KEYS: special dot prefixed keyring name bug fix

commit a4e3b8d7 upstream.

Dot prefixed keyring names are supposed to be reserved for the
kernel, but add_key() calls key_get_type_from_user(), which
incorrectly verifies the 'type' field, not the 'description' field.
This patch verifies the 'description' field isn't dot prefixed,
when creating a new keyring, and removes the dot prefix test in
key_get_type_from_user().

Changelog v6:
- whitespace and other cleanup

Changelog v5:
- Only prevent userspace from creating a dot prefixed keyring, not
  regular keys  - Dmitry
Reported-by: Dmitry Kasatkin <d.kasatkin@samsung.com>
Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
Acked-by: David Howells <dhowells@redhat.com>
[bwh: Backported to 3.2: adjust context, indentation]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

security/keys/keyctl.c

@@ -35,8 +35,6 @@ static int key_get_type_from_user(char *type,
 		return ret;
 	if (ret == 0 || ret >= len)
 		return -EINVAL;
-	if (type[0] == '.')
-		return -EPERM;
 	type[len - 1] = '\0';
 	return 0;
 }
@@ -75,6 +73,10 @@ SYSCALL_DEFINE5(add_key, const char __user *, _type,
 	if (IS_ERR(description)) {
 		ret = PTR_ERR(description);
 		goto error;
+	} else if ((description[0] == '.') &&
+		   (strncmp(type, "keyring", 7) == 0)) {
+		ret = -EPERM;
+		goto error2;
 	}
 
 	/* pull the payload in if one was supplied */