Re: fs: out of bounds on stack in iov_iter_advance

[Ross Zwisler]

On Sat, Oct 17, 2015 at 03:22:19PM -0400, Sasha Levin wrote:
> On 09/30/2015 05:30 PM, Sasha Levin wrote:
> > On 09/17/2015 10:24 PM, Sasha Levin wrote:
> >> On 08/19/2015 01:46 AM, Al Viro wrote:
> >>>> or mapping->a_ops->direct_IO() returned more
> >>>>> than 'count'.
> >>> 	Was there DAX involved?  ->direct_IO() in there is blkdev_direct_IO(),
> >>> which takes rather different paths in those cases...
> >>>
> >>
> >> So I've traced this all the way back to dax_io(). I can trigger this with:
> >>
> >> diff --git a/fs/dax.c b/fs/dax.c
> >> index 93bf2f9..2cdb8a5 100644
> >> --- a/fs/dax.c
> >> +++ b/fs/dax.c
> >> @@ -178,6 +178,7 @@ static ssize_t dax_io(struct inode *inode, struct iov_iter *iter,
> >>         if (need_wmb)
> >>                 wmb_pmem();
> >>
> >> +       WARN_ON((pos == start) && (pos - start > iov_iter_count(iter)));
> >>         return (pos == start) ? retval : pos - start;
> >>  }
> >>
> >> So it seems that iter gets moved twice here: once in dax_io(), and once again
> >> back at generic_file_read_iter().
> >>
> >> I don't see how it ever worked. Am I missing something?
> > 
> > Ping?
> 
> Ping?

I'll try and find time to look at this issue this week.  Sasha, do you have a
more targeted reproducer, or is still just the trinity fuzzer?
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