linux-kernel - Re: [PATCH v2] mtdchar: prevent unbounded allocation in MEMWRITE ioctl

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Message-Id: <20211203133721.1449880-1-miquel.raynal@bootlin.com>
Date:   Fri,  3 Dec 2021 14:37:20 +0100
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     Michał Kępień <kernel@...pniu.pl>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>
Cc:     Boris Brezillon <boris.brezillon@...labora.com>,
        linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] mtdchar: prevent unbounded allocation in MEMWRITE ioctl

On Tue, 2021-11-30 at 11:31:49 UTC, =?utf-8?b?TWljaGHFgiBLxJlwaWXFhA==?= wrote:
> In the mtdchar_write_ioctl() function, memdup_user() is called with its
> 'len' parameter set to verbatim values provided by user space via a
> struct mtd_write_req.  Both the 'len' and 'ooblen' fields of that
> structure are 64-bit unsigned integers, which means the MEMWRITE ioctl
> can trigger unbounded kernel memory allocation requests.
> 
> Fix by iterating over the buffers provided by user space in a loop,
> processing at most mtd->erasesize bytes in each iteration.  Adopt some
> checks from mtd_check_oob_ops() to retain backward user space
> compatibility.
> 
> Suggested-by: Boris Brezillon <boris.brezillon@...labora.com>
> Signed-off-by: Michał Kępień <kernel@...pniu.pl>

Applied to https://git.kernel.org/pub/scm/linux/kernel/git/mtd/linux.git mtd/next, thanks.

Miquel