[PATCH v2] vxlan: allow for dynamic source ip selection

[Johannes Kimmel]

By setting 'auto', the zero address or the empty string as source
address (option ipaddr, option ip6addr), vxlan will choose one
dynamically. This helps in setups where a wan ip or prefix changes.

This corresponse to setting up an vxlan tunnel with:

proto vxlan6:
    # ip link add vx0 type vxlan id ID local :: ...
proto vxlan:
    # ip link add vx0 type vxlan id ID local 0.0.0.0 ...

While it is possible to not specify a source ip at all, the kernel will
default to setting up a ipv4 tunnel. The kernel will take any hint from
source and peer ips to figure out, what tunnel type to use. To make sure
we setup an ipv6 tunnel for proto vxlan6, this workaround is needed.

Specifying 'inherit' as source ip, the old behaviour is used whereby
a source ip is calculated once from the tunlink interface.

This will not change the behaviour of currently working configurations.
However this will allow former broken configurations, namely those not
specifying both a source address and tunnel interface, to setup a
tunnel interface. Previously those configurations weren't reporting an
error and were stueck in a setup loop like in Bug FS#3426.

This change lifts the currently very strict behaviour and should fix the
following bug:

Fixes: FS#3426
Ref: https://bugs.openwrt.org/index.php?do=details&task_id=3426

V2:
  - bump PKG_RELEASE
  - add small explaination about behaviour changes

Signed-off-by: Johannes Kimmel <fff at bareminimum.eu>
---
 package/network/config/vxlan/Makefile       |  2 +-
 package/network/config/vxlan/files/vxlan.sh | 55 ++++++++++++---------
 2 files changed, 34 insertions(+), 23 deletions(-)

diff --git a/package/network/config/vxlan/Makefile b/package/network/config/vxlan/Makefile
index 0b4d6713f9..97972d6d85 100644
--- a/package/network/config/vxlan/Makefile
+++ b/package/network/config/vxlan/Makefile
@@ -1,7 +1,7 @@
 include $(TOPDIR)/rules.mk
 
 PKG_NAME:=vxlan
-PKG_RELEASE:=6
+PKG_RELEASE:=7
 PKG_LICENSE:=GPL-2.0
 
 include $(INCLUDE_DIR)/package.mk
diff --git a/package/network/config/vxlan/files/vxlan.sh b/package/network/config/vxlan/files/vxlan.sh
index 5c1c484c47..579964b385 100755
--- a/package/network/config/vxlan/files/vxlan.sh
+++ b/package/network/config/vxlan/files/vxlan.sh
@@ -114,18 +114,23 @@ proto_vxlan_setup() {
 
 	( proto_add_host_dependency "$cfg" '' "$tunlink" )
 
-	[ -z "$ipaddr" ] && {
-		local wanif="$tunlink"
-		if [ -z "$wanif" ] && ! network_find_wan wanif; then
-			proto_notify_error "$cfg" "NO_WAN_LINK"
-			exit
-		fi
+	case "$ipaddr" in
+		"inherit")
+			local wanif="$tunlink"
+			if [ -z "$wanif" ] && ! network_find_wan wanif; then
+				proto_notify_error "$cfg" "NO_WAN_LINK"
+				exit
+			fi
 
-		if ! network_get_ipaddr ipaddr "$wanif"; then
-			proto_notify_error "$cfg" "NO_WAN_LINK"
-			exit
-		fi
-	}
+			if ! network_get_ipaddr ipaddr "$wanif"; then
+				proto_notify_error "$cfg" "NO_WAN_LINK"
+				exit
+			fi
+			;;
+		"auto"|"")
+			ipaddr="0.0.0.0"
+			;;
+	esac
 
 	vxlan_generic_setup "$cfg" 'vxlan' "$ipaddr" "$peeraddr"
 }
@@ -138,18 +143,24 @@ proto_vxlan6_setup() {
 
 	( proto_add_host_dependency "$cfg" '' "$tunlink" )
 
-	[ -z "$ip6addr" ] && {
-		local wanif="$tunlink"
-		if [ -z "$wanif" ] && ! network_find_wan6 wanif; then
-			proto_notify_error "$cfg" "NO_WAN_LINK"
-			exit
-		fi
+	case "$ip6addr" in
+		"inherit")
+			local wanif="$tunlink"
+			if [ -z "$wanif" ] && ! network_find_wan6 wanif; then
+				proto_notify_error "$cfg" "NO_WAN_LINK"
+				exit
+			fi
 
-		if ! network_get_ipaddr6 ip6addr "$wanif"; then
-			proto_notify_error "$cfg" "NO_WAN_LINK"
-			exit
-		fi
-	}
+			if ! network_get_ipaddr6 ip6addr "$wanif"; then
+				proto_notify_error "$cfg" "NO_WAN_LINK"
+				exit
+			fi
+			;;
+		"auto"|"")
+			# ensure tunnel via ipv6
+			ip6addr="::"
+			;;
+	esac
 
 	vxlan_generic_setup "$cfg" 'vxlan6' "$ip6addr" "$peer6addr"
 }
-- 
2.29.2