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- /* nf_nat_helper.c - generic support functions for NAT helpers
- *
- * (C) 2000-2002 Harald Welte <laforge@netfilter.org>
- * (C) 2003-2006 Netfilter Core Team <coreteam@netfilter.org>
- * (C) 2007-2012 Patrick McHardy <kaber@trash.net>
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License version 2 as
- * published by the Free Software Foundation.
- */
- #include <linux/module.h>
- #include <linux/gfp.h>
- #include <linux/types.h>
- #include <linux/skbuff.h>
- #include <linux/tcp.h>
- #include <linux/udp.h>
- #include <net/tcp.h>
- #include <net/netfilter/nf_conntrack.h>
- #include <net/netfilter/nf_conntrack_helper.h>
- #include <net/netfilter/nf_conntrack_ecache.h>
- #include <net/netfilter/nf_conntrack_expect.h>
- #include <net/netfilter/nf_conntrack_seqadj.h>
- #include <net/netfilter/nf_nat.h>
- #include <net/netfilter/nf_nat_l3proto.h>
- #include <net/netfilter/nf_nat_l4proto.h>
- #include <net/netfilter/nf_nat_core.h>
- #include <net/netfilter/nf_nat_helper.h>
- /* Frobs data inside this packet, which is linear. */
- static void mangle_contents(struct sk_buff *skb,
- unsigned int dataoff,
- unsigned int match_offset,
- unsigned int match_len,
- const char *rep_buffer,
- unsigned int rep_len)
- {
- unsigned char *data;
- BUG_ON(skb_is_nonlinear(skb));
- data = skb_network_header(skb) + dataoff;
- /* move post-replacement */
- memmove(data + match_offset + rep_len,
- data + match_offset + match_len,
- skb_tail_pointer(skb) - (skb_network_header(skb) + dataoff +
- match_offset + match_len));
- /* insert data from buffer */
- memcpy(data + match_offset, rep_buffer, rep_len);
- /* update skb info */
- if (rep_len > match_len) {
- pr_debug("nf_nat_mangle_packet: Extending packet by "
- "%u from %u bytes\n", rep_len - match_len, skb->len);
- skb_put(skb, rep_len - match_len);
- } else {
- pr_debug("nf_nat_mangle_packet: Shrinking packet from "
- "%u from %u bytes\n", match_len - rep_len, skb->len);
- __skb_trim(skb, skb->len + rep_len - match_len);
- }
- if (nf_ct_l3num((struct nf_conn *)skb->nfct) == NFPROTO_IPV4) {
- /* fix IP hdr checksum information */
- ip_hdr(skb)->tot_len = htons(skb->len);
- ip_send_check(ip_hdr(skb));
- } else
- ipv6_hdr(skb)->payload_len =
- htons(skb->len - sizeof(struct ipv6hdr));
- }
- /* Unusual, but possible case. */
- static int enlarge_skb(struct sk_buff *skb, unsigned int extra)
- {
- if (skb->len + extra > 65535)
- return 0;
- if (pskb_expand_head(skb, 0, extra - skb_tailroom(skb), GFP_ATOMIC))
- return 0;
- return 1;
- }
- /* Generic function for mangling variable-length address changes inside
- * NATed TCP connections (like the PORT XXX,XXX,XXX,XXX,XXX,XXX
- * command in FTP).
- *
- * Takes care about all the nasty sequence number changes, checksumming,
- * skb enlargement, ...
