nth;
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unsigned int tcp_hdr_size;
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iph = ip_hdr(skb);
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tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
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nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
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GFP_ATOMIC);
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if (nskb == NULL)
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return;
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skb_reserve(nskb, MAX_TCP_HEADER);
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niph = synproxy_build_ip(nskb, iph->saddr, iph->daddr);
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skb_reset_transport_header(nskb);
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nth = (struct tcphdr *)skb_put(nskb, tcp_hdr_size);
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nth->source = th->source;
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nth->dest = th->dest;
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nth->seq = htonl(recv_seq - 1);
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/* ack_seq is used to relay our ISN to the synproxy hook to initialize
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* sequence number translation once a connection tracking entry exists.
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*/
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nth->ack_seq = htonl(ntohl(th->ack_seq) - 1);
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tcp_flag_word(nth) = TCP_FLAG_SYN;
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if (opts->options & XT_SYNPROXY_OPT_ECN)
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tcp_flag_word(nth) |= TCP_FLAG_ECE | TCP_FLAG_CWR;
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nth->doff = tcp_hdr_size / 4;
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nth->window = th->window;
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nth->check = 0;
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nth->urg_ptr = 0;
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synproxy_build_options(nth, opts);
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synproxy_send_tcp(skb, nskb, &snet->tmpl->ct_general, IP_CT_NEW,
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niph, nth, tcp_hdr_size);
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}
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static void
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synproxy_send_server_ack(const struct synproxy_net *snet,
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const struct ip_ct_tcp *state,
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const struct sk_buff *skb, const struct tcphdr *th,
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const struct synproxy_options *opts)
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{
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struct sk_buff *nskb;
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struct iphdr *iph, *niph;
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struct tcphdr *nth;
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unsigned int tcp_hdr_size;
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iph = ip_hdr(skb);
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tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
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nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
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GFP_ATOMIC);
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if (nskb == NULL)
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return;
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skb_reserve(nskb, MAX_TCP_HEADER);
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niph = synproxy_build_ip(nskb, iph->daddr, iph->saddr);
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skb_reset_transport_header(nskb);
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nth = (struct tcphdr *)skb_put(nskb, tcp_hdr_size);
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nth->source = th->dest;
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nth->dest = th->source;
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nth->seq = htonl(ntohl(th->ack_seq));
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nth->ack_seq = htonl(ntohl(th->seq) + 1);
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tcp_flag_word(nth) = TCP_FLAG_ACK;
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nth->doff = tcp_hdr_size / 4;
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nth->window = htons(state->seen[IP_CT_DIR_ORIGINAL].td_maxwin);
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nth->check = 0;
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nth->urg_ptr = 0;
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synproxy_build_options(nth, opts);
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synproxy_send_tcp(skb, nskb, NULL, 0, niph, nth, tcp_hdr_size);
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}
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static void
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synproxy_send_client_ack(const struct synproxy_net *snet,
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const struct sk_buff *skb, const struct tcphdr *th,
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const struct synproxy_options *opts)
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{
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struct sk_buff *nskb;
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struct iphdr *iph, *niph;
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struct tcphdr *nth;
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unsigned int tcp_hdr_size;
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iph = ip_hdr(skb);
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tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
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nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
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GFP_ATOMIC);
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if (nskb == NULL)
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return;
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skb_reserve(nskb, MAX_TCP_HEADER);
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niph = synproxy_build_ip(nskb, iph->saddr, iph->daddr);
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skb_reset_transport_header(nskb);
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nth = (struct tcphdr *)skb_put(nskb, tcp_hdr_size);
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nth->source = th->source;
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nth->dest = th->dest;
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nth->seq = htonl(ntohl(th->seq) + 1);
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nth->ack_seq = th->ack_seq;
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tcp_flag_word(nth) = TCP_FLAG_ACK;
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nth->doff = tcp_hdr_size / 4;
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nth->window = ntohs(htons(th->window) >> opts->wscale);
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nth->check = 0;
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nth->urg_ptr = 0;
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synproxy_build_options(nth, opts);
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synproxy_send_tcp(skb, nskb, NULL, 0, niph, nth, tcp_hdr_size);
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}
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static bool
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synproxy_recv_client_ack(const struct synproxy_net *snet,
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const struct sk_buff *skb, const struct tcphdr *th,
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struct synproxy_options *opts, u32 recv_seq)
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{
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int mss;
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mss = __cookie_v4_check(ip_hdr(skb), th, ntohl(th->ack_seq) - 1);
