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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id F17C0C433EF for ; Fri, 21 Jan 2022 11:18:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1350161AbiAULSB convert rfc822-to-8bit (ORCPT ); Fri, 21 Jan 2022 06:18:01 -0500 Received: from relay1-d.mail.gandi.net ([217.70.183.193]:50611 "EHLO relay1-d.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231467AbiAULSB (ORCPT ); Fri, 21 Jan 2022 06:18:01 -0500 Received: (Authenticated sender: miquel.raynal@bootlin.com) by mail.gandi.net (Postfix) with ESMTPSA id 3595A240002; Fri, 21 Jan 2022 11:17:49 +0000 (UTC) Date: Fri, 21 Jan 2022 12:17:48 +0100 From: Miquel Raynal To: Dan Carpenter Cc: Joern Engel , yangerkun , Richard Weinberger , Vignesh Raghavendra , linux-mtd@lists.infradead.org, kernel-janitors@vger.kernel.org Subject: Re: [PATCH] mtd: phram: Prevent divide by zero bug in phram_setup() Message-ID: <20220121121748.24e98015@xps13> In-Reply-To: <20220121053836.GA27293@kili> References: <20220121053836.GA27293@kili> Organization: Bootlin X-Mailer: Claws Mail 3.17.7 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Precedence: bulk List-ID: X-Mailing-List: kernel-janitors@vger.kernel.org Hi Dan, dan.carpenter@oracle.com wrote on Fri, 21 Jan 2022 08:38:36 +0300: > The problem is that "erasesize" is a uint32_t type so it might be Don't you mean uint64_t here? Otherwise I don't get the sentence. > non-zero but the truncated "(uint32_t)erasesize" value *is* zero. That s/*is*/*can* be/ ? (again, if my understanding is correct). > would lead to the divide by zero bug. > > Avoid the bug by delaying the divide until after we have validated > that "erasesize" is reasonable. I don't really get the fix. If "erasesize" is big enough, then (uint32_t)erasesize can however be zero. But checking if erasesize is zero beforehands does not fix the situation. Or am I missing something? > Fixes: dc2b3e5cbc80 ("mtd: phram: use div_u64_rem to stop overwrite len in phram_setup") > Signed-off-by: Dan Carpenter > --- > drivers/mtd/devices/phram.c | 12 ++++++++---- > 1 file changed, 8 insertions(+), 4 deletions(-) > > diff --git a/drivers/mtd/devices/phram.c b/drivers/mtd/devices/phram.c > index 6ed6c51fac69..d503821a3e60 100644 > --- a/drivers/mtd/devices/phram.c > +++ b/drivers/mtd/devices/phram.c > @@ -264,16 +264,20 @@ static int phram_setup(const char *val) > } > } > > - if (erasesize) > - div_u64_rem(len, (uint32_t)erasesize, &rem); > - > if (len == 0 || erasesize == 0 || erasesize > len > - || erasesize > UINT_MAX || rem) { > + || erasesize > UINT_MAX) { > parse_err("illegal erasesize or len\n"); > ret = -EINVAL; > goto error; > } > > + div_u64_rem(len, (uint32_t)erasesize, &rem); > + if (rem) { > + parse_err("len is not multiple of erasesize\n"); > + ret = -EINVAL; > + goto error; > + } > + > ret = register_device(name, start, len, (uint32_t)erasesize); > if (ret) > goto error; Thanks, Miquèl