The timer dev->stat_monitor can schedule the delayed work dev->wq and
the delayed work dev->wq can also arm the dev->stat_monitor timer.
When the device is detaching, the net_device will be deallocated. but
the net_device private data could still be dereferenced in delayed work
or timer handler. As a result, the UAF bugs will happen.
One racy situation is shown below:
(Thread 1) | (Thread 2)
lan78xx_stat_monitor() |
... | lan78xx_disconnect()
lan78xx_defer_kevent() | ...
... | cancel_delayed_work_sync(&dev->wq);
schedule_delayed_work() | ...
(wait some time) | free_netdev(net); //free net_device
lan78xx_delayedwork() |
//use net_device private data |
dev-> //use |
Although we use cancel_delayed_work_sync() to cancel the delayed work
in lan78xx_disconnect(), it could still be scheduled in timer handler
lan78xx_stat_monitor().
Another racy situation is shown below:
(Thread 1) | (Thread 2)
lan78xx_delayedwork |
mod_timer() | lan78xx_disconnect()
| cancel_delayed_work_sync()
(wait some time) | if (timer_pending(&dev->stat_monitor))
| del_timer_sync(&dev->stat_monitor);
lan78xx_stat_monitor() | ...
lan78xx_defer_kevent() | free_netdev(net); //free
//use net_device private data|
dev-> //use |
Although we use del_timer_sync() to delete the timer, the function
timer_pending() returns 0 when the timer is activated. As a result,
the del_timer_sync() will not be executed and the timer could be
re-armed.
In order to mitigate this bug, We use timer_shutdown_sync() to shutdown
the timer and then use cancel_delayed_work_sync() to cancel the delayed
work. As a result, the net_device could be deallocated safely.
What's more, the dev->flags is set to EVENT_DEV_DISCONNECT in
lan78xx_disconnect(). But it could still be set to EVENT_STAT_UPDATE
in lan78xx_stat_monitor(). So this patch put the set_bit() behind
timer_shutdown_sync().
Fixes: 77dfff5bb7e2 ("lan78xx: Fix race condition in disconnect handling")
Signed-off-by: Duoming Zhou <[email protected]>
---
drivers/net/usb/lan78xx.c | 7 ++-----
1 file changed, 2 insertions(+), 5 deletions(-)
diff --git a/drivers/net/usb/lan78xx.c b/drivers/net/usb/lan78xx.c
index c458c030fad..59cde06aa7f 100644
--- a/drivers/net/usb/lan78xx.c
+++ b/drivers/net/usb/lan78xx.c
@@ -4224,8 +4224,6 @@ static void lan78xx_disconnect(struct usb_interface *intf)
if (!dev)
return;
- set_bit(EVENT_DEV_DISCONNECT, &dev->flags);
-
netif_napi_del(&dev->napi);
udev = interface_to_usbdev(intf);
@@ -4233,6 +4231,8 @@ static void lan78xx_disconnect(struct usb_interface *intf)
unregister_netdev(net);
+ timer_shutdown_sync(&dev->stat_monitor);
+ set_bit(EVENT_DEV_DISCONNECT, &dev->flags);
cancel_delayed_work_sync(&dev->wq);
phydev = net->phydev;
@@ -4247,9 +4247,6 @@ static void lan78xx_disconnect(struct usb_interface *intf)
usb_scuttle_anchored_urbs(&dev->deferred);
- if (timer_pending(&dev->stat_monitor))
- del_timer_sync(&dev->stat_monitor);
-
lan78xx_unbind(dev, intf);
lan78xx_free_tx_resources(dev);
--
2.17.1
Hello:
This patch was applied to netdev/net.git (main)
by David S. Miller <[email protected]>:
On Wed, 26 Jul 2023 16:14:07 +0800 you wrote:
> The timer dev->stat_monitor can schedule the delayed work dev->wq and
> the delayed work dev->wq can also arm the dev->stat_monitor timer.
>
> When the device is detaching, the net_device will be deallocated. but
> the net_device private data could still be dereferenced in delayed work
> or timer handler. As a result, the UAF bugs will happen.
>
> [...]
Here is the summary with links:
- [net] net: usb: lan78xx: reorder cleanup operations to avoid UAF bugs
https://git.kernel.org/netdev/net/c/1e7417c188d0
You are awesome, thank you!
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