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Tue, 7 Jun 2022 22:23:12 +0200 (CEST) Received: from lithops.sigma-star.at ([127.0.0.1]) by localhost (lithops.sigma-star.at [127.0.0.1]) (amavisd-new, port 10026) with ESMTP id 7tquQMvYHDkA; Tue, 7 Jun 2022 22:23:12 +0200 (CEST) Received: from lithops.sigma-star.at (lithops.sigma-star.at [195.201.40.130]) by lithops.sigma-star.at (Postfix) with ESMTP id 9CD0D61B8B5A; Tue, 7 Jun 2022 22:23:12 +0200 (CEST) Date: Tue, 7 Jun 2022 22:23:12 +0200 (CEST) From: Richard Weinberger To: =?utf-8?B?TWljaGHFgiBLxJlwaWXFhA==?= Cc: Miquel Raynal , Vignesh Raghavendra , linux-mtd , linux-kernel Message-ID: <1710081060.147491.1654633392520.JavaMail.zimbra@nod.at> In-Reply-To: <20220516070601.11428-2-kernel@kempniu.pl> References: <20220516070601.11428-1-kernel@kempniu.pl> <20220516070601.11428-2-kernel@kempniu.pl> Subject: Re: [PATCH 1/2] mtdchar: prevent integer overflow in a safety check MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT X-Originating-IP: [195.201.40.130] X-Mailer: Zimbra 8.8.12_GA_3807 (ZimbraWebClient - FF97 (Linux)/8.8.12_GA_3809) Thread-Topic: mtdchar: prevent integer overflow in a safety check Thread-Index: JX134mBLLXSr5mg7slOI+t/fmFEWJA== Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org ----- Ursprüngliche Mail ----- > Von: "Michał Kępień" > An: "Miquel Raynal" , "richard" , "Vignesh Raghavendra" > CC: "linux-mtd" , "linux-kernel" > Gesendet: Montag, 16. Mai 2022 09:06:00 > Betreff: [PATCH 1/2] mtdchar: prevent integer overflow in a safety check > Commit 6420ac0af95d ("mtdchar: prevent unbounded allocation in MEMWRITE > ioctl") added a safety check to mtdchar_write_ioctl() which attempts to > ensure that the write request sent by user space does not extend beyond > the MTD device's size. However, that check contains an addition of two > struct mtd_write_req fields, 'start' and 'len', both of which are u64 > variables. The result of that addition can overflow, allowing the > safety check to be bypassed. > > The arguably simplest fix - changing the data types of the relevant > struct mtd_write_req fields - is not feasible as it would break user > space. > > Fix by making mtdchar_write_ioctl() truncate the value provided by user > space in the 'len' field of struct mtd_write_req, so that only the lower > 32 bits of that field are used, preventing the overflow. > > While the 'ooblen' field of struct mtd_write_req is not currently used > in any similarly flawed safety check, also truncate it to 32 bits, for > consistency with the 'len' field and with other MTD routines handling > OOB data. > > Update include/uapi/mtd/mtd-abi.h accordingly. > > Suggested-by: Richard Weinberger > Signed-off-by: Michał Kępień > --- > drivers/mtd/mtdchar.c | 3 +++ > include/uapi/mtd/mtd-abi.h | 4 ++-- > 2 files changed, 5 insertions(+), 2 deletions(-) > > diff --git a/drivers/mtd/mtdchar.c b/drivers/mtd/mtdchar.c > index d0f9c4b0285c..b2700f8467ff 100644 > --- a/drivers/mtd/mtdchar.c > +++ b/drivers/mtd/mtdchar.c > @@ -615,6 +615,9 @@ static int mtdchar_write_ioctl(struct mtd_info *mtd, > if (!usr_oob) > req.ooblen = 0; > > + req.len &= 0xffffffff; > + req.ooblen &= 0xffffffff; > + Yeah, I think it is reasonable to limit write requests to 4GiB. Thanks, //richard