From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id BD2A9324B06 for ; Mon, 6 Jul 2026 01:26:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783301161; cv=none; b=QuyS5Ozl0mcw/b5WvyQUfmNZlnNVW/tUmMuJDbHIubE8cy9RB2A/jqBKRBZJN04FfSpsXZmM5D9+raDBp+8tOpH8ngSd7vJ4kyoJTOt1Y4zK7XdT+QQSvx493bdAPOoHfVIMep6bBv8nQr0TD6eif5ja8VtOtUXdO2kyrtcu2bI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783301161; c=relaxed/simple; bh=tfGHcxuvL67BSVc7BqAnAwchj6NvBIOGRdby5ZFndoM=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=OTQ58LD9HBk5YYY0Ef1sYfzWwQbM0FkY3YtPoAa6kbPlVWar3/0lBMJWwl60ZUvq0rFZo36SNERunkGQPOgxvGFIECmCQllgRD5sbwOJS/+X1TdyHLtbAOVeXux3OKOCbEH+NwOZu+Yd9pmE5dS4XEWlxy5cu5YdpISRDcer4KA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=bft88HQV; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="bft88HQV" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 250341F00A3A; Mon, 6 Jul 2026 01:26:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1783301160; bh=cPCmDFImn4TZFAYG11yn+Eo2T+i7NfGZ0U08jzeODio=; h=From:Date:Subject:References:In-Reply-To:To:Cc; b=bft88HQVAXIfghj4g48iWSsn87XTex+zp/GJNWDKSTxqqLKjbl3WZrTiHRbYemtSq dizHaFE4meRlOjjWjx5DdziyuhjuVp6xuwUfREJos+oHnuyOuJ6STZpbsO3B1px7eg z6fbkYo3Vyld6qz/EDuOtp2Gmyq9dKohTlewRIfoYahGdGzvjd36c8H4bUNr1cux9X Zn6UvA5kRwnr+PkjTafv9xmpcKwMt3ZosI0O9KB21D4ef8ht9u5dyx/AKFRISdlJF0 lMTfMs6CAmkbrTC4a/bIM4+2NpDZWLoWAhRoHinKLTwlhRlMbeskzLllwih/oIEOi1 2Kj8BwBHO1juA== From: Chuck Lever Date: Sun, 05 Jul 2026 21:25:38 -0400 Subject: [PATCH v2 2/6] NFSD: Prevent client use-after-free during delegation revoke Precedence: bulk X-Mailing-List: linux-nfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20260705-cel-v2-2-d88c3b68e8bc@kernel.org> References: <20260705-cel-v2-0-d88c3b68e8bc@kernel.org> In-Reply-To: <20260705-cel-v2-0-d88c3b68e8bc@kernel.org> To: Jeff Layton , NeilBrown , Olga Kornievskaia , Dai Ngo , Tom Talpey Cc: linux-nfs@vger.kernel.org, Chuck Lever X-Mailer: b4 0.16-dev X-Developer-Signature: v=1; a=openpgp-sha256; l=4290; i=cel@kernel.org; h=from:subject:message-id; bh=tfGHcxuvL67BSVc7BqAnAwchj6NvBIOGRdby5ZFndoM=; b=owEBbQKS/ZANAwAKATNqszNvZn+XAcsmYgBqSwQmCCeJ6eCO+NPPUB7m+EkyQelPHLD1D2HbV FSq3R4bAEmJAjMEAAEKAB0WIQQosuWwEobfJDzyPv4zarMzb2Z/lwUCaksEJgAKCRAzarMzb2Z/ l+mMEACqXH7OO+Fq5p45BphnRLK2WrVIgBC4rBGMdGRUCij7KDEIZB1YEcj7hMoehMyg061QOsa kj/JS4OO3jMcZUoExptpY0O/5NOETZf/z+0xdiy9PlbKU8Qcgftlcvv+2L1ZILnT5UxE7UhUOCD D7HWGWQPYXO++xe9mHAI40UJaJsWf4yAMqtmNIZt9GUebpgaGb2M50GmLtL2ueJ5bnX4nHGFPui Iagl6UzBpwfrezEKjWWPMxCxKTghHZym30Vo/SM9pUtUJ7/ZQdDa6beL2JnA7WVJHMVDsS8P64i hKafbUzP0cVdWNp8K7DSsZnKEqqapBHm8BGUvRn9/tGFOpSmWdjbPQSNslhIzNBVCA1ZFFGZQgR C4uSmLTCb734ASalGNS4yYEAOxTCAXrBvYWw0QFvigy86agX7oQdtrnxNLQdoeEexRoUf9z3bX7 0zu0wX5RekytGUseJ8Nofl38mJno9eWk1DjotSpgONBs/v8LOM635YFij+/Hxht/KlbuR5m6ZKE 94RzX6JJ0RIRa6NUKsvC5AwXwybo7UZWfHXQsXiM1fssBRvGnA83LwbkQQhhKC9nObAsFdcTJvy m/jnZKHW6JRqcgdJFNeMAvMjIIP41E5Iw46cwb/lVinf277u1QeUCc8mYQ88iNx8lQqThxzPKWF iKtS0Q5SrekLHpg== X-Developer-Key: i=cel@kernel.org; a=openpgp; fpr=28B2E5B01286DF243CF23EFE336AB3336F667F97 A delegation stateid stores only a bare pointer to its owning nfs4_client; a reference on the stateid does not keep the client alive. The client outlives its stateids solely because __destroy_client() drains every delegation from cl_delegations and cl_revoked before free_client() runs. nfs4_laundromat() breaks that invariant. It unhashes an expired delegation from cl_delegations under deleg_lock, drops the lock, and calls revoke_delegation(), which reacquires clp->cl_lock and links the delegation onto clp->cl_revoked. Between the unhash and the revoke the delegation is on neither client-reachable list, so client_has_state() can report no remaining state. Every path that can free a client holding delegations first requires cl_rpc_users to be zero: DESTROY_CLIENTID and a superseding EXCHANGE_ID gate on mark_client_expired_locked(), and the admin "expire" write waits in force_expire_client(). The laundromat holds no such reference. A client whose recalled delegation has just timed out -- a rebooted client whose new incarnation supersedes the old one, say -- can therefore run __destroy_client() to completion and free the client while revoke_delegation() is still about to dereference clp->cl_lock and clp->cl_revoked, a use-after-free. Pin the client with cl_rpc_users across the revoke so the teardown paths block until it completes and then reap it from cl_revoked themselves. A client already expiring reaps its own delegations, so skip it and leave the delegation on del_recall_lru for __destroy_client() to handle. Fixes: 3bd64a5ba171 ("nfsd4: implement SEQ4_STATUS_RECALLABLE_STATE_REVOKED") Signed-off-by: Chuck Lever --- fs/nfsd/netns.h | 6 ++++-- fs/nfsd/nfs4state.c | 23 +++++++++++++++++++++++ 2 files changed, 27 insertions(+), 2 deletions(-) diff --git a/fs/nfsd/netns.h b/fs/nfsd/netns.h index 03724bef10a7..a7bd7b67fa4f 100644 --- a/fs/nfsd/netns.h +++ b/fs/nfsd/netns.h @@ -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 */ diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c index e000ed3e96e9..efeb2a2e9c8f 100644 --- a/fs/nfsd/nfs4state.c +++ b/fs/nfsd/nfs4state.c @@ -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(<, 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); -- 2.54.0