netdev - Re: [PATCH 1/1] be2net: Detach interface for avoiding a system crash

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Date:   Mon, 1 Apr 2019 16:25:53 +0000
From:   Saeed Mahameed <saeedm@...lanox.com>
To:     "sathya.perla@...adcom.com" <sathya.perla@...adcom.com>,
        "sriharsha.basavapatna@...adcom.com" 
        <sriharsha.basavapatna@...adcom.com>,
        "fyang@...e.com" <fyang@...e.com>,
        "somnath.kotur@...adcom.com" <somnath.kotur@...adcom.com>,
        "ajit.khaparde@...adcom.com" <ajit.khaparde@...adcom.com>,
        "davem@...emloft.net" <davem@...emloft.net>
CC:     "firogm@...il.com" <firogm@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH 1/1] be2net: Detach interface for avoiding a system crash

On Mon, 2019-04-01 at 20:24 +0800, Firo Yang wrote:
> This crash is triggered by a user-after-free since lake of
> the synchronization of a race condition between 
> be_update_queues() modifying multi-purpose channels of
> network device and be_tx_timeout().
> 
> BUG: unable to handle kernel NULL pointer dereference at (null)
> Call Trace:
> be_tx_timeout+0xa5/0x360 [be2net]
> dev_watchdog+0x1d8/0x210
> call_timer_fn+0x32/0x140
> 
> To fix it, detach the interface before modifying
> multi-purpose channels of network device.
> 
> Signed-off-by: Firo Yang <fyang@...e.com>
> ---
>  drivers/net/ethernet/emulex/benet/be_main.c | 12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/net/ethernet/emulex/benet/be_main.c
> b/drivers/net/ethernet/emulex/benet/be_main.c
> index d5026909dec5..25d0128bf684 100644
> --- a/drivers/net/ethernet/emulex/benet/be_main.c
> +++ b/drivers/net/ethernet/emulex/benet/be_main.c
> @@ -4705,6 +4705,8 @@ int be_update_queues(struct be_adapter
> *adapter)
>  	struct net_device *netdev = adapter->netdev;
>  	int status;
>  
> +	netif_device_detach(netdev);
> +

This will reduce the probability, but will not do the trick.
since this will not guarantee that the dev_watchdog is disabled.

what you need is proper locking mechanism and/or scheduling the
tx_timeout handling out of atomic context if a mutex will be required.

netif_device_detach is a too heavy hammer for such synchronizations
tasks.

>  	if (netif_running(netdev))
>  		be_close(netdev);
>  
> @@ -4719,21 +4721,21 @@ int be_update_queues(struct be_adapter
> *adapter)
>  	be_clear_queues(adapter);
>  	status = be_cmd_if_destroy(adapter, adapter->if_handle,  0);
>  	if (status)
> -		return status;
> +		goto out;
>  
>  	if (!msix_enabled(adapter)) {
>  		status = be_msix_enable(adapter);
>  		if (status)
> -			return status;
> +			goto out;
>  	}
>  
>  	status = be_if_create(adapter);
>  	if (status)
> -		return status;
> +		goto out;
>  
>  	status = be_setup_queues(adapter);
>  	if (status)
> -		return status;
> +		goto out;
>  
>  	be_schedule_worker(adapter);
>  
> @@ -4748,6 +4750,8 @@ int be_update_queues(struct be_adapter
> *adapter)
>  	if (netif_running(netdev))
>  		status = be_open(netdev);
>  
> +out:
> +	netif_device_attach(netdev);
>  	return status;
>  }
>