Re: [PATCH 04/29] vfs: strengthen checking of file range inputs to generic_remap_checks

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Thu, Oct 18, 2018 at 01:41:56AM +0100, Al Viro wrote:
> On Wed, Oct 17, 2018 at 03:44:43PM -0700, Darrick J. Wong wrote:
> > +static int generic_access_check_limits(struct file *file, loff_t pos,
> > +				       loff_t *count)
> > +{
> > +	struct inode *inode = file->f_mapping->host;
> > +
> > +	/* Don't exceed the LFS limits. */
> > +	if (unlikely(pos + *count > MAX_NON_LFS &&
> > +				!(file->f_flags & O_LARGEFILE))) {
> > +		if (pos >= MAX_NON_LFS)
> > +			return -EFBIG;
> > +		*count = min(*count, (loff_t)MAX_NON_LFS - pos);
> 
> 	Can that can be different from MAX_NON_LFS - pos?
> 
> > +	}
> > +
> > +	/*
> > +	 * Don't operate on ranges the page cache doesn't support.
> > +	 *
> > +	 * If we have written data it becomes a short write.  If we have
> > +	 * exceeded without writing data we send a signal and return EFBIG.
> > +	 * Linus frestrict idea will clean these up nicely..
> > +	 */
> > +	if (unlikely(pos >= inode->i_sb->s_maxbytes))
> > +		return -EFBIG;
> > +
> > +	*count = min(*count, inode->i_sb->s_maxbytes - pos);
> > +	return 0;
> > +}
> 
> Anyway, I would rather do this here:
> 
> 	struct inode *inode = file->f_mapping->host;
> 	loff_t max_size = inode->i_sb->s_maxbytes;
> 
> 	if (!(file->f_flags & O_LARGEFILE))
> 		max_size = MAX_NON_LFS;
> 
> 	if (unlikely(pos >= max_size))
> 		return -EFBIG;
> 	*count = min(*count, max_size - pos);
> 	return 0;

Sounds much better to me. :)

--D