[PATCH] net: can: fix use-after-free in ems_usb_disconnect

Pavel Skripkin
2021-06-17T18:51:59Z

In ems_usb_disconnect() dev pointer, which is
netdev private data, is used after free_candev() call:

if (dev) {
unregister_netdev(dev->netdev);
free_candev(dev->netdev);

unlink_all_urbs(dev);

usb_free_urb(dev->intr_urb);

kfree(dev->intr_in_buffer);
kfree(dev->tx_msg_buffer);
}

Fix it by simply moving free_candev() at the end of
the block.

Fail log:
BUG: KASAN: use-after-free in ems_usb_disconnect
Read of size 8 at addr ffff88804e041008 by task kworker/1:2/2895

CPU: 1 PID: 2895 Comm: kworker/1:2 Not tainted 5.13.0-rc5+ #164
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.14.0-0-g155821a-rebuilt.opensuse.4
Workqueue: usb_hub_wq hub_event
Call Trace:
dump_stack (lib/dump_stack.c:122)
print_address_description.constprop.0.cold (mm/kasan/report.c:234)
kasan_report.cold (mm/kasan/report.c:420 mm/kasan/report.c:436)
ems_usb_disconnect (drivers/net/can/usb/ems_usb.c:683 drivers/net/can/usb/ems_usb.c:1058)

Fixes: 702171adeed3 ("ems_usb: Added support for EMS CPC-USB/ARM7 CAN/USB interface")
Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
---
drivers/net/can/usb/ems_usb.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/can/usb/ems_usb.c b/drivers/net/can/usb/ems_usb.c
index 5af69787d9d5..0a37af4a3fa4 100644
--- a/drivers/net/can/usb/ems_usb.c
+++ b/drivers/net/can/usb/ems_usb.c
@@ -1053,7 +1053,6 @@ static void ems_usb_disconnect(struct usb_interface *intf)

if (dev) {
unregister_netdev(dev->netdev);
- free_candev(dev->netdev);

unlink_all_urbs(dev);

@@ -1061,6 +1060,8 @@ static void ems_usb_disconnect(struct usb_interface *intf)

kfree(dev->intr_in_buffer);
kfree(dev->tx_msg_buffer);
+
+ free_candev(dev->netdev);
}
}

--
2.32.0