xref: /linux/net/netfilter/nf_conntrack_seqadj.c (revision 4f2c0a4acffbec01079c28f839422e64ddeff004)
1 // SPDX-License-Identifier: GPL-2.0-only
2 #include <linux/types.h>
3 #include <linux/netfilter.h>
4 #include <net/tcp.h>
5 
6 #include <net/netfilter/nf_conntrack.h>
7 #include <net/netfilter/nf_conntrack_extend.h>
8 #include <net/netfilter/nf_conntrack_seqadj.h>
9 
nf_ct_seqadj_init(struct nf_conn * ct,enum ip_conntrack_info ctinfo,s32 off)10 int nf_ct_seqadj_init(struct nf_conn *ct, enum ip_conntrack_info ctinfo,
11 		      s32 off)
12 {
13 	enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
14 	struct nf_conn_seqadj *seqadj;
15 	struct nf_ct_seqadj *this_way;
16 
17 	if (off == 0)
18 		return 0;
19 
20 	set_bit(IPS_SEQ_ADJUST_BIT, &ct->status);
21 
22 	seqadj = nfct_seqadj(ct);
23 	this_way = &seqadj->seq[dir];
24 	this_way->offset_before	 = off;
25 	this_way->offset_after	 = off;
26 	return 0;
27 }
28 EXPORT_SYMBOL_GPL(nf_ct_seqadj_init);
29 
nf_ct_seqadj_set(struct nf_conn * ct,enum ip_conntrack_info ctinfo,__be32 seq,s32 off)30 int nf_ct_seqadj_set(struct nf_conn *ct, enum ip_conntrack_info ctinfo,
31 		     __be32 seq, s32 off)
32 {
33 	struct nf_conn_seqadj *seqadj = nfct_seqadj(ct);
34 	enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
35 	struct nf_ct_seqadj *this_way;
36 
37 	if (off == 0)
38 		return 0;
39 
40 	if (unlikely(!seqadj)) {
41 		WARN_ONCE(1, "Missing nfct_seqadj_ext_add() setup call\n");
42 		return 0;
43 	}
44 
45 	set_bit(IPS_SEQ_ADJUST_BIT, &ct->status);
46 
47 	spin_lock_bh(&ct->lock);
48 	this_way = &seqadj->seq[dir];
49 	if (this_way->offset_before == this_way->offset_after ||
50 	    before(this_way->correction_pos, ntohl(seq))) {
51 		this_way->correction_pos = ntohl(seq);
52 		this_way->offset_before	 = this_way->offset_after;
53 		this_way->offset_after	+= off;
54 	}
55 	spin_unlock_bh(&ct->lock);
56 	return 0;
57 }
58 EXPORT_SYMBOL_GPL(nf_ct_seqadj_set);
59 
nf_ct_tcp_seqadj_set(struct sk_buff * skb,struct nf_conn * ct,enum ip_conntrack_info ctinfo,s32 off)60 void nf_ct_tcp_seqadj_set(struct sk_buff *skb,
61 			  struct nf_conn *ct, enum ip_conntrack_info ctinfo,
62 			  s32 off)
63 {
64 	const struct tcphdr *th;
65 
66 	if (nf_ct_protonum(ct) != IPPROTO_TCP)
67 		return;
68 
69 	th = (struct tcphdr *)(skb_network_header(skb) + ip_hdrlen(skb));
70 	nf_ct_seqadj_set(ct, ctinfo, th->seq, off);
71 }
72 EXPORT_SYMBOL_GPL(nf_ct_tcp_seqadj_set);
73 
74 /* Adjust one found SACK option including checksum correction */
nf_ct_sack_block_adjust(struct sk_buff * skb,struct tcphdr * tcph,unsigned int sackoff,unsigned int sackend,struct nf_ct_seqadj * seq)75 static void nf_ct_sack_block_adjust(struct sk_buff *skb,
76 				    struct tcphdr *tcph,
77 				    unsigned int sackoff,
78 				    unsigned int sackend,
79 				    struct nf_ct_seqadj *seq)
80 {
81 	while (sackoff < sackend) {
82 		struct tcp_sack_block_wire *sack;
83 		__be32 new_start_seq, new_end_seq;
84 
85 		sack = (void *)skb->data + sackoff;
86 		if (after(ntohl(sack->start_seq) - seq->offset_before,
87 			  seq->correction_pos))
88 			new_start_seq = htonl(ntohl(sack->start_seq) -
89 					seq->offset_after);
90 		else
91 			new_start_seq = htonl(ntohl(sack->start_seq) -
92 					seq->offset_before);
93 
94 		if (after(ntohl(sack->end_seq) - seq->offset_before,
95 			  seq->correction_pos))
96 			new_end_seq = htonl(ntohl(sack->end_seq) -
97 				      seq->offset_after);
98 		else
99 			new_end_seq = htonl(ntohl(sack->end_seq) -
100 				      seq->offset_before);
101 
102 		pr_debug("sack_adjust: start_seq: %u->%u, end_seq: %u->%u\n",
103 			 ntohl(sack->start_seq), ntohl(new_start_seq),
104 			 ntohl(sack->end_seq), ntohl(new_end_seq));
105 
106 		inet_proto_csum_replace4(&tcph->check, skb,
107 					 sack->start_seq, new_start_seq, false);
108 		inet_proto_csum_replace4(&tcph->check, skb,
109 					 sack->end_seq, new_end_seq, false);
110 		sack->start_seq = new_start_seq;
111 		sack->end_seq = new_end_seq;
