Re: [PATCH 14/31] libext2fs: Fix ext2fs_open2() truncation of the superblock parameter

Darrick J. Wong
2013-10-08T17:47:36Z

On Tue, Oct 08, 2013 at 11:58:59AM -0400, Theodore Ts'o wrote:
> On Mon, Sep 30, 2013 at 06:28:12PM -0700, Darrick J. Wong wrote:
> > Since it's possible for very large filesystems to store backup superblocks at
> > very large (> 2^32) block numbers, we need to be able to handle the case of a
> > caller directing us to read one of these high-numbered backups.
> >
> > Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
>
> Hmm... This is technically true, but I'm wondering how much we should
> care. In practice, users almost always use the first couple of backup
> superblocks. I could imagine a situation with a RAID array where the
> first disk(s) were trashed, so we needed to use a backup superblock
> beyond 2**32, but it's a bit unlikely.

True, it seems unlikely now that one would ever need to use the backup sbs
beyond 2^32, but since mke2fs is writing them there, we ought to be able to use
them.

For now, though, it's truncating the top 32 bits of a (usually) user-specified
value, so if we don't extend the API we ought to at least complain and exit.

> If there was some other reason why we needed to add a new ext2fs_open3
> variant, it would certainly be a good thing to fix. But I'm wondering
> if it's worth adding a new interface just for this.
>
> Is there perhaps any other extensions to ext2fs_open() that we might
> want to make, either now or in the future?

I don't have any off the top of my head, but I'll think about it.

--D
>
> Regards,
>
> - Ted
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