From c7232c9979cba684c50b64c513c4a83c9aa70563 Mon Sep 17 00:00:00 2001 From: Patrick McHardy Date: Sun, 26 Aug 2012 19:14:06 +0200 Subject: netfilter: add protocol independent NAT core Convert the IPv4 NAT implementation to a protocol independent core and address family specific modules. Signed-off-by: Patrick McHardy --- net/netfilter/nf_nat_helper.c | 435 ++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 435 insertions(+) create mode 100644 net/netfilter/nf_nat_helper.c (limited to 'net/netfilter/nf_nat_helper.c') diff --git a/net/netfilter/nf_nat_helper.c b/net/netfilter/nf_nat_helper.c new file mode 100644 index 000000000000..23c2b38676a6 --- /dev/null +++ b/net/netfilter/nf_nat_helper.c @@ -0,0 +1,435 @@ +/* nf_nat_helper.c - generic support functions for NAT helpers + * + * (C) 2000-2002 Harald Welte + * (C) 2003-2006 Netfilter Core Team + * + * 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 +#include +#include +#include +#include +#include +#include + +#include +#include +#include +#include +#include +#include +#include +#include +#include + +#define DUMP_OFFSET(x) \ + pr_debug("offset_before=%d, offset_after=%d, correction_pos=%u\n", \ + x->offset_before, x->offset_after, x->correction_pos); + +static DEFINE_SPINLOCK(nf_nat_seqofs_lock); + +/* Setup TCP sequence correction given this change at this sequence */ +static inline void +adjust_tcp_sequence(u32 seq, + int sizediff, + struct nf_conn *ct, + enum ip_conntrack_info ctinfo) +{ + enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo); + struct nf_conn_nat *nat = nfct_nat(ct); + struct nf_nat_seq *this_way = &nat->seq[dir]; + + pr_debug("adjust_tcp_sequence: seq = %u, sizediff = %d\n", + seq, sizediff); + + pr_debug("adjust_tcp_sequence: Seq_offset before: "); + DUMP_OFFSET(this_way); + + spin_lock_bh(&nf_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; + } + spin_unlock_bh(&nf_nat_seqofs_lock); + + pr_debug("adjust_tcp_sequence: Seq_offset after: "); + DUMP_OFFSET(this_way); +} + +/* Get the offset value, for conntrack */ +s16 nf_nat_get_offset(const struct nf_conn *ct, + enum ip_conntrack_dir dir, + u32 seq) +{ + struct nf_conn_nat *nat = nfct_nat(ct); + struct nf_nat_seq *this_way; + s16 offset; + + if (!nat) + return 0; + + this_way = &nat->seq[dir]; + spin_lock_bh(&nf_nat_seqofs_lock); + offset = after(seq, this_way->correction_pos) + ? this_way->offset_after : this_way->offset_before; + spin_unlock_bh(&nf_nat_seqofs_lock); + + return offset; +} + +/* 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 - (skb->network_header + 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; +} + +void nf_nat_set_seq_adjust(struct nf_conn *ct, enum ip_conntrack_info ctinfo, + __be32 seq, s16 off) +{ + if (!off) + return; + set_bit(IPS_SEQ_ADJUST_BIT, &ct->status); + adjust_tcp_sequence(ntohl(seq), off, ct, ctinfo); + nf_conntrack_event_cache(IPCT_NATSEQADJ, ct); +} +EXPORT_SYMBOL_GPL(nf_nat_set_seq_adjust); + +void nf_nat_tcp_seq_adjust(struct sk_buff *skb, struct nf_conn *ct, + u32 ctinfo, int off) +{ + const struct tcphdr *th; + + if (nf_ct_protonum(ct) != IPPROTO_TCP) + return; + + th = (struct tcphdr *)(skb_network_header(skb)+ ip_hdrlen(skb)); + nf_nat_set_seq_adjust(ct, ctinfo, th->seq, off); +} +EXPORT_SYMBOL_GPL(nf_nat_tcp_seq_adjust); + +/* 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_nat_set_seq_adjust(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); + +/* 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 nf_nat_seq *natseq) +{ + while (sackoff < sackend) { + struct tcp_sack_block_wire *sack; + __be32 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 = htonl(ntohl(sack->start_seq) + - natseq->offset_after); + else + new_start_seq = htonl(ntohl(sack->start_seq) + - natseq->offset_before); + + if (after(ntohl(sack->end_seq) - natseq->offset_before, + natseq->correction_pos)) + new_end_seq = htonl(ntohl(sack->end_seq) + - natseq->offset_after); + else + new_end_seq = htonl(ntohl(sack->end_seq) + - natseq->offset_before); + + pr_debug("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); + + inet_proto_csum_replace4(&tcph->check, skb, + sack->start_seq, new_start_seq, 0); + inet_proto_csum_replace4(&tcph->check, skb, + sack->end_seq, new_end_seq, 0); + sack->start_seq = new_start_seq; + sack->end_seq = new_end_seq; + sackoff += sizeof(*sack); + } +} + +/* TCP SACK sequence number adjustment */ +static inline unsigned int +nf_nat_sack_adjust(struct sk_buff *skb, + unsigned int protoff, + struct tcphdr *tcph, + struct nf_conn *ct, + enum ip_conntrack_info ctinfo) +{ + unsigned int dir, optoff, optend; + struct nf_conn_nat *nat = nfct_nat(ct); + + optoff = protoff + sizeof(struct tcphdr); + optend = protoff + tcph->doff * 4; + + if (!skb_make_writable(skb, optend)) + return 0; + + dir = CTINFO2DIR(ctinfo); + + while (optoff < optend) { + /* Usually: option, length. */ + unsigned char *op = skb->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(skb, tcph, optoff+2, + optoff+op[1], &nat->seq[!dir]); + optoff += op[1]; + } + } + return 1; +} + +/* TCP sequence number adjustment. Returns 1 on success, 0 on failure */ +int +nf_nat_seq_adjust(struct sk_buff *skb, + struct nf_conn *ct, + enum ip_conntrack_info ctinfo, + unsigned int protoff) +{ + struct tcphdr *tcph; + int dir; + __be32 newseq, newack; + s16 seqoff, ackoff; + struct nf_conn_nat *nat = nfct_nat(ct); + struct nf_nat_seq *this_way, *other_way; + + dir = CTINFO2DIR(ctinfo); + + this_way = &nat->seq[dir]; + other_way = &nat->seq[!dir]; + + if (!skb_make_writable(skb, protoff + sizeof(*tcph))) + return 0; + + tcph = (void *)skb->data + protoff; + if (after(ntohl(tcph->seq), this_way->correction_pos)) + seqoff = this_way->offset_after; + else + seqoff = this_way->offset_before; + + if (after(ntohl(tcph->ack_seq) - other_way->offset_before, + other_way->correction_pos)) + ackoff = other_way->offset_after; + else + ackoff = other_way->offset_before; + + newseq = htonl(ntohl(tcph->seq) + seqoff); + newack = htonl(ntohl(tcph->ack_seq) - ackoff); + + inet_proto_csum_replace4(&tcph->check, skb, tcph->seq, newseq, 0); + inet_proto_csum_replace4(&tcph->check, skb, tcph->ack_seq, newack, 0); + + pr_debug("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; + + return nf_nat_sack_adjust(skb, protoff, tcph, ct, ctinfo); +} + +/* 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); -- cgit v1.2.3