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.rst |
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 |
35 | * along with this library; if not, see <http://www.gnu.org/licenses/>. |
36 | */ |
37 | |
38 | #include <linux/module.h> |
39 | #include <linux/slab.h> |
40 | #include <linux/cred.h> |
41 | #include <linux/dns_resolver.h> |
42 | #include <linux/err.h> |
43 | #include <net/net_namespace.h> |
44 | |
45 | #include <keys/dns_resolver-type.h> |
46 | #include <keys/user-type.h> |
47 | |
48 | #include "internal.h" |
49 | |
50 | /** |
51 | * dns_query - Query the DNS |
52 | * @net: The network namespace to operate in. |
53 | * @type: Query type (or NULL for straight host->IP lookup) |
54 | * @name: Name to look up |
55 | * @namelen: Length of name |
56 | * @options: Request options (or NULL if no options) |
57 | * @_result: Where to place the returned data (or NULL) |
58 | * @_expiry: Where to store the result expiry time (or NULL) |
59 | * @invalidate: Always invalidate the key after use |
60 | * |
61 | * The data will be returned in the pointer at *result, if provided, and the |
62 | * caller is responsible for freeing it. |
63 | * |
64 | * The description should be of the form "[<query_type>:]<domain_name>", and |
65 | * the options need to be appropriate for the query type requested. If no |
66 | * query_type is given, then the query is a straight hostname to IP address |
67 | * lookup. |
68 | * |
69 | * The DNS resolution lookup is performed by upcalling to userspace by way of |
70 | * requesting a key of type dns_resolver. |
71 | * |
72 | * Returns the size of the result on success, -ve error code otherwise. |
73 | */ |
74 | int dns_query(struct net *net, |
75 | const char *type, const char *name, size_t namelen, |
76 | const char *options, char **_result, time64_t *_expiry, |
77 | bool invalidate) |
78 | { |
79 | struct key *rkey; |
80 | struct user_key_payload *upayload; |
81 | const struct cred *saved_cred; |
82 | size_t typelen, desclen; |
83 | char *desc, *cp; |
84 | int ret, len; |
85 | |
86 | kenter("%s,%*.*s,%zu,%s" , |
87 | type, (int)namelen, (int)namelen, name, namelen, options); |
88 | |
89 | if (!name || namelen == 0) |
90 | return -EINVAL; |
91 | |
92 | /* construct the query key description as "[<type>:]<name>" */ |
93 | typelen = 0; |
94 | desclen = 0; |
95 | if (type) { |
96 | typelen = strlen(type); |
97 | if (typelen < 1) |
98 | return -EINVAL; |
99 | desclen += typelen + 1; |
100 | } |
101 | |
102 | if (namelen < 3 || namelen > 255) |
103 | return -EINVAL; |
104 | desclen += namelen + 1; |
105 | |
106 | desc = kmalloc(size: desclen, GFP_KERNEL); |
107 | if (!desc) |
108 | return -ENOMEM; |
109 | |
110 | cp = desc; |
111 | if (type) { |
112 | memcpy(cp, type, typelen); |
113 | cp += typelen; |
114 | *cp++ = ':'; |
115 | } |
116 | memcpy(cp, name, namelen); |
117 | cp += namelen; |
118 | *cp = '\0'; |
119 | |
120 | if (!options) |
121 | options = "" ; |
122 | kdebug("call request_key(,%s,%s)" , desc, options); |
123 | |
124 | /* make the upcall, using special credentials to prevent the use of |
125 | * add_key() to preinstall malicious redirections |
126 | */ |
127 | saved_cred = override_creds(dns_resolver_cache); |
128 | rkey = request_key_net(&key_type_dns_resolver, desc, net, options); |
129 | revert_creds(saved_cred); |
130 | kfree(objp: desc); |
131 | if (IS_ERR(ptr: rkey)) { |
132 | ret = PTR_ERR(ptr: rkey); |
133 | goto out; |
134 | } |
135 | |
136 | down_read(sem: &rkey->sem); |
137 | set_bit(KEY_FLAG_ROOT_CAN_INVAL, addr: &rkey->flags); |
138 | rkey->perm |= KEY_USR_VIEW; |
139 | |
140 | ret = key_validate(key: rkey); |
141 | if (ret < 0) |
142 | goto put; |
143 | |
144 | /* If the DNS server gave an error, return that to the caller */ |
145 | ret = PTR_ERR(ptr: rkey->payload.data[dns_key_error]); |
146 | if (ret) |
147 | goto put; |
148 | |
149 | upayload = user_key_payload_locked(key: rkey); |
150 | len = upayload->datalen; |
151 | |
152 | if (_result) { |
153 | ret = -ENOMEM; |
154 | *_result = kmemdup_nul(s: upayload->data, len, GFP_KERNEL); |
155 | if (!*_result) |
156 | goto put; |
157 | } |
158 | |
159 | if (_expiry) |
160 | *_expiry = rkey->expiry; |
161 | |
162 | ret = len; |
163 | put: |
164 | up_read(sem: &rkey->sem); |
165 | if (invalidate) |
166 | key_invalidate(key: rkey); |
167 | key_put(key: rkey); |
168 | out: |
169 | kleave(" = %d" , ret); |
170 | return ret; |
171 | } |
172 | EXPORT_SYMBOL(dns_query); |
173 | |