mwan3: use helper library for mwan3track

Rather than using a special mwan3 user to manage mwan3track's tracking packets, this commit implements a small helper library to bind to device and to set a fwmark so that the tracking packets can be routed out of the correct interface. This provides a consistent method for binding to a device rather than relying on various packages potentially buggy implementations. For example: #8139 and #12836 This helper issue also allows for more tracking methods to be added even if they do not have a command line option to bind to device, such as iperf3 (eg #13050). Signed-off-by: Aaron Goodman <aaronjg@stanford.edu>
2020-10-11 18:37:25 -04:00 · 2020-10-11 18:37:25 -04:00 · bbbc6127ab
commit bbbc6127ab
parent fb4a2d99ef
5 changed files with 312 additions and 121 deletions
--- a/net/mwan3/Makefile
+++ b/net/mwan3/Makefile
@ -8,10 +8,11 @@
 include $(TOPDIR)/rules.mk

 PKG_NAME:=mwan3
-PKG_VERSION:=2.9.0
+PKG_VERSION:=2.10.0
 PKG_RELEASE:=1
 PKG_MAINTAINER:=Florian Eckert <fe@dev.tdt.de>
 PKG_LICENSE:=GPL-2.0
+PKG_CONFIG_DEPENDS:=CONFIG_IPV6

 include $(INCLUDE_DIR)/package.mk

@ -61,8 +62,13 @@ fi
 exit 0
 endef

+define Build/Compile
+	$(TARGET_CC) $(CFLAGS) $(LDFLAGS) $(FPIC) -shared -o $(PKG_BUILD_DIR)/libwrap_mwan3_sockopt.so.1.0 $(if $(CONFIG_IPV6),-DCONFIG_IPV6) $(PKG_BUILD_DIR)/sockopt_wrap.c -ldl
+endef
+
 define Package/mwan3/install
-$(CP) ./files/* $(1)
+	$(CP) ./files/* $(1)
+	$(CP) $(PKG_BUILD_DIR)/libwrap_mwan3_sockopt.so.1.0 $(1)/lib/mwan3/
 endef

 $(eval $(call BuildPackage,mwan3))
--- a/net/mwan3/files/lib/mwan3/common.sh
+++ b/net/mwan3/files/lib/mwan3/common.sh
@ -8,8 +8,19 @@ get_uptime() {
 IP4="ip -4"
 IP6="ip -6"
 SCRIPTNAME="$(basename "$0")"
+
+MWAN3_STATUS_DIR="/var/run/mwan3"
 MWAN3TRACK_STATUS_DIR="/var/run/mwan3track"

+MWAN3_INTERFACE_MAX=""
+
+MMX_MASK=""
+MMX_DEFAULT=""
+MMX_BLACKHOLE=""
+MM_BLACKHOLE=""
+
+MMX_UNREACHABLE=""
+MM_UNREACHABLE=""
 MAX_SLEEP=$(((1<<31)-1))

 LOG()
@ -21,6 +32,21 @@ LOG()
 	[ "$facility" = "debug" ] && return
 	logger -t "${SCRIPTNAME}[$$]" -p $facility "$*"
 }
+
+mwan3_get_true_iface()
+{
+	local family V
+	_true_iface=$2
+	config_get family "$2" family ipv4
+	if [ "$family" = "ipv4" ]; then
+		V=4
+	elif [ "$family" = "ipv6" ]; then
+		V=6
+	fi
+	ubus call "network.interface.${2}_${V}" status &>/dev/null && _true_iface="${2}_${V}"
+	export "$1=$_true_iface"
+}
+
 mwan3_get_src_ip()
 {
 	local family _src_ip true_iface device addr_cmd default_ip IP sed_str
@ -149,4 +175,3 @@ mwan3_count_one_bits()
 	done
 	echo $count
 }
->>>>>>> 2a4e0dc6d... review comments
--- a/net/mwan3/files/lib/mwan3/mwan3.sh
+++ b/net/mwan3/files/lib/mwan3/mwan3.sh
@ -22,16 +22,7 @@ IPv6_REGEX="${IPv6_REGEX}::(ffff(:0{1,4}){0,1}:){0,1}((25[0-5]|(2[0-4]|1{0,1}[0-
 IPv6_REGEX="${IPv6_REGEX}([0-9a-fA-F]{1,4}:){1,4}:((25[0-5]|(2[0-4]|1{0,1}[0-9]){0,1}[0-9])\.){3,3}(25[0-5]|(2[0-4]|1{0,1}[0-9]){0,1}[0-9])"
 IPv4_REGEX="((25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)"

