[PATCH 2/2 nf-next] netfilter: synproxy: fix reset of ct seqadj when reopening a connection

[Fernando Fernandez Mancera <fmancera@suse.de>]

SYNPROXY is resetting conntrack seqadj when a closed connection is
re-opened, but it was using nf_ct_seqadj_init() which is a no-op for a
zero offset.

This patch introduces nf_ct_seqadj_reset() which sets the offset values
directly to zero and avoid setting IPS_SEQ_ADJUST_BIT flag, it changes
SYNPROXY code to use it when needed.

Fixes: 48b1de4c110a ("netfilter: add SYNPROXY core/target")
Signed-off-by: Fernando Fernandez Mancera <fmancera@suse.de>
---
Note: this is targeted at nf-next because it is really unlikely to hit
this issue. In essence, it is a problem only if the re-opened connection
offset calculation is 0 too.
---
 include/net/netfilter/nf_conntrack_seqadj.h |  1 +
 net/netfilter/nf_conntrack_seqadj.c         | 17 +++++++++++++++++
 net/netfilter/nf_synproxy_core.c            |  4 ++--
 3 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/include/net/netfilter/nf_conntrack_seqadj.h b/include/net/netfilter/nf_conntrack_seqadj.h
index 883c414b768e..0f5bbb14a25a 100644
--- a/include/net/netfilter/nf_conntrack_seqadj.h
+++ b/include/net/netfilter/nf_conntrack_seqadj.h
@@ -33,6 +33,7 @@ static inline struct nf_conn_seqadj *nfct_seqadj_ext_add(struct nf_conn *ct)
 
 int nf_ct_seqadj_init(struct nf_conn *ct, enum ip_conntrack_info ctinfo,
 		      s32 off);
+void nf_ct_seqadj_reset(struct nf_conn *ct, enum ip_conntrack_info ctinfo);
 int nf_ct_seqadj_set(struct nf_conn *ct, enum ip_conntrack_info ctinfo,
 		     __be32 seq, s32 off);
 void nf_ct_tcp_seqadj_set(struct sk_buff *skb, struct nf_conn *ct,
diff --git a/net/netfilter/nf_conntrack_seqadj.c b/net/netfilter/nf_conntrack_seqadj.c
index d75e8dafb189..b7b166a8ad58 100644
--- a/net/netfilter/nf_conntrack_seqadj.c
+++ b/net/netfilter/nf_conntrack_seqadj.c
@@ -31,6 +31,23 @@ int nf_ct_seqadj_init(struct nf_conn *ct, enum ip_conntrack_info ctinfo,
 }
 EXPORT_SYMBOL_GPL(nf_ct_seqadj_init);
 
+void nf_ct_seqadj_reset(struct nf_conn *ct, enum ip_conntrack_info ctinfo)
+{
+	struct nf_conn_seqadj *seqadj = nfct_seqadj(ct);
+	enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
+	struct nf_ct_seqadj *this_way;
+
+	if (unlikely(!seqadj))
+		return;
+
+	spin_lock_bh(&ct->lock);
+	this_way = &seqadj->seq[dir];
+	this_way->offset_before	 = 0;
+	this_way->offset_after	 = 0;
+	spin_unlock_bh(&ct->lock);
+}
+EXPORT_SYMBOL_GPL(nf_ct_seqadj_reset);
+
 int nf_ct_seqadj_set(struct nf_conn *ct, enum ip_conntrack_info ctinfo,
 		     __be32 seq, s32 off)
 {
diff --git a/net/netfilter/nf_synproxy_core.c b/net/netfilter/nf_synproxy_core.c
index acd360515972..37f88702980a 100644
--- a/net/netfilter/nf_synproxy_core.c
+++ b/net/netfilter/nf_synproxy_core.c
@@ -686,7 +686,7 @@ ipv4_synproxy_hook(void *priv, struct sk_buff *skb,
 		 * adjustments, they will get initialized once the connection is
 		 * reestablished.
 		 */
-		nf_ct_seqadj_init(ct, ctinfo, 0);
+		nf_ct_seqadj_reset(ct, ctinfo);
 		synproxy->tsoff = 0;
 		this_cpu_inc(snet->stats->conn_reopened);
 		fallthrough;
@@ -1116,7 +1116,7 @@ ipv6_synproxy_hook(void *priv, struct sk_buff *skb,
 		 * adjustments, they will get initialized once the connection is
 		 * reestablished.
 		 */
-		nf_ct_seqadj_init(ct, ctinfo, 0);
+		nf_ct_seqadj_reset(ct, ctinfo);
 		synproxy->tsoff = 0;
 		this_cpu_inc(snet->stats->conn_reopened);
 		fallthrough;
-- 
2.55.0