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![Gao Feng](/assets/img/avatar_default.png)
It is valid that the TCP RST packet which does not set ack flag, and bytes of ack number are zero. But current seqadj codes would adjust the "0" ack to invalid ack number. Actually seqadj need to check the ack flag before adjust it for these RST packets. The following is my test case client is 10.26.98.245, and add one iptable rule: iptables -I INPUT -p tcp --sport 12345 -m connbytes --connbytes 2: --connbytes-dir reply --connbytes-mode packets -j REJECT --reject-with tcp-reset This iptables rule could generate on TCP RST without ack flag. server:10.172.135.55 Enable the synproxy with seqadjust by the following iptables rules iptables -t raw -A PREROUTING -i eth0 -p tcp -d 10.172.135.55 --dport 12345 -m tcp --syn -j CT --notrack iptables -A INPUT -i eth0 -p tcp -d 10.172.135.55 --dport 12345 -m conntrack --ctstate INVALID,UNTRACKED -j SYNPROXY --sack-perm --timestamp --wscale 7 --mss 1460 iptables -A OUTPUT -o eth0 -p tcp -s 10.172.135.55 --sport 12345 -m conntrack --ctstate INVALID,UNTRACKED -m tcp --tcp-flags SYN,RST,ACK SYN,ACK -j ACCEPT The following is my test result. 1. packet trace on client root@routers:/tmp# tcpdump -i eth0 tcp port 12345 -n tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes IP 10.26.98.245.45154 > 10.172.135.55.12345: Flags [S], seq 3695959829, win 29200, options [mss 1460,sackOK,TS val 452367884 ecr 0,nop,wscale 7], length 0 IP 10.172.135.55.12345 > 10.26.98.245.45154: Flags [S.], seq 546723266, ack 3695959830, win 0, options [mss 1460,sackOK,TS val 15643479 ecr 452367884, nop,wscale 7], length 0 IP 10.26.98.245.45154 > 10.172.135.55.12345: Flags [.], ack 1, win 229, options [nop,nop,TS val 452367885 ecr 15643479], length 0 IP 10.172.135.55.12345 > 10.26.98.245.45154: Flags [.], ack 1, win 226, options [nop,nop,TS val 15643479 ecr 452367885], length 0 IP 10.26.98.245.45154 > 10.172.135.55.12345: Flags [R], seq 3695959830, win 0, length 0 2. seqadj log on server [62873.867319] Adjusting sequence number from 602341895->546723267, ack from 3695959830->3695959830 [62873.867644] Adjusting sequence number from 602341895->546723267, ack from 3695959830->3695959830 [62873.869040] Adjusting sequence number from 3695959830->3695959830, ack from 0->55618628 To summarize, it is clear that the seqadj codes adjust the 0 ack when receive one TCP RST packet without ack. Signed-off-by: Gao Feng <fgao@ikuai8.com> Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
248 lines
6.4 KiB
C
248 lines
6.4 KiB
C
#include <linux/types.h>
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#include <linux/netfilter.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_extend.h>
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#include <net/netfilter/nf_conntrack_seqadj.h>
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int nf_ct_seqadj_init(struct nf_conn *ct, enum ip_conntrack_info ctinfo,
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s32 off)
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{
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enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
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struct nf_conn_seqadj *seqadj;
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struct nf_ct_seqadj *this_way;
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if (off == 0)
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return 0;
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set_bit(IPS_SEQ_ADJUST_BIT, &ct->status);
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seqadj = nfct_seqadj(ct);
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this_way = &seqadj->seq[dir];
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this_way->offset_before = off;
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this_way->offset_after = off;
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return 0;
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}
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EXPORT_SYMBOL_GPL(nf_ct_seqadj_init);
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int nf_ct_seqadj_set(struct nf_conn *ct, enum ip_conntrack_info ctinfo,
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__be32 seq, s32 off)
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{
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struct nf_conn_seqadj *seqadj = nfct_seqadj(ct);
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enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
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struct nf_ct_seqadj *this_way;
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if (off == 0)
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return 0;
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if (unlikely(!seqadj)) {
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WARN_ONCE(1, "Missing nfct_seqadj_ext_add() setup call\n");
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return 0;
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}
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set_bit(IPS_SEQ_ADJUST_BIT, &ct->status);
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spin_lock_bh(&ct->lock);
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this_way = &seqadj->seq[dir];
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if (this_way->offset_before == this_way->offset_after ||
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before(this_way->correction_pos, ntohl(seq))) {
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this_way->correction_pos = ntohl(seq);
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this_way->offset_before = this_way->offset_after;
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this_way->offset_after += off;
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}
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spin_unlock_bh(&ct->lock);
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return 0;
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}
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EXPORT_SYMBOL_GPL(nf_ct_seqadj_set);
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void nf_ct_tcp_seqadj_set(struct sk_buff *skb,
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struct nf_conn *ct, enum ip_conntrack_info ctinfo,
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s32 off)
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{
