comedi: vmk80xx: fix transfer-buffer overflows

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>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Link: https://lore.kernel.org/r/20211025114532.4599-4-johan@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/comedi/drivers/vmk80xx.c b/drivers/comedi/drivers/vmk80xx.c
index 9f92081..f2c1572 100644 (file)
--- 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;