Linux kernel mirror (for testing)
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1// SPDX-License-Identifier: LGPL-2.1-or-later
2/* Upcall routine, designed to work as a key type and working through
3 * /sbin/request-key to contact userspace when handling DNS queries.
4 *
5 * See Documentation/networking/dns_resolver.rst
6 *
7 * Copyright (c) 2007 Igor Mammedov
8 * Author(s): Igor Mammedov (niallain@gmail.com)
9 * Steve French (sfrench@us.ibm.com)
10 * Wang Lei (wang840925@gmail.com)
11 * David Howells (dhowells@redhat.com)
12 *
13 * The upcall wrapper used to make an arbitrary DNS query.
14 *
15 * This function requires the appropriate userspace tool dns.upcall to be
16 * installed and something like the following lines should be added to the
17 * /etc/request-key.conf file:
18 *
19 * create dns_resolver * * /sbin/dns.upcall %k
20 *
21 * For example to use this module to query AFSDB RR:
22 *
23 * create dns_resolver afsdb:* * /sbin/dns.afsdb %k
24 */
25
26#include <linux/module.h>
27#include <linux/slab.h>
28#include <linux/cred.h>
29#include <linux/dns_resolver.h>
30#include <linux/err.h>
31#include <net/net_namespace.h>
32
33#include <keys/dns_resolver-type.h>
34#include <keys/user-type.h>
35
36#include "internal.h"
37
38/**
39 * dns_query - Query the DNS
40 * @net: The network namespace to operate in.
41 * @type: Query type (or NULL for straight host->IP lookup)
42 * @name: Name to look up
43 * @namelen: Length of name
44 * @options: Request options (or NULL if no options)
45 * @_result: Where to place the returned data (or NULL)
46 * @_expiry: Where to store the result expiry time (or NULL)
47 * @invalidate: Always invalidate the key after use
48 *
49 * The data will be returned in the pointer at *result, if provided, and the
50 * caller is responsible for freeing it.
51 *
52 * The description should be of the form "[<query_type>:]<domain_name>", and
53 * the options need to be appropriate for the query type requested. If no
54 * query_type is given, then the query is a straight hostname to IP address
55 * lookup.
56 *
57 * The DNS resolution lookup is performed by upcalling to userspace by way of
58 * requesting a key of type dns_resolver.
59 *
60 * Returns the size of the result on success, -ve error code otherwise.
61 */
62int dns_query(struct net *net,
63 const char *type, const char *name, size_t namelen,
64 const char *options, char **_result, time64_t *_expiry,
65 bool invalidate)
66{
67 struct key *rkey;
68 struct user_key_payload *upayload;
69 size_t typelen, desclen;
70 char *desc, *cp;
71 int ret, len;
72
73 kenter("%s,%*.*s,%zu,%s",
74 type, (int)namelen, (int)namelen, name, namelen, options);
75
76 if (!name || namelen == 0)
77 return -EINVAL;
78
79 /* construct the query key description as "[<type>:]<name>" */
80 typelen = 0;
81 desclen = 0;
82 if (type) {
83 typelen = strlen(type);
84 if (typelen < 1)
85 return -EINVAL;
86 desclen += typelen + 1;
87 }
88
89 if (namelen < 3 || namelen > 255)
90 return -EINVAL;
91 desclen += namelen + 1;
92
93 desc = kmalloc(desclen, GFP_KERNEL);
94 if (!desc)
95 return -ENOMEM;
96
97 cp = desc;
98 if (type) {
99 memcpy(cp, type, typelen);
100 cp += typelen;
101 *cp++ = ':';
102 }
103 memcpy(cp, name, namelen);
104 cp += namelen;
105 *cp = '\0';
106
107 if (!options)
108 options = "";
109 kdebug("call request_key(,%s,%s)", desc, options);
110
111 /* make the upcall, using special credentials to prevent the use of
112 * add_key() to preinstall malicious redirections
113 */
114 scoped_with_creds(dns_resolver_cache)
115 rkey = request_key_net(&key_type_dns_resolver, desc, net, options);
116 kfree(desc);
117 if (IS_ERR(rkey)) {
118 ret = PTR_ERR(rkey);
119 goto out;
120 }
121
122 down_read(&rkey->sem);
123 set_bit(KEY_FLAG_ROOT_CAN_INVAL, &rkey->flags);
124 rkey->perm |= KEY_USR_VIEW;
125
126 ret = key_validate(rkey);
127 if (ret < 0)
128 goto put;
129
130 /* If the DNS server gave an error, return that to the caller */
131 ret = PTR_ERR(rkey->payload.data[dns_key_error]);
132 if (ret)
133 goto put;
134
135 upayload = user_key_payload_locked(rkey);
136 len = upayload->datalen;
137
138 if (_result) {
139 ret = -ENOMEM;
140 *_result = kmemdup_nul(upayload->data, len, GFP_KERNEL);
141 if (!*_result)
142 goto put;
143 }
144
145 if (_expiry)
146 *_expiry = rkey->expiry;
147
148 ret = len;
149put:
150 up_read(&rkey->sem);
151 if (invalidate)
152 key_invalidate(rkey);
153 key_put(rkey);
154out:
155 kleave(" = %d", ret);
156 return ret;
157}
158EXPORT_SYMBOL(dns_query);