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/*
* Copyright (c) 2021 Cisco and/or its affiliates.
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at:
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include "ip_sas.h"
#include <vppinfra/types.h>
#include <vnet/ip/ip_interface.h>
#include <vnet/fib/fib_table.h>
#include <vnet/ip/ip6_link.h>
#include <vppinfra/byte_order.h>
/*
* This file implement source address selection for VPP applications
* (e.g. ping, DNS, ICMP)
* It does not yet implement full fledged RFC6724 SAS.
* SAS assumes every IP enabled interface has an address. The algorithm will
* not go and hunt for a suitable IP address on other interfaces than the
* output interface or the specified preferred sw_if_index.
* That means that an interface with just an IPv6 link-local address must also
* be configured with an unnumbered configuration pointing to a numbered
* interface.
*/
static int
ip6_sas_commonlen (const ip6_address_t *a1, const ip6_address_t *a2)
{
u64 fa = clib_net_to_host_u64 (a1->as_u64[0]) ^
clib_net_to_host_u64 (a2->as_u64[0]);
if (fa == 0)
{
u64 la = clib_net_to_host_u64 (a1->as_u64[1]) ^
clib_net_to_host_u64 (a2->as_u64[1]);
if (la == 0)
return 128;
return 64 + __builtin_clzll (la);
}
else
{
return __builtin_clzll (fa);
}
}
static int
ip4_sas_commonlen (const ip4_address_t *a1, const ip4_address_t *a2)
{
if (!a1 || !a2)
return 0;
u64 a =
clib_net_to_host_u32 (a1->as_u32) ^ clib_net_to_host_u32 (a2->as_u32);
if (a == 0)
return 32;
return __builtin_clz (a);
}
/*
* walk all addresses on an interface:
* - prefer a source matching the scope of the destination address.
* - last resort pick the source address with the longest
* common prefix with destination
* NOTE: This should at some point implement RFC6724.
*/
bool
ip6_sas_by_sw_if_index (u32 sw_if_index, const ip6_address_t *dst,
ip6_address_t *src)
{
ip_interface_address_t *ia = 0;
ip_lookup_main_t *lm6 = &ip6_main.lookup_main;
ip6_address_t *tmp, *bestsrc = 0;
int bestlen = 0, l;
if (ip6_address_is_link_local_unicast (dst) ||
dst->as_u32[0] == clib_host_to_net_u32 (0xff020000))
{
const ip6_address_t *ll = ip6_get_link_local_address (sw_if_index);
if (NULL == ll)
{
return false;
}
ip6_address_copy (src, ll);
return true;
}
foreach_ip_interface_address (
lm6, ia, sw_if_index, 1, ({
if (ia->flags & IP_INTERFACE_ADDRESS_FLAG_STALE)
continue;
tmp = ip_interface_address_get_address (lm6, ia);
l = ip6_sas_commonlen (tmp, dst);
if (l > bestlen || bestsrc == 0)
{
bestsrc = tmp;
bestlen = l;
}
}));
if (bestsrc)
{
ip6_address_copy (src, bestsrc);
return true;
}
return false;
}
/*
* walk all addresses on an interface and pick the source address with the
* longest common prefix with destination.
*/
bool
ip4_sas_by_sw_if_index (u32 sw_if_index, const ip4_address_t *dst,
ip4_address_t *src)
{
ip_interface_address_t *ia = 0;
ip_lookup_main_t *lm4 = &ip4_main.lookup_main;
ip4_address_t *tmp, *bestsrc = 0;
int bestlen = 0, l;
foreach_ip_interface_address (
lm4, ia, sw_if_index, 1, ({
if (ia->flags & IP_INTERFACE_ADDRESS_FLAG_STALE)
continue;
tmp = ip_interface_address_get_address (lm4, ia);
l = ip4_sas_commonlen (tmp, dst);
if (l > bestlen || bestsrc == 0)
{
bestsrc = tmp;
bestlen = l;
}
}));
if (bestsrc)
{
src->as_u32 = bestsrc->as_u32;
return true;
}
return false;
}
/*
* table_id must be set. Default = 0.
* sw_if_index is the interface to pick SA from otherwise ~0 will pick from
* outbound interface.
*
* NOTE: What to do if multiple output interfaces?
*
*/
bool
ip6_sas (u32 table_id, u32 sw_if_index, const ip6_address_t *dst,
ip6_address_t *src)
{
fib_prefix_t prefix;
u32 if_index = sw_if_index;
/* If sw_if_index is not specified use the output interface. */
if (sw_if_index == ~0)
{
clib_memcpy (&prefix.fp_addr.ip6, dst, sizeof (*dst));
prefix.fp_proto = FIB_PROTOCOL_IP6;
prefix.fp_len = 128;
u32 fib_index = fib_table_find (prefix.fp_proto, table_id);
if (fib_index == (u32) ~0)
return false;
fib_node_index_t fei = fib_table_lookup (fib_index, &prefix);
if (fei == FIB_NODE_INDEX_INVALID)
return false;
u32 output_sw_if_index = fib_entry_get_resolving_interface (fei);
if (output_sw_if_index == ~0)
return false;
if_index = output_sw_if_index;
}
return ip6_sas_by_sw_if_index (if_index, dst, src);
}
/*
* table_id must be set. Default = 0.
* sw_if_index is the interface to pick SA from otherwise ~0 will pick from
* outbound interface.
*
* NOTE: What to do if multiple output interfaces?
*
*/
bool
ip4_sas (u32 table_id, u32 sw_if_index, const ip4_address_t *dst,
ip4_address_t *src)
{
fib_prefix_t prefix;
u32 if_index = sw_if_index;
/* If sw_if_index is not specified use the output interface. */
if (sw_if_index == ~0)
{
clib_memcpy (&prefix.fp_addr.ip4, dst, sizeof (*dst));
prefix.fp_proto = FIB_PROTOCOL_IP4;
prefix.fp_len = 32;
u32 fib_index = fib_table_find (prefix.fp_proto, table_id);
if (fib_index == (u32) ~0)
return false;
fib_node_index_t fei = fib_table_lookup (fib_index, &prefix);
if (fei == FIB_NODE_INDEX_INVALID)
return false;
u32 output_sw_if_index = fib_entry_get_resolving_interface (fei);
if (output_sw_if_index == ~0)
return false;
if_index = output_sw_if_index;
}
return ip4_sas_by_sw_if_index (if_index, dst, src);
}
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