1 /* Temporary, thread-local resolver state.
2 Copyright (C) 2017-2023 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
9
10 The GNU C Library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
14
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, see
17 <https://www.gnu.org/licenses/>. */
18
19 /* struct resolv_context objects are allocated on the heap,
20 initialized by __resolv_context_get (and its variants), and
21 destroyed by __resolv_context_put.
22
23 A nested call to __resolv_context_get (after another call to
24 __resolv_context_get without a matching __resolv_context_put call,
25 on the same thread) returns the original pointer, instead of
26 allocating a new context. This prevents unexpected reloading of
27 the resolver configuration. Care is taken to keep the context in
28 sync with the thread-local _res object. (This does not happen with
29 __resolv_context_get_override.)
30
31 In contrast to struct __res_state, struct resolv_context is not
32 affected by ABI compatibility concerns.
33
34 For the benefit of the res_n* functions, a struct __res_state
35 pointer is included in the context object, and a separate
36 initialization function is provided. */
37
38 #ifndef _RESOLV_CONTEXT_H
39 #define _RESOLV_CONTEXT_H
40
41 #include <bits/types/res_state.h>
42 #include <resolv/resolv_conf.h>
43 #include <stdbool.h>
44 #include <stddef.h>
45
46 /* Temporary resolver state. */
47 struct resolv_context
48 {
49 struct __res_state *resp; /* Backing resolver state. */
50
51 /* Extended resolver state. This is set to NULL if the
52 __resolv_context_get functions are unable to locate an associated
53 extended state. In this case, the configuration data in *resp
54 has to be used; otherwise, the data from *conf should be
55 preferred (because it is a superset). */
56 struct resolv_conf *conf;
57
58 /* The following fields are for internal use within the
59 resolv_context module. */
60 size_t __refcount; /* Count of reusages by the get functions. */
61 bool __from_res; /* True if created from _res. */
62
63 /* Single-linked list of resolver contexts. Used for memory
64 deallocation on thread cancellation. */
65 struct resolv_context *__next;
66 };
67
68 /* Return the current temporary resolver context, or NULL if there was
69 an error (indicated by errno). A call to this function must be
70 paired with a call to __resolv_context_put. */
71 struct resolv_context *__resolv_context_get (void)
72 __attribute__ ((warn_unused_result));
73 libc_hidden_proto (__resolv_context_get)
74
75 /* Deallocate the temporary resolver context. Converse of
76 __resolv_context_get. Do nothing if CTX is NULL. */
77 void __resolv_context_put (struct resolv_context *ctx);
78 libc_hidden_proto (__resolv_context_put)
79
80 /* Like __resolv_context_get, but the _res structure can be partially
81 initialized and those changes will not be overwritten. */
82 struct resolv_context *__resolv_context_get_preinit (void)
83 __attribute__ ((warn_unused_result));
84 libc_hidden_proto (__resolv_context_get_preinit)
85
86 /* Wrap a struct __res_state object in a struct resolv_context object.
87 A call to this function must be paired with a call to
88 __resolv_context_put. */
89 struct resolv_context *__resolv_context_get_override (struct __res_state *)
90 __attribute__ ((nonnull (1), warn_unused_result));
91 libc_hidden_proto (__resolv_context_get_override)
92
93 /* Return the search path entry at INDEX, or NULL if there are fewer
94 than INDEX entries. */
95 static __attribute__ ((nonnull (1), unused)) const char *
96 __resolv_context_search_list (const struct resolv_context *ctx, size_t index)
97 {
98 if (ctx->conf != NULL)
99 {
100 if (index < ctx->conf->search_list_size)
101 return ctx->conf->search_list[index];
102 else
103 return NULL;
104 }
105 /* Fallback. ctx->resp->dnsrch is a NULL-terminated array. */
106 for (size_t i = 0; ctx->resp->dnsrch[i] != NULL && i < MAXDNSRCH; ++i)
107 if (i == index)
108 return ctx->resp->dnsrch[i];
109 return NULL;
110 }
111
112 /* Return the number of name servers. */
113 static __attribute__ ((nonnull (1), unused)) size_t
114 __resolv_context_nameserver_count (const struct resolv_context *ctx)
115 {
116 if (ctx->conf != NULL)
117 return ctx->conf->nameserver_list_size;
118 else
119 return ctx->resp->nscount;
120 }
121
122 /* Return a pointer to the socket address of the name server INDEX, or
123 NULL if the index is out of bounds. */
124 static __attribute__ ((nonnull (1), unused)) const struct sockaddr *
125 __resolv_context_nameserver (const struct resolv_context *ctx, size_t index)
126 {
127 if (ctx->conf != NULL)
128 {
129 if (index < ctx->conf->nameserver_list_size)
130 return ctx->conf->nameserver_list[index];
131 }
132 else
133 if (index < ctx->resp->nscount)
134 {
135 if (ctx->resp->nsaddr_list[index].sin_family != 0)
136 return (const struct sockaddr *) &ctx->resp->nsaddr_list[index];
137 else
138 return (const struct sockaddr *) &ctx->resp->_u._ext.nsaddrs[index];
139 }
140 return NULL;
141 }
142
143 /* Return the number of sort list entries. */
144 static __attribute__ ((nonnull (1), unused)) size_t
145 __resolv_context_sort_count (const struct resolv_context *ctx)
146 {
147 if (ctx->conf != NULL)
148 return ctx->conf->sort_list_size;
149 else
150 return ctx->resp->nsort;
151 }
152
153 /* Return the sort list entry at INDEX. */
154 static __attribute__ ((nonnull (1), unused)) struct resolv_sortlist_entry
155 __resolv_context_sort_entry (const struct resolv_context *ctx, size_t index)
156 {
157 if (ctx->conf != NULL)
158 {
159 if (index < ctx->conf->sort_list_size)
160 return ctx->conf->sort_list[index];
161 /* Fall through. */
162 }
163 else if (index < ctx->resp->nsort)
164 return (struct resolv_sortlist_entry)
165 {
166 .addr = ctx->resp->sort_list[index].addr,
167 .mask = ctx->resp->sort_list[index].mask,
168 };
169
170 return (struct resolv_sortlist_entry) { .mask = 0, };
171 }
172
173 /* Called during thread shutdown to free the associated resolver
174 context (mostly in response to cancellation, otherwise the
175 __resolv_context_get/__resolv_context_put pairing will already have
176 deallocated the context object). */
177 void __resolv_context_freeres (void) attribute_hidden;
178
179 #endif /* _RESOLV_CONTEXT_H */