[PATCH net v2] net: netfilter: Fix port selection of FTP for NF_NAT_RANGE_PROTO_SPECIFIED

[Cole Dishington]

FTP port selection ignores specified port ranges (with iptables
masquerade --to-ports) when creating an expectation, based on
FTP commands PORT or PASV, for the data connection.

Co-developed-by: Anthony Lineham <anthony.lineham@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Anthony Lineham <anthony.lineham@xxxxxxxxxxxxxxxxxxx>
Co-developed-by: Scott Parlane <scott.parlane@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Scott Parlane <scott.parlane@xxxxxxxxxxxxxxxxxxx>
Co-developed-by: Blair Steven <blair.steven@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Blair Steven <blair.steven@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Cole Dishington <Cole.Dishington@xxxxxxxxxxxxxxxxxxx>
---

Notes:
    Thanks for your time reviewing!
    
    Changes:
    - Avoid storing full range structure, only store min_proto and max_proto.
    - Store min and max_proto on nf_conn_nat rather than nf_conn.
    - Only store extra range info on nf_conn if NF_NAT_RANGE_PROTO_SPECIFIED and
      fallback to selecting from full port range.
    - Try to get same port if it matches the range.
    - Added net tag to subject.

 include/net/netfilter/nf_nat.h |  6 +++++
 net/netfilter/nf_nat_core.c    | 17 +++++++++----
 net/netfilter/nf_nat_ftp.c     | 44 +++++++++++++++++++++++++---------
 net/netfilter/nf_nat_helper.c  | 10 ++++++++
 4 files changed, 62 insertions(+), 15 deletions(-)

diff --git a/include/net/netfilter/nf_nat.h b/include/net/netfilter/nf_nat.h
index 0d412dd63707..231cffc16722 100644
--- a/include/net/netfilter/nf_nat.h
+++ b/include/net/netfilter/nf_nat.h
@@ -27,12 +27,18 @@ union nf_conntrack_nat_help {
 #endif
 };
 
+struct nf_conn_nat_range_info {
+	union nf_conntrack_man_proto    min_proto;
+	union nf_conntrack_man_proto    max_proto;
+};
+
 /* The structure embedded in the conntrack structure. */
 struct nf_conn_nat {
 	union nf_conntrack_nat_help help;
 #if IS_ENABLED(CONFIG_NF_NAT_MASQUERADE)
 	int masq_index;
 #endif
+	struct nf_conn_nat_range_info range_info;
 };
 
 /* Set up the info structure to map into this range. */
diff --git a/net/netfilter/nf_nat_core.c b/net/netfilter/nf_nat_core.c
index ea923f8cf9c4..5412e9cf8189 100644
--- a/net/netfilter/nf_nat_core.c
+++ b/net/netfilter/nf_nat_core.c
@@ -397,10 +397,10 @@ find_best_ips_proto(const struct nf_conntrack_zone *zone,
  *
  * Per-protocol part of tuple is initialized to the incoming packet.
  */
-static void nf_nat_l4proto_unique_tuple(struct nf_conntrack_tuple *tuple,
-					const struct nf_nat_range2 *range,
-					enum nf_nat_manip_type maniptype,
-					const struct nf_conn *ct)
+void nf_nat_l4proto_unique_tuple(struct nf_conntrack_tuple *tuple,
+				 const struct nf_nat_range2 *range,
+				 enum nf_nat_manip_type maniptype,
+				 const struct nf_conn *ct)
 {
 	unsigned int range_size, min, max, i, attempts;
 	__be16 *keyptr;
@@ -601,6 +601,7 @@ nf_nat_setup_info(struct nf_conn *ct,
 		  const struct nf_nat_range2 *range,
 		  enum nf_nat_manip_type maniptype)
 {
+	struct nf_conn_nat *nat;
 	struct net *net = nf_ct_net(ct);
 	struct nf_conntrack_tuple curr_tuple, new_tuple;
 
@@ -623,6 +624,14 @@ nf_nat_setup_info(struct nf_conn *ct,
 			   &ct->tuplehash[IP_CT_DIR_REPLY].tuple);
 
 	get_unique_tuple(&new_tuple, &curr_tuple, range, ct, maniptype);
+	if (range && (range->flags & NF_NAT_RANGE_PROTO_SPECIFIED)) {
+		nat = nf_ct_nat_ext_add(ct);
+		if (WARN_ON_ONCE(!nat))
+			return NF_DROP;
+
+		nat->range_info.min_proto = range->min_proto;
+		nat->range_info.max_proto = range->max_proto;
+	}
 