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const struct tcphdr *th;
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if (nf_ct_protonum(ct) != IPPROTO_TCP)
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return;
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th = (struct tcphdr *)(skb_network_header(skb) + ip_hdrlen(skb));
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nf_ct_seqadj_set(ct, ctinfo, th->seq, off);
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}
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EXPORT_SYMBOL_GPL(nf_ct_tcp_seqadj_set);
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/* Adjust one found SACK option including checksum correction */
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static void nf_ct_sack_block_adjust(struct sk_buff *skb,
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struct tcphdr *tcph,
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unsigned int sackoff,
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unsigned int sackend,
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struct nf_ct_seqadj *seq)
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{
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while (sackoff < sackend) {
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struct tcp_sack_block_wire *sack;
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__be32 new_start_seq, new_end_seq;
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sack = (void *)skb->data + sackoff;
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if (after(ntohl(sack->start_seq) - seq->offset_before,
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seq->correction_pos))
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new_start_seq = htonl(ntohl(sack->start_seq) -
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seq->offset_after);
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else
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new_start_seq = htonl(ntohl(sack->start_seq) -
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seq->offset_before);
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if (after(ntohl(sack->end_seq) - seq->offset_before,
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seq->correction_pos))
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new_end_seq = htonl(ntohl(sack->end_seq) -
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seq->offset_after);
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else
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new_end_seq = htonl(ntohl(sack->end_seq) -
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seq->offset_before);
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pr_debug("sack_adjust: start_seq: %u->%u, end_seq: %u->%u\n",
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ntohl(sack->start_seq), ntohl(new_start_seq),
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ntohl(sack->end_seq), ntohl(new_end_seq));
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inet_proto_csum_replace4(&tcph->check, skb,
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sack->start_seq, new_start_seq, false);
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inet_proto_csum_replace4(&tcph->check, skb,
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sack->end_seq, new_end_seq, false);
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sack->start_seq = new_start_seq;
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sack->end_seq = new_end_seq;
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sackoff += sizeof(*sack);
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}
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}
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/* TCP SACK sequence number adjustment */
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static unsigned int nf_ct_sack_adjust(struct sk_buff *skb,
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unsigned int protoff,
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struct tcphdr *tcph,
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struct nf_conn *ct,
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enum ip_conntrack_info ctinfo)
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{
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unsigned int dir, optoff, optend;
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struct nf_conn_seqadj *seqadj = nfct_seqadj(ct);
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optoff = protoff + sizeof(struct tcphdr);
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optend = protoff + tcph->doff * 4;
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if (!skb_make_writable(skb, optend))
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return 0;
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dir = CTINFO2DIR(ctinfo);
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while (optoff < optend) {
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/* Usually: option, length. */
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unsigned char *op = skb->data + optoff;
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switch (op[0]) {
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case TCPOPT_EOL:
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return 1;
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case TCPOPT_NOP:
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optoff++;
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continue;
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default:
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/* no partial options */
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if (optoff + 1 == optend ||
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optoff + op[1] > optend ||
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op[1] < 2)
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return 0;
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if (op[0] == TCPOPT_SACK &&
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op[1] >= 2+TCPOLEN_SACK_PERBLOCK &&
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((op[1] - 2) % TCPOLEN_SACK_PERBLOCK) == 0)
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nf_ct_sack_block_adjust(skb, tcph, optoff + 2,
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optoff+op[1],
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&seqadj->seq[!dir]);
