From: Carlos Maiolino <cmaiolino@redhat.com>
To: "Darrick J. Wong" <darrick.wong@oracle.com>
Cc: linux-fsdevel@vger.kernel.org, hch@lst.de, adilger@dilger.ca,
jaegeuk@kernel.org, miklos@szeredi.hu, rpeterso@redhat.com,
linux-xfs@vger.kernel.org
Subject: Re: [PATCH 4/9] fibmap: Use bmap instead of ->bmap method in ioctl_fibmap
Date: Mon, 5 Aug 2019 12:27:30 +0200 [thread overview]
Message-ID: <20190805102729.ooda6sg65j65ojd4@pegasus.maiolino.io> (raw)
In-Reply-To: <20190802151400.GG7138@magnolia>
On Fri, Aug 02, 2019 at 08:14:00AM -0700, Darrick J. Wong wrote:
> On Fri, Aug 02, 2019 at 11:19:39AM +0200, Carlos Maiolino wrote:
> > Hi Darrick.
> >
> > > > + return error;
> > > > +
> > > > + block = ur_block;
> > > > + error = bmap(inode, &block);
> > > > +
> > > > + if (error)
> > > > + ur_block = 0;
> > > > + else
> > > > + ur_block = block;
> > >
> > > What happens if ur_block > INT_MAX? Shouldn't we return zero (i.e.
> > > error) instead of truncating the value? Maybe the code does this
> > > somewhere else? Here seemed like the obvious place for an overflow
> > > check as we go from sector_t to int.
> > >
> >
> > The behavior should still be the same. It will get truncated, unfortunately. I
> > don't think we can actually change this behavior and return zero instead of
> > truncating it.
>
> But that's even worse, because the programs that rely on FIBMAP will now
> receive *incorrect* results that may point at a different file and
> definitely do not point at the correct file block.
How is this worse? This is exactly what happens today, on the original FIBMAP
implementation.
Maybe I am not seeing something or having a different thinking you have, but
this is the behavior we have now, without my patches. And we can't really change
it; the user view of this implementation.
That's why I didn't try to change the result, so the truncation still happens.
>
> Note also that the iomap (and therefore xfs) implementation WARNs on
> integer overflow and returns 0 (error) to prevent an incorrect access.
It does not really prevent anything. It just issue a warning saying the result
will be truncated, in an attempt to notify the FIBMAP interface user that he/she
can't trust the result, but it does not prevent a truncated result to be
returned. And IIRC, iomap is the only interface now that cares about issuing a
warning.
I think the *best* we could do here, is to make the new bmap() to issue the same
kind of WARN() iomap does, but we can't really change the end result.
>
> --D
>
> > > --D
> > >
> > > > +
> > > > + error = put_user(ur_block, p);
> > > > +
> > > > + return error;
> > > > }
> > > >
> > > > /**
> > > > --
> > > > 2.20.1
> > > >
> >
> > --
> > Carlos
--
Carlos
next prev parent reply other threads:[~2019-08-05 10:27 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-31 14:12 [PATCH 0/9 V4] New ->fiemap infrastructure and ->bmap removal Carlos Maiolino
2019-07-31 14:12 ` [PATCH 1/9] fs: Enable bmap() function to properly return errors Carlos Maiolino
2019-07-31 14:12 ` [PATCH 2/9] cachefiles: drop direct usage of ->bmap method Carlos Maiolino
2019-07-31 14:12 ` [PATCH 3/9] ecryptfs: drop direct calls to ->bmap Carlos Maiolino
2019-07-31 14:12 ` [PATCH 4/9] fibmap: Use bmap instead of ->bmap method in ioctl_fibmap Carlos Maiolino
2019-07-31 23:12 ` Darrick J. Wong
2019-08-02 9:19 ` Carlos Maiolino
2019-08-02 15:14 ` Darrick J. Wong
2019-08-05 10:27 ` Carlos Maiolino [this message]
2019-08-05 15:12 ` Darrick J. Wong
2019-08-06 5:38 ` Christoph Hellwig
2019-08-06 12:07 ` Carlos Maiolino
2019-08-06 14:48 ` Darrick J. Wong
2019-08-08 7:17 ` Carlos Maiolino
2019-08-06 12:02 ` Carlos Maiolino
2019-08-06 22:41 ` Luis Chamberlain
2019-08-07 14:42 ` Darrick J. Wong
2019-08-08 7:12 ` Carlos Maiolino
2019-08-08 18:53 ` Andreas Dilger
2019-08-19 10:10 ` Carlos Maiolino
2019-07-31 14:12 ` [PATCH 5/9] fs: Move start and length fiemap fields into fiemap_extent_info Carlos Maiolino
2019-07-31 23:28 ` Darrick J. Wong
2019-08-02 9:51 ` Carlos Maiolino
2019-08-02 15:15 ` Darrick J. Wong
2019-08-05 9:40 ` Carlos Maiolino
2019-08-06 5:39 ` Christoph Hellwig
2019-07-31 14:12 ` [PATCH 6/9] iomap: Remove length and start fields from iomap_fiemap Carlos Maiolino
2019-07-31 23:24 ` Darrick J. Wong
2019-07-31 14:12 ` [PATCH 7/9] fiemap: Use a callback to fill fiemap extents Carlos Maiolino
2019-07-31 23:26 ` Darrick J. Wong
2019-07-31 14:12 ` [PATCH 8/9] Use FIEMAP for FIBMAP calls Carlos Maiolino
2019-07-31 23:22 ` Darrick J. Wong
2019-07-31 23:31 ` Darrick J. Wong
2019-08-02 13:52 ` Carlos Maiolino
2019-08-06 5:41 ` Christoph Hellwig
2019-08-02 13:48 ` Carlos Maiolino
2019-08-02 15:29 ` Darrick J. Wong
2019-08-05 10:38 ` Carlos Maiolino
2019-08-06 5:46 ` Christoph Hellwig
2019-07-31 14:12 ` [PATCH 9/9] xfs: Get rid of ->bmap Carlos Maiolino
2019-07-31 23:30 ` Darrick J. Wong
2019-08-02 10:20 ` [PATCH 0/9 V4] New ->fiemap infrastructure and ->bmap removal Carlos Maiolino
2019-08-08 8:27 [PATCH 0/9 V5] " Carlos Maiolino
2019-08-08 8:27 ` [PATCH 4/9] fibmap: Use bmap instead of ->bmap method in ioctl_fibmap Carlos Maiolino
2019-08-08 20:38 ` kbuild test robot
2019-08-14 11:01 ` Carlos Maiolino
2019-08-14 11:08 ` Christoph Hellwig
2019-09-11 13:43 [PATCH 0/9 V6] New ->fiemap infrastructure and ->bmap removal Carlos Maiolino
2019-09-11 13:43 ` [PATCH 4/9] fibmap: Use bmap instead of ->bmap method in ioctl_fibmap Carlos Maiolino
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