linux-kernel - Re: [patch] xfs: check for underflow in xfs_iformat

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Message-ID: <20130815154733.GB26086@mwanda>
Date:	Thu, 15 Aug 2013 18:47:33 +0300
From:	Dan Carpenter <dan.carpenter@...cle.com>
To:	Ben Myers <bpm@....com>
Cc:	Jeff Liu <jeff.liu@...cle.com>, Alex Elder <elder@...nel.org>,
	xfs@....sgi.com, linux-kernel@...r.kernel.org,
	kernel-janitors@...r.kernel.org
Subject: Re: [patch] xfs: check for underflow in xfs_iformat_fork()

On Thu, Aug 15, 2013 at 09:37:06AM -0500, Ben Myers wrote:
> Hey Dan & Jeff,
> 
> On Thu, Aug 15, 2013 at 06:10:43PM +0800, Jeff Liu wrote:
> > On 08/15/2013 01:53 PM, Dan Carpenter wrote:
> > 
> > > The "di_size" variable comes from the disk and it's a signed 64 bit.
> > > We check the upper limit but we should check for negative numbers as
> > > well.
> > > 
> > > Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
> > > 
> > > diff --git a/fs/xfs/xfs_inode_fork.c b/fs/xfs/xfs_inode_fork.c
> > > index 123971b..849fc70 100644
> > > --- a/fs/xfs/xfs_inode_fork.c
> > > +++ b/fs/xfs/xfs_inode_fork.c
> > > @@ -167,7 +167,8 @@ xfs_iformat_fork(
> > >  			}
> > >  
> > >  			di_size = be64_to_cpu(dip->di_size);
> > > -			if (unlikely(di_size > XFS_DFORK_DSIZE(dip, ip->i_mount))) {
> > > +			if (unlikely(di_size < 0 ||
> > 
> > But the di_size is initialized to ZERO while allocating a new inode on disk.
> > I wonder if that is better to ASSERT in this case because the current check
> > is used to make sure that the item is inlined, or we don't need it at all.
> 
> Hmm.  Dan's additional check looks good to me.  In this case I'd say the forced
> shutdown is more appropriate than an assert, because here we're reading the
> inode from disk, as opposed to looking at a structure that is already incore
> which we think we've initialized.  We want to handle unexpected inputs from
> disk without crashing even if we are CONFIG_XFS_DEBUG.
> 
> How did you come across this one?
> 

These are static checker things...  It's too false positive prone to
push on the real world yet.

regards,
dan carpenter

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