ACK: [PATCH 1/1] ath6kl: fix a NULL-ptr-deref bug in ath6kl_usb_alloc_urb_from_pipe()

[Connor Kuehl]

On 10/3/19 8:47 AM, Tyler Hicks wrote:
> From: Hui Peng <benquike at gmail.com>
> 
> The `ar_usb` field of `ath6kl_usb_pipe_usb_pipe` objects
> are initialized to point to the containing `ath6kl_usb` object
> according to endpoint descriptors read from the device side, as shown
> below in `ath6kl_usb_setup_pipe_resources`:
> 
> for (i = 0; i < iface_desc->desc.bNumEndpoints; ++i) {
> 	endpoint = &iface_desc->endpoint[i].desc;
> 
> 	// get the address from endpoint descriptor
> 	pipe_num = ath6kl_usb_get_logical_pipe_num(ar_usb,
> 						endpoint->bEndpointAddress,
> 						&urbcount);
> 	......
> 	// select the pipe object
> 	pipe = &ar_usb->pipes[pipe_num];
> 
> 	// initialize the ar_usb field
> 	pipe->ar_usb = ar_usb;
> }
> 
> The driver assumes that the addresses reported in endpoint
> descriptors from device side  to be complete. If a device is
> malicious and does not report complete addresses, it may trigger
> NULL-ptr-deref `ath6kl_usb_alloc_urb_from_pipe` and
> `ath6kl_usb_free_urb_to_pipe`.
> 
> This patch fixes the bug by preventing potential NULL-ptr-deref
> (CVE-2019-15098).
> 
> Signed-off-by: Hui Peng <benquike at gmail.com>
> Reported-by: Hui Peng <benquike at gmail.com>
> Reported-by: Mathias Payer <mathias.payer at nebelwelt.net>
> Reviewed-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
> Signed-off-by: Kalle Valo <kvalo at codeaurora.org>
> 
> CVE-2019-15098
> 
> (cherry picked from commit 39d170b3cb62ba98567f5c4f40c27b5864b304e5)
> Signed-off-by: Tyler Hicks <tyhicks at canonical.com>

Clean cherry pick. Patch description features a nice walkthrough, too.

Acked-by: Connor Kuehl <connor.kuehl at canonical.com>

> ---
>   drivers/net/wireless/ath/ath6kl/usb.c | 8 ++++++++
>   1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/net/wireless/ath/ath6kl/usb.c b/drivers/net/wireless/ath/ath6kl/usb.c
> index 4defb7a0330f..53b66e9434c9 100644
> --- a/drivers/net/wireless/ath/ath6kl/usb.c
> +++ b/drivers/net/wireless/ath/ath6kl/usb.c
> @@ -132,6 +132,10 @@ ath6kl_usb_alloc_urb_from_pipe(struct ath6kl_usb_pipe *pipe)
>   	struct ath6kl_urb_context *urb_context = NULL;
>   	unsigned long flags;
>   
> +	/* bail if this pipe is not initialized */
> +	if (!pipe->ar_usb)
> +		return NULL;
> +
>   	spin_lock_irqsave(&pipe->ar_usb->cs_lock, flags);
>   	if (!list_empty(&pipe->urb_list_head)) {
>   		urb_context =
> @@ -150,6 +154,10 @@ static void ath6kl_usb_free_urb_to_pipe(struct ath6kl_usb_pipe *pipe,
>   {
>   	unsigned long flags;
>   
> +	/* bail if this pipe is not initialized */
> +	if (!pipe->ar_usb)
> +		return;
> +
>   	spin_lock_irqsave(&pipe->ar_usb->cs_lock, flags);
>   	pipe->urb_cnt++;
>   
>