Re: [PATCH] RDMA/core: Fix use-after-free when netns exit races compat dev removal

[Leon Romanovsky <leon@kernel.org>]

On Tue, Aug 18, 2026 at 11:09:20AM +0300, Serhat Kumral wrote:
> A compat device is removed from two places: disable_device() during the
> ib device unregistration, and rdma_dev_exit_net() when the netns it
> belongs to dies. remove_one_compat_dev() lets the xa_erase() decide
> which of the two performs the removal, but drops compat_devs_mutex
> before device_del(), so the caller that finds nothing to erase returns
> without waiting for the removal the other one is running.
> 
> When that caller is rdma_dev_exit_net(), cleanup_net() carries on while
> the compat device is still alive. Its kobject is tagged with the dying
> net, so the device_del() still in progress dereferences net->uevent_sock
> after uevent_net_exit() has freed it:
> 
>  CPU0 (ib-unreg-wq)                CPU1 (netns wq)
>  ------------------                ---------------
>  __ib_unregister_device()
>    disable_device()
>      remove_compat_devs()
>        remove_one_compat_dev()
>          xa_erase()
>          device_del(cdev)
>          ...
>                                    cleanup_net()
>                                      rdma_dev_exit_net()
>                                        remove_one_compat_dev()
>                                          xa_erase()
>                                        // returns without waiting
>                                      uevent_net_exit()
>                                        kfree(net->uevent_sock)
>          kobject_uevent_env()
>            net->uevent_sock->sk    // UAF
> 
>   BUG: KASAN: slab-use-after-free in kobject_uevent_env+0xb6f/0xc80
>   Read of size 8 at addr ffff888103806490 by task kworker/u16:1/41
>   Workqueue: ib-unreg-wq ib_unregister_work
>   Call Trace:
>    kobject_uevent_env+0xb6f/0xc80
>    device_del+0x737/0xc10
>    disable_device+0x1ad/0x230
>    __ib_unregister_device+0x229/0x3f0
>   Freed by task 12:
>    kfree+0x1b3/0x550
>    ops_undo_list+0x273/0x8c0
>    cleanup_net+0x3b3/0x720

Please don't trim kernel panic logs. Please post the full output,
including the steps required to reproduce the issue.

Thanks

> 
> Fix by holding compat_devs_mutex across the whole removal, so that once
> remove_one_compat_dev() returns the compat device is gone no matter
> which caller removed it.
> 
> Fixes: 4e0f7b907072 ("RDMA/core: Implement compat device/sysfs tree in net namespace")
> Assisted-by: Claude:claude-opus-5
> Signed-off-by: Serhat Kumral <serhatkumral1@gmail.com>
> ---
> With this patch applied the report no longer shows up.
> 
>  drivers/infiniband/core/device.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/infiniband/core/device.c b/drivers/infiniband/core/device.c
> index d954eda63134..a80ac69ef986 100644
> --- a/drivers/infiniband/core/device.c
> +++ b/drivers/infiniband/core/device.c
> @@ -1005,14 +1005,20 @@ static void remove_one_compat_dev(struct ib_device *device, u32 id)
>  {
>  	struct ib_core_device *cdev;
>  
> +	/*
> +	 * Hold the lock across device_del(): the other remover may have won
> +	 * the xa_erase() and still be inside device_del(), and the netns exit
> +	 * path has to wait for it instead of letting cleanup_net() free the
> +	 * netns state the compat device is still tagged with.
> +	 */
>  	mutex_lock(&device->compat_devs_mutex);
>  	cdev = xa_erase(&device->compat_devs, id);
> -	mutex_unlock(&device->compat_devs_mutex);
>  	if (cdev) {
>  		ib_free_port_attrs(cdev);
>  		device_del(&cdev->dev);
>  		put_device(&cdev->dev);
>  	}
> +	mutex_unlock(&device->compat_devs_mutex);
>  }
>  
>  static void remove_compat_devs(struct ib_device *device)
> -- 
> 2.53.0
>