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NFSD: Prevent client use-after-free during NFSv4.0 revoked-state cleanup

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nfs40_clean_admin_revoked() takes a stateid reference under
clp->cl_lock, drops nn->client_lock, and calls
nfsd4_drop_revoked_stid(), which dereferences the stateid's client
through s->sc_client->cl_lock.  The stateid reference does not pin the
client, so a teardown racing the dropped lock can free the client
while nfsd4_drop_revoked_stid() is still using it.

This cleanup runs from the laundromat, so a periodic sweep can race
force_expire_client() driven by a write to the clients/<id>/ctl file.

Skip a client that is already expiring and otherwise pin it with
cl_rpc_users under client_lock before dropping the lock, matching
nfsd4_revoke_states().

Fixes: d688d8585e ("nfsd: allow admin-revoked NFSv4.0 state to be freed.")
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-v4-5-1d519d9be0cb@kernel.org
Signed-off-by: Chuck Lever <cel@kernel.org>
This commit is contained in:
Chuck Lever 2026-07-09 13:40:28 -04:00
parent 2108de5356
commit 7b4f8a1586
1 changed files with 6 additions and 0 deletions
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6
fs/nfsd/nfs4state.c
View File

@ -7452,16 +7452,22 @@ static void nfs40_clean_admin_revoked(struct nfsd_net *nn,
if (atomic_read(&clp->cl_admin_revoked) == 0)
continue;
if (is_client_expired(clp))
continue;
spin_lock(&clp->cl_lock);
idr_for_each_entry_ul(&clp->cl_stateids, stid, tmp, id)
if (stid->sc_status & SC_STATUS_ADMIN_REVOKED) {
refcount_inc(&stid->sc_count);
atomic_inc(&clp->cl_rpc_users);
spin_unlock(&nn->client_lock);
/* this function drops ->cl_lock */
nfsd4_drop_revoked_stid(stid);
nfs4_put_stid(stid);
spin_lock(&nn->client_lock);
if (atomic_dec_and_test(&clp->cl_rpc_users) &&
is_client_expired(clp))
wake_up_all(&expiry_wq);
goto retry;
}
spin_unlock(&clp->cl_lock);