Re: [PATCH v3] nfsd: prevent a double put of revoked layout stateids

[Jeff Layton <jlayton@kernel.org>]

On Wed, 2026-10-14 at 15:12 +0900, Jinpyo Lee wrote:
> nfsd4_free_stateid() finds an admin-revoked layout stateid with
> find_stateid_locked(), which does not acquire a reference. The layout
> case drops cl_lock without marking the stateid closed, then stops fence
> work and calls nfs4_put_stid() without owning a reference. Concurrent
> disposal can therefore access a freed layout stateid or drop a reference
> owned by another holder.
> 
> Mark the layout stateid CLOSED under cl_lock. Take a temporary reference
> before dropping cl_lock and hold it while stopping fence work and
> draining the remaining layout segments, then release it with the final
> put. The IDR owns no layout reference.
> 
> Use cl_lock for the CLOSED update in LAYOUTRETURN as well, matching the
> common stateid locking rule. Retain ls_mutex through that update and
> recheck CLOSED under cl_lock after taking ls_mutex in LAYOUTGET, so a
> stale LAYOUTGET cannot add a segment after the drain. Also make the newly
> allocated layout stateid the error-path put target.
> 
> Make revoked-stateid disposal idempotent with SC_STATUS_FREED under
> cl_lock. An in-flight reference can keep an admin-revoked OPEN, LOCK, or
> DELEG stateid in the IDR after disposal. Restrict
> nfs40_clean_admin_revoked() to v4.0 clients and skip FREED entries so its
> retry loop cannot repeatedly select the same stateid or consume references
> owned by other callers. Use FREED rather than CLOSED to guard disposal:
> delegation recall rejection can set CLOSED before the first disposal call.
> 
> Reject FREED stateids in FREE_STATEID and TEST_STATEID as well, so a
> stateid retained by an in-flight reference returns BAD_STATEID after
> successful disposal instead of success or ADMIN_REVOKED.
> 
> Validation used nfsd-testing at c32fef6c476d. The patched x86_64 kernel
> and modules were built with GCC 12.2 and booted with Generic KASAN,
> lockdep, modular NFSD, and pNFS SCSI layout support. Basic NFSv4.2,
> NFSv4.0, and NFSv3 read/write/unmount smoke tests passed.
> 
> Targeted runs forced concurrent two-slot FREE_STATEID, LAYOUTGET and
> LAYOUTRETURN overlaps around ls_mutex, and an NFSv4.0 cleaner retry while
> a READ held an OPEN stateid reference. Stateids were reaped once, stale
> requests returned BAD_STATEID, and the NFSv4.0 cleaner did not process
> the NFSv4.1 client. No KASAN, lockdep, refcount, list-corruption, Oops, or
> kernel BUG report occurred; kernel taint remained zero.
> 
> The vulnerability research and validation were conducted by members of
> the Tobabz team as part of the Best of the Best 15th program.
> 
> Fixes: 86b9898920a6 ("NFSD: Handle layout stid in nfsd4_drop_revoked_stid()")
> Suggested-by: Chuck Lever <cel@kernel.org>
> Cc: stable@vger.kernel.org
> Assisted-by: LLM
> Signed-off-by: Jinpyo Lee <bint4b13@gmail.com>
> ---
> Changes in v3:
> 
> - Address the v4.0 disposal issue reported by Sashiko and forwarded by
>   Jeff Layton: claim disposal with FREED under cl_lock and skip FREED
>   stateids in the admin-revocation scan.
> - Preserve first-time disposal of delegations already marked CLOSED, and
>   reject FREED stateids in FREE_STATEID and TEST_STATEID.
> - Rebase onto nfsd-testing c32fef6c476daa5830f600614657baee59c83339
>   and add targeted runtime validation.
