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 3E2173AEF3A for ; Mon, 6 Jul 2026 17:29:28 +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=1783358970; cv=none; b=fhr3t9S77NIOlf7V+N2AUSrAqycKdJPiubKzQmoxsOK/sp9ovcj9FwpC/8aec1PlW/OJnrB1MzLgmvMQE5l9PnL5RXqn9lwj2rz2sr/iULnzULOcXAMGtonLSquZvTmBDXPHz1BFkvmr+5q0YM1f37zql7M7WXwzTnzJrerTTbc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783358970; c=relaxed/simple; bh=qCADXsj5dh52OKQc80USjThFxhnxdTkNjLcy4huDTww=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=eg5Eh4T0z8rMK5Qx9onNoGjzPQn6xdQkgIm5Mc6tSPx4hz+O6VayqCysO+QwOFwzXrg5RMsjwh2S1NSU66ssGcJOQRECcjFbZqQBQwOH+Q5UT9A3ZFMGe/4Wp0sKXCEqJ60xq0IhT66qPESg6xlRDZAEVYR5Q3zOnW6x1+XlUTg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=JV8CCUke; 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="JV8CCUke" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 43F2B1F000E9; Mon, 6 Jul 2026 17:29:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1783358968; bh=WHkF8dgJkhd0zubW5Y27UY2ihiS3jvWaRk4Lg4XC6K8=; h=Subject:From:To:Cc:Date:In-Reply-To:References; b=JV8CCUkeP5FwcVXv6w0+HxrX2ISGtiAadgfsNVjnutvSfVWyWbiBvesKHDTTQZLI6 x22fQpRjc9lHHfLX2f7cagIiQw/gF9bIN4UcfRsaF1jOdvYHnO0WZIPmddGFjq7Vi6 VJs5hL6Ic2hX9d+kv0lrhbHR2Qc+/4jSu8m3RjWcMGfGClRWg4QFTIlmjR1o4hW85r oSOjr/HtOZYBwa1AvI2LALV8l1kM3bybNbmNx5ftAMkuYzgb9wHNXOPXIJTiz4oOhD IbXQZ5/ExOyNVmsczS+H0Xn/7U8UJpfexs1/MQlXqo9QEwBczijRqS2oEUJbvsNd0Q 3riGUt8iCinQQ== Message-ID: <39785ebf72eb7eeb09e006f40b7c2b38cbc0b083.camel@kernel.org> Subject: Re: [PATCH v2 2/6] NFSD: Prevent client use-after-free during delegation revoke From: Jeff Layton To: Chuck Lever , NeilBrown , Olga Kornievskaia , Dai Ngo , Tom Talpey Cc: linux-nfs@vger.kernel.org Date: Mon, 06 Jul 2026 13:29:26 -0400 In-Reply-To: <20260705-cel-v2-2-d88c3b68e8bc@kernel.org> References: <20260705-cel-v2-0-d88c3b68e8bc@kernel.org> <20260705-cel-v2-2-d88c3b68e8bc@kernel.org> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV T2h6v8i8YqsATFPwO4nuiTmL6I40ZofxVd+9wdRI4Db8yUNA4ZSP2nqLcLtFjClYRBoJvRWvsv4lm 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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. >=20 > 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. >=20 > 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. >=20 > 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. >=20 > Fixes: 3bd64a5ba171 ("nfsd4: implement SEQ4_STATUS_RECALLABLE_STATE_REVOK= ED") > Signed-off-by: Chuck Lever > --- > fs/nfsd/netns.h | 6 ++++-- > fs/nfsd/nfs4state.c | 23 +++++++++++++++++++++++ > 2 files changed, 27 insertions(+), 2 deletions(-) >=20 > 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; > =20 > - /* 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; > =20 > @@ -124,7 +125,8 @@ struct nfsd_net { > =20 > struct delayed_work laundromat_work; > =20 > - /* 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; > =20 > /* 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 =3D nn->nfsd4_lease > }; > struct nfs4_cpntf_state *cps; > + struct nfs4_client *clp; > copy_stateid_t *cps_t; > int i; > =20 > @@ -7485,6 +7486,18 @@ nfs4_laundromat(struct nfsd_net *nn) > dp =3D list_entry (pos, struct nfs4_delegation, dl_recall_lru); > if (!state_expired(<, dp->dl_time)) > break; > + clp =3D 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 =3D list_first_entry(&reaplist, struct nfs4_delegation, > dl_recall_lru); > + clp =3D 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); > + } > } > =20 > spin_lock(&nn->client_lock); Reviewed-by: Jeff Layton