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

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: [PATCH] xfs: zero proper structure size for geometry calls
From: Eric Sandeen <sandeen@xxxxxxxxxxx>
Date: Mon, 28 Feb 2011 21:01:05 -0600
Cc: Jeffrey Hundstad <jeffrey.hundstad@xxxxxxxx>, Dan Rosenberg <drosenberg@xxxxxxxxxxxxx>, Eugene Teo <eugeneteo@xxxxxxxxxx>, xfs@xxxxxxxxxxx
In-reply-to: <20110301025944.GG3087@dastard>
References: <4D6C28A5.60905@xxxxxxxx> <4D6C4DEE.6020902@xxxxxxxxxxx> <20110301025944.GG3087@dastard>
User-agent: Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.6; en-US; rv:1.9.2.13) Gecko/20101207 Thunderbird/3.1.7
On 2/28/11 8:59 PM, Dave Chinner wrote:
> 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.

Ok, I can resend, I was going to do that but most of xfs uses the other style 
so wasn't sure.

-Eric

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