host-local: don't allocate past RangeEnd

When RangeEnd is given, a.end = RangeEnd+1.

If when getSearchRange() is called and lastReservedIP equals
RangeEnd, a.nextIP() only compares lastReservedIP (which in this
example is RangeEnd) against a.end (which in this example is
RangeEnd+1) and they clearly don't match, so a.nextIP() returns
start=RangeEnd+1 and end=RangeEnd.

Get() happily allocates RangeEnd+1 because it only compares 'cur'
to the end returned by getSearchRange(), not to a.end, and thus
allocates past RangeEnd.

Since a.end is inclusive (eg, host-local will allocate a.end) the
fix is to simply set a.end equal to RangeEnd.

plugins/ipam/host-local/allocator.go

@@ -25,7 +25,9 @@ import (
 )
 
 type IPAllocator struct {
+	// start is inclusive and may be allocated
 	start net.IP
+	// end is inclusive and may be allocated
 	end   net.IP
 	conf  *IPAMConfig
 	store backend.Store
@@ -56,7 +58,7 @@ func NewIPAllocator(conf *IPAMConfig, store backend.Store) (*IPAllocator, error)
 			return nil, err
 		}
 		// RangeEnd is inclusive
-		end = ip.NextIP(conf.RangeEnd)
+		end = conf.RangeEnd
 	}
 	return &IPAllocator{start, end, conf, store}, nil
 }