Re: [PATCH 1/2] xfs: rewrite getbmap using the xfs_iext_* helpers

[Christoph Hellwig <hch@lst.de>]

On Wed, Sep 20, 2017 at 04:08:24PM -0700, Darrick J. Wong wrote:
> > I'm still wondering why we allocate a potentially large getbmapx buffer,
> > fill it out, and only then format the results to userspace?  I think
> > getbmap (the ioctl) is now the only user of these functions, so can't
> > we just call the formatter directly from _getbmap_report_one and
> > _getbmap_report_hole, like what getfsmap does?
> > 
> > (I also feel like I've asked this before, so apologies if I'm merely
> > forgetting the answer.)
> 
> Oh right, it's because we have the inode locked, and copying things to
> userspace could incur a page fault, which we can't risk with the inode
> locked because some malicious person could create a fragmented file with
> a bmap request header at the start of the file, mmap the file, and call
> bmap on the fragmented file with the pointer being the mmap region.

Yes.

Can I get a Reviewed-by: tag now? :)