linux-kernel - [PATCH 3.16 16/25] ath6kl: fix a NULL-ptr-deref bug in ath6kl_usb_alloc_urb_from

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Message-ID: <lsq.1573602477.324913677@decadent.org.uk>
Date:   Tue, 12 Nov 2019 23:48:13 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Mathias Payer" <mathias.payer@...elwelt.net>,
        "Hui Peng" <benquike@...il.com>,
        "Kalle Valo" <kvalo@...eaurora.org>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>
Subject: [PATCH 3.16 16/25] ath6kl: fix a NULL-ptr-deref bug in
 ath6kl_usb_alloc_urb_from_pipe()

3.16.77-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Hui Peng <benquike@...il.com>

commit 39d170b3cb62ba98567f5c4f40c27b5864b304e5 upstream.

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@...il.com>
Reported-by: Hui Peng <benquike@...il.com>
Reported-by: Mathias Payer <mathias.payer@...elwelt.net>
Reviewed-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Kalle Valo <kvalo@...eaurora.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/net/wireless/ath/ath6kl/usb.c | 8 ++++++++
 1 file changed, 8 insertions(+)

--- 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 at
 	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(
 {
 	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++;