ath6kl: fix a NULL-ptr-deref bug in ath6kl_usb_alloc_urb_from_pipe()

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@gmail.com>
Reported-by: Hui Peng <benquike@gmail.com>
Reported-by: Mathias Payer <mathias.payer@nebelwelt.net>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

diff --git a/drivers/net/wireless/ath/ath6kl/usb.c b/drivers/net/wireless/ath/ath6kl/usb.c
index 4defb7a0330f430c181c5873fee7376401e92611..53b66e9434c99845dbbaa8b31aaa0e74e0a67fc8 100644 (file)
--- 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++;