Bug#891857: busybox: Special case for /32 subnets not working as expected

[Yuval Freund <yuval.freund@profitbricks.com>]

Package: busybox
Severity: normal

Dear Maintainer,

Many of our customers would like to use the debian installer in order to set up their own VMs. Our DHCP servers currently offer addresses with /32 subnets, and we've come to realize that the debian installer does not properly configure the default route.

A fix for /32 has already been implemented in an earlier version of busybox, but it doesn't seem to work as expected, because the interface isn't defined while adding the relevant route.

Here's a suggested fix, which would probably also clear up what I mean:

##################################################################

--- tree/debian/tree/busybox-udeb/etc/udhcpc/default.script     2018-03-01 15:45:33.000000000 +0100
+++ tree/debian/tree/busybox-udeb/etc/udhcpc/default.script_proposed    2018-03-01 15:47:37.259206527 +0100
@@ -68,7 +68,7 @@

                # special case for /32 subnets, use onlink when adding routes
                [ ".$subnet" = .255.255.255.255 ] \
-                        && onlink=onlink || onlink=
+                        && onlink="dev $interface onlink" || onlink=
                for r in "$router"; do
                        ip -4 route add default via "$r" $onlink
                done

##################################################################

We would appreciate it if you could patch all current/relevant versions to use this fix.

Thank you!

Yuval Freund, ProfitBricks GmbH