> Von: Darrick J. Wong [darrick.wong@xxxxxxxxxx]
> Gesendet: Dienstag, 22. August 2017 18:41
> An: Christoph Hellwig
> Cc: Markus Stockhausen; pmenzel@xxxxxxxxxxxxx; linux-xfs@xxxxxxxxxxxxxxx
> Betreff: Re: another possible integer truncation in xfs
>
> On Mon, Aug 21, 2017 at 10:16:03AM +0200, Christoph Hellwig wrote:
> > On Mon, Aug 21, 2017 at 08:01:03AM +0000, Markus Stockhausen wrote:
> > > Hi Christoph,
> > >
> > > out of curiosity I looked for other use cases of min_t in xfs. At least
> > > until 4.12 there is a similar constellation in xfs_dir2_leaf_readbuf:
> > >
> > > if (trim_map) {
> > > mip->map_blocks -= geo->fsbcount;
> > > /*
> > > * Loop to get rid of the extents for the
> > > * directory block.
> > > */
> > > for (i = geo->fsbcount; i > 0; ) {
> > > j = min_t(int, map->br_blockcount, i);
> > > map->br_blockcount -= j;
> > > map->br_startblock += j;
> > > map->br_startoff += j;
> > >
> > > The loop could go havoc if map->br_blockcount is larger than
> > > 2G. If you think it could classify for stable feel free to add it too.
>
> "2G"... are you concerned about an integer overflow if map->br_blockcount
> is a value larger than 2147483647, or if *map itself represents an
> extent longer than 2GiB? (I'm pretty sure you're talking about the
> first scenario, but the units here are ambiguous.)
>
> I /think/ the correct answer here is that file extent records can't ever
> be longer than 2^20 blocks so this min_t ought to be fine.
Hi Darrick,
It was just the same educated guess as the first spotting. 64 bit
variables minified by their lower 32 bits. Thus truncation "could"
lead to strange side effects. If it cannot happen - sorry for the
noise.
Markus
> --D
>
> > I don't think it has a chance to be larger in practice, but we should
> > fix it anyway. I'll prepare a patch.
> >
> > Thanks for spotting this!
> > --
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