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Re: kernel panic - stack-protector: kernel stack is corrupted in: f87aca

To: Eric Sandeen <sandeen@xxxxxxxxxxx>
Subject: Re: kernel panic - stack-protector: kernel stack is corrupted in: f87aca93
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Tue, 1 Mar 2011 13:57:26 +1100
Cc: Jeffrey Hundstad <jeffrey.hundstad@xxxxxxxx>, xfs@xxxxxxxxxxx
In-reply-to: <4D6C4CC5.5030909@xxxxxxxxxxx>
References: <4D6C28A5.60905@xxxxxxxx> <4D6C372E.6030105@xxxxxxxxxxx> <4D6C45EE.80203@xxxxxxxx> <4D6C4CC5.5030909@xxxxxxxxxxx>
User-agent: Mutt/1.5.20 (2009-06-14)
On Mon, Feb 28, 2011 at 07:32:53PM -0600, Eric Sandeen wrote:
> On 2/28/11 7:03 PM, Jeffrey Hundstad wrote:
> > Sadly, I didn't have the vmlinux file around anymore.  I'll be glad to 
> > recreate it when I get in tomorrow.  However, I have revered commit 
> > 3a3675b7f23f83ca8c67c9c2b6edf707fd28d1ba and the problem seems to have 
> > vanished.  I'm guessing the stack at this point is a little to fragile for 
> > a memset.  The patch is:
> 
> Ok, no worries, if the below commit is the culprit for sure, that's enough...
> 
> So, whoopsies.
> 
> STATIC int
> xfs_ioc_fsgeometry_v1(
>         xfs_mount_t             *mp,
>         void                    __user *arg)
> {
>         xfs_fsop_geom_v1_t      fsgeo;
>         int                     error;
> 
>         error = xfs_fs_geometry(mp, (xfs_fsop_geom_t *)&fsgeo, 3);
> 
> what we really have is an xfs_fsop_geom_v1_t, but cast to a xfs_fsop_geom_t.
> 
> xfs_fs_geometry() zeroes it out to the tune of sizeof (xfs_fsop_geom_t)
> 
> the latter is bigger, with the addition of
> 
>       __u32           logsunit;
> 
> so we overwrite memory that's not ours.  :(  Seems like we should zero
> in the callers, when we know how much is really on the stack.  I'll follow
> up with a patch; pity this one was fast-tracked for security, I think :(

Fmeh - the differences in structure size, alignment and padding on
different platforms was why I suggested that memset() is a
preferable fix to just setting a single field. I didn't look any
further at the patch before it was committed so I didn't catch the
fact that it was busted in the first place...

Just another example of Occam's Eraser(*) in action, I'd say.

Cheers,

Dave

(*) From the Fortune Cookie database:

OCCAM'S ERASER:
  The philosophical principle that even the simplest solution is
  bound to have something wrong with it.
-- 
Dave Chinner
david@xxxxxxxxxxxxx

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