5 files changed, 536 insertions, 0 deletions

diff --git a/net/dns_resolver/Kconfig b/net/dns_resolver/Kconfig
new file mode 100644
index 000000000000..50d49f7e0472
--- /dev/null
+++ b/net/dns_resolver/Kconfig
@@ -0,0 +1,27 @@
+#
+# Configuration for DNS Resolver
+#
+config DNS_RESOLVER
+        tristate "DNS Resolver support"
+        depends on NET && KEYS
+        help
+          Saying Y here will include support for the DNS Resolver key type
+          which can be used to make upcalls to perform DNS lookups in
+          userspace.
+
+          DNS Resolver is used to query DNS server for information.  Examples
+          being resolving a UNC hostname element to an IP address for CIFS or
+          performing a DNS query for AFSDB records so that AFS can locate a
+          cell's volume location database servers.
+
+          DNS Resolver is used by the CIFS and AFS modules, and would support
+          SMB2 later.  DNS Resolver is supported by the userspace upcall
+          helper "/sbin/dns.resolver" via /etc/request-key.conf.
+
+          See <file:Documentation/networking/dns_resolver.txt> for further
+          information.
+
+          To compile this as a module, choose M here: the module will be called
+          dnsresolver.
+
+          If unsure, say N.
diff --git a/net/dns_resolver/Makefile b/net/dns_resolver/Makefile
new file mode 100644
index 000000000000..c0ef4e71dc49
--- /dev/null
+++ b/net/dns_resolver/Makefile
@@ -0,0 +1,7 @@
+#
+# Makefile for the Linux DNS Resolver.
+#
+
+obj-$(CONFIG_DNS_RESOLVER) += dns_resolver.o
+
+dns_resolver-objs :=  dns_key.o dns_query.o
diff --git a/net/dns_resolver/dns_key.c b/net/dns_resolver/dns_key.c
new file mode 100644
index 000000000000..739435a6af39
--- /dev/null
+++ b/net/dns_resolver/dns_key.c
@@ -0,0 +1,293 @@
+/* Key type used to cache DNS lookups made by the kernel
+ *
+ * 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)
+ *
+ *   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/moduleparam.h>
+#include <linux/slab.h>
+#include <linux/string.h>
+#include <linux/kernel.h>
+#include <linux/keyctl.h>
+#include <linux/err.h>
+#include <linux/seq_file.h>
+#include <keys/dns_resolver-type.h>
+#include <keys/user-type.h>
+#include "internal.h"
+
+MODULE_DESCRIPTION("DNS Resolver");
+MODULE_AUTHOR("Wang Lei");
+MODULE_LICENSE("GPL");
+
+unsigned dns_resolver_debug;
+module_param_named(debug, dns_resolver_debug, uint, S_IWUSR | S_IRUGO);
+MODULE_PARM_DESC(debug, "DNS Resolver debugging mask");
+
+const struct cred *dns_resolver_cache;
+
+#define DNS_ERRORNO_OPTION      "dnserror"
+
+/*
+ * Instantiate a user defined key for dns_resolver.
+ *
+ * The data must be a NUL-terminated string, with the NUL char accounted in
+ * datalen.
