[PATCH v2] mtdchar: prevent unbounded allocation in MEMWRITE ioctl

[Miquel Raynal]

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 at collabora.com>
> Signed-off-by: Michał Kępień <kernel at kempniu.pl>

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

Miquel