net: vxlan: Add nolocalbypass option to vxlan.

If a packet needs to be encapsulated towards a local destination IP, the
packet will undergo a "local bypass" and be injected into the Rx path as
if it was received by the target VXLAN device without undergoing
encapsulation. If such a device does not exist, the packet will be
dropped.

There are scenarios where we do not want to perform such a bypass, but
instead want the packet to be encapsulated and locally received by a
user space program for post-processing.

To that end, add a new VXLAN device attribute that controls whether a
"local bypass" is performed or not. Default to performing a bypass to
maintain existing behavior.
Signed-off-by: Vladimir Nikishkin <vladimir@nikishkin.pw>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/vxlan/vxlan_core.c

@@ -2352,7 +2352,8 @@ static int encap_bypass_if_local(struct sk_buff *skb, struct net_device *dev,
 #endif
 	/* Bypass encapsulation if the destination is local */
 	if (rt_flags & RTCF_LOCAL &&
-	    !(rt_flags & (RTCF_BROADCAST | RTCF_MULTICAST))) {
+	    !(rt_flags & (RTCF_BROADCAST | RTCF_MULTICAST)) &&
+	    vxlan->cfg.flags & VXLAN_F_LOCALBYPASS) {
 		struct vxlan_dev *dst_vxlan;
 
 		dst_release(dst);
@@ -3172,6 +3173,7 @@ static void vxlan_raw_setup(struct net_device *dev)
 }
 
 static const struct nla_policy vxlan_policy[IFLA_VXLAN_MAX + 1] = {
+	[IFLA_VXLAN_UNSPEC]     = { .strict_start_type = IFLA_VXLAN_LOCALBYPASS },
 	[IFLA_VXLAN_ID]		= { .type = NLA_U32 },
 	[IFLA_VXLAN_GROUP]	= { .len = sizeof_field(struct iphdr, daddr) },
 	[IFLA_VXLAN_GROUP6]	= { .len = sizeof(struct in6_addr) },
@@ -3202,6 +3204,7 @@ static const struct nla_policy vxlan_policy[IFLA_VXLAN_MAX + 1] = {
 	[IFLA_VXLAN_TTL_INHERIT]	= { .type = NLA_FLAG },
 	[IFLA_VXLAN_DF]		= { .type = NLA_U8 },
 	[IFLA_VXLAN_VNIFILTER]	= { .type = NLA_U8 },
+	[IFLA_VXLAN_LOCALBYPASS]	= NLA_POLICY_MAX(NLA_U8, 1),
 };
 
 static int vxlan_validate(struct nlattr *tb[], struct nlattr *data[],
@@ -4011,6 +4014,17 @@ static int vxlan_nl2conf(struct nlattr *tb[], struct nlattr *data[],
 			conf->flags |= VXLAN_F_UDP_ZERO_CSUM_TX;
 	}
 
+	if (data[IFLA_VXLAN_LOCALBYPASS]) {
+		err = vxlan_nl2flag(conf, data, IFLA_VXLAN_LOCALBYPASS,
+				    VXLAN_F_LOCALBYPASS, changelink,
+				    true, extack);
+		if (err)
+			return err;
+	} else if (!changelink) {
+		/* default to local bypass on a new device */
+		conf->flags |= VXLAN_F_LOCALBYPASS;
+	}
+
 	if (data[IFLA_VXLAN_UDP_ZERO_CSUM6_TX]) {
 		err = vxlan_nl2flag(conf, data, IFLA_VXLAN_UDP_ZERO_CSUM6_TX,
 				    VXLAN_F_UDP_ZERO_CSUM6_TX, changelink,
@@ -4232,6 +4246,7 @@ static size_t vxlan_get_size(const struct net_device *dev)
 		nla_total_size(sizeof(__u8)) + /* IFLA_VXLAN_UDP_ZERO_CSUM6_RX */
 		nla_total_size(sizeof(__u8)) + /* IFLA_VXLAN_REMCSUM_TX */
 		nla_total_size(sizeof(__u8)) + /* IFLA_VXLAN_REMCSUM_RX */
+		nla_total_size(sizeof(__u8)) + /* IFLA_VXLAN_LOCALBYPASS */
 		0;
 }
 
@@ -4308,7 +4323,9 @@ static int vxlan_fill_info(struct sk_buff *skb, const struct net_device *dev)
 	    nla_put_u8(skb, IFLA_VXLAN_REMCSUM_TX,
 		       !!(vxlan->cfg.flags & VXLAN_F_REMCSUM_TX)) ||
 	    nla_put_u8(skb, IFLA_VXLAN_REMCSUM_RX,
-		       !!(vxlan->cfg.flags & VXLAN_F_REMCSUM_RX)))
+		       !!(vxlan->cfg.flags & VXLAN_F_REMCSUM_RX)) ||
+	    nla_put_u8(skb, IFLA_VXLAN_LOCALBYPASS,
+		       !!(vxlan->cfg.flags & VXLAN_F_LOCALBYPASS)))
 		goto nla_put_failure;
 
 	if (nla_put(skb, IFLA_VXLAN_PORT_RANGE, sizeof(ports), &ports))

include/net/vxlan.h

@@ -328,6 +328,7 @@ struct vxlan_dev {
 #define VXLAN_F_TTL_INHERIT		0x10000
 #define VXLAN_F_VNIFILTER               0x20000
 #define VXLAN_F_MDB			0x40000
+#define VXLAN_F_LOCALBYPASS		0x80000
 
 /* Flags that are used in the receive path. These flags must match in
  * order for a socket to be shareable
@@ -348,7 +349,8 @@ struct vxlan_dev {
 					 VXLAN_F_UDP_ZERO_CSUM6_TX |	\
 					 VXLAN_F_UDP_ZERO_CSUM6_RX |	\
 					 VXLAN_F_COLLECT_METADATA  |	\
-					 VXLAN_F_VNIFILTER)
+					 VXLAN_F_VNIFILTER         |    \
+					 VXLAN_F_LOCALBYPASS)
 
 struct net_device *vxlan_dev_create(struct net *net, const char *name,
 				    u8 name_assign_type, struct vxlan_config *conf);

include/uapi/linux/if_link.h

@@ -828,6 +828,7 @@ enum {
 	IFLA_VXLAN_TTL_INHERIT,
 	IFLA_VXLAN_DF,
 	IFLA_VXLAN_VNIFILTER, /* only applicable with COLLECT_METADATA mode */
+	IFLA_VXLAN_LOCALBYPASS,
 	__IFLA_VXLAN_MAX
 };
 #define IFLA_VXLAN_MAX	(__IFLA_VXLAN_MAX - 1)