linux-kernel - Re: [Xen-devel] [PATCH linux-next] xen/multicall: xen_mc

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Message-ID: <51156A91.5070801@cantab.net>
Date:	Fri, 08 Feb 2013 21:13:53 +0000
From:	David Vrabel <dvrabel@...tab.net>
To:	Tim Gardner <tim.gardner@...onical.com>
CC:	linux-kernel@...r.kernel.org,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	xen-devel@...ts.xensource.com,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	x86@...nel.org, stable@...r.kernel.org,
	virtualization@...ts.linux-foundation.org,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [Xen-devel] [PATCH linux-next] xen/multicall: xen_mc_callback():
 avoid buffer overflow

On 08/02/2013 20:34, Tim Gardner wrote:
> This buffer overflow was introduced with 91e0c5f3dad47838cb2ecc1865ce789a0b7182b1
> (2.6.24).

There's no buffer overflow here. xen_mc_flush() resets b->cbidx.

David

>  arch/x86/xen/multicalls.c |    3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/xen/multicalls.c b/arch/x86/xen/multicalls.c
> index 0d82003..5270407 100644
> --- a/arch/x86/xen/multicalls.c
> +++ b/arch/x86/xen/multicalls.c
> @@ -195,9 +195,10 @@ void xen_mc_callback(void (*fn)(void *), void *data)
>  	struct mc_buffer *b = &__get_cpu_var(mc_buffer);
>  	struct callback *cb;
>  
> -	if (b->cbidx == MC_BATCH) {
> +	if (b->cbidx >= MC_BATCH) {
>  		trace_xen_mc_flush_reason(XEN_MC_FL_CALLBACK);
>  		xen_mc_flush();
> +		return;
>  	}
>  
>  	trace_xen_mc_callback(fn, data);
> 

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