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if (mss == 0) {
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this_cpu_inc(snet->stats->cookie_invalid);
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return false;
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}
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this_cpu_inc(snet->stats->cookie_valid);
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opts->mss = mss;
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opts->options |= XT_SYNPROXY_OPT_MSS;
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if (opts->options & XT_SYNPROXY_OPT_TIMESTAMP)
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synproxy_check_timestamp_cookie(opts);
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synproxy_send_server_syn(snet, skb, th, opts, recv_seq);
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return true;
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}
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static unsigned int
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synproxy_tg4(struct sk_buff *skb, const struct xt_action_param *par)
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{
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const struct xt_synproxy_info *info = par->targinfo;
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struct synproxy_net *snet = synproxy_pernet(dev_net(par->in));
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struct synproxy_options opts = {};
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struct tcphdr *th, _th;
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if (nf_ip_checksum(skb, par->hooknum, par->thoff, IPPROTO_TCP))
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return NF_DROP;
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th = skb_header_pointer(skb, par->thoff, sizeof(_th), &_th);
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if (th == NULL)
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return NF_DROP;
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if (!synproxy_parse_options(skb, par->thoff, th, &opts))
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return NF_DROP;
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if (th->syn && !(th->ack || th->fin || th->rst)) {
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/* Initial SYN from client */
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this_cpu_inc(snet->stats->syn_received);
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if (th->ece && th->cwr)
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opts.options |= XT_SYNPROXY_OPT_ECN;
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opts.options &= info->options;
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if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
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synproxy_init_timestamp_cookie(info, &opts);
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else
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opts.options &= ~(XT_SYNPROXY_OPT_WSCALE |
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XT_SYNPROXY_OPT_SACK_PERM |
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XT_SYNPROXY_OPT_ECN);
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synproxy_send_client_synack(skb, th, &opts);
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return NF_DROP;
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} else if (th->ack && !(th->fin || th->rst || th->syn)) {
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/* ACK from client */
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synproxy_recv_client_ack(snet, skb, th, &opts, ntohl(th->seq));
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return NF_DROP;
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}
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return XT_CONTINUE;
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}
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static unsigned int ipv4_synproxy_hook(const struct nf_hook_ops *ops,
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struct sk_buff *skb,
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const struct net_device *in,
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const struct net_device *out,
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int (*okfn)(struct sk_buff *))
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{
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struct synproxy_net *snet = synproxy_pernet(dev_net(in ? : out));
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enum ip_conntrack_info ctinfo;
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struct nf_conn *ct;
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struct nf_conn_synproxy *synproxy;
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struct synproxy_options opts = {};
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const struct ip_ct_tcp *state;
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struct tcphdr *th, _th;
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unsigned int thoff;
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ct = nf_ct_get(skb, &ctinfo);
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if (ct == NULL)
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return NF_ACCEPT;
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synproxy = nfct_synproxy(ct);
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if (synproxy == NULL)
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return NF_ACCEPT;
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if (nf_is_loopback_packet(skb))
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return NF_ACCEPT;
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thoff = ip_hdrlen(skb);
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th = skb_header_pointer(skb, thoff, sizeof(_th), &_th);
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if (th == NULL)
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return NF_DROP;
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state = &ct->proto.tcp;
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switch (state->state) {
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case TCP_CONNTRACK_CLOSE:
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if (th->rst && !test_bit(IPS_SEEN_REPLY_BIT, &ct->status)) {
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nf_ct_seqadj_init(ct, ctinfo, synproxy->isn -
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ntohl(th->seq) + 1);
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break;
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}
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if (!th->syn || th->ack ||
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CTINFO2DIR(ctinfo) != IP_CT_DIR_ORIGINAL)
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break;
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/* Reopened connection - reset the sequence number and timestamp
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* adjustments, they will get initialized once the connection is
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* reestablished.
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*/
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nf_ct_seqadj_init(ct, ctinfo, 0);
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synproxy->tsoff = 0;
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this_cpu_inc(snet->stats->conn_reopened);
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/* fall through */
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case TCP_CONNTRACK_SYN_SENT:
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if (!synproxy_parse_options(skb, thoff, th, &opts))
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return NF_DROP;
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if (!th->syn && th->ack &&
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CTINFO2DIR(ctinfo) == IP_CT_DIR_ORIGINAL) {
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/* Keep-Alives are sent with SEG.SEQ = SND.NXT-1,
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* therefore we need to add 1 to make the SYN sequence
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* number match the one of first SYN.
