41d73ec053
Split out sequence number adjustments from NAT and move them to the conntrack core to make them usable for SYN proxying. The sequence number adjustment information is moved to a seperate extend. The extend is added to new conntracks when a NAT mapping is set up for a connection using a helper. As a side effect, this saves 24 bytes per connection with NAT in the common case that a connection does not have a helper assigned. Signed-off-by: Patrick McHardy <kaber@trash.net> Tested-by: Martin Topholm <mph@one.com> Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com> Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
213 lines
6.2 KiB
C
213 lines
6.2 KiB
C
/* nf_nat_helper.c - generic support functions for NAT helpers
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*
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* (C) 2000-2002 Harald Welte <laforge@netfilter.org>
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* (C) 2003-2006 Netfilter Core Team <coreteam@netfilter.org>
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* (C) 2007-2012 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/gfp.h>
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#include <linux/types.h>
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#include <linux/skbuff.h>
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#include <linux/tcp.h>
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#include <linux/udp.h>
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#include <net/tcp.h>
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#include <net/netfilter/nf_conntrack.h>
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#include <net/netfilter/nf_conntrack_helper.h>
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#include <net/netfilter/nf_conntrack_ecache.h>
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#include <net/netfilter/nf_conntrack_expect.h>
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#include <net/netfilter/nf_conntrack_seqadj.h>
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#include <net/netfilter/nf_nat.h>
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#include <net/netfilter/nf_nat_l3proto.h>
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#include <net/netfilter/nf_nat_l4proto.h>
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#include <net/netfilter/nf_nat_core.h>
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#include <net/netfilter/nf_nat_helper.h>
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/* Frobs data inside this packet, which is linear. */
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static void mangle_contents(struct sk_buff *skb,
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unsigned int dataoff,
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unsigned int match_offset,
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unsigned int match_len,
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const char *rep_buffer,
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unsigned int rep_len)
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{
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unsigned char *data;
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BUG_ON(skb_is_nonlinear(skb));
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data = skb_network_header(skb) + dataoff;
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/* move post-replacement */
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memmove(data + match_offset + rep_len,
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data + match_offset + match_len,
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skb_tail_pointer(skb) - (skb_network_header(skb) + dataoff +
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match_offset + match_len));
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/* insert data from buffer */
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memcpy(data + match_offset, rep_buffer, rep_len);
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/* update skb info */
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if (rep_len > match_len) {
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pr_debug("nf_nat_mangle_packet: Extending packet by "
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"%u from %u bytes\n", rep_len - match_len, skb->len);
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skb_put(skb, rep_len - match_len);
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} else {
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pr_debug("nf_nat_mangle_packet: Shrinking packet from "
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"%u from %u bytes\n", match_len - rep_len, skb->len);
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__skb_trim(skb, skb->len + rep_len - match_len);
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}
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if (nf_ct_l3num((struct nf_conn *)skb->nfct) == NFPROTO_IPV4) {
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/* fix IP hdr checksum information */
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ip_hdr(skb)->tot_len = htons(skb->len);
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ip_send_check(ip_hdr(skb));
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} else
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ipv6_hdr(skb)->payload_len =
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htons(skb->len - sizeof(struct ipv6hdr));
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}
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/* Unusual, but possible case. */
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static int enlarge_skb(struct sk_buff *skb, unsigned int extra)
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{
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if (skb->len + extra > 65535)
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return 0;
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if (pskb_expand_head(skb, 0, extra - skb_tailroom(skb), GFP_ATOMIC))
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return 0;
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return 1;
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}
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/* Generic function for mangling variable-length address changes inside
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* NATed TCP connections (like the PORT XXX,XXX,XXX,XXX,XXX,XXX
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* command in FTP).
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*
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* Takes care about all the nasty sequence number changes, checksumming,
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* skb enlargement, ...