+ *
+ * If the data contains a '#' characters, then we take the clause after each
+ * one to be an option of the form 'key=value'.  The actual data of interest is
+ * the string leading up to the first '#'.  For instance:
+ *
+ *        "ip1,ip2,...#foo=bar"
+ */
+static int
+dns_resolver_instantiate(struct key *key, const void *_data, size_t datalen)
+{
+        struct user_key_payload *upayload;
+        unsigned long derrno;
+        int ret;
+        size_t result_len = 0;
+        const char *data = _data, *end, *opt;
+
+        kenter("%%%d,%s,'%s',%zu",
+               key->serial, key->description, data, datalen);
+
+        if (datalen <= 1 || !data || data[datalen - 1] != '\0')
+                return -EINVAL;
+        datalen--;
+
+        /* deal with any options embedded in the data */
+        end = data + datalen;
+        opt = memchr(data, '#', datalen);
+        if (!opt) {
+                /* no options: the entire data is the result */
+                kdebug("no options");
+                result_len = datalen;
+        } else {
+                const char *next_opt;
+
+                result_len = opt - data;
+                opt++;
+                kdebug("options: '%s'", opt);
+                do {
+                        const char *eq;
+                        int opt_len, opt_nlen, opt_vlen, tmp;
+
+                        next_opt = memchr(opt, '#', end - opt) ?: end;
+                        opt_len = next_opt - opt;
+                        if (!opt_len) {
+                                printk(KERN_WARNING
+                                       "Empty option to dns_resolver key %d\n",
+                                       key->serial);
+                                return -EINVAL;
+                        }
+
+                        eq = memchr(opt, '=', opt_len) ?: end;
+                        opt_nlen = eq - opt;
+                        eq++;
+                        opt_vlen = next_opt - eq; /* will be -1 if no value */
+
+                        tmp = opt_vlen >= 0 ? opt_vlen : 0;
+                        kdebug("option '%*.*s' val '%*.*s'",
+                               opt_nlen, opt_nlen, opt, tmp, tmp, eq);
+
+                        /* see if it's an error number representing a DNS error
+                         * that's to be recorded as the result in this key */
+                        if (opt_nlen == sizeof(DNS_ERRORNO_OPTION) - 1 &&
+                            memcmp(opt, DNS_ERRORNO_OPTION, opt_nlen) == 0) {
+                                kdebug("dns error number option");
+                                if (opt_vlen <= 0)
+                                        goto bad_option_value;
+
+                                ret = strict_strtoul(eq, 10, &derrno);
+                                if (ret < 0)
+                                        goto bad_option_value;
+
+                                if (derrno < 1 || derrno > 511)
+                                        goto bad_option_value;
+
+                                kdebug("dns error no. = %lu", derrno);
+                                key->type_data.x[0] = -derrno;
+                                continue;
+                        }
+
+                bad_option_value:
+                        printk(KERN_WARNING
+                               "Option '%*.*s' to dns_resolver key %d:"
+                               " bad/missing value\n",
+                               opt_nlen, opt_nlen, opt, key->serial);
+                        return -EINVAL;
+                } while (opt = next_opt + 1, opt < end);
+        }
+
+        /* don't cache the result if we're caching an error saying there's no
+         * result */
+        if (key->type_data.x[0]) {
+                kleave(" = 0 [h_error %ld]", key->type_data.x[0]);
+                return 0;
+        }
+
+        kdebug("store result");
+        ret = key_payload_reserve(key, result_len);
+        if (ret < 0)
+                return -EINVAL;
+
+        upayload = kmalloc(sizeof(*upayload) + result_len + 1, GFP_KERNEL);
+        if (!upayload) {
+                kleave(" = -ENOMEM");
+                return -ENOMEM;
+        }
+
+        upayload->datalen = result_len;
+        memcpy(upayload->data, data, result_len);
+        upayload->data[result_len] = '\0';
+        rcu_assign_pointer(key->payload.data, upayload);
+
+        kleave(" = 0");
+        return 0;
+}
+
+/*
+ * The description is of the form "[<type>:]<domain_name>"
+ *
+ * The domain name may be a simple name or an absolute domain name (which
+ * should end with a period).  The domain name is case-independent.
+ */
+static int
+dns_resolver_match(const struct key *key, const void *description)
+{
+        int slen, dlen, ret = 0;
+        const char *src = key->description, *dsp = description;
+
+        kenter("%s,%s", src, dsp);
+
+        if (!src || !dsp)
+                goto no_match;
+
+        if (strcasecmp(src, dsp) == 0)
+                goto matched;
+
+        slen = strlen(src);
+        dlen = strlen(dsp);
+        if (slen <= 0 || dlen <= 0)
+                goto no_match;
+        if (src[slen - 1] == '.')
+                slen--;
+        if (dsp[dlen - 1] == '.')
