1 /* LWIP service - addrpol.c - address policy table and values */
2 /*
3 * The main purpose of this module is to implement the address policy table
4 * described in RFC 6724. In general, the policy table is used for two
5 * purposes: source address selection, which is part of this service, and
6 * destination address selection, which is implemented in libc. NetBSD 7, the
7 * version that MINIX 3 is synced against at this moment, does not actually
8 * implement the libc part yet, though. That will change with NetBSD 8, where
9 * libc uses sysctl(7) to obtain the kernel's policy table, which itself can be
10 * changed with the new ip6addrctl(8) utility. Once we resync to NetBSD 8, we
11 * will also have to support this new functionality, and this module is where
12 * it would be implemented. Since NetBSD 7 is even lacking the necessary
13 * definitions, we cannot do that ahead of time, though. Thus, until then,
14 * this module is rather simple, as it only implements a static policy table
15 * used for source address selection. No changes beyond this module should be
16 * necessary, e.g. we are purposely not caching labels for local addresses.
17 */
18
19 #include "lwip.h"
20
21 /*
22 * Address policy table. Currently hardcoded to the default of RFC 6724.
23 * Sorted by prefix length, so that the first match is always also the longest.
24 */
25 static const struct {
26 ip_addr_t ipaddr;
27 unsigned int prefix;
28 int precedence;
29 int label;
30 } addrpol_table[] = {
31 { IPADDR6_INIT_HOST(0, 0, 0, 1), 128, 50, 0 },
32 { IPADDR6_INIT_HOST(0, 0, 0x0000ffffUL, 0), 96, 35, 4 },
33 { IPADDR6_INIT_HOST(0, 0, 0, 0), 96, 1, 3 },
34 { IPADDR6_INIT_HOST(0x20010000UL, 0, 0, 0), 32, 5, 5 },
35 { IPADDR6_INIT_HOST(0x20020000UL, 0, 0, 0), 16, 30, 2 },
36 { IPADDR6_INIT_HOST(0x3ffe0000UL, 0, 0, 0), 16, 1, 12 },
37 { IPADDR6_INIT_HOST(0xfec00000UL, 0, 0, 0), 10, 1, 11 },
38 { IPADDR6_INIT_HOST(0xfc000000UL, 0, 0, 0), 7, 3, 13 },
39 { IPADDR6_INIT_HOST(0, 0, 0, 0), 0, 40, 1 }
40 };
41
42 /*
43 * Obtain the label value for the given IP address from the address policy
44 * table. Currently only IPv6 addresses may be given. This function is linear
45 * in number of address policy table entries, requiring a relatively expensive
46 * normalization operation for each entry, so it should not be called lightly.
47 * Its results should not be cached beyond local contexts either, because the
48 * policy table itself may be changed from userland (in the future).
49 *
50 * TODO: convert IPv4 addresses to IPv4-mapped IPv6 addresses.
51 * TODO: embed the interface index in link-local addresses.
52 */
53 int
addrpol_get_label(const ip_addr_t * iporig)54 addrpol_get_label(const ip_addr_t * iporig)
55 {
56 ip_addr_t ipaddr;
57 unsigned int i;
58
59 assert(IP_IS_V6(iporig));
60
61 /*
62 * The policy table is sorted by prefix length such that the first
63 * match is also the one with the longest prefix, and as such the best.
64 */
65 for (i = 0; i < __arraycount(addrpol_table); i++) {
66 addr_normalize(&ipaddr, iporig, addrpol_table[i].prefix);
67
68 if (ip_addr_cmp(&addrpol_table[i].ipaddr, &ipaddr))
69 return addrpol_table[i].label;
70 }
71
72 /*
73 * We cannot possibly get here with the default policy table, because
74 * the last entry will always match. It is not clear what we should
75 * return if there is no matching entry, though. For now, we return
76 * the default label value for the default (::/0) entry, which is 1.
77 */
78 return 1;
79 }
80
81 /*
82 * Return an opaque positive value (possibly zero) that represents the scope of
83 * the given IP address. A larger value indicates a wider scope. The 'is_src'
84 * flag indicates whether the address is a source or a destination address,
85 * which affects the value returned for unknown addresses. A scope is a direct
86 * function of only the given address, so the result may be cached on a per-
87 * address basis without risking invalidation at any point in time.
88 */
89 int
addrpol_get_scope(const ip_addr_t * ipaddr,int is_src)90 addrpol_get_scope(const ip_addr_t * ipaddr, int is_src)
91 {
92 const ip6_addr_t *ip6addr;
93
94 /*
95 * For now, all IPv4 addresses are considered global. This function is
96 * currently called only for IPv6 addresses anyway.
97 */
98 if (IP_IS_V4(ipaddr))
99 return IP6_MULTICAST_SCOPE_GLOBAL;
100
101 assert(IP_IS_V6(ipaddr));
102
103 ip6addr = ip_2_ip6(ipaddr);
104
105 /*
106 * These are ordered not by ascending scope, but (roughly) by expected
107 * likeliness to match, for performance reasons.
108 */
109 if (ip6_addr_isglobal(ip6addr))
110 return IP6_MULTICAST_SCOPE_GLOBAL;
111
112 if (ip6_addr_islinklocal(ip6addr) || ip6_addr_isloopback(ip6addr))
113 return IP6_MULTICAST_SCOPE_LINK_LOCAL;
114
115 /*
116 * We deliberately deviate from RFC 6724 Sec. 3.1 by considering
117 * Unique-Local Addresses (ULAs) to be of smaller scope than global
118 * addresses, to avoid that during source address selection, a
119 * preferred ULA is picked over a deprecated global address when given
120 * a global address as destination, as that would likely result in
121 * broken two-way communication.
122 */
123 if (ip6_addr_isuniquelocal(ip6addr))
124 return IP6_MULTICAST_SCOPE_ORGANIZATION_LOCAL;
125
126 if (ip6_addr_ismulticast(ip6addr))
127 return ip6_addr_multicast_scope(ip6addr);
128
129 /* Site-local addresses are deprecated. */
130 if (ip6_addr_issitelocal(ip6addr))
131 return IP6_MULTICAST_SCOPE_SITE_LOCAL;
132
133 /*
134 * If the address is a source address, give it a scope beyond global to
135 * make sure that a "real" global address is picked first. If the
136 * address is a destination address, give it a global scope so as to
137 * pick "real" global addresses over unknown-scope source addresses.
138 */
139 if (is_src)
140 return IP6_MULTICAST_SCOPE_RESERVEDF; /* greater than GLOBAL */
141 else
142 return IP6_MULTICAST_SCOPE_GLOBAL;
143 }
144