 	if (!nf_ct_tuple_equal(&new_tuple, &curr_tuple)) {
 		struct nf_conntrack_tuple reply;
diff --git a/net/netfilter/nf_nat_ftp.c b/net/netfilter/nf_nat_ftp.c
index aace6768a64e..cf675dc589be 100644
--- a/net/netfilter/nf_nat_ftp.c
+++ b/net/netfilter/nf_nat_ftp.c
@@ -17,6 +17,10 @@
 #include <net/netfilter/nf_conntrack_helper.h>
 #include <net/netfilter/nf_conntrack_expect.h>
 #include <linux/netfilter/nf_conntrack_ftp.h>
+void nf_nat_l4proto_unique_tuple(struct nf_conntrack_tuple *tuple,
+				 const struct nf_nat_range2 *range,
+				 enum nf_nat_manip_type maniptype,
+				 const struct nf_conn *ct);
 
 #define NAT_HELPER_NAME "ftp"
 
@@ -72,8 +76,14 @@ static unsigned int nf_nat_ftp(struct sk_buff *skb,
 	u_int16_t port;
 	int dir = CTINFO2DIR(ctinfo);
 	struct nf_conn *ct = exp->master;
+	struct nf_conn_nat *nat = nfct_nat(ct);
+	struct nf_nat_range2 range = {};
 	char buffer[sizeof("|1||65535|") + INET6_ADDRSTRLEN];
 	unsigned int buflen;
+	int ret;
+
+	if (WARN_ON_ONCE(!nat))
+		return NF_DROP;
 
 	pr_debug("type %i, off %u len %u\n", type, matchoff, matchlen);
 
@@ -86,21 +96,33 @@ static unsigned int nf_nat_ftp(struct sk_buff *skb,
 	 * this one. */
 	exp->expectfn = nf_nat_follow_master;
 
-	/* Try to get same port: if not, try to change it. */
-	for (port = ntohs(exp->saved_proto.tcp.port); port != 0; port++) {
-		int ret;
+	if (htons(nat->range_info.min_proto.all) == 0 ||
+	    htons(nat->range_info.max_proto.all) == 0) {
+		range.min_proto.all = htons(1);
+		range.max_proto.all = htons(65535);
+	} else {
+		range.min_proto     = nat->range_info.min_proto;
+		range.max_proto     = nat->range_info.max_proto;
+	}
+	range.flags                 = NF_NAT_RANGE_PROTO_SPECIFIED;
 
-		exp->tuple.dst.u.tcp.port = htons(port);
+	/* Try to get same port if it matches NAT rule: if not, try to change it. */
+	ret = -1;
+	port = ntohs(exp->tuple.dst.u.tcp.port);
+	if (port != 0 && ntohs(range.min_proto.all) <= port &&
+	    port <= ntohs(range.max_proto.all)) {
 		ret = nf_ct_expect_related(exp, 0);
-		if (ret == 0)
-			break;
-		else if (ret != -EBUSY) {
-			port = 0;
-			break;
+	}
+	if (ret != 0 || port == 0) {
+		if (!dir) {
+			nf_nat_l4proto_unique_tuple(&exp->tuple, &range,
+						    NF_NAT_MANIP_DST,
+						    ct);
 		}
+		port = ntohs(exp->tuple.dst.u.tcp.port);
+		ret = nf_ct_expect_related(exp, 0);
 	}
-
-	if (port == 0) {
+	if (ret != 0 || port == 0) {
 		nf_ct_helper_log(skb, ct, "all ports in use");
 		return NF_DROP;
 	}
diff --git a/net/netfilter/nf_nat_helper.c b/net/netfilter/nf_nat_helper.c
index a263505455fc..29fa78cfdb9c 100644
--- a/net/netfilter/nf_nat_helper.c
+++ b/net/netfilter/nf_nat_helper.c
@@ -188,6 +188,16 @@ void nf_nat_follow_master(struct nf_conn *ct,
 	range.flags = NF_NAT_RANGE_MAP_IPS;
 	range.min_addr = range.max_addr
 		= ct->master->tuplehash[!exp->dir].tuple.dst.u3;
+	if (exp->master && !exp->dir) {
+		struct nf_conn_nat *nat = nfct_nat(exp->master);
+
+		if (nat && nat->range_info.min_proto.all != 0 &&
+		    nat->range_info.max_proto.all != 0) {
+			range.min_proto = nat->range_info.min_proto;
+			range.max_proto = nat->range_info.max_proto;
+			range.flags |= NF_NAT_RANGE_PROTO_SPECIFIED;
+		}
+	}
 	nf_nat_setup_info(ct, &range, NF_NAT_MANIP_SRC);
 
 	/* For DST manip, map port here to where it's expected. */
-- 
2.33.0