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NFSD: Prevent client use-after-free during delegation revoke

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A delegation stateid holds only a bare pointer to its owning
nfs4_client and does not keep it alive.  The client survives its
stateids only because __destroy_client() drains cl_delegations and
cl_revoked before free_client() runs.

nfs4_laundromat() breaks that invariant: it unhashes an
expired delegation from cl_delegations, drops deleg_lock, then
revoke_delegation() relinks it onto cl_revoked under cl_lock.  In that
window the delegation is on neither list, so client_has_state() can
report no remaining state.

Every teardown path first requires cl_rpc_users to be zero, but
the laundromat holds no such reference.  A client whose recalled
delegation has just timed out can therefore reach free_client()
while revoke_delegation() is still about to dereference cl_lock,
a use-after-free.

Pin the client with cl_rpc_users across the revoke so teardown blocks
until it completes, then reap the delegation from cl_revoked.  A client
already expiring reaps its own, so skip it and leave the delegation on
del_recall_lru.

Fixes: 3bd64a5ba1 ("nfsd4: implement SEQ4_STATUS_RECALLABLE_STATE_REVOKED")
Cc: stable@vger.kernel.org
Reviewed-by: NeilBrown <neil@brown.name>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Link: https://patch.msgid.link/20260709-cel-v4-2-1d519d9be0cb@kernel.org
Signed-off-by: Chuck Lever <cel@kernel.org>
This commit is contained in:
Chuck Lever 2026-07-09 13:40:25 -04:00
parent 5e2fa29d22
commit 4683ca76b3
2 changed files with 27 additions and 2 deletions
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6
fs/nfsd/netns.h
View File

@ -115,7 +115,8 @@ struct nfsd_net {
struct list_head client_lru;
struct list_head close_lru;
/* protects del_recall_lru and delegation hash/unhash */
/* protects del_recall_lru and delegation hash/unhash;
* nests outside client_lock */
spinlock_t deleg_lock ____cacheline_aligned;
struct list_head del_recall_lru;
@ -124,7 +125,8 @@ struct nfsd_net {
struct delayed_work laundromat_work;
/* client_lock protects the client lru list and session hash table */
/* client_lock protects the client lru list and session hash
* table; nests inside deleg_lock */
spinlock_t client_lock;
/* protects blocked_locks_lru */

23
fs/nfsd/nfs4state.c
View File

@ -7457,6 +7457,7 @@ nfs4_laundromat(struct nfsd_net *nn)
.new_timeo = nn->nfsd4_lease
};
struct nfs4_cpntf_state *cps;
struct nfs4_client *clp;
copy_stateid_t *cps_t;
int i;
@ -7485,6 +7486,18 @@ nfs4_laundromat(struct nfsd_net *nn)
dp = list_entry (pos, struct nfs4_delegation, dl_recall_lru);
if (!state_expired(&lt, dp->dl_time))
break;
clp = dp->dl_stid.sc_client;
spin_lock(&nn->client_lock);
if (is_client_expired(clp)) {
spin_unlock(&nn->client_lock);
continue;
}
/*
* Pin without reviving: get_client_locked() would
* flip a courtesy client back to NFSD4_ACTIVE.
*/
atomic_inc(&clp->cl_rpc_users);
spin_unlock(&nn->client_lock);
refcount_inc(&dp->dl_stid.sc_count);
unhash_delegation_locked(dp, SC_STATUS_REVOKED);
list_add(&dp->dl_recall_lru, &reaplist);
@ -7493,8 +7506,18 @@ nfs4_laundromat(struct nfsd_net *nn)
while (!list_empty(&reaplist)) {
dp = list_first_entry(&reaplist, struct nfs4_delegation,
dl_recall_lru);
clp = dp->dl_stid.sc_client;
list_del_init(&dp->dl_recall_lru);
revoke_delegation(dp);
/*
* Unpin without renewing: put_client_renew() would
* renew the reaped client's lease.
*/
if (atomic_dec_and_lock(&clp->cl_rpc_users, &nn->client_lock)) {
if (is_client_expired(clp))
wake_up_all(&expiry_wq);
spin_unlock(&nn->client_lock);
}
}
spin_lock(&nn->client_lock);