1 files changed, 159 insertions, 0 deletions

diff --git a/net/dns_resolver/dns_query.c b/net/dns_resolver/dns_query.c
new file mode 100644
index 000000000000..6c0cf31ea00d
--- /dev/null
+++ b/net/dns_resolver/dns_query.c
@@ -0,0 +1,159 @@
+/* Upcall routine, designed to work as a key type and working through
+ * /sbin/request-key to contact userspace when handling DNS queries.
+ *
+ * See Documentation/networking/dns_resolver.txt
+ *
+ *   Copyright (c) 2007 Igor Mammedov
+ *   Author(s): Igor Mammedov (niallain@gmail.com)
+ *              Steve French (sfrench@us.ibm.com)
+ *              Wang Lei (wang840925@gmail.com)
+ *              David Howells (dhowells@redhat.com)
+ *
+ *   The upcall wrapper used to make an arbitrary DNS query.
+ *
+ *   This function requires the appropriate userspace tool dns.upcall to be
+ *   installed and something like the following lines should be added to the
+ *   /etc/request-key.conf file:
+ *
+ *      create dns_resolver * * /sbin/dns.upcall %k
+ *
+ *   For example to use this module to query AFSDB RR:
+ *
+ *      create dns_resolver afsdb:* * /sbin/dns.afsdb %k
+ *
+ *   This library is free software; you can redistribute it and/or modify
+ *   it under the terms of the GNU Lesser General Public License as published
+ *   by the Free Software Foundation; either version 2.1 of the License, or
+ *   (at your option) any later version.
+ *
+ *   This library is distributed in the hope that it will be useful,
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See
+ *   the GNU Lesser General Public License for more details.
+ *
+ *   You should have received a copy of the GNU Lesser General Public License
+ *   along with this library; if not, write to the Free Software
+ *   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+ */
+
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/dns_resolver.h>
+#include <keys/dns_resolver-type.h>
+#include <keys/user-type.h>
+
+#include "internal.h"
+
+/*
+ * dns_query - Query the DNS
+ * @type: Query type (or NULL for straight host->IP lookup)
+ * @name: Name to look up
+ * @namelen: Length of name
+ * @options: Request options (or NULL if no options)
+ * @_result: Where to place the returned data.
+ * @_expiry: Where to store the result expiry time (or NULL)
+ *
+ * The data will be returned in the pointer at *result, and the caller is
+ * responsible for freeing it.
+ *
+ * The description should be of the form "[<query_type>:]<domain_name>", and
+ * the options need to be appropriate for the query type requested.  If no
+ * query_type is given, then the query is a straight hostname to IP address
+ * lookup.
+ *
+ * The DNS resolution lookup is performed by upcalling to userspace by way of
+ * requesting a key of type dns_resolver.
+ *
+ * Returns the size of the result on success, -ve error code otherwise.
+ */
+int dns_query(const char *type, const char *name, size_t namelen,
+              const char *options, char **_result, time_t *_expiry)
+{
+        struct key *rkey;
+        struct user_key_payload *upayload;
+        const struct cred *saved_cred;
+        size_t typelen, desclen;
+        char *desc, *cp;
+        int ret, len;
+
+        kenter("%s,%*.*s,%zu,%s",
+               type, (int)namelen, (int)namelen, name, namelen, options);
+
+        if (!name || namelen == 0 || !_result)
+                return -EINVAL;
+
+        /* construct the query key description as "[<type>:]<name>" */
+        typelen = 0;
+        desclen = 0;
+        if (type) {
+                typelen = strlen(type);
+                if (typelen < 1)
+                        return -EINVAL;
+                desclen += typelen + 1;
+        }
+
+        if (!namelen)
+                namelen = strlen(name);
+        if (namelen < 3)
+                return -EINVAL;
+        desclen += namelen + 1;
+
+        desc = kmalloc(desclen, GFP_KERNEL);
+        if (!desc)
+                return -ENOMEM;
+
+        cp = desc;
+        if (type) {
+                memcpy(cp, type, typelen);
+                cp += typelen;
+                *cp++ = ':';
+        }
+        memcpy(cp, name, namelen);
+        cp += namelen;
+        *cp = '\0';
+
+        if (!options)
+                options = "";
+        kdebug("call request_key(,%s,%s)", desc, options);
+
+        /* make the upcall, using special credentials to prevent the use of
+         * add_key() to preinstall malicious redirections
+         */
+        saved_cred = override_creds(dns_resolver_cache);
+        rkey = request_key(&key_type_dns_resolver, desc, options);
+        revert_creds(saved_cred);
+        kfree(desc);
+        if (IS_ERR(rkey)) {
+                ret = PTR_ERR(rkey);
+                goto out;
+        }
+
+        down_read(&rkey->sem);
+        rkey->perm |= KEY_USR_VIEW;
+
+        ret = key_validate(rkey);
+        if (ret < 0)
+                goto put;
+
+        upayload = rcu_dereference_protected(rkey->payload.data,
+                                             lockdep_is_held(&rkey->sem));
+        len = upayload->datalen;
+
+        ret = -ENOMEM;
+        *_result = kmalloc(len + 1, GFP_KERNEL);
+        if (!*_result)
+                goto put;
+
+        memcpy(*_result, upayload->data, len + 1);
+        if (_expiry)
+                *_expiry = rkey->expiry;
+
+        ret = len;
+put:
+        up_read(&rkey->sem);
+        key_put(rkey);
+out:
+        kleave(" = %d", ret);
+        return ret;
+}
+EXPORT_SYMBOL(dns_query);