On Wed, 09 Aug 2023, Greg Kroah-Hartman wrote:
> From: Duoming Zhou <duoming@xxxxxxxxxx>
>
> [ Upstream commit 1e7417c188d0a83fb385ba2dbe35fd2563f2b6f3 ]
>
> 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")
Any idea why this stopped at linux-6.4.y? The aforementioned Fixes:
commit also exists in linux-6.1.y and linux-5.15.y. I don't see any
earlier backport attempts or failure reports that would otherwise
explain this.
> Signed-off-by: Duoming Zhou <duoming@xxxxxxxxxx>
> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
> ---
> drivers/net/usb/lan78xx.c | 7 ++-----
> 1 file changed, 2 insertions(+), 5 deletions(-)
--
Lee Jones [李琼斯]
