Re: [PATCH] NFSD: fix use-after-free on source server when doing inter-server copy

[Olga Kornievskaia <olga.kornievskaia@gmail.com>]

On Mon, Aug 1, 2022 at 12:29 PM Chuck Lever III <chuck.lever@oracle.com> wrote:
>
>
>
> > On Jul 31, 2022, at 4:19 PM, Dai Ngo <dai.ngo@oracle.com> wrote:
> >
> > Use-after-free occurred when the laundromat tried to free expired
> > cpntf_state entry on the s2s_cp_stateids list after inter-server
> > copy completed. The sc_cp_list that the expired copy state was
> > inserted on was already freed.
> >
> > When COPY completes, the Linux client normally sends LOCKU(lock_state x),
> > FREE_STATEID(lock_state x) and CLOSE(open_state y) to the source server.
> > The nfs4_put_stid call from nfsd4_free_stateid cleans up the copy state
> > from the s2s_cp_stateids list before freeing the lock state's stid.
> >
> > However, sometimes the CLOSE was sent before the FREE_STATEID request.
> > When this happens, the nfsd4_close_open_stateid call from nfsd4_close
> > frees all lock states on its st_locks list without cleaning up the copy
> > state on the sc_cp_list list. When the time the FREE_STATEID arrives the
> > server returns BAD_STATEID since the lock state was freed. This causes
> > the use-after-free error to occur when the laundromat tries to free
> > the expired cpntf_state.
> >
> > This patch adds a call to nfs4_free_cpntf_statelist in
> > nfsd4_close_open_stateid to clean up the copy state before calling
> > free_ol_stateid_reaplist to free the lock state's stid on the reaplist.
> >
> > Signed-off-by: Dai Ngo <dai.ngo@oracle.com>
>
> I'm interested in Olga's comments as well, so I'm going to
> wait a bit before applying this one.

Sorry folks, I totally missed this thread.... I was on vacation, came
back and started working on this after running into the oops with
Chuck's new patch set..

Well as you saw from my other post that my solution is different and
suggests putting cleanup of the copy_notify states together with
idr_remove() of the stateid it was associated with.

> Also, did you figure out where this crash started to occur?
> I'd like to have a precise sense of whether this should be
> backported.

I'm not going to claim this is the first occurrence but Jorge first
ran into this while testing ssc over iwarp on the 5.15-rc4 kernel.

>
>
> > ---
> > fs/nfsd/nfs4state.c | 3 +++
> > 1 file changed, 3 insertions(+)
> >
> > diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> > index 9409a0dc1b76..749f51dff5c7 100644
> > --- a/fs/nfsd/nfs4state.c
> > +++ b/fs/nfsd/nfs4state.c
> > @@ -6608,6 +6608,7 @@ static void nfsd4_close_open_stateid(struct nfs4_ol_stateid *s)
> >       struct nfs4_client *clp = s->st_stid.sc_client;
> >       bool unhashed;
> >       LIST_HEAD(reaplist);
> > +     struct nfs4_ol_stateid *stp;
> >
> >       spin_lock(&clp->cl_lock);
> >       unhashed = unhash_open_stateid(s, &reaplist);
> > @@ -6616,6 +6617,8 @@ static void nfsd4_close_open_stateid(struct nfs4_ol_stateid *s)
> >               if (unhashed)
> >                       put_ol_stateid_locked(s, &reaplist);
> >               spin_unlock(&clp->cl_lock);
> > +             list_for_each_entry(stp, &reaplist, st_locks)
> > +                     nfs4_free_cpntf_statelist(clp->net, &stp->st_stid);
> >               free_ol_stateid_reaplist(&reaplist);
> >       } else {
> >               spin_unlock(&clp->cl_lock);
> > --
> > 2.9.5
> >
>
> --
> Chuck Lever
>
>
>