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;