> 
>  fs/nfsd/nfs4layouts.c | 34 ++++++++++++++++++++++++++++++++--
>  fs/nfsd/nfs4state.c   | 29 +++++++++++++++++++++++++----
>  fs/nfsd/pnfs.h        |  6 ++++++
>  fs/nfsd/state.h       |  6 +++---
>  4 files changed, 66 insertions(+), 9 deletions(-)
> 
> diff --git a/fs/nfsd/nfs4layouts.c b/fs/nfsd/nfs4layouts.c
> index 898776c9d..749ace97e 100644
> --- a/fs/nfsd/nfs4layouts.c
> +++ b/fs/nfsd/nfs4layouts.c
> @@ -312,6 +312,7 @@ nfsd4_preprocess_layout_stateid(struct svc_rqst *rqstp,
>  		status = nfserr_jukebox;
>  		if (!ls)
>  			goto out;
> +		stid = &ls->ls_stid;
>  		mutex_lock(&ls->ls_mutex);
>  	} else {
>  		ls = container_of(stid, struct nfs4_layout_stateid, ls_stid);
> @@ -324,6 +325,15 @@ nfsd4_preprocess_layout_stateid(struct svc_rqst *rqstp,
>  			goto out_unlock_stid;
>  	}
>  
> +	/* A new or looked-up stateid may have been closed before ls_mutex. */
> +	spin_lock(&stid->sc_client->cl_lock);
> +	if (stid->sc_status & SC_STATUS_CLOSED) {
> +		spin_unlock(&stid->sc_client->cl_lock);
> +		status = nfserr_bad_stateid;
> +		goto out_unlock_stid;
> +	}
> +	spin_unlock(&stid->sc_client->cl_lock);
> +
>  	*lsp = ls;
>  	return 0;
>  
> @@ -537,12 +547,18 @@ nfsd4_return_file_layouts(struct svc_rqst *rqstp,
>  			nfs4_inc_and_copy_stateid(&lrp->lr_sid, &ls->ls_stid);
>  		lrp->lrs_present = true;
>  	} else {
> -		trace_nfsd_layoutstate_unhash(&ls->ls_stid.sc_stateid);
> -		ls->ls_stid.sc_status |= SC_STATUS_CLOSED;
>  		lrp->lrs_present = false;
>  	}
>  	spin_unlock(&ls->ls_lock);
>  
> +	if (!lrp->lrs_present) {
> +		/* ls_mutex prevents a LAYOUTGET from adding another segment. */
> +		spin_lock(&ls->ls_stid.sc_client->cl_lock);
> +		ls->ls_stid.sc_status |= SC_STATUS_CLOSED;
> +		spin_unlock(&ls->ls_stid.sc_client->cl_lock);
> +		trace_nfsd_layoutstate_unhash(&ls->ls_stid.sc_stateid);
> +	}
> +
>  	mutex_unlock(&ls->ls_mutex);
>  	nfs4_put_stid(&ls->ls_stid);
>  	nfsd4_free_layouts(&reaplist);
> @@ -594,6 +610,20 @@ nfsd4_return_all_layouts(struct nfs4_layout_stateid *ls,
>  	spin_unlock(&ls->ls_lock);
>  }
>  
> +void nfsd4_return_revoked_layout(struct nfs4_layout_stateid *ls)
> +{
> +	LIST_HEAD(reaplist);
> +
> +	/*
> +	 * The caller holds a stateid reference until segment draining ends.
> +	 * Wait for any LAYOUTGET that passed the CLOSED check.
> +	 */
> +	mutex_lock(&ls->ls_mutex);
> +	nfsd4_return_all_layouts(ls, &reaplist);
> +	mutex_unlock(&ls->ls_mutex);
> +	nfsd4_free_layouts(&reaplist);
> +}
> +
>  void
>  nfsd4_return_all_client_layouts(struct nfs4_client *clp)
>  {
> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> index 26d2d56a5..0f1641eab 100644
> --- a/fs/nfsd/nfs4state.c
> +++ b/fs/nfsd/nfs4state.c
> @@ -5849,6 +5849,17 @@ static void nfsd4_drop_revoked_stid(struct nfs4_stid *s)
>  	struct nfs4_delegation *dp;
>  	bool unhashed;
>  
> +	/*
> +	 * In-flight references can keep a disposed stateid in the IDR.
> +	 * CLOSED alone is not sufficient: a delegation may be closed
> +	 * before its first call here.
> +	 */
> +	if (s->sc_status & SC_STATUS_FREED) {
> +		spin_unlock(&cl->cl_lock);
> +		return;
> +	}
> +	s->sc_status |= SC_STATUS_FREED;
> +
>  	switch (s->sc_type) {
>  	case SC_TYPE_OPEN:
>  		stp = openlockstateid(s);
> @@ -5867,15 +5878,22 @@ static void nfsd4_drop_revoked_stid(struct nfs4_stid *s)
>  	case SC_TYPE_DELEG:
>  		dp = delegstateid(s);
>  		list_del_init(&dp->dl_recall_lru);
> -		s->sc_status |= SC_STATUS_FREED;
>  		spin_unlock(&cl->cl_lock);
>  		nfs4_put_stid(s);
>  		break;
>  	case SC_TYPE_LAYOUT:
>  		ls = layoutstateid(s);
> +		s->sc_status |= SC_STATUS_CLOSED;
> +		/*
> +		 * The IDR does not own a layout stateid reference. Keep ls
> +		 * alive while draining worker and segment references below;
> +		 * the final put releases this temporary reference.
