linux-kernel - Re: [PATCH] wireless: wext: allocate space for NULL-termination for 32byte SSIDs

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Message-Id: <20091215.014308.77044043.davem@davemloft.net>
Date:	Tue, 15 Dec 2009 01:43:08 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	daniel@...aq.de
Cc:	linux-kernel@...r.kernel.org, dcbw@...hat.com,
	m.hirsch@...mfeld.com, netdev@...r.kernel.org,
	libertas-dev@...ts.infradead.org, stable@...nel.org,
	linux-wireless@...r.kernel.org
Subject: Re: [PATCH] wireless: wext: allocate space for NULL-termination
 for 32byte SSIDs

From: Daniel Mack <daniel@...aq.de>
Date: Sun, 13 Dec 2009 04:47:30 +0800

> We've experienced a long standing bug when quickly switching from
> ad-hoc to managed mode on a hardware using a Libertas chipset.

Can you please CC: linux-wireless for wireless patches?

Thanks.

> The effect is that after a number of mode transistions (sometimes as few
> as two sufficed), the kernel will oops at very strange locations, mostly
> in something like __kmem_alloc().
> 
> While the root cause turned out to be an issue with the wpa-supplicant
> which feeds the kernel driver with garbage, this occasion pointed out a
> bug in the wireless wext core when SSIDs with 32 byte lengths are passed
> from userspace. In this case, the string is not properly NULL-terminated
> which causes some other part to corrupt memory.
> 
> (In the particular case I observed, an SIOCSIWESSID was issued with
>  bogus data in iwp->pointer but iwp->length=32).
> 
> I admitedly couldn't find where the actual corruption itself happens,
> but with this trivial fix, I can't reproduce the bug anymore.
> 
> Signed-off-by: Daniel Mack <daniel@...aq.de>
> Cc: Dan Williams <dcbw@...hat.com>
> Cc: Michael Hirsch <m.hirsch@...mfeld.com>
> Cc: netdev@...r.kernel.org
> Cc: libertas-dev@...ts.infradead.org
> Cc: stable@...nel.org
> ---
>  net/wireless/wext.c |    4 ++--
>  1 files changed, 2 insertions(+), 2 deletions(-)
> ---
>  net/wireless/wext-core.c |    4 ++--
>  1 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/net/wireless/wext-core.c b/net/wireless/wext-core.c
> index 5e1656b..3d8f4b0 100644
> --- a/net/wireless/wext-core.c
> +++ b/net/wireless/wext-core.c
> @@ -759,8 +759,8 @@ static int ioctl_standard_iw_point(struct iw_point *iwp, unsigned int cmd,
>  		}
>  	}
>  
> -	/* kzalloc() ensures NULL-termination for essid_compat. */
> -	extra = kzalloc(extra_size, GFP_KERNEL);
> +	/* kzalloc() +1 ensures NULL-termination for essid_compat. */
> +	extra = kzalloc(extra_size + 1, GFP_KERNEL);
>  	if (!extra)
>  		return -ENOMEM;
>  
> -- 
> 1.6.3.3
> 
> --
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