- *
- * */
- int __nf_nat_mangle_tcp_packet(struct sk_buff *skb,
- struct nf_conn *ct,
- enum ip_conntrack_info ctinfo,
- unsigned int protoff,
- unsigned int match_offset,
- unsigned int match_len,
- const char *rep_buffer,
- unsigned int rep_len, bool adjust)
- {
- const struct nf_nat_l3proto *l3proto;
- struct tcphdr *tcph;
- int oldlen, datalen;
- if (!skb_make_writable(skb, skb->len))
- return 0;
- if (rep_len > match_len &&
- rep_len - match_len > skb_tailroom(skb) &&
- !enlarge_skb(skb, rep_len - match_len))
- return 0;
- SKB_LINEAR_ASSERT(skb);
- tcph = (void *)skb->data + protoff;
- oldlen = skb->len - protoff;
- mangle_contents(skb, protoff + tcph->doff*4,
- match_offset, match_len, rep_buffer, rep_len);
- datalen = skb->len - protoff;
- l3proto = __nf_nat_l3proto_find(nf_ct_l3num(ct));
- l3proto->csum_recalc(skb, IPPROTO_TCP, tcph, &tcph->check,
- datalen, oldlen);
- if (adjust && rep_len != match_len)
- nf_ct_seqadj_set(ct, ctinfo, tcph->seq,
- (int)rep_len - (int)match_len);
- return 1;
- }
- EXPORT_SYMBOL(__nf_nat_mangle_tcp_packet);
- /* Generic function for mangling variable-length address changes inside
- * NATed UDP connections (like the CONNECT DATA XXXXX MESG XXXXX INDEX XXXXX
- * command in the Amanda protocol)
- *
- * Takes care about all the nasty sequence number changes, checksumming,
- * skb enlargement, ...
- *
- * XXX - This function could be merged with nf_nat_mangle_tcp_packet which
- * should be fairly easy to do.
- */
- int
- nf_nat_mangle_udp_packet(struct sk_buff *skb,
- struct nf_conn *ct,
- enum ip_conntrack_info ctinfo,
- unsigned int protoff,
- unsigned int match_offset,
- unsigned int match_len,
- const char *rep_buffer,
- unsigned int rep_len)
- {
- const struct nf_nat_l3proto *l3proto;
- struct udphdr *udph;
- int datalen, oldlen;
- if (!skb_make_writable(skb, skb->len))
- return 0;
- if (rep_len > match_len &&
- rep_len - match_len > skb_tailroom(skb) &&
- !enlarge_skb(skb, rep_len - match_len))
- return 0;
- udph = (void *)skb->data + protoff;
- oldlen = skb->len - protoff;
- mangle_contents(skb, protoff + sizeof(*udph),
- match_offset, match_len, rep_buffer, rep_len);
- /* update the length of the UDP packet */
- datalen = skb->len - protoff;
- udph->len = htons(datalen);
- /* fix udp checksum if udp checksum was previously calculated */
- if (!udph->check && skb->ip_summed != CHECKSUM_PARTIAL)
- return 1;
- l3proto = __nf_nat_l3proto_find(nf_ct_l3num(ct));
- l3proto->csum_recalc(skb, IPPROTO_UDP, udph, &udph->check,
- datalen, oldlen);
- return 1;
- }
- EXPORT_SYMBOL(nf_nat_mangle_udp_packet);
- /* Setup NAT on this expected conntrack so it follows master. */
- /* If we fail to get a free NAT slot, we'll get dropped on confirm */
- void nf_nat_follow_master(struct nf_conn *ct,
- struct nf_conntrack_expect *exp)
- {
- struct nf_nat_range range;
- /* This must be a fresh one. */
- BUG_ON(ct->status & IPS_NAT_DONE_MASK);
- /* Change src to where master sends to */
- range.flags = NF_NAT_RANGE_MAP_IPS;
- range.min_addr = range.max_addr
- = ct->master->tuplehash[!exp->dir].tuple.dst.u3;
- nf_nat_setup_info(ct, &range, NF_NAT_MANIP_SRC);
- /* For DST manip, map port here to where it's expected. */
- range.flags = (NF_NAT_RANGE_MAP_IPS | NF_NAT_RANGE_PROTO_SPECIFIED);
- range.min_proto = range.max_proto = exp->saved_proto;
- range.min_addr = range.max_addr
- = ct->master->tuplehash[!exp->dir].tuple.src.u3;
- nf_nat_setup_info(ct, &range, NF_NAT_MANIP_DST);
- }
- EXPORT_SYMBOL(nf_nat_follow_master);
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