From patchwork Tue Aug 27 10:34:36 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Oliver Neukum X-Patchwork-Id: 11116619 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 574981395 for ; Tue, 27 Aug 2019 10:49:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 346FA217F5 for ; Tue, 27 Aug 2019 10:49:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726059AbfH0Kta (ORCPT ); Tue, 27 Aug 2019 06:49:30 -0400 Received: from mx2.suse.de ([195.135.220.15]:55408 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725793AbfH0Kta (ORCPT ); Tue, 27 Aug 2019 06:49:30 -0400 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 4640CACC4; Tue, 27 Aug 2019 10:49:28 +0000 (UTC) From: Oliver Neukum To: gregKH@linuxfoundation.org, linux-usb@vger.kernel.org Cc: Oliver Neukum Subject: [PATCH] USB: cdc-wdm: fix race between write and disconnect due to flag abuse Date: Tue, 27 Aug 2019 12:34:36 +0200 Message-Id: <20190827103436.21143-1-oneukum@suse.com> X-Mailer: git-send-email 2.16.4 Sender: linux-usb-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.org In case of a disconnect an ongoing flush() has to be made fail. Nevertheless we cannot be sure that any pending URB has already finished, so although they will never succeed, they still must not be touched. The clean solution for this is to check for WDM_IN_USE and WDM_DISCONNECTED in flush(). There is no point in ever clearing WDM_IN_USE, as no further writes make sense. The issue is as old as the driver. Fixes: afba937e540c9 ("USB: CDC WDM driver") Reported-by: syzbot+d232cca6ec42c2edb3fc@syzkaller.appspotmail.com Signed-off-by: Oliver Neukum --- drivers/usb/class/cdc-wdm.c | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-) diff --git a/drivers/usb/class/cdc-wdm.c b/drivers/usb/class/cdc-wdm.c index 1656f5155ab8..f9f7c8a5e091 100644 --- a/drivers/usb/class/cdc-wdm.c +++ b/drivers/usb/class/cdc-wdm.c @@ -588,10 +588,20 @@ static int wdm_flush(struct file *file, fl_owner_t id) { struct wdm_device *desc = file->private_data; - wait_event(desc->wait, !test_bit(WDM_IN_USE, &desc->flags)); + wait_event(desc->wait, + /* + * needs both flags. We cannot do with one + * because resetting it would cause a race + * with write() yet we need to signal + * a disconnect + */ + !test_bit(WDM_IN_USE, &desc->flags) || + test_bit(WDM_DISCONNECTING, &desc->flags)); /* cannot dereference desc->intf if WDM_DISCONNECTING */ - if (desc->werr < 0 && !test_bit(WDM_DISCONNECTING, &desc->flags)) + if (test_bit(WDM_DISCONNECTING, &desc->flags)) + return -ENODEV; + if (desc->werr < 0) dev_err(&desc->intf->dev, "Error in flush path: %d\n", desc->werr); @@ -975,8 +985,6 @@ static void wdm_disconnect(struct usb_interface *intf) spin_lock_irqsave(&desc->iuspin, flags); set_bit(WDM_DISCONNECTING, &desc->flags); set_bit(WDM_READ, &desc->flags); - /* to terminate pending flushes */ - clear_bit(WDM_IN_USE, &desc->flags); spin_unlock_irqrestore(&desc->iuspin, flags); wake_up_all(&desc->wait); mutex_lock(&desc->rlock);