> +		 */
> +		refcount_inc(&s->sc_count);
>  		list_del_init(&ls->ls_perclnt);
>  		spin_unlock(&cl->cl_lock);
>  		nfsd4_stop_layout_fence(ls);
> +		nfsd4_return_revoked_layout(ls);
>  		nfs4_put_stid(s);
>  		break;
>  	default:
> @@ -7901,6 +7919,8 @@ static void nfs40_clean_admin_revoked(struct nfsd_net *nn,
>  		unsigned long id, tmp;
>  		struct nfs4_stid *stid;
>  
> +		if (clp->cl_minorversion != 0)
> +			continue;
>  		if (atomic_read(&clp->cl_admin_revoked) == 0)
>  			continue;
>  		if (is_client_expired(clp))
> @@ -7908,7 +7928,8 @@ static void nfs40_clean_admin_revoked(struct nfsd_net *nn,
>  
>  		spin_lock(&clp->cl_lock);
>  		idr_for_each_entry_ul(&clp->cl_stateids, stid, tmp, id)
> -			if (stid->sc_status & SC_STATUS_ADMIN_REVOKED) {
> +			if ((stid->sc_status & SC_STATUS_ADMIN_REVOKED) &&
> +			    !(stid->sc_status & SC_STATUS_FREED)) {
>  				refcount_inc(&stid->sc_count);
>  				atomic_inc(&clp->cl_rpc_users);
>  				spin_unlock(&nn->client_lock);
> @@ -8340,7 +8361,7 @@ static __be32 nfsd4_validate_stateid(struct nfs4_client *cl, stateid_t *stateid)
>  		return status;
>  	spin_lock(&cl->cl_lock);
>  	s = find_stateid_locked(cl, stateid);
> -	if (!s)
> +	if (!s || s->sc_status & SC_STATUS_FREED)
>  		goto out_unlock;
>  	status = nfsd4_stid_check_stateid_generation(stateid, s, 1);
>  	if (status)
> @@ -8725,7 +8746,7 @@ nfsd4_free_stateid(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
>  
>  	spin_lock(&cl->cl_lock);
>  	s = find_stateid_locked(cl, stateid);
> -	if (!s || s->sc_status & SC_STATUS_CLOSED)
> +	if (!s || s->sc_status & (SC_STATUS_CLOSED | SC_STATUS_FREED))
>  		goto out_unlock;
>  	if (s->sc_status & SC_STATUS_ADMIN_REVOKED) {
>  		nfsd4_drop_revoked_stid(s);
> diff --git a/fs/nfsd/pnfs.h b/fs/nfsd/pnfs.h
> index 559df0e5b..9b0f17a4d 100644
> --- a/fs/nfsd/pnfs.h
> +++ b/fs/nfsd/pnfs.h
> @@ -75,6 +75,7 @@ struct nfsd4_deviceid_map *nfsd4_find_devid_map(int idx);
>  #ifdef CONFIG_NFSD_PNFS
>  void nfsd4_setup_layout_type(struct svc_export *exp);
>  void nfsd4_return_all_client_layouts(struct nfs4_client *);
> +void nfsd4_return_revoked_layout(struct nfs4_layout_stateid *ls);
>  void nfsd4_return_all_file_layouts(struct nfs4_client *clp,
>  		struct nfs4_file *fp);
>  void nfsd4_close_layout(struct nfs4_layout_stateid *ls);
> @@ -93,6 +94,11 @@ static inline void nfsd4_setup_layout_type(struct svc_export *exp)
>  static inline void nfsd4_return_all_client_layouts(struct nfs4_client *clp)
>  {
>  }
> +
> +static inline void nfsd4_return_revoked_layout(struct nfs4_layout_stateid *ls)
> +{
> +}
> +
>  static inline void nfsd4_return_all_file_layouts(struct nfs4_client *clp,
>  		struct nfs4_file *fp)
>  {
> diff --git a/fs/nfsd/state.h b/fs/nfsd/state.h
> index 79dfa47b8..924a98af7 100644
> --- a/fs/nfsd/state.h
> +++ b/fs/nfsd/state.h
> @@ -148,9 +148,8 @@ struct nfs4_stid {
>   * nn->deleg_lock protects sc_status for hashed delegation stateids.
>   * ->cl_lock protects the bits set as one is disposed of
>   * (SC_STATUS_CLOSED, SC_STATUS_FREEABLE, SC_STATUS_FREED) and
> - * sc_status for open and lock stateids. ->st_mutex also protects
> - * sc_status for open stateids. ->ls_lock protects sc_status for
> - * layout stateids.
> + * sc_status for open, lock, and layout stateids. ->st_mutex also protects
> + * sc_status for open stateids.
>   */
>  /*
>   * For an open stateid kept around *only* to process close replays.
> @@ -161,6 +160,7 @@ struct nfs4_stid {
>  #define SC_STATUS_REVOKED	BIT(1)
>  #define SC_STATUS_ADMIN_REVOKED	BIT(2)
>  #define SC_STATUS_FREEABLE	BIT(3)
> +/* Disposal has been claimed; in-flight references may still exist. */
>  #define SC_STATUS_FREED		BIT(4)
>  	unsigned short		sc_status;
>  
> 
> base-commit: c32fef6c476daa5830f600614657baee59c83339

Reviewed-by: Jeff Layton <jlayton@kernel.org>