[PATCH] nfsd: release layout stid on setlease failure

[Chris Mason <clm@meta.com>]

nfs4_alloc_stid() publishes the new stid into cl->cl_stateids via
idr_alloc_cyclic() under cl_lock before returning to
nfsd4_alloc_layout_stateid(). When nfsd4_layout_setlease() then
fails, the error path frees the layout stateid directly with
kmem_cache_free() without ever calling idr_remove(), leaving the
IDR slot pointing at freed slab memory. Any subsequent IDR walker
(states_show, client teardown) dereferences the dangling pointer.

The correct teardown for an IDR-published stid is nfs4_put_stid(),
which removes the IDR slot under cl_lock, dispatches sc_free
(nfsd4_free_layout_stateid) to release ls->ls_file via
nfsd4_close_layout(), and drops the nfs4_file reference in its
tail.

A second issue blocks that switch: nfsd4_free_layout_stateid()
unconditionally inspects ls->ls_fence_work via
delayed_work_pending() under ls_lock, but
INIT_DELAYED_WORK(&ls->ls_fence_work, ...) currently runs only
after the setlease call. On the setlease-failure path the
destructor would touch an uninitialized delayed_work.

    nfsd4_alloc_layout_stateid()
      nfs4_alloc_stid()           /* idr_alloc_cyclic under cl_lock */
      nfsd4_layout_setlease()     /* fails */
        nfs4_put_stid()
          nfsd4_free_layout_stateid()
            delayed_work_pending(&ls->ls_fence_work)  /* needs INIT */
            nfsd4_close_layout()  /* nfsd_file_put(ls->ls_file) */
          put_nfs4_file()

Fix by hoisting the ls_fenced / ls_fence_delay / INIT_DELAYED_WORK
initialization above the nfsd4_layout_setlease() call, and replace
the manual nfsd_file_put + put_nfs4_file + kmem_cache_free cleanup
with a single nfs4_put_stid(stp).

Fixes: c5c707f96fc9 ("nfsd: implement pNFS layout recalls")
Assisted-by: kres (claude-opus-4-7)
Signed-off-by: Chris Mason <clm@meta.com>
---
 fs/nfsd/nfs4layouts.c | 12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

diff --git a/fs/nfsd/nfs4layouts.c b/fs/nfsd/nfs4layouts.c
index 69e41105efdd..8e2929cffa7c 100644
--- a/fs/nfsd/nfs4layouts.c
+++ b/fs/nfsd/nfs4layouts.c
@@ -264,10 +264,12 @@ nfsd4_alloc_layout_stateid(struct nfsd4_compound_state *cstate,
 		ls->ls_file = find_any_file(fp);
 	BUG_ON(!ls->ls_file);
 
+	ls->ls_fenced = false;
+	ls->ls_fence_delay = 0;
+	INIT_DELAYED_WORK(&ls->ls_fence_work, nfsd4_layout_fence_worker);
+
 	if (nfsd4_layout_setlease(ls)) {
-		nfsd_file_put(ls->ls_file);
-		put_nfs4_file(fp);
-		kmem_cache_free(nfs4_layout_stateid_cache, ls);
+		nfs4_put_stid(stp);
 		return NULL;
 	}
 
@@ -280,10 +282,6 @@ nfsd4_alloc_layout_stateid(struct nfsd4_compound_state *cstate,
 	list_add(&ls->ls_perfile, &fp->fi_lo_states);
 	spin_unlock(&fp->fi_lock);
 
-	ls->ls_fenced = false;
-	ls->ls_fence_delay = 0;
-	INIT_DELAYED_WORK(&ls->ls_fence_work, nfsd4_layout_fence_worker);
-
 	trace_nfsd_layoutstate_alloc(&ls->ls_stid.sc_stateid);
 	return ls;
 }
-- 
2.52.0