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Re: [PATCH] xfs: zero proper structure size for geometry calls

To: Eric Sandeen <sandeen@xxxxxxxxxxx>
Subject: Re: [PATCH] xfs: zero proper structure size for geometry calls
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Tue, 1 Mar 2011 13:59:44 +1100
Cc: Jeffrey Hundstad <jeffrey.hundstad@xxxxxxxx>, Dan Rosenberg <drosenberg@xxxxxxxxxxxxx>, Eugene Teo <eugeneteo@xxxxxxxxxx>, xfs@xxxxxxxxxxx
In-reply-to: <4D6C4DEE.6020902@xxxxxxxxxxx>
References: <4D6C28A5.60905@xxxxxxxx> <4D6C4DEE.6020902@xxxxxxxxxxx>
User-agent: Mutt/1.5.20 (2009-06-14)
On Mon, Feb 28, 2011 at 07:37:50PM -0600, Eric Sandeen wrote:
> commit 493f3358cb289ccf716c5a14fa5bb52ab75943e5 added:
> 
> +       memset(geo, 0, sizeof(*geo)); 
> 
> but unfortunately we're dealing with a cast pointer here, and
> the caller may actually have a smaller structure on the stack.
> Zeroing out more leads to stack corruption traps:
> 
> Kernel panic - not syncing: stack-protector: Kernel stack is corrupted in: 
> f87aca93
> 
> Pid: 262, comm: xfs_fsr Not tainted 2.6.38-rc6-493f3358cb2+ #1
> Call Trace:
> 
> [<c12991ac>] ? panic+0x50/0x150
> [<c102ed71>] ? __stack_chk_fail+0x10/0x18
> [<f87aca93>] ? xfs_ioc_fsgeometry_v1+0x56/0x5d [xfs] 
> 
> Fix this by zeroing out the structure in the callers, where we know
> the actual size.
> 
> Reported-by: Jeffrey Hundstad <jeffrey.hundstad@xxxxxxxx>
> Signed-off-by: Eric Sandeen <sandeen@xxxxxxxxxx>
> ---
> 
> diff --git a/fs/xfs/linux-2.6/xfs_ioctl.c b/fs/xfs/linux-2.6/xfs_ioctl.c
> index f5e2a19..34e401f 100644
> --- a/fs/xfs/linux-2.6/xfs_ioctl.c
> +++ b/fs/xfs/linux-2.6/xfs_ioctl.c
> @@ -698,6 +698,7 @@ xfs_ioc_fsgeometry_v1(
>       xfs_fsop_geom_v1_t      fsgeo;
>       int                     error;
>  
> +     memset(&fsgeo, 0, sizeof(xfs_fsop_geom_v1_t));

I'd prefer that sizeof(fsgeo) is used here. That means if the type
is changed, then memset doesn't need to be. Same for all the rest
of the memset calls.

Otherwise,

Reviewed-by: Dave Chinner <dchinner@xxxxxxxxxx>

Cheers,

Dave.
-- 
Dave Chinner
david@xxxxxxxxxxxxx

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