6.1-stable review patch. If anyone has any objections, please let me know.
------------------
From: Jeff Layton <jlayton@kernel.org>
commit 3b0c3595db99bb4bebd7c8aa8a36f3c50e411bb7 upstream.
Copy-notify stateids live in the s2s_cp_stateids IDR and on their parent
stid's sc_cp_list, pinned by a single membership reference.
_free_cpntf_state_locked() only unlinks an entry once its refcount reaches
zero, so any revoke path that runs while a concurrent
find_cpntf_state()/manage_cpntf_state() holder has elevated cs_count drops
the reference without unlinking, leaving the entry discoverable with its
membership reference already consumed. A second revoke or a laundromat tick
then frees it while the reader still holds the pointer -- a
KASAN-detectable use-after-free at the reader's nfs4_put_cpntf_state().
This affected all three revoke paths:
- The parent-stid drain (nfs4_free_cpntf_statelist()) repeatedly called
_free_cpntf_state_locked() on the first list entry; a holder that had
bumped cs_count made it return early, so the next iteration
re-decremented and burned the holder's reference.
- OFFLOAD_CANCEL (manage_cpntf_state()) and laundromat expiry likewise
used _free_cpntf_state_locked() and could drop 2->1 without unlinking.
Add revoke_cpntf_state_locked(), which unhashes the entry from the IDR and
sc_cp_list first (deferring the final free to any holder), and use it from
all three revoke paths. The drain now walks with list_for_each_entry_safe()
and revokes each entry unconditionally, so it terminates in one pass per
entry regardless of cs_count. The unhash is gated on
!list_empty(&cps->cp_list); the idr_remove() gate matters because
idr_alloc_cyclic() may have recycled the so_id by then. Keep
_free_cpntf_state_locked() for the reference-holder put path only, where a
concurrent revoke may already have unlinked the entry (its list_del_init()
then a no-op).
Fixes: 624322f1adc5 ("NFSD add COPY_NOTIFY operation")
Cc: <redacted>
Assisted-by: Claude:claude-opus-4-7
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Link: https://patch.msgid.link/20260710-nfsd-testing-v3-6-a0ff7db6aa3e@kernel.org (local)
Signed-off-by: Chuck Lever <cel@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/nfsd/nfs4state.c | 78 +++++++++++++++++++++++++++++++++++++++++-----------
1 file changed, 62 insertions(+), 16 deletions(-)
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -1066,18 +1066,66 @@ void nfs4_free_copy_state(struct nfsd4_c
spin_unlock(&nn->s2s_cp_lock);
}
+/*
+ * Drop the parent's reference on an already-unlinked cpntf entry. If a
+ * concurrent holder still owns a reference, its nfs4_put_cpntf_state() does
+ * the final free.
+ *
+ * nn->s2s_cp_lock must be held.
+ */
+static void put_cpntf_state_unlinked_locked(struct nfs4_cpntf_state *cps)
+{
+ WARN_ON_ONCE(cps->cp_stateid.cs_type != NFS4_COPYNOTIFY_STID);
+ WARN_ON_ONCE(!list_empty(&cps->cp_list));
+
+ if (refcount_dec_and_test(&cps->cp_stateid.cs_count))
+ kfree(cps);
+}
+
+/*
+ * Unhash from the IDR and sc_cp_list. Gated on list_empty() to avoid
+ * evicting a recycled so_id.
+ */
+static void nfsd4_unhash_cpntf_state(struct nfsd_net *nn, struct nfs4_cpntf_state *cps)
+{
+ lockdep_assert_held(&nn->s2s_cp_lock);
+
+ if (!list_empty(&cps->cp_list)) {
+ list_del_init(&cps->cp_list);
+ idr_remove(&nn->s2s_cp_stateids, cps->cp_stateid.cs_stid.si_opaque.so_id);
+ }
+}
+
+/*
+ * Revoke a copy-notify stateid: unlink it from the IDR and sc_cp_list first
+ * so no new finder can discover it, then drop the membership reference. Every
+ * revoke path (cancel, laundromat, drain) must use this rather than
+ * _free_cpntf_state_locked(), which unlinks only at refcount zero and so could
+ * let a second revoke free the entry under a concurrent reader.
+ *
+ * nn->s2s_cp_lock must be held.
+ */
+static void revoke_cpntf_state_locked(struct nfsd_net *nn,
+ struct nfs4_cpntf_state *cps)
+{
+ nfsd4_unhash_cpntf_state(nn, cps);
+ put_cpntf_state_unlinked_locked(cps);
+}
+
static void nfs4_free_cpntf_statelist(struct net *net, struct nfs4_stid *stid)
{
- struct nfs4_cpntf_state *cps;
+ struct nfs4_cpntf_state *cps, *tmp;
struct nfsd_net *nn;
nn = net_generic(net, nfsd_net_id);
spin_lock(&nn->s2s_cp_lock);
- while (!list_empty(&stid->sc_cp_list)) {
- cps = list_first_entry(&stid->sc_cp_list,
- struct nfs4_cpntf_state, cp_list);
- _free_cpntf_state_locked(nn, cps);
- }
+ /*
+ * Revoke unlinks each entry before dropping the parent's reference, so
+ * the drain terminates in one pass per entry regardless of cs_count; a
+ * concurrent holder does the final kfree via nfs4_put_cpntf_state().
+ */
+ list_for_each_entry_safe(cps, tmp, &stid->sc_cp_list, cp_list)
+ revoke_cpntf_state_locked(nn, cps);
spin_unlock(&nn->s2s_cp_lock);
}
@@ -6226,7 +6274,7 @@ nfs4_laundromat(struct nfsd_net *nn)
cps = container_of(cps_t, struct nfs4_cpntf_state, cp_stateid);
if (cps->cp_stateid.cs_type == NFS4_COPYNOTIFY_STID &&
state_expired(<, cps->cpntf_time))
- _free_cpntf_state_locked(nn, cps);
+ revoke_cpntf_state_locked(nn, cps);
}
spin_unlock(&nn->s2s_cp_lock);
nfs4_get_client_reaplist(nn, &reaplist, <);
@@ -6604,16 +6652,14 @@ nfs4_check_file(struct svc_rqst *rqstp,
out:
return status;
}
-static void
-_free_cpntf_state_locked(struct nfsd_net *nn, struct nfs4_cpntf_state *cps)
+
+static void _free_cpntf_state_locked(struct nfsd_net *nn, struct nfs4_cpntf_state *cps)
{
WARN_ON_ONCE(cps->cp_stateid.cs_type != NFS4_COPYNOTIFY_STID);
- if (!refcount_dec_and_test(&cps->cp_stateid.cs_count))
- return;
- list_del_init(&cps->cp_list);
- idr_remove(&nn->s2s_cp_stateids,
- cps->cp_stateid.cs_stid.si_opaque.so_id);
- kfree(cps);
+ if (refcount_dec_and_test(&cps->cp_stateid.cs_count)) {
+ nfsd4_unhash_cpntf_state(nn, cps);
+ kfree(cps);
+ }
}
/*
* A READ from an inter server to server COPY will have a@@ -6650,7 +6696,7 @@ __be32 manage_cpntf_state(struct nfsd_ne
state = NULL;
goto unlock;
} else {
- _free_cpntf_state_locked(nn, state);
+ revoke_cpntf_state_locked(nn, state);
}
}
unlock: