linux-kernel - Re: [PATCH] Prevent USB hub remove oops

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Date:	Tue, 26 Feb 2013 11:07:30 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Daniel J Blueman <daniel@...ascale-asia.com>
cc:	linux-usb@...r.kernel.org, <linux-kernel@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Sarah Sharp <sarah.a.sharp@...ux.intel.com>,
	Steffen Persvold <sp@...ascale.com>
Subject: Re: [PATCH] Prevent USB hub remove oops

On Tue, 26 Feb 2013, Daniel J Blueman wrote:

> When initialisation of one or more USB hub ports fails, we can hit a null
> pointer dereference when dropping the hub. Analysis shows there's a false
> assumption about the ports being setup, so address this.

> Signed-off-by: Daniel J Blueman <daniel@...ascale-asia.com>
> ---
>  drivers/usb/core/hub.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
> index cbf7168..a7abc57 100644
> --- a/drivers/usb/core/hub.c
> +++ b/drivers/usb/core/hub.c
> @@ -1263,7 +1263,7 @@ static void hub_quiesce(struct usb_hub *hub, enum hub_quiescing_type type)
>  	if (type != HUB_SUSPEND) {
>  		/* Disconnect all the children */
>  		for (i = 0; i < hdev->maxchild; ++i) {
> -			if (hub->ports[i]->child)
> +			if (hub->ports[i] && hub->ports[i]->child)
>  				usb_disconnect(&hub->ports[i]->child);
>  		}
>  	}

You missed a case.  What happens if hub->ports is NULL?

Also, what about this code in hub_disconnect?

	for (i = 0; i < hdev->maxchild; i++)
		usb_hub_remove_port_device(hub, i + 1);

All of these problems can be fixed in hub_configure by setting
hub->maxchild to the total number of allocated ports (or 0 if hub_ports
can't be allocated).

Alan Stern

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