From 2108de53568a64936a0da3e04d85c35df98d3fb6 Mon Sep 17 00:00:00 2001 From: Chuck Lever Date: Thu, 9 Jul 2026 13:40:27 -0400 Subject: [PATCH] NFSD: Prevent client use-after-free during export state revocation nfsd4_revoke_export_states() has the same use-after-free as nfsd4_revoke_states(): it drops nn->client_lock across revoke_one_stid() and the following read of clp->cl_minorversion, but the stateid reference it holds does not pin the client. A teardown racing the dropped lock can free the client while revoke_one_stid() still dereferences it. exportfs -u drives this path through NFSD_CMD_UNLOCK_EXPORT, so an administrator removing an export can race a client expiry. 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: 2eac189bb059 ("NFSD: Add NFSD_CMD_UNLOCK_EXPORT netlink command") Reviewed-by: NeilBrown Reviewed-by: Jeff Layton Link: https://patch.msgid.link/20260709-cel-v4-4-1d519d9be0cb@kernel.org Signed-off-by: Chuck Lever --- fs/nfsd/nfs4state.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-) diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c index 565fa2ff5ba5..9de535a2a4bb 100644 --- a/fs/nfsd/nfs4state.c +++ b/fs/nfsd/nfs4state.c @@ -2055,10 +2055,14 @@ void nfsd4_revoke_export_states(struct nfsd_net *nn, const struct path *path) struct nfs4_client *clp; retry: list_for_each_entry(clp, head, cl_idhash) { - struct nfs4_stid *stid = find_one_export_stid( - clp, path, - sc_types); + struct nfs4_stid *stid; + + /* Skip or pin clp as in nfsd4_revoke_states(). */ + if (is_client_expired(clp)) + continue; + stid = find_one_export_stid(clp, path, sc_types); if (stid) { + atomic_inc(&clp->cl_rpc_users); spin_unlock(&nn->client_lock); revoke_one_stid(nn, clp, stid); nfs4_put_stid(stid); @@ -2066,6 +2070,9 @@ void nfsd4_revoke_export_states(struct nfsd_net *nn, const struct path *path) if (clp->cl_minorversion == 0) nn->nfs40_last_revoke = ktime_get_boottime_seconds(); + if (atomic_dec_and_test(&clp->cl_rpc_users) && + is_client_expired(clp)) + wake_up_all(&expiry_wq); goto retry; } }