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SubjectRe: [PATCH 1/5] comedi: ni_usb6501: fix NULL-deref in command paths
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On 25/10/2021 12:45, Johan Hovold wrote:
> The driver uses endpoint-sized USB transfer buffers but had no sanity
> checks on the sizes. This can lead to zero-size-pointer dereferences or
> overflowed transfer buffers in ni6501_port_command() and
> ni6501_counter_command() if a (malicious) device has smaller max-packet
> sizes than expected (or when doing descriptor fuzz testing).
>
> Add the missing sanity checks to probe().
>
> Fixes: a03bb00e50ab ("staging: comedi: add NI USB-6501 support")
> Cc: stable@vger.kernel.org # 3.18
> Cc: Luca Ellero <luca.ellero@brickedbrain.com>
> Signed-off-by: Johan Hovold <johan@kernel.org>
> ---
> drivers/comedi/drivers/ni_usb6501.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/drivers/comedi/drivers/ni_usb6501.c b/drivers/comedi/drivers/ni_usb6501.c
> index 5b6d9d783b2f..eb2e5c23f25d 100644
> --- a/drivers/comedi/drivers/ni_usb6501.c
> +++ b/drivers/comedi/drivers/ni_usb6501.c
> @@ -144,6 +144,10 @@ static const u8 READ_COUNTER_RESPONSE[] = {0x00, 0x01, 0x00, 0x10,
> 0x00, 0x00, 0x00, 0x02,
> 0x00, 0x00, 0x00, 0x00};
>
> +/* Largest supported packets */
> +static const size_t TX_MAX_SIZE = sizeof(SET_PORT_DIR_REQUEST);
> +static const size_t RX_MAX_SIZE = sizeof(READ_PORT_RESPONSE);
> +
> enum commands {
> READ_PORT,
> WRITE_PORT,
> @@ -486,12 +490,16 @@ static int ni6501_find_endpoints(struct comedi_device *dev)
> ep_desc = &iface_desc->endpoint[i].desc;
>
> if (usb_endpoint_is_bulk_in(ep_desc)) {
> + if (usb_endpoint_maxp(ep_desc) < RX_MAX_SIZE)
> + continue;
> if (!devpriv->ep_rx)
> devpriv->ep_rx = ep_desc;
> continue;
> }
>
> if (usb_endpoint_is_bulk_out(ep_desc)) {
> + if (usb_endpoint_maxp(ep_desc) < TX_MAX_SIZE)
> + continue;
> if (!devpriv->ep_tx)
> devpriv->ep_tx = ep_desc;
> continue;
>

Perhaps it should return an error if the first encountered bulk-in
endpoint has the wrong size or the first encountered bulk-out endpoint
has the wrong size. Something like:

if (usb_endpoint_is_bulk_in(ep_desc)) {
if (!devpriv->ep_rx) {
if (usb_endpoint_maxp(ep_desc) < RX_MAX_SIZE)
break;
}
continue;

(similar for bulk-out with TX_MAX_SIZE)

--
-=( Ian Abbott <abbotti@mev.co.uk> || MEV Ltd. is a company )=-
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