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 */
dns_query(struct net * net,const char * type,const char * name,size_t namelen,const char * options,char ** _result,time64_t * _expiry,bool invalidate)62 int 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 user_key_payload *upayload;
68 struct key *rkey;
69 int ret, len;
70 char *desc;
71
72 kenter("%s,%*.*s,%zu,%s",
73 type, (int)namelen, (int)namelen, name, namelen, options);
74
75 if (!name || namelen < 1 || namelen > 255)
76 return -EINVAL;
77 if (type && *type == '\0')
78 return -EINVAL;
79
80 /* construct the query key description as "[<type>:]<name>" */
81 if (type)
82 desc = kasprintf(GFP_KERNEL, "%s:%.*s", type, (int)namelen, name);
83 else
84 desc = kmemdup_nul(name, namelen, GFP_KERNEL);
85 if (!desc)
86 return -ENOMEM;
87
88 if (!options)
89 options = "";
90 kdebug("call request_key(,%s,%s)", desc, options);
91
92 /* make the upcall, using special credentials to prevent the use of
93 * add_key() to preinstall malicious redirections
94 */
95 scoped_with_creds(dns_resolver_cache)
96 rkey = request_key_net(&key_type_dns_resolver, desc, net, options);
97 kfree(desc);
98 if (IS_ERR(rkey)) {
99 ret = PTR_ERR(rkey);
100 goto out;
101 }
102
103 down_read(&rkey->sem);
104 set_bit(KEY_FLAG_ROOT_CAN_INVAL, &rkey->flags);
105 rkey->perm |= KEY_USR_VIEW;
106
107 ret = key_validate(rkey);
108 if (ret < 0)
109 goto put;
110
111 /* If the DNS server gave an error, return that to the caller */
112 ret = PTR_ERR(rkey->payload.data[dns_key_error]);
113 if (ret)
114 goto put;
115
116 upayload = user_key_payload_locked(rkey);
117 len = upayload->datalen;
118
119 if (_result) {
120 ret = -ENOMEM;
121 *_result = kmemdup_nul(upayload->data, len, GFP_KERNEL);
122 if (!*_result)
123 goto put;
124 }
125
126 if (_expiry)
127 *_expiry = rkey->expiry;
128
129 ret = len;
130 put:
131 up_read(&rkey->sem);
132 if (invalidate)
133 key_invalidate(rkey);
134 key_put(rkey);
135 out:
136 kleave(" = %d", ret);
137 return ret;
138 }
139 EXPORT_SYMBOL(dns_query);
140