netfilter: nf_nat: support mangling a single TCP packet multiple times

nf_nat_mangle_tcp_packet() can currently only handle a single mangling
per window because it only maintains two sequence adjustment positions:
the one before the last adjustment and the one after.

This patch makes sequence number adjustment tracking in
nf_nat_mangle_tcp_packet() optional and allows a helper to manually
update the offsets after the packet has been fully handled.

Signed-off-by: Patrick McHardy <kaber@trash.net>

1 files changed, 23 insertions, 16 deletions

diff --git a/net/ipv4/netfilter/nf_nat_helper.c b/net/ipv4/netfilter/nf_nat_helper.c
index 7f10a6be0191..4b6af4bb1f50 100644
--- a/net/ipv4/netfilter/nf_nat_helper.c
+++ b/net/ipv4/netfilter/nf_nat_helper.c
@@ -141,6 +141,17 @@ static int enlarge_skb(struct sk_buff *skb, unsigned int extra)
         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);
+
 /* Generic function for mangling variable-length address changes inside
  * NATed TCP connections (like the PORT XXX,XXX,XXX,XXX,XXX,XXX
  * command in FTP).
@@ -149,14 +160,13 @@ static int enlarge_skb(struct sk_buff *skb, unsigned int extra)
  * skb enlargement, ...
  *
  * */
-int
-nf_nat_mangle_tcp_packet(struct sk_buff *skb,
-                         struct nf_conn *ct,
-                         enum ip_conntrack_info ctinfo,
-                         unsigned int match_offset,
-                         unsigned int match_len,
-                         const char *rep_buffer,
-                         unsigned int rep_len)
+int __nf_nat_mangle_tcp_packet(struct sk_buff *skb,
+                               struct nf_conn *ct,
+                               enum ip_conntrack_info ctinfo,
+                               unsigned int match_offset,
+                               unsigned int match_len,
+                               const char *rep_buffer,
+                               unsigned int rep_len, bool adjust)
 {
         struct rtable *rt = skb_rtable(skb);
         struct iphdr *iph;
@@ -202,16 +212,13 @@ nf_nat_mangle_tcp_packet(struct sk_buff *skb,
                 inet_proto_csum_replace2(&tcph->check, skb,
                                          htons(oldlen), htons(datalen), 1);
 
-        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);
-                nf_conntrack_event_cache(IPCT_NATSEQADJ, ct);
-        }
+        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);
+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