From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_2 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 15241C010C2 for ; Tue, 5 Nov 2019 11:31:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E07682190F for ; Tue, 5 Nov 2019 11:31:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730904AbfKELbT (ORCPT ); Tue, 5 Nov 2019 06:31:19 -0500 Received: from mx2.suse.de ([195.135.220.15]:36390 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1730645AbfKELbS (ORCPT ); Tue, 5 Nov 2019 06:31:18 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 7519BB249; Tue, 5 Nov 2019 11:31:16 +0000 (UTC) Message-ID: <1572952516.2921.6.camel@suse.com> Subject: Re: KMSAN: uninit-value in cdc_ncm_set_dgram_size From: Oliver Neukum To: =?ISO-8859-1?Q?Bj=F8rn?= Mork , syzbot Cc: davem@davemloft.net, glider@google.com, linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org, netdev@vger.kernel.org, syzkaller-bugs@googlegroups.com Date: Tue, 05 Nov 2019 12:15:16 +0100 In-Reply-To: <87ftj32v6y.fsf@miraculix.mork.no> References: <00000000000013c4c1059625a655@google.com> <87ftj32v6y.fsf@miraculix.mork.no> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.26.6 Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org Am Montag, den 04.11.2019, 22:22 +0100 schrieb Bjørn Mork: > This looks like a false positive to me. max_datagram_size is two bytes > declared as > > __le16 max_datagram_size; > > and the code leading up to the access on drivers/net/usb/cdc_ncm.c:587 > is: > > /* read current mtu value from device */ > err = usbnet_read_cmd(dev, USB_CDC_GET_MAX_DATAGRAM_SIZE, > USB_TYPE_CLASS | USB_DIR_IN | USB_RECIP_INTERFACE, > 0, iface_no, &max_datagram_size, 2); At this point err can be 1. > if (err < 0) { > dev_dbg(&dev->intf->dev, "GET_MAX_DATAGRAM_SIZE failed\n"); > goto out; > } > > if (le16_to_cpu(max_datagram_size) == ctx->max_datagram_size) > > > > AFAICS, there is no way max_datagram_size can be uninitialized here. > usbnet_read_cmd() either read 2 bytes into it or returned an error, No. usbnet_read_cmd() will return the number of bytes transfered up to the number requested or an error. > causing the access to be skipped. Or am I missing something? Yes. You can get half the MTU. We have a similar class of bugs with MAC addresses. Regards Oliver