[PATCH 4.9 24/44] staging: comedi: vmk80xx: Fix possible double-free of ->usb_rx_buf

[Greg Kroah-Hartman]

From: Ian Abbott <abbo...@mev.co.uk>

commit 663d294b4768bfd89e529e069bffa544a830b5bf upstream.

`vmk80xx_alloc_usb_buffers()` is called from `vmk80xx_auto_attach()` to
allocate RX and TX buffers for USB transfers.  It allocates
`devpriv->usb_rx_buf` followed by `devpriv->usb_tx_buf`.  If the
allocation of `devpriv->usb_tx_buf` fails, it frees
`devpriv->usb_rx_buf`,  leaving the pointer set dangling, and returns an
error.  Later, `vmk80xx_detach()` will be called from the core comedi
module code to clean up.  `vmk80xx_detach()` also frees both
`devpriv->usb_rx_buf` and `devpriv->usb_tx_buf`, but
`devpriv->usb_rx_buf` may have already been freed, leading to a
double-free error.  Fix it by removing the call to
`kfree(devpriv->usb_rx_buf)` from `vmk80xx_alloc_usb_buffers()`, relying
on `vmk80xx_detach()` to free the memory.

Signed-off-by: Ian Abbott <abbo...@mev.co.uk>
Cc: stable <sta...@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 drivers/staging/comedi/drivers/vmk80xx.c |    4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

--- a/drivers/staging/comedi/drivers/vmk80xx.c
+++ b/drivers/staging/comedi/drivers/vmk80xx.c
@@ -691,10 +691,8 @@ static int vmk80xx_alloc_usb_buffers(str
 
        size = usb_endpoint_maxp(devpriv->ep_tx);
        devpriv->usb_tx_buf = kzalloc(size, GFP_KERNEL);
-       if (!devpriv->usb_tx_buf) {
-               kfree(devpriv->usb_rx_buf);
+       if (!devpriv->usb_tx_buf)
                return -ENOMEM;
-       }
 
        return 0;
 }