DNS: Separate out CIFS DNS Resolver code
[linux-2.6.git] / fs / cifs / dns_resolve.c
index aa967e7..0eb8702 100644 (file)
@@ -4,6 +4,8 @@
  *   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)
  *
  *   Contains the CIFS DFS upcall routines used for hostname to
  *   IP address translation.
  */
 
 #include <linux/slab.h>
-#include <linux/keyctl.h>
-#include <linux/key-type.h>
-#include <keys/user-type.h>
+#include <linux/dns_resolver.h>
 #include "dns_resolve.h"
 #include "cifsglob.h"
 #include "cifsproto.h"
 #include "cifs_debug.h"
 
-static const struct cred *dns_resolver_cache;
-
-/* Checks if supplied name is IP address
- * returns:
- *             1 - name is IP
- *             0 - name is not IP
- */
-static int
-is_ip(const char *name, int len)
-{
-       struct sockaddr_storage ss;
-
-       return cifs_convert_address((struct sockaddr *)&ss, name, len);
-}
-
-static int
-dns_resolver_instantiate(struct key *key, const void *data,
-               size_t datalen)
-{
-       int rc = 0;
-       char *ip;
-
-       /* make sure this looks like an address */
-       if (!is_ip(data, datalen))
-               return -EINVAL;
-
-       ip = kmalloc(datalen + 1, GFP_KERNEL);
-       if (!ip)
-               return -ENOMEM;
-
-       memcpy(ip, data, datalen);
-       ip[datalen] = '\0';
-
-       key->type_data.x[0] = datalen;
-       key->payload.data = ip;
-
-       return rc;
-}
-
-static void
-dns_resolver_destroy(struct key *key)
-{
-       kfree(key->payload.data);
-}
-
-struct key_type key_type_dns_resolver = {
-       .name        = "dns_resolver",
-       .def_datalen = sizeof(struct in_addr),
-       .describe    = user_describe,
-       .instantiate = dns_resolver_instantiate,
-       .destroy     = dns_resolver_destroy,
-       .match       = user_match,
-};
-
-/* Resolves server name to ip address.
- * input:
- *     unc - server UNC
- * output:
- *     *ip_addr - pointer to server ip, caller responcible for freeing it.
- * return the length of the returned string on success
+/**
+ * dns_resolve_server_name_to_ip - Resolve UNC server name to ip address.
+ * @unc: UNC path specifying the server
+ * @ip_addr: Where to return the IP address.
+ *
+ * The IP address will be returned in string form, and the caller is
+ * responsible for freeing it.
+ *
+ * Returns length of result on success, -ve on error.
  */
 int
 dns_resolve_server_name_to_ip(const char *unc, char **ip_addr)
 {
-       const struct cred *saved_cred;
-       int rc = -EAGAIN;
-       struct key *rkey = ERR_PTR(-EAGAIN);
+       struct sockaddr_storage ss;
+       const char *hostname, *sep;
        char *name;
-       char *data = NULL;
-       int len;
+       int len, rc;
 
        if (!ip_addr || !unc)
                return -EINVAL;
 
-       /* search for server name delimiter */
        len = strlen(unc);
        if (len < 3) {
                cFYI(1, "%s: unc is too short: %s", __func__, unc);
                return -EINVAL;
        }
-       len -= 2;
-       name = memchr(unc+2, '\\', len);
-       if (!name) {
-               cFYI(1, "%s: probably server name is whole unc: %s",
-                                       __func__, unc);
-       } else {
-               len = (name - unc) - 2/* leading // */;
-       }
-
-       name = kmalloc(len+1, GFP_KERNEL);
-       if (!name) {
-               rc = -ENOMEM;
-               return rc;
-       }
-       memcpy(name, unc+2, len);
-       name[len] = 0;
-
-       if (is_ip(name, len)) {
-               cFYI(1, "%s: it is IP, skipping dns upcall: %s",
-                                       __func__, name);
-               data = name;
-               goto skip_upcall;
-       }
 
-       saved_cred = override_creds(dns_resolver_cache);
-       rkey = request_key(&key_type_dns_resolver, name, "");
-       revert_creds(saved_cred);
-       if (!IS_ERR(rkey)) {
-               if (!(rkey->perm & KEY_USR_VIEW)) {
-                       down_read(&rkey->sem);
-                       rkey->perm |= KEY_USR_VIEW;
-                       up_read(&rkey->sem);
-               }
-               len = rkey->type_data.x[0];
-               data = rkey->payload.data;
-       } else {
-               cERROR(1, "%s: unable to resolve: %s", __func__, name);
-               goto out;
-       }
-
-skip_upcall:
-       if (data) {
-               *ip_addr = kmalloc(len + 1, GFP_KERNEL);
-               if (*ip_addr) {
-                       memcpy(*ip_addr, data, len + 1);
-                       if (!IS_ERR(rkey))
-                               cFYI(1, "%s: resolved: %s to %s", __func__,
-                                                       name,
-                                                       *ip_addr
-                                       );
-                       rc = len;
-               } else {
-                       rc = -ENOMEM;
-               }
-               if (!IS_ERR(rkey))
-                       key_put(rkey);
-       }
+       /* Discount leading slashes for cifs */
+       len -= 2;
+       hostname = unc + 2;
 
-out:
-       kfree(name);
+       /* Search for server name delimiter */
+       sep = memchr(hostname, '\\', len);
+       if (sep)
+               len = sep - unc;
+       else
+               cFYI(1, "%s: probably server name is whole unc: %s",
+                    __func__, unc);
+
+       /* Try to interpret hostname as an IPv4 or IPv6 address */
+       rc = cifs_convert_address((struct sockaddr *)&ss, hostname, len);
+       if (rc > 0)
+               goto name_is_IP_address;
+
+       /* Perform the upcall */
+       rc = dns_query(NULL, hostname, len, NULL, ip_addr, NULL);
+       if (rc < 0)
+               cERROR(1, "%s: unable to resolve: %*.*s",
+                      __func__, len, len, hostname);
+       else
+               cFYI(1, "%s: resolved: %*.*s to %s",
+                    __func__, len, len, hostname, *ip_addr);
        return rc;
-}
 
-int __init cifs_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)
+name_is_IP_address:
+       name = kmalloc(len + 1, GFP_KERNEL);
+       if (!name)
                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;
+       memcpy(name, hostname, len);
+       name[len] = 0;
+       cFYI(1, "%s: unc is IP, skipping dns upcall: %s", __func__, name);
+       *ip_addr = name;
        return 0;
-
-failed_put_key:
-       key_put(keyring);
-failed_put_cred:
-       put_cred(cred);
-       return ret;
-}
-
-void cifs_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);
 }