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Subject[PATCH 5.10 15/21] comedi: vmk80xx: fix transfer-buffer overflows
From: Johan Hovold <>

commit a23461c47482fc232ffc9b819539d1f837adf2b1 upstream.

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: # 2.6.31
Signed-off-by: Johan Hovold <>
Reviewed-by: Ian Abbott <>
Signed-off-by: Greg Kroah-Hartman <>
drivers/staging/comedi/drivers/vmk80xx.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

--- a/drivers/staging/comedi/drivers/vmk80xx.c
+++ b/drivers/staging/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 {
@@ -678,12 +680,12 @@ static int vmk80xx_alloc_usb_buffers(str
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;

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