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*
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* */
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int __nf_nat_mangle_tcp_packet(struct sk_buff *skb,
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struct nf_conn *ct,
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enum ip_conntrack_info ctinfo,
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unsigned int protoff,
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unsigned int match_offset,
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unsigned int match_len,
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const char *rep_buffer,
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unsigned int rep_len, bool adjust)
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{
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const struct nf_nat_l3proto *l3proto;
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struct tcphdr *tcph;
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int oldlen, datalen;
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if (!skb_make_writable(skb, skb->len))
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return 0;
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if (rep_len > match_len &&
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rep_len - match_len > skb_tailroom(skb) &&
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!enlarge_skb(skb, rep_len - match_len))
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return 0;
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SKB_LINEAR_ASSERT(skb);
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tcph = (void *)skb->data + protoff;
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oldlen = skb->len - protoff;
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mangle_contents(skb, protoff + tcph->doff*4,
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match_offset, match_len, rep_buffer, rep_len);
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datalen = skb->len - protoff;
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l3proto = __nf_nat_l3proto_find(nf_ct_l3num(ct));
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l3proto->csum_recalc(skb, IPPROTO_TCP, tcph, &tcph->check,
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datalen, oldlen);
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if (adjust && rep_len != match_len)
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nf_ct_seqadj_set(ct, ctinfo, tcph->seq,
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(int)rep_len - (int)match_len);
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return 1;
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}
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EXPORT_SYMBOL(__nf_nat_mangle_tcp_packet);
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/* Generic function for mangling variable-length address changes inside
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* NATed UDP connections (like the CONNECT DATA XXXXX MESG XXXXX INDEX XXXXX
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* command in the Amanda protocol)
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*
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* Takes care about all the nasty sequence number changes, checksumming,
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* skb enlargement, ...
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*
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* XXX - This function could be merged with nf_nat_mangle_tcp_packet which
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* should be fairly easy to do.
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*/
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int
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nf_nat_mangle_udp_packet(struct sk_buff *skb,
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struct nf_conn *ct,
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enum ip_conntrack_info ctinfo,
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unsigned int protoff,
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unsigned int match_offset,
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unsigned int match_len,
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const char *rep_buffer,
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unsigned int rep_len)
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{
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const struct nf_nat_l3proto *l3proto;
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struct udphdr *udph;
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int datalen, oldlen;
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if (!skb_make_writable(skb, skb->len))
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return 0;
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if (rep_len > match_len &&
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rep_len - match_len > skb_tailroom(skb) &&
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!enlarge_skb(skb, rep_len - match_len))
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return 0;
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udph = (void *)skb->data + protoff;
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oldlen = skb->len - protoff;
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mangle_contents(skb, protoff + sizeof(*udph),
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match_offset, match_len, rep_buffer, rep_len);
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/* update the length of the UDP packet */
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datalen = skb->len - protoff;
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udph->len = htons(datalen);
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/* fix udp checksum if udp checksum was previously calculated */
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if (!udph->check && skb->ip_summed != CHECKSUM_PARTIAL)
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return 1;
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l3proto = __nf_nat_l3proto_find(nf_ct_l3num(ct));
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l3proto->csum_recalc(skb, IPPROTO_UDP, udph, &udph->check,
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datalen, oldlen);
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return 1;
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}
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EXPORT_SYMBOL(nf_nat_mangle_udp_packet);
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/* Setup NAT on this expected conntrack so it follows master. */
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/* If we fail to get a free NAT slot, we'll get dropped on confirm */
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void nf_nat_follow_master(struct nf_conn *ct,
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struct nf_conntrack_expect *exp)
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{
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struct nf_nat_range range;
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/* This must be a fresh one. */
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BUG_ON(ct->status & IPS_NAT_DONE_MASK);
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/* Change src to where master sends to */
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range.flags = NF_NAT_RANGE_MAP_IPS;
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range.min_addr = range.max_addr
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= ct->master->tuplehash[!exp->dir].tuple.dst.u3;
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nf_nat_setup_info(ct, &range, NF_NAT_MANIP_SRC);
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/* For DST manip, map port here to where it's expected. */
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range.flags = (NF_NAT_RANGE_MAP_IPS | NF_NAT_RANGE_PROTO_SPECIFIED);
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range.min_proto = range.max_proto = exp->saved_proto;
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range.min_addr = range.max_addr
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= ct->master->tuplehash[!exp->dir].tuple.src.u3;
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nf_nat_setup_info(ct, &range, NF_NAT_MANIP_DST);
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}
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EXPORT_SYMBOL(nf_nat_follow_master);
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