Re: [PATCH] HSI: ssi_protocol: Fix use after free vulnerability in ssi_protocol Driver Due to Race Condition

[Sebastian Reichel]

Hi,

On Wed, Sep 11, 2024 at 11:19:15PM GMT, Kaixin Wang wrote:
> In the ssi_protocol_probe function, &ssi->work is bound with
> ssip_xmit_work, In ssip_pn_setup, the ssip_pn_xmit function
> within the ssip_pn_ops structure is capable of starting the
> work.
> 
> If we remove the module which will call ssi_protocol_remove
> to make a cleanup, it will free ssi through kfree(ssi),
> while the work mentioned above will be used. The sequence
> of operations that may lead to a UAF bug is as follows:
> 
> CPU0                                    CPU1
> 
>                         | ssip_xmit_work
> ssi_protocol_remove     |
> kfree(ssi);             |
>                         | struct hsi_client *cl = ssi->cl;
>                         | // use ssi
> 
> Fix it by ensuring that the work is canceled before proceeding
> with the cleanup in ssi_protocol_remove
> 
> Signed-off-by: Kaixin Wang <kxwang23@xxxxxxxxxxxxxx>
> ---

This does not even compile :(

During module removal the network device is unregistered (and thus
stopped), which calls ssip_reset(), which should stop any activity
regarding traffic exchange. That's the right place to cancel the
work.

Greetings,

-- Sebastian

>  drivers/hsi/clients/ssi_protocol.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/hsi/clients/ssi_protocol.c b/drivers/hsi/clients/ssi_protocol.c
> index afe470f3661c..3506c70e3505 100644
> --- a/drivers/hsi/clients/ssi_protocol.c
> +++ b/drivers/hsi/clients/ssi_protocol.c
> @@ -1155,6 +1155,7 @@ static int ssi_protocol_remove(struct device *dev)
>  	unregister_netdev(ssi->netdev);
>  	ssip_free_cmds(ssi);
>  	hsi_client_set_drvdata(cl, NULL);
> +	cancel_work_sync(&ssi->work)
>  	kfree(ssi);
>  
>  	return 0;
> -- 
> 2.25.1
> 
>

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