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=-6.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=unavailable 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 20C8EC34022 for ; Thu, 27 Feb 2020 14:02:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E6A8F20578 for ; Thu, 27 Feb 2020 14:02:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1582812174; bh=xagn8kmwgvViA4wMu5F0KPD03kbdfnDbrYabCaPa2J8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=BFTS6jlA8QIh2viasthjEcQYLBjvPflxms6IJHoGcidm5txsrucIIwOA7XuXlgPOM FF7YH3wUJ0EMIEud4Kuebubm4puNtoV1qWcKB30LrBP8qOxNd7c5iYfTsjRBX76dIq RDz1uLHZJHFXkZg5MLeuX/S96KqBhkpFf342jLXM= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1733223AbgB0OCx (ORCPT ); Thu, 27 Feb 2020 09:02:53 -0500 Received: from mail.kernel.org ([198.145.29.99]:37710 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1733202AbgB0OCu (ORCPT ); Thu, 27 Feb 2020 09:02:50 -0500 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 28C0E246B6; Thu, 27 Feb 2020 14:02:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1582812169; bh=xagn8kmwgvViA4wMu5F0KPD03kbdfnDbrYabCaPa2J8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=kcJspthNseOyI/+ond4D4HlPSp7bJ2/dU9qrIr6+4gJIFD0fRoK9ru1gXYVdQU5fu 4OdMeSXBvSosB7uAwshEWrURbsUdG2+s0rRMS3Kyp5/brzr6AZv9CwOQl3y01fSSOz 4ZLYGAglMuCqKIUK3Ouy043a6C7OKXw3LdVBpHgw= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Jordy Zomer , Willy Tarreau , Dan Carpenter , Linus Torvalds Subject: [PATCH 4.19 12/97] floppy: check FDC index for errors before assigning it Date: Thu, 27 Feb 2020 14:36:20 +0100 Message-Id: <20200227132216.601985562@linuxfoundation.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20200227132214.553656188@linuxfoundation.org> References: <20200227132214.553656188@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Linus Torvalds commit 2e90ca68b0d2f5548804f22f0dd61145516171e3 upstream. Jordy Zomer reported a KASAN out-of-bounds read in the floppy driver in wait_til_ready(). Which on the face of it can't happen, since as Willy Tarreau points out, the function does no particular memory access. Except through the FDCS macro, which just indexes a static allocation through teh current fdc, which is always checked against N_FDC. Except the checking happens after we've already assigned the value. The floppy driver is a disgrace (a lot of it going back to my original horrd "design"), and has no real maintainer. Nobody has the hardware, and nobody really cares. But it still gets used in virtual environment because it's one of those things that everybody supports. The whole thing should be re-written, or at least parts of it should be seriously cleaned up. The 'current fdc' index, which is used by the FDCS macro, and which is often shadowed by a local 'fdc' variable, is a prime example of how not to write code. But because nobody has the hardware or the motivation, let's just fix up the immediate problem with a nasty band-aid: test the fdc index before actually assigning it to the static 'fdc' variable. Reported-by: Jordy Zomer Cc: Willy Tarreau Cc: Dan Carpenter Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- drivers/block/floppy.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) --- a/drivers/block/floppy.c +++ b/drivers/block/floppy.c @@ -852,14 +852,17 @@ static void reset_fdc_info(int mode) /* selects the fdc and drive, and enables the fdc's input/dma. */ static void set_fdc(int drive) { + unsigned int new_fdc = fdc; + if (drive >= 0 && drive < N_DRIVE) { - fdc = FDC(drive); + new_fdc = FDC(drive); current_drive = drive; } - if (fdc != 1 && fdc != 0) { + if (new_fdc >= N_FDC) { pr_info("bad fdc value\n"); return; } + fdc = new_fdc; set_dor(fdc, ~0, 8); #if N_FDC > 1 set_dor(1 - fdc, ~8, 0);