linux-kernel - Re: [PATCH] floppy: Avoid memory access beyond the array bounds in setup_rw

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Date:   Fri, 26 Oct 2018 08:21:19 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     Kyungtae Kim <kt0755@...il.com>, Jens Axboe <axboe@...nel.dk>
Cc:     jikos@...nel.org, Byoungyoung Lee <lifeasageek@...il.com>,
        DaeRyong Jeong <threeearcat@...il.com>,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] floppy: Avoid memory access beyond the array bounds in
 setup_rw_floppy()

On Fri, 2018-10-26 at 10:39 -0400, Kyungtae Kim wrote:
> setup_rw_floppy() writes some bytes of array cmd to the floppy disk
> controller, depending on cmd_count.
> Although the size of array cmd is fixed like 16, cmd_count can be much
> larger through raw_cmd_ioctl().
> Noticed there is no bound check for this, thereby leading to invalid
> memory access.

Against which kernel tree did you prepare this patch? Just above the code
you want to insert I found the following:

	if (ptr->cmd_count > 33) ...

Why does that statement compare cmd_count with 33? Is that comparison correct
or not? Anyway, I don't think it makes sense first to compare cmd_count against
33 and next to compare it against 16 ...

> +       if (ptr->cmd_count > ARRAY_SIZE(ptr->cmd))
> +               return -EINVAL;

This comparison looks suspicious to me. Almost every comparison of the type
"... > ARRAY_SIZE()" I have seen so far was wrong and should be changed into
"... >= ARRAY_SIZE()" instead.

Bart.