gtp: support SGSN-side tunnels

The GTP-tunnel driver is explicitly GGSN-side as it searches for PDP
contexts based on the incoming packets _destination_ address.  If we
want to place ourselves on the SGSN side of the  tunnel, then we want
to be identifying PDP contexts based on _source_ address.

Let it be noted that in a "real" configuration this module would never
be used:  the SGSN normally does not see IP packets as input.  The
justification for this functionality is for PGW load-testing applications
where the input to the SGSN is locally generally IP traffic.

This patch adds a "role" argument at GTP-link creation time to specify
whether we are on the GGSN or SGSN side of the tunnel; this flag is then
used to determine which part of the IP packet to use in determining
the PDP context.
Signed-off-by: Jonas Bonn <jonas@southpole.se>
Acked-by: Pablo Neira Ayuso <pablo@netfilter.org>
Acked-by: Harald Welte <laforge@gnumonks.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/gtp.c

@@ -74,6 +74,7 @@ struct gtp_dev {
 
 	struct net_device	*dev;
 
+	unsigned int		role;
 	unsigned int		hash_size;
 	struct hlist_head	*tid_hash;
 	struct hlist_head	*addr_hash;
@@ -154,8 +155,8 @@ static struct pdp_ctx *ipv4_pdp_find(struct gtp_dev *gtp, __be32 ms_addr)
 	return NULL;
 }
 
-static bool gtp_check_src_ms_ipv4(struct sk_buff *skb, struct pdp_ctx *pctx,
-				  unsigned int hdrlen)
+static bool gtp_check_ms_ipv4(struct sk_buff *skb, struct pdp_ctx *pctx,
+				  unsigned int hdrlen, unsigned int role)
 {
 	struct iphdr *iph;
 
@@ -164,27 +165,31 @@ static bool gtp_check_src_ms_ipv4(struct sk_buff *skb, struct pdp_ctx *pctx,
 
 	iph = (struct iphdr *)(skb->data + hdrlen);
 
-	return iph->saddr == pctx->ms_addr_ip4.s_addr;
+	if (role == GTP_ROLE_SGSN)
+		return iph->daddr == pctx->ms_addr_ip4.s_addr;
+	else
+		return iph->saddr == pctx->ms_addr_ip4.s_addr;
 }
 
-/* Check if the inner IP source address in this packet is assigned to any
+/* Check if the inner IP address in this packet is assigned to any
  * existing mobile subscriber.
  */
-static bool gtp_check_src_ms(struct sk_buff *skb, struct pdp_ctx *pctx,
-			     unsigned int hdrlen)
+static bool gtp_check_ms(struct sk_buff *skb, struct pdp_ctx *pctx,
+			     unsigned int hdrlen, unsigned int role)
 {
 	switch (ntohs(skb->protocol)) {
 	case ETH_P_IP:
-		return gtp_check_src_ms_ipv4(skb, pctx, hdrlen);
+		return gtp_check_ms_ipv4(skb, pctx, hdrlen, role);
 	}
 	return false;
 }
 
-static int gtp_rx(struct pdp_ctx *pctx, struct sk_buff *skb, unsigned int hdrlen)
+static int gtp_rx(struct pdp_ctx *pctx, struct sk_buff *skb,
+			unsigned int hdrlen, unsigned int role)
 {
 	struct pcpu_sw_netstats *stats;
 
-	if (!gtp_check_src_ms(skb, pctx, hdrlen)) {
+	if (!gtp_check_ms(skb, pctx, hdrlen, role)) {
 		netdev_dbg(pctx->dev, "No PDP ctx for this MS\n");
 		return 1;
 	}
@@ -239,7 +244,7 @@ static int gtp0_udp_encap_recv(struct gtp_dev *gtp, struct sk_buff *skb)
 		return 1;
 	}
 
-	return gtp_rx(pctx, skb, hdrlen);
+	return gtp_rx(pctx, skb, hdrlen, gtp->role);
 }
 
 static int gtp1u_udp_encap_recv(struct gtp_dev *gtp, struct sk_buff *skb)
@@ -281,7 +286,7 @@ static int gtp1u_udp_encap_recv(struct gtp_dev *gtp, struct sk_buff *skb)
 		return 1;
 	}
 
-	return gtp_rx(pctx, skb, hdrlen);
+	return gtp_rx(pctx, skb, hdrlen, gtp->role);
 }
 
 static void gtp_encap_destroy(struct sock *sk)
@@ -481,7 +486,11 @@ static int gtp_build_skb_ip4(struct sk_buff *skb, struct net_device *dev,
 	 * Prepend PDP header with TEI/TID from PDP ctx.
 	 */
 	iph = ip_hdr(skb);
-	pctx = ipv4_pdp_find(gtp, iph->daddr);
+	if (gtp->role == GTP_ROLE_SGSN)
+		pctx = ipv4_pdp_find(gtp, iph->saddr);
+	else
+		pctx = ipv4_pdp_find(gtp, iph->daddr);
+
 	if (!pctx) {
 		netdev_dbg(dev, "no PDP ctx found for %pI4, skip\n",
 			   &iph->daddr);
@@ -685,6 +694,7 @@ static const struct nla_policy gtp_policy[IFLA_GTP_MAX + 1] = {
 	[IFLA_GTP_FD0]			= { .type = NLA_U32 },
 	[IFLA_GTP_FD1]			= { .type = NLA_U32 },
 	[IFLA_GTP_PDP_HASHSIZE]		= { .type = NLA_U32 },
+	[IFLA_GTP_ROLE]			= { .type = NLA_U32 },
 };
 
 static int gtp_validate(struct nlattr *tb[], struct nlattr *data[])
@@ -810,6 +820,7 @@ static int gtp_encap_enable(struct gtp_dev *gtp, struct nlattr *data[])
 {
 	struct sock *sk1u = NULL;
 	struct sock *sk0 = NULL;
+	unsigned int role = GTP_ROLE_GGSN;
 
 	if (data[IFLA_GTP_FD0]) {
 		u32 fd0 = nla_get_u32(data[IFLA_GTP_FD0]);
@@ -830,8 +841,15 @@ static int gtp_encap_enable(struct gtp_dev *gtp, struct nlattr *data[])
 		}
 	}
 
+	if (data[IFLA_GTP_ROLE]) {
+		role = nla_get_u32(data[IFLA_GTP_ROLE]);
+		if (role > GTP_ROLE_SGSN)
+			return -EINVAL;
+	}
+
 	gtp->sk0 = sk0;
 	gtp->sk1u = sk1u;
+	gtp->role = role;
 
 	return 0;
 }

include/uapi/linux/if_link.h

@@ -538,11 +538,18 @@ enum {
 #define IFLA_PPP_MAX (__IFLA_PPP_MAX - 1)
 
 /* GTP section */
+
+enum ifla_gtp_role {
+	GTP_ROLE_GGSN = 0,
+	GTP_ROLE_SGSN,
+};
+
 enum {
 	IFLA_GTP_UNSPEC,
 	IFLA_GTP_FD0,
 	IFLA_GTP_FD1,
 	IFLA_GTP_PDP_HASHSIZE,
+	IFLA_GTP_ROLE,
 	__IFLA_GTP_MAX,
 };
 #define IFLA_GTP_MAX (__IFLA_GTP_MAX - 1)