linux-kernel - Re: [PATCH 1/1] tcpm: Fix possible buffer overflows in tcpm_queue

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Message-ID: <20201211100939.GJ1594451@kuha.fi.intel.com>
Date:   Fri, 11 Dec 2020 12:09:39 +0200
From:   Heikki Krogerus <heikki.krogerus@...ux.intel.com>
To:     Xiaohui Zhang <ruc_zhangxiaohui@....com>
Cc:     Guenter Roeck <linux@...ck-us.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] tcpm: Fix possible buffer overflows in tcpm_queue_vdm

Hi,

On Wed, Dec 09, 2020 at 11:07:16AM +0800, Xiaohui Zhang wrote:
> From: Zhang Xiaohui <ruc_zhangxiaohui@....com>
> 
> tcpm_queue_vdm() calls memcpy() without checking the destination
> size may trigger a buffer overflower.

Thanks for the patch, but I didn't actually see any place where that
could happen. I think the idea is that the callers make sure the count
does not exceed VDO_MAX_SIZE before calling the function.

> Signed-off-by: Zhang Xiaohui <ruc_zhangxiaohui@....com>
> ---
>  drivers/usb/typec/tcpm/tcpm.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/typec/tcpm/tcpm.c b/drivers/usb/typec/tcpm/tcpm.c
> index 55535c4f6..fcd331f33 100644
> --- a/drivers/usb/typec/tcpm/tcpm.c
> +++ b/drivers/usb/typec/tcpm/tcpm.c
> @@ -1045,7 +1045,7 @@ static void tcpm_queue_vdm(struct tcpm_port *port, const u32 header,
>  
>  	port->vdo_count = cnt + 1;

That should have been fixed as well, no?

>  	port->vdo_data[0] = header;
> -	memcpy(&port->vdo_data[1], data, sizeof(u32) * cnt);
> +	memcpy(&port->vdo_data[1], data, min_t(int, sizeof(u32) * cnt, VDO_MAX_SIZE - 1));
>  	/* Set ready, vdm state machine will actually send */
>  	port->vdm_retries = 0;
>  	port->vdm_state = VDM_STATE_READY;

Unless I'm missing something, I don't think this patch is needed.

thanks,

-- 
heikki