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optoff += op[1];
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}
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}
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return 1;
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}
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/* TCP sequence number adjustment. Returns 1 on success, 0 on failure */
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int nf_ct_seq_adjust(struct sk_buff *skb,
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struct nf_conn *ct, enum ip_conntrack_info ctinfo,
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unsigned int protoff)
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{
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enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
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struct tcphdr *tcph;
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__be32 newseq, newack;
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s32 seqoff, ackoff;
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struct nf_conn_seqadj *seqadj = nfct_seqadj(ct);
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struct nf_ct_seqadj *this_way, *other_way;
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int res = 1;
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this_way = &seqadj->seq[dir];
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other_way = &seqadj->seq[!dir];
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if (!skb_make_writable(skb, protoff + sizeof(*tcph)))
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return 0;
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tcph = (void *)skb->data + protoff;
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spin_lock_bh(&ct->lock);
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if (after(ntohl(tcph->seq), this_way->correction_pos))
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seqoff = this_way->offset_after;
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else
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seqoff = this_way->offset_before;
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newseq = htonl(ntohl(tcph->seq) + seqoff);
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inet_proto_csum_replace4(&tcph->check, skb, tcph->seq, newseq, false);
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pr_debug("Adjusting sequence number from %u->%u\n",
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ntohl(tcph->seq), ntohl(newseq));
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tcph->seq = newseq;
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if (!tcph->ack)
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goto out;
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if (after(ntohl(tcph->ack_seq) - other_way->offset_before,
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other_way->correction_pos))
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ackoff = other_way->offset_after;
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else
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ackoff = other_way->offset_before;
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newack = htonl(ntohl(tcph->ack_seq) - ackoff);
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inet_proto_csum_replace4(&tcph->check, skb, tcph->ack_seq, newack,
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false);
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pr_debug("Adjusting ack number from %u->%u, ack from %u->%u\n",
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ntohl(tcph->seq), ntohl(newseq), ntohl(tcph->ack_seq),
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ntohl(newack));
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tcph->ack_seq = newack;
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res = nf_ct_sack_adjust(skb, protoff, tcph, ct, ctinfo);
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out:
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spin_unlock_bh(&ct->lock);
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return res;
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}
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EXPORT_SYMBOL_GPL(nf_ct_seq_adjust);
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s32 nf_ct_seq_offset(const struct nf_conn *ct,
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enum ip_conntrack_dir dir,
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u32 seq)
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{
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struct nf_conn_seqadj *seqadj = nfct_seqadj(ct);
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struct nf_ct_seqadj *this_way;
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if (!seqadj)
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return 0;
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this_way = &seqadj->seq[dir];
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return after(seq, this_way->correction_pos) ?
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this_way->offset_after : this_way->offset_before;
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}
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EXPORT_SYMBOL_GPL(nf_ct_seq_offset);
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static struct nf_ct_ext_type nf_ct_seqadj_extend __read_mostly = {
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.len = sizeof(struct nf_conn_seqadj),
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.align = __alignof__(struct nf_conn_seqadj),
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.id = NF_CT_EXT_SEQADJ,
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};
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int nf_conntrack_seqadj_init(void)
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{
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return nf_ct_extend_register(&nf_ct_seqadj_extend);
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}
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void nf_conntrack_seqadj_fini(void)
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{
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nf_ct_extend_unregister(&nf_ct_seqadj_extend);
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}
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