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1a4240f4 WL |
1 | /* Upcall routine, designed to work as a key type and working through |
2 | * /sbin/request-key to contact userspace when handling DNS queries. | |
3 | * | |
4 | * See Documentation/networking/dns_resolver.txt | |
5 | * | |
6 | * Copyright (c) 2007 Igor Mammedov | |
7 | * Author(s): Igor Mammedov (niallain@gmail.com) | |
8 | * Steve French (sfrench@us.ibm.com) | |
9 | * Wang Lei (wang840925@gmail.com) | |
10 | * David Howells (dhowells@redhat.com) | |
11 | * | |
12 | * The upcall wrapper used to make an arbitrary DNS query. | |
13 | * | |
14 | * This function requires the appropriate userspace tool dns.upcall to be | |
15 | * installed and something like the following lines should be added to the | |
16 | * /etc/request-key.conf file: | |
17 | * | |
18 | * create dns_resolver * * /sbin/dns.upcall %k | |
19 | * | |
20 | * For example to use this module to query AFSDB RR: | |
21 | * | |
22 | * create dns_resolver afsdb:* * /sbin/dns.afsdb %k | |
23 | * | |
24 | * This library is free software; you can redistribute it and/or modify | |
25 | * it under the terms of the GNU Lesser General Public License as published | |
26 | * by the Free Software Foundation; either version 2.1 of the License, or | |
27 | * (at your option) any later version. | |
28 | * | |
29 | * This library is distributed in the hope that it will be useful, | |
30 | * but WITHOUT ANY WARRANTY; without even the implied warranty of | |
31 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See | |
32 | * the GNU Lesser General Public License for more details. | |
33 | * | |
34 | * You should have received a copy of the GNU Lesser General Public License | |
c057b190 | 35 | * along with this library; if not, see <http://www.gnu.org/licenses/>. |
1a4240f4 WL |
36 | */ |
37 | ||
38 | #include <linux/module.h> | |
39 | #include <linux/slab.h> | |
40 | #include <linux/dns_resolver.h> | |
af352fe9 | 41 | #include <linux/err.h> |
1a4240f4 WL |
42 | #include <keys/dns_resolver-type.h> |
43 | #include <keys/user-type.h> | |
44 | ||
45 | #include "internal.h" | |
46 | ||
ff9517a6 | 47 | /** |
1a4240f4 WL |
48 | * dns_query - Query the DNS |
49 | * @type: Query type (or NULL for straight host->IP lookup) | |
50 | * @name: Name to look up | |
51 | * @namelen: Length of name | |
52 | * @options: Request options (or NULL if no options) | |
53 | * @_result: Where to place the returned data. | |
54 | * @_expiry: Where to store the result expiry time (or NULL) | |
55 | * | |
56 | * The data will be returned in the pointer at *result, and the caller is | |
57 | * responsible for freeing it. | |
58 | * | |
59 | * The description should be of the form "[<query_type>:]<domain_name>", and | |
60 | * the options need to be appropriate for the query type requested. If no | |
61 | * query_type is given, then the query is a straight hostname to IP address | |
62 | * lookup. | |
63 | * | |
64 | * The DNS resolution lookup is performed by upcalling to userspace by way of | |
65 | * requesting a key of type dns_resolver. | |
66 | * | |
67 | * Returns the size of the result on success, -ve error code otherwise. | |
68 | */ | |
69 | int dns_query(const char *type, const char *name, size_t namelen, | |
70 | const char *options, char **_result, time_t *_expiry) | |
71 | { | |
72 | struct key *rkey; | |
73 | struct user_key_payload *upayload; | |
74 | const struct cred *saved_cred; | |
75 | size_t typelen, desclen; | |
76 | char *desc, *cp; | |
77 | int ret, len; | |
78 | ||
79 | kenter("%s,%*.*s,%zu,%s", | |
80 | type, (int)namelen, (int)namelen, name, namelen, options); | |
81 | ||
82 | if (!name || namelen == 0 || !_result) | |
83 | return -EINVAL; | |
84 | ||
85 | /* construct the query key description as "[<type>:]<name>" */ | |
86 | typelen = 0; | |
87 | desclen = 0; | |
88 | if (type) { | |
89 | typelen = strlen(type); | |
90 | if (typelen < 1) | |
91 | return -EINVAL; | |
92 | desclen += typelen + 1; | |
93 | } | |
94 | ||
95 | if (!namelen) | |
9638f671 MS |
96 | namelen = strnlen(name, 256); |
97 | if (namelen < 3 || namelen > 255) | |
1a4240f4 WL |
98 | return -EINVAL; |
99 | desclen += namelen + 1; | |
100 | ||
101 | desc = kmalloc(desclen, GFP_KERNEL); | |
102 | if (!desc) | |
103 | return -ENOMEM; | |
104 | ||
105 | cp = desc; | |
106 | if (type) { | |
107 | memcpy(cp, type, typelen); | |
108 | cp += typelen; | |
109 | *cp++ = ':'; | |
110 | } | |
111 | memcpy(cp, name, namelen); | |
112 | cp += namelen; | |
113 | *cp = '\0'; | |
114 | ||
115 | if (!options) | |
116 | options = ""; | |
117 | kdebug("call request_key(,%s,%s)", desc, options); | |
118 | ||
119 | /* make the upcall, using special credentials to prevent the use of | |
120 | * add_key() to preinstall malicious redirections | |
121 | */ | |
122 | saved_cred = override_creds(dns_resolver_cache); | |
123 | rkey = request_key(&key_type_dns_resolver, desc, options); | |
124 | revert_creds(saved_cred); | |
125 | kfree(desc); | |
126 | if (IS_ERR(rkey)) { | |
127 | ret = PTR_ERR(rkey); | |
128 | goto out; | |
129 | } | |
130 | ||
131 | down_read(&rkey->sem); | |
0c7774ab | 132 | set_bit(KEY_FLAG_ROOT_CAN_INVAL, &rkey->flags); |
1a4240f4 WL |
133 | rkey->perm |= KEY_USR_VIEW; |
134 | ||
135 | ret = key_validate(rkey); | |
136 | if (ret < 0) | |
137 | goto put; | |
138 | ||
4a2d7892 WL |
139 | /* If the DNS server gave an error, return that to the caller */ |
140 | ret = rkey->type_data.x[0]; | |
141 | if (ret) | |
142 | goto put; | |
143 | ||
1a4240f4 WL |
144 | upayload = rcu_dereference_protected(rkey->payload.data, |
145 | lockdep_is_held(&rkey->sem)); | |
146 | len = upayload->datalen; | |
147 | ||
148 | ret = -ENOMEM; | |
149 | *_result = kmalloc(len + 1, GFP_KERNEL); | |
150 | if (!*_result) | |
151 | goto put; | |
152 | ||
84a7c0b1 | 153 | memcpy(*_result, upayload->data, len); |
640d7efe | 154 | (*_result)[len] = '\0'; |
84a7c0b1 | 155 | |
1a4240f4 WL |
156 | if (_expiry) |
157 | *_expiry = rkey->expiry; | |
158 | ||
159 | ret = len; | |
160 | put: | |
161 | up_read(&rkey->sem); | |
162 | key_put(rkey); | |
163 | out: | |
164 | kleave(" = %d", ret); | |
165 | return ret; | |
166 | } | |
167 | EXPORT_SYMBOL(dns_query); |