-MWAN3_STATUS_DIR="/var/run/mwan3"
-MWAN3_INTERFACE_MAX=""
 DEFAULT_LOWEST_METRIC=256
-MMX_MASK=""
-MMX_DEFAULT=""
-MMX_BLACKHOLE=""
-MM_BLACKHOLE=""
-
-MMX_UNREACHABLE=""
-MM_UNREACHABLE=""

 command -v ip6tables > /dev/null
 NO_IPV6=$?
@ -80,20 +71,6 @@ mwan3_update_iface_to_table()
 	config_foreach update_table interface
 }

-mwan3_get_true_iface()
-{
-	local family V
-	_true_iface=$2
-	config_get family "$iface" family ipv4
-	if [ "$family" = "ipv4" ]; then
-		V=4
-	elif [ "$family" = "ipv6" ]; then
-		V=6
-	fi
-	ubus call "network.interface.${iface}_${V}" status &>/dev/null && _true_iface="${iface}_${V}"
-	export "$1=$_true_iface"
-}
-
 mwan3_route_line_dev()
 {
 	# must have mwan3 config already loaded
@ -129,63 +106,6 @@ mwan3_count_one_bits()
 	echo $count
 }

-# maps the 1st parameter so it only uses the bits allowed by the bitmask (2nd parameter)
-# which means spreading the bits of the 1st parameter to only use the bits that are set to 1 in the 2nd parameter
-# 0 0 0 0 0 1 0 1 (0x05) 1st parameter
-# 1 0 1 0 1 0 1 0 (0xAA) 2nd parameter
-#     1   0   1          result
-mwan3_id2mask()
-{
-	local bit_msk bit_val result
-	bit_val=0
-	result=0
-	for bit_msk in $(seq 0 31); do
-		if [ $((($2>>bit_msk)&1)) = "1" ]; then
-			if [ $((($1>>bit_val)&1)) = "1" ]; then
-				result=$((result|(1<<bit_msk)))
-			fi
-			bit_val=$((bit_val+1))
-		fi
-	done
-	printf "0x%x" $result
-}
-
-mwan3_init()
-{
-	local bitcnt
-	local mmdefault
-
-	[ -d $MWAN3_STATUS_DIR ] || mkdir -p $MWAN3_STATUS_DIR/iface_state
-
-	# mwan3's MARKing mask (at least 3 bits should be set)
-	if [ -e "${MWAN3_STATUS_DIR}/mmx_mask" ]; then
-		MMX_MASK=$(cat "${MWAN3_STATUS_DIR}/mmx_mask")
-		MWAN3_INTERFACE_MAX=$(uci_get_state mwan3 globals iface_max)
-	else
-		config_load mwan3
-		config_get MMX_MASK globals mmx_mask '0x3F00'
-		echo "$MMX_MASK"| tr 'A-F' 'a-f' > "${MWAN3_STATUS_DIR}/mmx_mask"
-		LOG debug "Using firewall mask ${MMX_MASK}"
-
-		bitcnt=$(mwan3_count_one_bits MMX_MASK)
-		mmdefault=$(((1<<bitcnt)-1))
-		MWAN3_INTERFACE_MAX=$((mmdefault-3))
-		uci_toggle_state mwan3 globals iface_max "$MWAN3_INTERFACE_MAX"
-		LOG debug "Max interface count is ${MWAN3_INTERFACE_MAX}"
-	fi
-
-	# mark mask constants
-	bitcnt=$(mwan3_count_one_bits MMX_MASK)
-	mmdefault=$(((1<<bitcnt)-1))
-	MM_BLACKHOLE=$((mmdefault-2))
-	MM_UNREACHABLE=$((mmdefault-1))
-
-	# MMX_DEFAULT should equal MMX_MASK
-	MMX_DEFAULT=$(mwan3_id2mask mmdefault MMX_MASK)
-	MMX_BLACKHOLE=$(mwan3_id2mask MM_BLACKHOLE MMX_MASK)
-	MMX_UNREACHABLE=$(mwan3_id2mask MM_UNREACHABLE MMX_MASK)
-}
-
 mwan3_lock() {
 	lock /var/run/mwan3.lock
 	#LOG debug "$1 $2 (lock)"
@ -281,7 +201,7 @@ mwan3_set_connected_ipv4()

 mwan3_set_connected_ipv6()
 {
-	local connected_network_v6 source_network_v6 error
+	local connected_network_v6 error
 	local update=""
 	[ $NO_IPV6 -eq 0 ] || return

