linux-kernel - Re: [PATCH 3/5] comedi: vmk80xx: fix transfer-buffer overflows

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Date:   Tue, 26 Oct 2021 15:32:28 +0100
From:   Ian Abbott <abbotti@....co.uk>
To:     Johan Hovold <johan@...nel.org>,
        H Hartley Sweeten <hsweeten@...ionengravers.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH 3/5] comedi: vmk80xx: fix transfer-buffer overflows

On 25/10/2021 12:45, Johan Hovold wrote:
> The driver uses endpoint-sized USB transfer buffers but up until
> recently had no sanity checks on the sizes.
> 
> Commit e1f13c879a7c ("staging: comedi: check validity of wMaxPacketSize
> of usb endpoints found") inadvertently fixed NULL-pointer dereferences
> when accessing the transfer buffers in case a malicious device has a
> zero wMaxPacketSize.
> 
> Make sure to allocate buffers large enough to handle also the other
> accesses that are done without a size check (e.g. byte 18 in
> vmk80xx_cnt_insn_read() for the VMK8061_MODEL) to avoid writing beyond
> the buffers, for example, when doing descriptor fuzzing.
> 
> The original driver was for a low-speed device with 8-byte buffers.
> Support was later added for a device that uses bulk transfers and is
> presumably a full-speed device with a maximum 64-byte wMaxPacketSize.
> 
> Fixes: 985cafccbf9b ("Staging: Comedi: vmk80xx: Add k8061 support")
> Cc: stable@...r.kernel.org      # 2.6.31
> Signed-off-by: Johan Hovold <johan@...nel.org>
> ---
>   drivers/comedi/drivers/vmk80xx.c | 6 ++++--
>   1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/comedi/drivers/vmk80xx.c b/drivers/comedi/drivers/vmk80xx.c
> index 9f920819cd74..f2c1572d0cd7 100644
> --- a/drivers/comedi/drivers/vmk80xx.c
> +++ b/drivers/comedi/drivers/vmk80xx.c
> @@ -90,6 +90,8 @@ enum {
>   #define IC3_VERSION		BIT(0)
>   #define IC6_VERSION		BIT(1)
>   
> +#define MIN_BUF_SIZE		64
> +
>   enum vmk80xx_model {
>   	VMK8055_MODEL,
>   	VMK8061_MODEL
> @@ -678,12 +680,12 @@ static int vmk80xx_alloc_usb_buffers(struct comedi_device *dev)
>   	struct vmk80xx_private *devpriv = dev->private;
>   	size_t size;
>   
> -	size = usb_endpoint_maxp(devpriv->ep_rx);
> +	size = max(usb_endpoint_maxp(devpriv->ep_rx), MIN_BUF_SIZE);
>   	devpriv->usb_rx_buf = kzalloc(size, GFP_KERNEL);
>   	if (!devpriv->usb_rx_buf)
>   		return -ENOMEM;
>   
> -	size = usb_endpoint_maxp(devpriv->ep_tx);
> +	size = max(usb_endpoint_maxp(devpriv->ep_rx), MIN_BUF_SIZE);
>   	devpriv->usb_tx_buf = kzalloc(size, GFP_KERNEL);
>   	if (!devpriv->usb_tx_buf)
>   		return -ENOMEM;
> 

Looks good, thanks!

Reviewed-by: Ian Abbott <abbotti@....co.uk>

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