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

J. Bruce Fields
2021-02-20T03:21:56Z

On Fri, Feb 19, 2021 at 05:31:58PM -0800, dai.ngo@oracle.com wrote:
> If this is the cause why we don't drop the mount after the copy
> then I can restore the patch and look into this problem. Unfortunately,
> all my test machines are down for maintenance until Sunday/Monday.

I think we can take some time to figure out what's actually going on
here before reverting anything.

--b.

>
> -Dai
>
> On 2/19/21 5:09 PM, J. Bruce Fields wrote:
> >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
> >>>