@ -292,10 +212,6 @@ mwan3_set_connected_ipv6()
 		mwan3_push_update -! add mwan3_connected_v6 "$connected_network_v6"
 	done

-	mwan3_push_update -! create mwan3_source_v6 hash:net family inet6
-	for source_network_v6 in $($IP6 addr ls | sed -ne 's/ *inet6 \([^ \/]*\).* scope global.*/\1/p'); do
-		mwan3_push_update -! add mwan3_source_v6 "$source_network_v6"
-	done
 	mwan3_push_update -! add mwan3_connected mwan3_connected_v6
 	error=$(echo "$update" | $IPS restore 2>&1) || LOG error "set_connected_ipv6: $error"
 }
@ -384,15 +300,10 @@ mwan3_set_general_iptables()
 						  -p ipv6-icmp \
 						  -m icmp6 --icmpv6-type 137 \
 						  -j RETURN
-				# do not mangle outgoing echo request
-				mwan3_push_update -A mwan3_hook \
-						  -m set --match-set mwan3_source_v6 src \
-						  -p ipv6-icmp \
-						  -m icmp6 --icmpv6-type 128 \
-						  -j RETURN

 			fi
 			mwan3_push_update -A mwan3_hook \
+					  -m mark --mark 0x0/$MMX_MASK \
 					  -j CONNMARK --restore-mark --nfmask "$MMX_MASK" --ctmask "$MMX_MASK"
 			mwan3_push_update -A mwan3_hook \
 					  -m mark --mark 0x0/$MMX_MASK \
--- a/net/mwan3/files/usr/sbin/mwan3track
+++ b/net/mwan3/files/usr/sbin/mwan3track
@ -19,6 +19,11 @@ stop_subprocs() {
 	[ -n "$TRACK_PID" ] && kill "$TRACK_PID" && unset TRACK_PID
 }

+WRAP() {
+	# shellcheck disable=SC2048
+	FAMILY=$FAMILY DEVICE=$DEVICE SRCIP=$SRC_IP FWMARK=$MMX_DEFAULT LD_PRELOAD=/lib/mwan3/libwrap_mwan3_sockopt.so.1.0 $*
+}
+
 clean_up() {
 	LOG notice "Stopping mwan3track for interface \"${INTERFACE}\". Status was \"${STATUS}\""
 	stop_subprocs
@ -58,10 +63,6 @@ validate_track_method() {
 				LOG warn "Missing httping. Please install httping package."
 				return 1
 			}
-			[ -n "$2" ] && { [ "$2" = "0.0.0.0" ] || [ "$2" = "::" ]; } && {
-				LOG warn "Cannot determine source IP for the interface which is required by httping."
-				return 1
-			}
 			;;
 		nping-*)
 			command -v nping 1>/dev/null 2>&1 || {
@ -76,6 +77,12 @@ validate_track_method() {
 	esac
 }

+validate_wrap() {
+	[ -x /lib/mwan3/libwrap_mwan3_sockopt.so.1.0 ] && return
+	LOG error "Missing libwrap_mwan3_sockopt. Please reinstall mwan3." &&
+		exit 1
+}
+
 disconnected() {
 	STATUS='offline'
 	echo "offline" > $MWAN3TRACK_STATUS_DIR/$INTERFACE/STATUS
@ -124,17 +131,6 @@ firstconnect() {

 	mwan3_get_src_ip SRC_IP $true_iface

-	# pinging IPv6 hosts with an interface is troublesome
-	# https://bugs.openwrt.org/index.php?do=details&task_id=2897
-	# https://bugs.openwrt.org/index.php?do=details&task_id=2167
-	# https://forum.openwrt.org/t/ping-and-traceroute-failing-for-eth0-3-on-ipv6/44680/11
-	# so use the IP address of the interface
-	if [ "$family" = "ipv6" ]; then
-		SOURCE="$SRC_IP"
-	else
-		SOURCE="$DEVICE"
-	fi
-
 	LOG debug "firstconnect: called on $INTERFACE/$true_iface ($DEVICE). Status is $STATUS. SRC_IP is $SRC_IP"

