linux-kernel - Re: [PATCH] tty: vt: add a bounds checking in vt_do_kdgkb

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Date:   Thu, 8 Sep 2022 10:10:12 +0200
From:   Jiri Slaby <jirislaby@...nel.org>
To:     Hangyu Hua <hbh25y@...il.com>, gregkh@...uxfoundation.org,
        changlianzhi@...ontech.com, dmitry.torokhov@...il.com
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tty: vt: add a bounds checking in vt_do_kdgkb_ioctl()

On 08. 09. 22, 9:54, Hangyu Hua wrote:
> As array_index_nospec's comments indicate，a bounds checking need to add
> before calling array_index_nospec.
> 
> Signed-off-by: Hangyu Hua <hbh25y@...il.com>
> ---
>   drivers/tty/vt/keyboard.c | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/tty/vt/keyboard.c b/drivers/tty/vt/keyboard.c
> index be8313cdbac3..b9845455df79 100644
> --- a/drivers/tty/vt/keyboard.c
> +++ b/drivers/tty/vt/keyboard.c
> @@ -2067,6 +2067,9 @@ int vt_do_kdgkb_ioctl(int cmd, struct kbsentry __user *user_kdgkb, int perm)
>   	if (get_user(kb_func, &user_kdgkb->kb_func))
>   		return -EFAULT;
>   
> +	if (kb_func >= MAX_NR_FUNC)

kb_func is unsigned char and MAX_NR_FUNC is 256. So this should be 
eliminated by the compiler anyway.

But the check might be a good idea if we ever decide to support more 
keys. But will/can we? I am not so sure, so adding it right now is kind 
of superfluous. In any way we'd need to introduce a completely different 
iterface/ioctls.

> +		return -EFAULT;

EINVAL would be more appropriate, IMO.

> +
>   	kb_func = array_index_nospec(kb_func, MAX_NR_FUNC);
>   
>   	switch (cmd) {

thanks,
-- 
js
suse labs