diff options
Diffstat (limited to 'net/ipv4/netfilter/ip_nat_helper.c')
-rw-r--r-- | net/ipv4/netfilter/ip_nat_helper.c | 430 |
1 files changed, 430 insertions, 0 deletions
diff --git a/net/ipv4/netfilter/ip_nat_helper.c b/net/ipv4/netfilter/ip_nat_helper.c new file mode 100644 index 00000000000..1637b96d8c0 --- /dev/null +++ b/net/ipv4/netfilter/ip_nat_helper.c @@ -0,0 +1,430 @@ +/* ip_nat_helper.c - generic support functions for NAT helpers + * + * (C) 2000-2002 Harald Welte <laforge@netfilter.org> + * (C) 2003-2004 Netfilter Core Team <coreteam@netfilter.org> + * + * 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. + * + * 14 Jan 2002 Harald Welte <laforge@gnumonks.org>: + * - add support for SACK adjustment + * 14 Mar 2002 Harald Welte <laforge@gnumonks.org>: + * - merge SACK support into newnat API + * 16 Aug 2002 Brian J. Murrell <netfilter@interlinx.bc.ca>: + * - make ip_nat_resize_packet more generic (TCP and UDP) + * - add ip_nat_mangle_udp_packet + */ +#include <linux/config.h> +#include <linux/module.h> +#include <linux/kmod.h> +#include <linux/types.h> +#include <linux/timer.h> +#include <linux/skbuff.h> +#include <linux/netfilter_ipv4.h> +#include <net/checksum.h> +#include <net/icmp.h> +#include <net/ip.h> +#include <net/tcp.h> +#include <net/udp.h> + +#define ASSERT_READ_LOCK(x) MUST_BE_READ_LOCKED(&ip_nat_lock) +#define ASSERT_WRITE_LOCK(x) MUST_BE_WRITE_LOCKED(&ip_nat_lock) + +#include <linux/netfilter_ipv4/ip_conntrack.h> +#include <linux/netfilter_ipv4/ip_conntrack_helper.h> +#include <linux/netfilter_ipv4/ip_nat.h> +#include <linux/netfilter_ipv4/ip_nat_protocol.h> +#include <linux/netfilter_ipv4/ip_nat_core.h> +#include <linux/netfilter_ipv4/ip_nat_helper.h> +#include <linux/netfilter_ipv4/listhelp.h> + +#if 0 +#define DEBUGP printk +#define DUMP_OFFSET(x) printk("offset_before=%d, offset_after=%d, correction_pos=%u\n", x->offset_before, x->offset_after, x->correction_pos); +#else +#define DEBUGP(format, args...) +#define DUMP_OFFSET(x) +#endif + +static DECLARE_LOCK(ip_nat_seqofs_lock); + +/* Setup TCP sequence correction given this change at this sequence */ +static inline void +adjust_tcp_sequence(u32 seq, + int sizediff, + struct ip_conntrack *ct, + enum ip_conntrack_info ctinfo) +{ + int dir; + struct ip_nat_seq *this_way, *other_way; + + DEBUGP("ip_nat_resize_packet: old_size = %u, new_size = %u\n", + (*skb)->len, new_size); + + dir = CTINFO2DIR(ctinfo); + + this_way = &ct->nat.info.seq[dir]; + other_way = &ct->nat.info.seq[!dir]; + + DEBUGP("ip_nat_resize_packet: Seq_offset before: "); + DUMP_OFFSET(this_way); + + LOCK_BH(&ip_nat_seqofs_lock); + + /* SYN adjust. If it's uninitialized, or this is after last + * correction, record it: we don't handle more than one + * adjustment in the window, but do deal with common case of a + * retransmit */ + if (this_way->offset_before == this_way->offset_after + || before(this_way->correction_pos, seq)) { + this_way->correction_pos = seq; + this_way->offset_before = this_way->offset_after; + this_way->offset_after += sizediff; + } + UNLOCK_BH(&ip_nat_seqofs_lock); + + DEBUGP("ip_nat_resize_packet: Seq_offset after: "); + DUMP_OFFSET(this_way); +} + +/* 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 = (unsigned char *)skb->nh.iph + dataoff; + + /* move post-replacement */ + memmove(data + match_offset + rep_len, + data + match_offset + match_len, + skb->tail - (data + match_offset + match_len)); + + /* insert data from buffer */ + memcpy(data + match_offset, rep_buffer, rep_len); + + /* update skb info */ + if (rep_len > match_len) { + DEBUGP("ip_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 { + DEBUGP("ip_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); + } + + /* fix IP hdr checksum information */ + skb->nh.iph->tot_len = htons(skb->len); + ip_send_check(skb->nh.iph); +} + +/* Unusual, but possible case. */ +static int enlarge_skb(struct sk_buff **pskb, unsigned int extra) +{ + struct sk_buff *nskb; + + if ((*pskb)->len + extra > 65535) + return 0; + + nskb = skb_copy_expand(*pskb, skb_headroom(*pskb), extra, GFP_ATOMIC); + if (!nskb) + return 0; + + /* Transfer socket to new skb. */ + if ((*pskb)->sk) + skb_set_owner_w(nskb, (*pskb)->sk); +#ifdef CONFIG_NETFILTER_DEBUG + nskb->nf_debug = (*pskb)->nf_debug; +#endif + kfree_skb(*pskb); + *pskb = nskb; + 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 +ip_nat_mangle_tcp_packet(struct sk_buff **pskb, + struct ip_conntrack *ct, + enum ip_conntrack_info ctinfo, + unsigned int match_offset, + unsigned int match_len, + const char *rep_buffer, + unsigned int rep_len) +{ + struct iphdr *iph; + struct tcphdr *tcph; + int datalen; + + if (!skb_ip_make_writable(pskb, (*pskb)->len)) + return 0; + + if (rep_len > match_len + && rep_len - match_len > skb_tailroom(*pskb) + && !enlarge_skb(pskb, rep_len - match_len)) + return 0; + + SKB_LINEAR_ASSERT(*pskb); + + iph = (*pskb)->nh.iph; + tcph = (void *)iph + iph->ihl*4; + + mangle_contents(*pskb, iph->ihl*4 + tcph->doff*4, + match_offset, match_len, rep_buffer, rep_len); + + datalen = (*pskb)->len - iph->ihl*4; + tcph->check = 0; + tcph->check = tcp_v4_check(tcph, datalen, iph->saddr, iph->daddr, + csum_partial((char *)tcph, datalen, 0)); + + if (rep_len != match_len) { + set_bit(IPS_SEQ_ADJUST_BIT, &ct->status); + adjust_tcp_sequence(ntohl(tcph->seq), + (int)rep_len - (int)match_len, + ct, ctinfo); + /* Tell TCP window tracking about seq change */ + ip_conntrack_tcp_update(*pskb, ct, CTINFO2DIR(ctinfo)); + } + return 1; +} + +/* 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 ip_nat_mangle_tcp_packet which + * should be fairly easy to do. + */ +int +ip_nat_mangle_udp_packet(struct sk_buff **pskb, + struct ip_conntrack *ct, + enum ip_conntrack_info ctinfo, + unsigned int match_offset, + unsigned int match_len, + const char *rep_buffer, + unsigned int rep_len) +{ + struct iphdr *iph; + struct udphdr *udph; + + /* UDP helpers might accidentally mangle the wrong packet */ + iph = (*pskb)->nh.iph; + if ((*pskb)->len < iph->ihl*4 + sizeof(*udph) + + match_offset + match_len) + return 0; + + if (!skb_ip_make_writable(pskb, (*pskb)->len)) + return 0; + + if (rep_len > match_len + && rep_len - match_len > skb_tailroom(*pskb) + && !enlarge_skb(pskb, rep_len - match_len)) + return 0; + + iph = (*pskb)->nh.iph; + udph = (void *)iph + iph->ihl*4; + mangle_contents(*pskb, iph->ihl*4 + sizeof(*udph), + match_offset, match_len, rep_buffer, rep_len); + + /* update the length of the UDP packet */ + udph->len = htons((*pskb)->len - iph->ihl*4); + + /* fix udp checksum if udp checksum was previously calculated */ + if (udph->check) { + int datalen = (*pskb)->len - iph->ihl * 4; + udph->check = 0; + udph->check = csum_tcpudp_magic(iph->saddr, iph->daddr, + datalen, IPPROTO_UDP, + csum_partial((char *)udph, + datalen, 0)); + } + + return 1; +} + +/* Adjust one found SACK option including checksum correction */ +static void +sack_adjust(struct sk_buff *skb, + struct tcphdr *tcph, + unsigned int sackoff, + unsigned int sackend, + struct ip_nat_seq *natseq) +{ + while (sackoff < sackend) { + struct tcp_sack_block *sack; + u_int32_t new_start_seq, new_end_seq; + + sack = (void *)skb->data + sackoff; + if (after(ntohl(sack->start_seq) - natseq->offset_before, + natseq->correction_pos)) + new_start_seq = ntohl(sack->start_seq) + - natseq->offset_after; + else + new_start_seq = ntohl(sack->start_seq) + - natseq->offset_before; + new_start_seq = htonl(new_start_seq); + + if (after(ntohl(sack->end_seq) - natseq->offset_before, + natseq->correction_pos)) + new_end_seq = ntohl(sack->end_seq) + - natseq->offset_after; + else + new_end_seq = ntohl(sack->end_seq) + - natseq->offset_before; + new_end_seq = htonl(new_end_seq); + + DEBUGP("sack_adjust: start_seq: %d->%d, end_seq: %d->%d\n", + ntohl(sack->start_seq), new_start_seq, + ntohl(sack->end_seq), new_end_seq); + + tcph->check = + ip_nat_cheat_check(~sack->start_seq, new_start_seq, + ip_nat_cheat_check(~sack->end_seq, + new_end_seq, + tcph->check)); + sack->start_seq = new_start_seq; + sack->end_seq = new_end_seq; + sackoff += sizeof(*sack); + } +} + +/* TCP SACK sequence number adjustment */ +static inline unsigned int +ip_nat_sack_adjust(struct sk_buff **pskb, + struct tcphdr *tcph, + struct ip_conntrack *ct, + enum ip_conntrack_info ctinfo) +{ + unsigned int dir, optoff, optend; + + optoff = (*pskb)->nh.iph->ihl*4 + sizeof(struct tcphdr); + optend = (*pskb)->nh.iph->ihl*4 + tcph->doff*4; + + if (!skb_ip_make_writable(pskb, optend)) + return 0; + + dir = CTINFO2DIR(ctinfo); + + while (optoff < optend) { + /* Usually: option, length. */ + unsigned char *op = (*pskb)->data + optoff; + + switch (op[0]) { + case TCPOPT_EOL: + return 1; + case TCPOPT_NOP: + optoff++; + continue; + default: + /* no partial options */ + if (optoff + 1 == optend + || optoff + op[1] > optend + || op[1] < 2) + return 0; + if (op[0] == TCPOPT_SACK + && op[1] >= 2+TCPOLEN_SACK_PERBLOCK + && ((op[1] - 2) % TCPOLEN_SACK_PERBLOCK) == 0) + sack_adjust(*pskb, tcph, optoff+2, + optoff+op[1], + &ct->nat.info.seq[!dir]); + optoff += op[1]; + } + } + return 1; +} + +/* TCP sequence number adjustment. Returns 1 on success, 0 on failure */ +int +ip_nat_seq_adjust(struct sk_buff **pskb, + struct ip_conntrack *ct, + enum ip_conntrack_info ctinfo) +{ + struct tcphdr *tcph; + int dir, newseq, newack; + struct ip_nat_seq *this_way, *other_way; + + dir = CTINFO2DIR(ctinfo); + + this_way = &ct->nat.info.seq[dir]; + other_way = &ct->nat.info.seq[!dir]; + + if (!skb_ip_make_writable(pskb, (*pskb)->nh.iph->ihl*4+sizeof(*tcph))) + return 0; + + tcph = (void *)(*pskb)->data + (*pskb)->nh.iph->ihl*4; + if (after(ntohl(tcph->seq), this_way->correction_pos)) + newseq = ntohl(tcph->seq) + this_way->offset_after; + else + newseq = ntohl(tcph->seq) + this_way->offset_before; + newseq = htonl(newseq); + + if (after(ntohl(tcph->ack_seq) - other_way->offset_before, + other_way->correction_pos)) + newack = ntohl(tcph->ack_seq) - other_way->offset_after; + else + newack = ntohl(tcph->ack_seq) - other_way->offset_before; + newack = htonl(newack); + + tcph->check = ip_nat_cheat_check(~tcph->seq, newseq, + ip_nat_cheat_check(~tcph->ack_seq, + newack, + tcph->check)); + + DEBUGP("Adjusting sequence number from %u->%u, ack from %u->%u\n", + ntohl(tcph->seq), ntohl(newseq), ntohl(tcph->ack_seq), + ntohl(newack)); + + tcph->seq = newseq; + tcph->ack_seq = newack; + + if (!ip_nat_sack_adjust(pskb, tcph, ct, ctinfo)) + return 0; + + ip_conntrack_tcp_update(*pskb, ct, dir); + + return 1; +} + +/* 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 ip_nat_follow_master(struct ip_conntrack *ct, + struct ip_conntrack_expect *exp) +{ + struct ip_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 = IP_NAT_RANGE_MAP_IPS; + range.min_ip = range.max_ip + = ct->master->tuplehash[!exp->dir].tuple.dst.ip; + /* hook doesn't matter, but it has to do source manip */ + ip_nat_setup_info(ct, &range, NF_IP_POST_ROUTING); + + /* For DST manip, map port here to where it's expected. */ + range.flags = (IP_NAT_RANGE_MAP_IPS | IP_NAT_RANGE_PROTO_SPECIFIED); + range.min = range.max = exp->saved_proto; + range.min_ip = range.max_ip + = ct->master->tuplehash[!exp->dir].tuple.src.ip; + /* hook doesn't matter, but it has to do destination manip */ + ip_nat_setup_info(ct, &range, NF_IP_PRE_ROUTING); +} |