 	STARTED=1
@ -159,7 +155,8 @@ main() {
 	local recovery_interval down up size
 	local keep_failure_interval check_quality failure_latency
 	local recovery_latency failure_loss recovery_loss
-	local max_ttl httping_ssl family track_ips
+
+	local max_ttl httping_ssl track_ips

 	INTERFACE=$1
 	STATUS=""
@ -171,9 +168,10 @@ main() {
 	trap if_up USR2

 	config_load mwan3
+	config_get FAMILY $INTERFACE family ipv4
 	config_get track_method $INTERFACE track_method ping
 	config_get_bool httping_ssl $INTERFACE httping_ssl 0
-	validate_track_method $track_method $SRC_IP || {
+	validate_track_method $track_method || {
 		track_method=ping
 		if validate_track_method $track_method; then
 			LOG warn "Using ping to track interface $INTERFACE avaliability"
@ -219,17 +217,13 @@ main() {
 			if [ $host_up_count -lt $reliability ]; then
 				case "$track_method" in
 					ping)
-						# pinging IPv6 hosts with an interface is troublesome
-						# https://bugs.openwrt.org/index.php?do=details&task_id=2897
-						# so get the IP address of the interface and use that instead
-
 						if [ $check_quality -eq 0 ]; then
-							$PING -${family#ipv} -I ${SOURCE} -c $count -W $timeout -s $size -t $max_ttl -q $track_ip &> /dev/null &
+							WRAP $PING -${FAMILY#ipv} -c $count -W $timeout -s $size -t $max_ttl -q $track_ip &> /dev/null &
 							TRACK_PID=$!
 							wait $TRACK_PID
 							result=$?
 						else
-							$PING -${family#ipv} -I ${SOURCE} -c $count -W $timeout -s $size -t $max_ttl -q $track_ip 2>/dev/null > $TRACK_OUTPUT &
+							WRAP $PING -${family#ipv} -I ${SOURCE} -c $count -W $timeout -s $size -t $max_ttl -q $track_ip 2>/dev/null > $TRACK_OUTPUT &
 							TRACK_PID=$!
 							wait $TRACK_PID
 							ping_status=$?
@ -243,23 +237,23 @@ main() {
 						fi
 					;;
 					arping)
-						arping -I $DEVICE -c $count -w $timeout -q $track_ip &> /dev/null &
+						WRAP arping -I $DEVICE -c $count -w $timeout -q $track_ip &> /dev/null &
 						TRACK_PID=$!
 						wait $TRACK_PID
 						result=$?
 					;;
 					httping)
 						if [ "$httping_ssl" -eq 1 ]; then
-							httping -y $SRC_IP -c $count -t $timeout -q "https://$track_ip" &> /dev/null &
+							WRAP httping -c $count -t $timeout -q "https://$track_ip" &> /dev/null &
 						else
-							httping -y $SRC_IP -c $count -t $timeout -q "http://$track_ip" &> /dev/null &
+							WRAP httping -c $count -t $timeout -q "http://$track_ip" &> /dev/null &
 						fi
 						TRACK_PID=$!
 						wait $TRACK_PID
 						result=$?
 					;;
 					nping-*)
-						nping -c $count $track_ip --${FAMILY#nping-} > $TRACK_OUTPUT &
+						WRAP nping -c $count $track_ip --${FAMILY#nping-} > $TRACK_OUTPUT &
 						TRACK_PID=$!
 						wait $TRACK_PID
 						result=$(grep $TRACK_OUTPUT Lost | awk '{print $12}')
--- a/net/mwan3/src/sockopt_wrap.c
+++ b/net/mwan3/src/sockopt_wrap.c
@ -0,0 +1,255 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2020 Aaron Goodman <aaronjg@alumni.stanford.edu>. All Rights Reserved.
+ */
+
+/*
+ * sockopt_wrap.c provides a shared library that intercepts syscalls to various
+ * networking functions to bind the sockets a source IP address and network device
+ * and to set the firewall mark on otugoing packets. Parameters are set using the
+ * DEVICE, SRCIP, FWMARK environment variables.