112 		sackoff += sizeof(*sack);
113 	}
114 }
115 
116 /* TCP SACK sequence number adjustment */
nf_ct_sack_adjust(struct sk_buff * skb,unsigned int protoff,struct nf_conn * ct,enum ip_conntrack_info ctinfo)117 static unsigned int nf_ct_sack_adjust(struct sk_buff *skb,
118 				      unsigned int protoff,
119 				      struct nf_conn *ct,
120 				      enum ip_conntrack_info ctinfo)
121 {
122 	struct tcphdr *tcph = (void *)skb->data + protoff;
123 	struct nf_conn_seqadj *seqadj = nfct_seqadj(ct);
124 	unsigned int dir, optoff, optend;
125 
126 	optoff = protoff + sizeof(struct tcphdr);
127 	optend = protoff + tcph->doff * 4;
128 
129 	if (skb_ensure_writable(skb, optend))
130 		return 0;
131 
132 	tcph = (void *)skb->data + protoff;
133 	dir = CTINFO2DIR(ctinfo);
134 
135 	while (optoff < optend) {
136 		/* Usually: option, length. */
137 		unsigned char *op = skb->data + optoff;
138 
139 		switch (op[0]) {
140 		case TCPOPT_EOL:
141 			return 1;
142 		case TCPOPT_NOP:
143 			optoff++;
144 			continue;
145 		default:
146 			/* no partial options */
147 			if (optoff + 1 == optend ||
148 			    optoff + op[1] > optend ||
149 			    op[1] < 2)
150 				return 0;
151 			if (op[0] == TCPOPT_SACK &&
152 			    op[1] >= 2+TCPOLEN_SACK_PERBLOCK &&
153 			    ((op[1] - 2) % TCPOLEN_SACK_PERBLOCK) == 0)
154 				nf_ct_sack_block_adjust(skb, tcph, optoff + 2,
155 							optoff+op[1],
156 							&seqadj->seq[!dir]);
157 			optoff += op[1];
158 		}
159 	}
160 	return 1;
161 }
162 
163 /* TCP sequence number adjustment.  Returns 1 on success, 0 on failure */
nf_ct_seq_adjust(struct sk_buff * skb,struct nf_conn * ct,enum ip_conntrack_info ctinfo,unsigned int protoff)164 int nf_ct_seq_adjust(struct sk_buff *skb,
165 		     struct nf_conn *ct, enum ip_conntrack_info ctinfo,
166 		     unsigned int protoff)
167 {
168 	enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
169 	struct tcphdr *tcph;
170 	__be32 newseq, newack;
171 	s32 seqoff, ackoff;
172 	struct nf_conn_seqadj *seqadj = nfct_seqadj(ct);
173 	struct nf_ct_seqadj *this_way, *other_way;
174 	int res = 1;
175 
176 	this_way  = &seqadj->seq[dir];
177 	other_way = &seqadj->seq[!dir];
178 
179 	if (skb_ensure_writable(skb, protoff + sizeof(*tcph)))
180 		return 0;
181 
182 	tcph = (void *)skb->data + protoff;
183 	spin_lock_bh(&ct->lock);
184 	if (after(ntohl(tcph->seq), this_way->correction_pos))
185 		seqoff = this_way->offset_after;
186 	else
187 		seqoff = this_way->offset_before;
188 
189 	newseq = htonl(ntohl(tcph->seq) + seqoff);
190 	inet_proto_csum_replace4(&tcph->check, skb, tcph->seq, newseq, false);
191 	pr_debug("Adjusting sequence number from %u->%u\n",
192 		 ntohl(tcph->seq), ntohl(newseq));
193 	tcph->seq = newseq;
194 
195 	if (!tcph->ack)
196 		goto out;
197 
198 	if (after(ntohl(tcph->ack_seq) - other_way->offset_before,
199 		  other_way->correction_pos))
200 		ackoff = other_way->offset_after;
201 	else
202 		ackoff = other_way->offset_before;
203 
204 	newack = htonl(ntohl(tcph->ack_seq) - ackoff);
205 	inet_proto_csum_replace4(&tcph->check, skb, tcph->ack_seq, newack,
206 				 false);
207 	pr_debug("Adjusting ack number from %u->%u, ack from %u->%u\n",
208 		 ntohl(tcph->seq), ntohl(newseq), ntohl(tcph->ack_seq),
209 		 ntohl(newack));
210 	tcph->ack_seq = newack;
211 
212 	res = nf_ct_sack_adjust(skb, protoff, ct, ctinfo);
213 out:
214 	spin_unlock_bh(&ct->lock);
215 
216 	return res;
217 }
218 EXPORT_SYMBOL_GPL(nf_ct_seq_adjust);
219 
nf_ct_seq_offset(const struct nf_conn * ct,enum ip_conntrack_dir dir,u32 seq)220 s32 nf_ct_seq_offset(const struct nf_conn *ct,
221 		     enum ip_conntrack_dir dir,
222 		     u32 seq)
223 {
224 	struct nf_conn_seqadj *seqadj = nfct_seqadj(ct);
225 	struct nf_ct_seqadj *this_way;
226 
227 	if (!seqadj)
228 		return 0;
229 
230 	this_way = &seqadj->seq[dir];
231 	return after(seq, this_way->correction_pos) ?
232 		 this_way->offset_after : this_way->offset_before;
233 }
234 EXPORT_SYMBOL_GPL(nf_ct_seq_offset);
235