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*/
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if (synproxy_recv_client_ack(snet, skb, th, &opts,
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ntohl(th->seq) + 1))
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this_cpu_inc(snet->stats->cookie_retrans);
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return NF_DROP;
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}
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synproxy->isn = ntohl(th->ack_seq);
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if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
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synproxy->its = opts.tsecr;
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break;
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case TCP_CONNTRACK_SYN_RECV:
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if (!th->syn || !th->ack)
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break;
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if (!synproxy_parse_options(skb, thoff, th, &opts))
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return NF_DROP;
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if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
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synproxy->tsoff = opts.tsval - synproxy->its;
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opts.options &= ~(XT_SYNPROXY_OPT_MSS |
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XT_SYNPROXY_OPT_WSCALE |
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XT_SYNPROXY_OPT_SACK_PERM);
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swap(opts.tsval, opts.tsecr);
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synproxy_send_server_ack(snet, state, skb, th, &opts);
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nf_ct_seqadj_init(ct, ctinfo, synproxy->isn - ntohl(th->seq));
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swap(opts.tsval, opts.tsecr);
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synproxy_send_client_ack(snet, skb, th, &opts);
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consume_skb(skb);
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return NF_STOLEN;
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default:
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break;
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}
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synproxy_tstamp_adjust(skb, thoff, th, ct, ctinfo, synproxy);
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return NF_ACCEPT;
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}
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static int synproxy_tg4_check(const struct xt_tgchk_param *par)
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{
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const struct ipt_entry *e = par->entryinfo;
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if (e->ip.proto != IPPROTO_TCP ||
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e->ip.invflags & XT_INV_PROTO)
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return -EINVAL;
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return nf_ct_l3proto_try_module_get(par->family);
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}
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static void synproxy_tg4_destroy(const struct xt_tgdtor_param *par)
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{
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nf_ct_l3proto_module_put(par->family);
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}
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static struct xt_target synproxy_tg4_reg __read_mostly = {
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.name = "SYNPROXY",
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.family = NFPROTO_IPV4,
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.hooks = (1 << NF_INET_LOCAL_IN) | (1 << NF_INET_FORWARD),
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.target = synproxy_tg4,
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.targetsize = sizeof(struct xt_synproxy_info),
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.checkentry = synproxy_tg4_check,
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.destroy = synproxy_tg4_destroy,
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.me = THIS_MODULE,
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};
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static struct nf_hook_ops ipv4_synproxy_ops[] __read_mostly = {
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{
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.hook = ipv4_synproxy_hook,
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.owner = THIS_MODULE,
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.pf = NFPROTO_IPV4,
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.hooknum = NF_INET_LOCAL_IN,
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.priority = NF_IP_PRI_CONNTRACK_CONFIRM - 1,
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},
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{
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.hook = ipv4_synproxy_hook,
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.owner = THIS_MODULE,
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.pf = NFPROTO_IPV4,
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.hooknum = NF_INET_POST_ROUTING,
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.priority = NF_IP_PRI_CONNTRACK_CONFIRM - 1,
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},
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};
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static int __init synproxy_tg4_init(void)
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{
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int err;
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err = nf_register_hooks(ipv4_synproxy_ops,
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ARRAY_SIZE(ipv4_synproxy_ops));
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if (err < 0)
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goto err1;
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err = xt_register_target(&synproxy_tg4_reg);
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if (err < 0)
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goto err2;
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return 0;
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err2:
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nf_unregister_hooks(ipv4_synproxy_ops, ARRAY_SIZE(ipv4_synproxy_ops));
|
|
err1:
|
|
return err;
|
|
}
|
|
|
|
static void __exit synproxy_tg4_exit(void)
|
|
{
|
|
xt_unregister_target(&synproxy_tg4_reg);
|
|
nf_unregister_hooks(ipv4_synproxy_ops, ARRAY_SIZE(ipv4_synproxy_ops));
|
|
}
|
|
|
|
module_init(synproxy_tg4_init);
|
|
module_exit(synproxy_tg4_exit);
|
|
|
|
MODULE_LICENSE("GPL");
|
|
MODULE_AUTHOR("Patrick McHardy <kaber@trash.net>");
|