[PATCH net v3] 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:
    - Removed check for port == 0.
    - Added nf_nat_l4proto_unique_tuple() to include/net/netfilter/nf_nat.h.
    - Simplify htons/ntohs calls.
    - Move away from conditional call of nf_nat_l4proto_unique_tuple() to applying full range to dst port
      if ftp active with PORT/ePORT is used.
    - Remove check for exp->master != NULL.
    
    Comments:
    - dir is the direction of the ftp PORT/PASV request, so exp->dir is the direction
      of the data connection. In nat helper, the range should be applied on !exp->dir
      source port since this is the connection from the client.

 include/net/netfilter/nf_nat.h | 11 ++++++++++
 net/netfilter/nf_nat_core.c    | 17 +++++++++++----
 net/netfilter/nf_nat_ftp.c     | 38 +++++++++++++++++++++++-----------
 net/netfilter/nf_nat_helper.c  | 10 +++++++++
 4 files changed, 60 insertions(+), 16 deletions(-)

diff --git a/include/net/netfilter/nf_nat.h b/include/net/netfilter/nf_nat.h
index 0d412dd63707..89796ed2aad3 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. */
@@ -40,6 +46,11 @@ unsigned int nf_nat_setup_info(struct nf_conn *ct,
 			       const struct nf_nat_range2 *range,
 			       enum nf_nat_manip_type maniptype);
 
+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);
+
 extern unsigned int nf_nat_alloc_null_binding(struct nf_conn *ct,
 					      unsigned int hooknum);
 
diff --git a/net/netfilter/nf_nat_core.c b/net/netfilter/nf_nat_core.c
index ea923f8cf9c4..edfd72524c38 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;
@@ -623,6 +623,15 @@ 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)) {
+		struct nf_conn_nat *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..f14e53e8dc04 100644
--- a/net/netfilter/nf_nat_ftp.c
+++ b/net/netfilter/nf_nat_ftp.c
@@ -72,8 +72,14 @@ 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 +92,29 @@ 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;
+	/* Avoid applying range to external ports */
+	if (!exp->dir || !nat->range_info.min_proto.all || !nat->range_info.max_proto.all) {
+		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;
+
+	/* Try to get same port if it matches range */
+	ret = -1;
+	port = ntohs(exp->tuple.dst.u.tcp.port);
+	if (ntohs(range.min_proto.all) <= port && port <= ntohs(range.max_proto.all))
+		ret = nf_ct_expect_related(exp, 0);
 
-		exp->tuple.dst.u.tcp.port = htons(port);
+	/* Same port is not available, try to change it */
+	if (ret != 0) {
+		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 (ret == 0)
-			break;
-		else if (ret != -EBUSY) {
-			port = 0;
-			break;
-		}
 	}
-
-	if (port == 0) {
+	if (ret != 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..718fc423bc44 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->dir) {
+		struct nf_conn_nat *nat = nfct_nat(exp->master);
+
+		if (nat && nat->range_info.min_proto.all &&
+		    nat->range_info.max_proto.all) {
+			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