--- fs/cifs/dns_resolve.c
+++ fs/cifs/dns_resolve.c
@@ -23,12 +23,16 @@
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
+#include <linux/keyctl.h>
+#include <linux/key-type.h>
#include <keys/user-type.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
@@ -93,6 +97,7 @@ struct key_type key_type_dns_resolver =
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);
char *name;
@@ -132,8 +137,15 @@ dns_resolve_server_name_to_ip(const char
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 {
@@ -164,4 +176,61 @@ out:
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)
+ 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;
+ return 0;
+
+failed_put_key:
+ key_put(keyring);
+failed_put_cred:
+ put_cred(cred);
+ return ret;
+}
+void __exit 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);
+}
projects / ziggy471-frankenstein-kernel.git / blobdiff