wg-quick: darwin: properly parse netstat -nr output

Looking at the source [1], it appears that the interface is always the
4th argument, regardless of the family:

C1.	if (fam != old_fam) // FALSE

P1.	p_sockaddr(params, &addr.u_sa, &mask.u_sa, rtm->rtm_flags,
	    WID_DST(addr.u_sa.sa_family));

P2.	p_sockaddr(params, rti_info[RTAX_GATEWAY], NULL, RTF_HOST,
	    WID_GW(addr.u_sa.sa_family));

C2.	if (params->lflag && (rtm->rtm_addrs & RTA_IFA)) // FALSE

P3.	p_flags(rtm->rtm_flags, "%-10.10s ");

C3.	if (params->lflag) // FALSE

P4. 	printf("%*.*s", WID_IF(addr.u_sa.sa_family),
		WID_IF(addr.u_sa.sa_family), ifname);

Because C1, C2, and C3 evaluate to false, interface is always in the 4th
argument.

[1] https://github.com/apple-oss-distributions/network_cmds/blob/97e27e6244c16d399bfeb254315ddc5828711c56/netstat.tproj/route.c#L328

Reported-by: Florian Uekermann <florian@uekermann.me>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

diff --git a/src/wg-quick/darwin.bash b/src/wg-quick/darwin.bash
index 0e870625eb72495ff992e87257374ba4f3395a23..0179afb190f606fa7d856ebddc81f0b6b85344c9 100755 (executable)
--- a/src/wg-quick/darwin.bash
+++ b/src/wg-quick/darwin.bash
@@ -131,14 +131,14 @@ add_if() {
 del_routes() {
        [[ -n $REAL_INTERFACE ]] || return 0
        local todelete=( ) destination gateway netif
-       while read -r destination _ _ _ _ netif _; do
+       while read -r destination _ _ netif _; do
                [[ $netif == "$REAL_INTERFACE" ]] && todelete+=( "$destination" )
        done < <(netstat -nr -f inet)
        for destination in "${todelete[@]}"; do
                cmd route -q -n delete -inet "$destination" >/dev/null || true
        done
        todelete=( )
-       while read -r destination gateway _ netif; do
+       while read -r destination gateway _ netif _; do
                [[ $netif == "$REAL_INTERFACE" || ( $netif == lo* && $gateway == "$REAL_INTERFACE" ) ]] && todelete+=( "$destination" )
        done < <(netstat -nr -f inet6)
        for destination in "${todelete[@]}"; do
@@ -177,7 +177,7 @@ set_mtu() {
                cmd ifconfig "$REAL_INTERFACE" mtu "$MTU"
                return
        fi
-       while read -r destination _ _ _ _ netif _; do
+       while read -r destination _ _ netif _; do
                if [[ $destination == default ]]; then
                        defaultif="$netif"
                        break