Re: [PATCH 1/2] NFSD: Fix use-after-free warning when doing inter-server copy

J. Bruce Fields
2021-02-20T01:10:04Z

Dai, do you have a copy of the original use-after-free warning?

--b.

On Fri, Feb 19, 2021 at 07:18:53PM -0500, Olga Kornievskaia wrote:
> Hi Dai (Bruce),
>
> This patch is what broke the mount that's now left behind between the
> source server and the destination server. We are no longer dropping
> the necessary reference on the mount to go away. I haven't been paying
> as much attention as I should have been to the changes. The original
> code called fput(src) so a simple refcount of the file. Then things
> got complicated and moved to nfsd_file_put(). So I don't understand
> complexity. But we need to do some kind of put to decrement the needed
> reference on the superblock. Bruce any ideas? Can we go back to
> fput()?
>
> On Thu, Oct 29, 2020 at 3:08 PM Dai Ngo <dai.ngo@oracle.com> wrote:
> >
> > The source file nfsd_file is not constructed the same as other
> > nfsd_file's via nfsd_file_alloc. nfsd_file_put should not be
> > called to free the object; nfsd_file_put is not the inverse of
> > kzalloc, instead kfree is called by nfsd4_do_async_copy when done.
> >
> > Fixes: ce0887ac96d3 ("NFSD add nfs4 inter ssc to nfsd4_copy")
> > Signed-off-by: Dai Ngo <dai.ngo@oracle.com>
> > ---
> > fs/nfsd/nfs4proc.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
> > index ad2fa1a8e7ad..9c43cad7e408 100644
> > --- a/fs/nfsd/nfs4proc.c
> > +++ b/fs/nfsd/nfs4proc.c
> > @@ -1299,7 +1299,7 @@ nfsd4_cleanup_inter_ssc(struct vfsmount *ss_mnt, struct nfsd_file *src,
> > struct nfsd_file *dst)
> > {
> > nfs42_ssc_close(src->nf_file);
> > - nfsd_file_put(src);
> > + /* 'src' is freed by nfsd4_do_async_copy */
> > nfsd_file_put(dst);
> > mntput(ss_mnt);
> > }
> > --
> > 2.20.1.1226.g1595ea5.dirty
> >