+ *
+ *  Additionally the FAMILY environment variable can be set to either 'ipv4' or
+ *  'ipv6' to cause sockets opened with ipv6 or ipv4 to fail, respectively.
+ *
+ *  Each environment variable is optional, and if not set, the library will not
+ *  enforce the particular parameter.
+ */
+
+#define _GNU_SOURCE
+#include <dlfcn.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <arpa/inet.h>
+#include <net/ethernet.h>
+#include <linux/if_packet.h>
+#include <net/if.h>
+
+static int (*next_socket)(int domain, int type, int protocol);
+static int (*next_setsockopt)(int sockfd, int level, int optname,
+                              const void *optval, socklen_t optlen);
+static int (*next_bind)(int sockfd, const struct sockaddr *addr, socklen_t addrlen);
+static int (*next_close)(int fd);
+static ssize_t (*next_send)(int sockfd, const void *buf, size_t len, int flags);
+static ssize_t (*next_sendto)(int sockfd, const void *buf, size_t len, int flags,
+                              const struct sockaddr *dest_addr, socklen_t addrlen);
+static ssize_t (*next_sendmsg)(int sockfd, const struct msghdr *msg, int flags);
+static int (*next_connect)(int sockfd, const struct sockaddr *addr,
+                           socklen_t addrlen);
+static int device=0;
+static struct sockaddr_in source4 = {0};
+#ifdef CONFIG_IPV6
+static struct sockaddr_in6 source6 = {0};
+#endif
+static struct sockaddr * source = 0;
+static int sockaddr_size = 0;
+static int is_bound [1024] = {0};
+
+#define next_func(x)\
+void set_next_##x(){\
+	if (next_##x) return;\
+	next_##x = dlsym(RTLD_NEXT, #x);\
+	dlerror_handle();\
+	return;\
+}
+
+void dlerror_handle()
+{
+	char *msg;
+	if ((msg = dlerror()) != NULL) {
+		fprintf(stderr, "socket: dlopen failed : %s\n", msg);
+		fflush(stderr);
+		exit(EXIT_FAILURE);
+	}
+}
+
+next_func(bind);
+next_func(close);
+next_func(setsockopt);
+next_func(socket);
+next_func(send);
+next_func(sendto);
+next_func(sendmsg);
+next_func(connect);
+
+void dobind(int sockfd)
+{
+	if (source && sockfd < 1024 && !is_bound[sockfd]) {
+		set_next_bind();
+		if (next_bind(sockfd, source, sockaddr_size)) {
+			perror("failed to bind to ip address");
+			next_close(sockfd);
+			exit(EXIT_FAILURE);
+		}
+		is_bound[sockfd] = 1;
+	}
+}
+
+int connect(int sockfd, const struct sockaddr *addr, socklen_t addrlen)
+{
+	set_next_connect();
+	dobind(sockfd);
+	return next_connect(sockfd, addr, addrlen);
+}
+
+ssize_t send(int sockfd, const void *buf, size_t len, int flags)
+{
+	set_next_send();
+	dobind(sockfd);
+	return next_send(sockfd, buf, len, flags);
+}
+
+ssize_t sendto(int sockfd, const void *buf, size_t len, int flags,
+               const struct sockaddr *dest_addr, socklen_t addrlen)
+{
+	set_next_sendto();
+	dobind(sockfd);
+	return next_sendto(sockfd, buf, len, flags, dest_addr, addrlen);
+}
+
+ssize_t sendmsg(int sockfd, const struct msghdr *msg, int flags)
+{
+	set_next_sendmsg();
+	dobind(sockfd);
+	return next_sendmsg(sockfd, msg, flags);
+}
+
+int bind (int sockfd, const struct sockaddr *addr, socklen_t addrlen)
+{
+	set_next_bind();
+	if (device && addr->sa_family == AF_PACKET) {
+		((struct sockaddr_ll*)addr)->sll_ifindex=device;
+	}
+	else if (source && addr->sa_family == AF_INET) {
+		((struct sockaddr_in*)addr)->sin_addr = source4.sin_addr;
