/* 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_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>

#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);