+                dlen--;
+        if (slen != dlen || strncasecmp(src, dsp, slen) != 0)
+                goto no_match;
+
+matched:
+        ret = 1;
+no_match:
+        kleave(" = %d", ret);
+        return ret;
+}
+
+/*
+ * Describe a DNS key
+ */
+static void dns_resolver_describe(const struct key *key, struct seq_file *m)
+{
+        int err = key->type_data.x[0];
+
+        seq_puts(m, key->description);
+        if (err)
+                seq_printf(m, ": %d", err);
+        else
+                seq_printf(m, ": %u", key->datalen);
+}
+
+struct key_type key_type_dns_resolver = {
+        .name           = "dns_resolver",
+        .instantiate    = dns_resolver_instantiate,
+        .match          = dns_resolver_match,
+        .revoke         = user_revoke,
+        .destroy        = user_destroy,
+        .describe       = dns_resolver_describe,
+        .read           = user_read,
+};
+
+static int __init init_dns_resolver(void)
+{
+        struct cred *cred;
+        struct key *keyring;
+        int ret;
+
+        printk(KERN_NOTICE "Registering the %s key type\n",
+               key_type_dns_resolver.name);
+
+        /* create an override credential set with a special thread keyring in
+         * which DNS requests are cached
+         *
+         * this is used to prevent malicious redirections from being installed
+         * with add_key().
+         */
+        cred = prepare_kernel_cred(NULL);
+        if (!cred)
+                return -ENOMEM;
+
+        keyring = key_alloc(&key_type_keyring, ".dns_resolver", 0, 0, cred,
+                            (KEY_POS_ALL & ~KEY_POS_SETATTR) |
+                            KEY_USR_VIEW | KEY_USR_READ,
+                            KEY_ALLOC_NOT_IN_QUOTA);
+        if (IS_ERR(keyring)) {
+                ret = PTR_ERR(keyring);
+                goto failed_put_cred;
+        }
+
+        ret = key_instantiate_and_link(keyring, NULL, 0, NULL, NULL);
+        if (ret < 0)
+                goto failed_put_key;
+
+        ret = register_key_type(&key_type_dns_resolver);
+        if (ret < 0)
+                goto failed_put_key;
+
+        /* instruct request_key() to use this special keyring as a cache for
+         * the results it looks up */
+        cred->thread_keyring = keyring;
+        cred->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING;
+        dns_resolver_cache = cred;
+
+        kdebug("DNS resolver keyring: %d\n", key_serial(keyring));
+        return 0;
+
+failed_put_key:
+        key_put(keyring);
+failed_put_cred:
+        put_cred(cred);
+        return ret;
+}
+
+static void __exit exit_dns_resolver(void)
+{
+        key_revoke(dns_resolver_cache->thread_keyring);
+        unregister_key_type(&key_type_dns_resolver);
+        put_cred(dns_resolver_cache);
+        printk(KERN_NOTICE "Unregistered %s key type\n",
+               key_type_dns_resolver.name);
+}
+
+module_init(init_dns_resolver)
+module_exit(exit_dns_resolver)
+MODULE_LICENSE("GPL");
diff --git a/net/dns_resolver/dns_query.c b/net/dns_resolver/dns_query.c
new file mode 100644
index 000000000000..c32be292c7e3
--- /dev/null
+++ b/net/dns_resolver/dns_query.c
@@ -0,0 +1,165 @@
+/* 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 <linux/err.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;
+
+        /* If the DNS server gave an error, return that to the caller */
+        ret = rkey->type_data.x[0];
+        if (ret)
+                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);
diff --git a/net/dns_resolver/internal.h b/net/dns_resolver/internal.h
new file mode 100644
index 000000000000..189ca9e9b785
--- /dev/null
+++ b/net/dns_resolver/internal.h
@@ -0,0 +1,44 @@
+/*
+ *   Copyright (c) 2010 Wang Lei
+ *   Author(s): Wang Lei (wang840925@gmail.com). All Rights Reserved.
+ *
+ *   Internal DNS Rsolver stuff
+ *
+ *   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/compiler.h>
+#include <linux/kernel.h>
+#include <linux/sched.h>
+
+/*
+ * dns_key.c
+ */
+extern const struct cred *dns_resolver_cache;
+
+/*
+ * debug tracing
+ */
+extern unsigned dns_resolver_debug;
+
+#define kdebug(FMT, ...)                                \
+do {                                                    \
+        if (unlikely(dns_resolver_debug))               \
+                printk(KERN_DEBUG "[%-6.6s] "FMT"\n",   \
+                       current->comm, ##__VA_ARGS__);   \
+} while (0)
+
+#define kenter(FMT, ...) kdebug("==> %s("FMT")", __func__, ##__VA_ARGS__)
+#define kleave(FMT, ...) kdebug("<== %s()"FMT"", __func__, ##__VA_ARGS__)