Re: [PATCH 4/4] fs: Fix possible use-after-free with AIO

[Jan Kara <jack@suse.cz>]

On Wed 23-01-13 10:02:09, Jeff Moyer wrote:
> Jan Kara <jack@suse.cz> writes:
> 
> > Running AIO is pinning inode in memory using file reference. Once AIO
> > is completed using aio_complete(), file reference is put and inode can
> > be freed from memory. So we have to be sure that calling aio_complete()
> > is the last thing we do with the inode.
> >
> > CC: Christoph Hellwig <hch@infradead.org>
> > CC: Jens Axboe <axboe@kernel.dk>
> > CC: Jeff Moyer <jmoyer@redhat.com>
> > CC: stable@vger.kernel.org
> > Signed-off-by: Jan Kara <jack@suse.cz>
> > ---
> >  fs/direct-io.c |    2 +-
> >  1 files changed, 1 insertions(+), 1 deletions(-)
> >
> > diff --git a/fs/direct-io.c b/fs/direct-io.c
> > index cf5b44b..f853263 100644
> > --- a/fs/direct-io.c
> > +++ b/fs/direct-io.c
> > @@ -261,9 +261,9 @@ static ssize_t dio_complete(struct dio *dio, loff_t offset, ssize_t ret, bool is
> >  		dio->end_io(dio->iocb, offset, transferred,
> >  			    dio->private, ret, is_async);
> >  	} else {
> > +		inode_dio_done(dio->inode);
> >  		if (is_async)
> >  			aio_complete(dio->iocb, ret, 0);
> > -		inode_dio_done(dio->inode);
> >  	}
> 
> OK, so this is only a problem if nobody is waiting in inode_dio_wait,
> yes?  Good catch, though it seems incredibly unlikely anyone would trip
> over this in practice (since fput is done in a worker thread, or
> deferred).
  Yes, it's mostly a theoretical race.

> Acked-by: Jeff Moyer <jmoyer@redhat.com>
  Thanks.

								Honza
-- 
Jan Kara <jack@suse.cz>
SUSE Labs, CR