linux-kernel - Re: [PATCH] char: ppdev: fixed a validation issue

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Message-ID: <YYoUYOyyP4EFYTSJ@kroah.com>
Date:   Tue, 9 Nov 2021 07:25:36 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Vihas Mak <makvihas@...il.com>
Cc:     sudipm.mukherjee@...il.com, arnd@...db.de,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] char: ppdev: fixed a validation issue

On Tue, Nov 09, 2021 at 12:28:18AM +0530, Vihas Mak wrote:
> Make sure the mode is a valid IEEE1284 mode.

What is a valid mode?

> Signed-off-by: Vihas Mak <makvihas@...il.com>
> ---
>  drivers/char/ppdev.c | 28 +++++++++++++++++++++++++++-
>  1 file changed, 27 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/char/ppdev.c b/drivers/char/ppdev.c
> index 38b46c7d1737..3b290cbf6c66 100644
> --- a/drivers/char/ppdev.c
> +++ b/drivers/char/ppdev.c
> @@ -333,6 +333,28 @@ static enum ieee1284_phase init_phase(int mode)
>  	return IEEE1284_PH_FWD_IDLE;
>  }
>  
> +/*
> + * Validate the mode and make sure the mode is power of two.
> + *
> + * IEEE1284_MODE_ECPRLE and IEEE1284_MODE_NIBBLE are exception
> + * to this so handle them accordingly.
> + */
> +

Why the extra line?

> +static int pp_validate_mode(int mode)

bool?

> +{
> +	if (mode == IEEE1284_MODE_ECPRLE || mode == IEEE1284_MODE_NIBBLE) {
> +		return 1;
> +	} else if (!(mode & (mode - 1)) &&
> +		   (mode & (IEEE1284_MODE_BYTE | IEEE1284_MODE_COMPAT |
> +			    IEEE1284_MODE_BECP | IEEE1284_MODE_ECP |
> +			    IEEE1284_MODE_ECPSWE | IEEE1284_MODE_EPP |
> +			    IEEE1284_MODE_EPPSL | IEEE1284_MODE_COMPAT |
> +			    IEEE1284_MODE_EPPSWE))) {
> +		return 1;
> +	}
> +	return 0;
> +}

How did you test this?  And why is this needed now?  What hardware was
working that is now not going to work with this driver?

thanks,

greg k-h