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Re: [patch] xfs: check for underflow in xfs_iformat_fork()

To: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Subject: Re: [patch] xfs: check for underflow in xfs_iformat_fork()
From: Ben Myers <bpm@xxxxxxx>
Date: Mon, 26 Aug 2013 11:12:52 -0500
Cc: Alex Elder <elder@xxxxxxxxxx>, kernel-janitors@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx, Jeff Liu <jeff.liu@xxxxxxxxxx>, Dave Chinner <david@xxxxxxxxxxxxx>
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20130826143714.GA6329@mwanda>
References: <20130815055338.GC23580@xxxxxxxxxxxxxx> <520CA923.4060409@xxxxxxxxxx> <20130815143706.GI7153@xxxxxxx> <20130815222650.GX6023@dastard> <20130823173613.GT5262@xxxxxxx> <20130826143714.GA6329@mwanda>
User-agent: Mutt/1.5.20 (2009-06-14)
Hey Dan,

On Mon, Aug 26, 2013 at 05:37:15PM +0300, Dan Carpenter wrote:
> On Fri, Aug 23, 2013 at 12:36:13PM -0500, Ben Myers wrote:
> > Dan,
> > 
> > On Fri, Aug 16, 2013 at 08:26:50AM +1000, Dave Chinner wrote:
> > > 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@xxxxxxxxxx>
> > > > > > 
> > > > > > 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.
> > > 
> > > There are lots of places where we only check di_size to be greater
> > > than some value, and don't check for it being less than zero. Hence
> > > I think that a better solution might be to di_size unsigned as that
> > > will catch "negative" sizes for all types of situations.
> > 
> > What do you say to making di_size unsigned?  Any interest?
> > 
> 
> I'm not the right person to change "lots of places".  Some of these
> are probably subtle.  Just give me the reported-by and I'm happy.

I'll apply this for now, and we'll see if someone is interested enough to pick
up the rest.

Thanks,
        Ben

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