+	}
+#ifdef CONFIG_IPV6
+	else if (source && addr->sa_family == AF_INET6) {
+		((struct sockaddr_in6*)addr)->sin6_addr = source6.sin6_addr;
+	}
+#endif
+	if (sockfd < 1024)
+		is_bound[sockfd] = 1;
+	return next_bind(sockfd, addr, addrlen);
+}
+
+int close (int sockfd)
+{
+	set_next_close();
+	if (sockfd < 1024)
+		is_bound[sockfd]=0;
+	return next_close(sockfd);
+}
+
+int setsockopt(int sockfd, int level, int optname, const void *optval, socklen_t optlen)
+{
+	set_next_setsockopt();
+	if (level == SOL_SOCKET && (optname == SO_MARK || optname == SO_BINDTODEVICE))
+		return 0;
+	return next_setsockopt(sockfd, level, optname, optval, optlen);
+}
+
+int socket(int domain, int type, int protocol)
+{
+	int handle;
+
+	const char *socket_str = getenv("DEVICE");
+	const char *srcip_str = getenv("SRCIP");
+	const char *fwmark_str = getenv("FWMARK");
+	const char *family_str = getenv("FAMILY");
+	const int iface_len = socket_str ? strnlen(socket_str, IFNAMSIZ) : 0;
+	int has_family = family_str && *family_str != 0;
+	int has_srcip = srcip_str && *srcip_str != 0;
+	const int fwmark = fwmark_str ? (int)strtol(fwmark_str, NULL, 0) : 0;
+
+	set_next_close();
+	set_next_socket();
+	set_next_send();
+	set_next_setsockopt();
+	set_next_sendmsg();
+	set_next_sendto();
+	set_next_connect();
+	if(has_family) {
+#ifdef CONFIG_IPV6
+		if(domain == AF_INET && strncmp(family_str,"ipv6",4) == 0)
+			return -1;
+#endif
+		if(domain == AF_INET6 && strncmp(family_str,"ipv4",4) == 0)
+			return -1;
+	}
+
+	if (domain != AF_INET
+#ifdef CONFIG_IPV6
+	    && domain != AF_INET6
+#endif
+		) {
+		return next_socket(domain, type, protocol);
+	}
+
+
+	if (iface_len > 0) {
+		if (iface_len == IFNAMSIZ) {
+			fprintf(stderr,"socket: Too long iface name\n");
+			fflush(stderr);
+			exit(EXIT_FAILURE);
+		}
+	}
+
+	if (has_srcip) {
+		int s;
+		void * addr_buf;
+		if (domain == AF_INET) {
+			addr_buf = &source4.sin_addr;
+			sockaddr_size=sizeof source4;
+			memset(&source4, 0, sockaddr_size);
+			source4.sin_family = domain;
+			source = (struct sockaddr*)&source4;
+		}
+#ifdef CONFIG_IPV6
+		else {
+			addr_buf = &source6.sin6_addr;
+			sockaddr_size=sizeof source6;
+			memset(&source6, 0, sockaddr_size);
+			source6.sin6_family=domain;
+			source = (struct sockaddr*)&source6;
+		}
+#endif
+		s = inet_pton(domain, srcip_str, addr_buf);
+		if (s == 0) {
+			fprintf(stderr, "socket: ip address invalid format for family %s\n",
+			        domain == AF_INET ? "AF_INET" : domain == AF_INET6 ?
+			        "AF_INET6" : "unknown");
+			return -1;
+		}
+		if (s < 0) {
+			perror("inet_pton");
+			exit(EXIT_FAILURE);
+		}
+	}
+
+	handle = next_socket(domain, type, protocol);
+	if (handle == -1 ) {
+		return handle;
+	}
+
+	if (iface_len > 0) {
+		device=if_nametoindex(socket_str);
+		if (next_setsockopt(handle, SOL_SOCKET, SO_BINDTODEVICE,
+		                    socket_str, iface_len + 1)) {
+			perror("socket: setting interface name failed with error");
+			next_close(handle);
+			exit(EXIT_FAILURE);
+		}
+	}
+
+	if (fwmark > 0) {
+		if (next_setsockopt(handle, SOL_SOCKET, SO_MARK,
+		                    &fwmark, sizeof fwmark)) {
+			perror("failed setting mark for socket");
+			next_close(handle);
+			exit(EXIT_FAILURE);
+		}
+	}
+	return handle;
+}