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Re: [PATCH v2] xfs: fix possible overflow in xfs_ioc_trim()

To: Lukas Czerner <lczerner@xxxxxxxxxx>
Subject: Re: [PATCH v2] xfs: fix possible overflow in xfs_ioc_trim()
From: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Date: Wed, 7 Sep 2011 07:21:55 -0400
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>, xfs@xxxxxxxxxxx
In-reply-to: <alpine.LFD.2.00.1109071200480.4579@xxxxxxxxxxxxxxxxxxxxxxxxxx>
References: <1315322977-22736-1-git-send-email-lczerner@xxxxxxxxxx> <20110906153301.GA21675@xxxxxxxxxxxxx> <alpine.LFD.2.00.1109071200480.4579@xxxxxxxxxxxxxxxxxxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Wed, Sep 07, 2011 at 12:05:14PM +0200, Lukas Czerner wrote:
> > > + if (len > max_blks)
> > > +         len = max_blks - start;
> > 
> > Is this really the correct check?
> > 
> > Shouldn't it be
> > 
> >     if (start + len > max_blks)
> >             len = max_blks - start;
> > 
> > I'd also just use the mp->m_sb.sb_dblocks value directly instead
> > of assigning it to a local variable.
> > 
> 
> Agh, you're right. I am bit too hasty I guess. I thought that
> 
> if (start_agno >= mp->m_sb.sb_agcount)
>       return -XFS_ERROR(EINVAL);
> 
> will cover us from the unreasonably big start, however if the file
> system has really huge number of AGs than it will fail to prevent the
> overflow, I am not sure if that is possible to happen, but what you
> proposed is definitely better.

The problem is that start could be very far into the fs, so checking
len alone won't help very much.  And we probably want a check if 
start + len is overflowing, too.

Care to update the test case to cover these cases as well?

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