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SubjectRe: [PATCH 3/5] comedi: vmk80xx: fix transfer-buffer overflows
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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@vger.kernel.org # 2.6.31
> Signed-off-by: Johan Hovold <johan@kernel.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@mev.co.uk>

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