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

[Tyler Hicks]

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>
---
 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++;
 
-- 
2.17.1