linux-kernel - Re: [PATCH] usb: core: fix information leak to userland

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Date:	Sat, 6 Nov 2010 14:21:50 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Vasiliy Kulikov <segooon@...il.com>
cc:	kernel-janitors@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Oliver Neukum <oliver@...kum.org>,
	Andi Kleen <ak@...ux.intel.com>,
	Chris Frey <cdfrey@...rsquare.net>,
	<linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] usb: core: fix information leak to userland

On Sat, 6 Nov 2010, Vasiliy Kulikov wrote:

> Structure usbdevfs_connectinfo is copied to userland with padding byted
> after "slow" field uninitialized.  It leads to leaking of contents of
> kernel stack memory.
> 
> Signed-off-by: Vasiliy Kulikov <segooon@...il.com>
> ---
>  Compile tested.
> 
>  drivers/usb/core/devio.c |    7 ++++---
>  1 files changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/usb/core/devio.c b/drivers/usb/core/devio.c
> index f1aaff6..045bb4b 100644
> --- a/drivers/usb/core/devio.c
> +++ b/drivers/usb/core/devio.c
> @@ -965,10 +965,11 @@ static int proc_getdriver(struct dev_state *ps, void __user *arg)
>  
>  static int proc_connectinfo(struct dev_state *ps, void __user *arg)
>  {
> -	struct usbdevfs_connectinfo ci;
> +	struct usbdevfs_connectinfo ci = {
> +		.devnum = ps->dev->devnum,
> +		.slow = ps->dev->speed == USB_SPEED_LOW
> +	};
>  
> -	ci.devnum = ps->dev->devnum;
> -	ci.slow = ps->dev->speed == USB_SPEED_LOW;
>  	if (copy_to_user(arg, &ci, sizeof(ci)))
>  		return -EFAULT;
>  	return 0;

Are you sure that adding an initializer like this will zero out the 
padding bytes?  It might be safer just to call memset.  This is not 
exactly a hot path, after all.

Alan Stern

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