From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 D5B7D24DD07 for ; Sat, 5 Jul 2025 11:15:12 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1751714112; cv=none; b=mpeF9+lg4koxXLSyywpXuNLzJ0lZyfmMv4A3dnd3RvbIWYNfKPnkqT4GL/AdLhxgKwU66afPEEf7akwSeoZ+o5Wfa5SjOidEfo2BMAD0KFLfhGQQhH8w2LBYPe/9Wm1jF33Rm3TAEgGczzoTpJ0Dv/ARO0c4MUWrN1jFQONwY+k= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1751714112; c=relaxed/simple; bh=YNf7HXFlvuNv3Z3FeMjDvtKPMu8ZgWdsWWb0qzCNEaY=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=pv81TOAY/RqHaPHjHws0vnhtOJCIAYsGvRfl40bunLPhv3i8xwOMW8kM9CppCbHN2ZjN+EnSR66ieT6rz7rwNh20PrI3dfh5E+2LAq10C7UWQ6mYJLe/9bzmSodkAioqqEp83IyFqe+Jo5LRIrwULufH4U3+n5+xzTn2bq/+1rQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=dzjHbzy+; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="dzjHbzy+" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D81A7C4CEED; Sat, 5 Jul 2025 11:15:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1751714112; bh=YNf7HXFlvuNv3Z3FeMjDvtKPMu8ZgWdsWWb0qzCNEaY=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=dzjHbzy+Nf09QdPZxjk35pr4H1UDxbTt4RerWsfPkqo7wKItPVoFyVgq+bSnTbIaM 6KY5iIlF/EygPlD8aP9ZssanYF5AyOt4/8XaLONjb2tX5aQJzrX+qfGRGsrbcEyIFp smdcTjJlHxprek/v56p9MMTWk98mj4FmiLg9xGtS6vGx1XCNYDfX5GFYP7k/ZRhd+y 5z/X48pVAY4PEvjbFL6PEBY54Di4+ZF5uQ1aHsqeFXqW+r8S95IYH4yDDhw2HUjhrk avdAVFBFa9AxT84PYy2obtVELKrQdg5ih1wxoJbiXregA3F1F7dD6PnAs5N1CCFlds 3+1X0gblIm8Jw== Message-ID: Subject: Re: [PATCH 1/2] nfsd: provide locking for v4_end_grace From: Jeff Layton To: NeilBrown , Chuck Lever Cc: linux-nfs@vger.kernel.org, Olga Kornievskaia , Dai Ngo , Tom Talpey , Li Lingfeng Date: Sat, 05 Jul 2025 07:15:10 -0400 In-Reply-To: <20250704072332.3278129-2-neil@brown.name> References: <20250704072332.3278129-1-neil@brown.name> <20250704072332.3278129-2-neil@brown.name> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV T2h6v8i8YqsATFPwO4nuiTmL6I40ZofxVd+9wdRI4Db8yUNA4ZSP2nqLcLtFjClYRBoJvRWvsv4lm 0OX6MYPtv76hka8lW4mnRmZqqx3UtfHX/hF/zH24Gj7A6sYKYLCU3YrI2Ogiu7/ksKcl7goQjpvtV 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uxp4CHBDVzAslUi2idy+xpsp47DWPxYFIRP3M8QG/aNW052LaPc0cedYxp8+9eiVUNpxF4SiU4i9J DfX/sn9XcfoVZIxMpCRE750zvJvcCUz9HojsrMQ1NFc7MFT1z3MOW2/RlzPcog7xvR5ENPH19ojRD CHqumUHRry+RF0lH00clzX/W8OrQJZtoBPXv9ahka/Vp7kEulcBJr1cH5Wz/WprhsIM7U9pse1f1g Yy9YbXtWctUz8uvDR7shsQxAhX3qO7DilMtuGo1v97I/Kx4gXQ52syh/w6EBny71CZrOgD6kJwPVV AaM1LRC28muq91WCFhs/nzHozpbzcheyGtMUI2Ao4K6mnY+3zIuXPygZMFr9KXE6fF7HzKxKuZMJO aEZCiDOq0anx6FmOzs5E6Jqdpo/mtI8beK+BE7Va6ni7YrQlnT0i3vaTVMTiCThbqsB20VrbMjlhp f8lfK1XVNbRq/R7GZ9zHESlsa35ha60yd/j3pu5hT2xyy8krV8vGhHvnJ1XRMJBAB/UYb6FyC7S+m QZIQXVeAA+smfTT0tDrisj1U5x6ZB9b3nBg65kc= Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.56.2 (3.56.2-1.fc42) Precedence: bulk X-Mailing-List: linux-nfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Fri, 2025-07-04 at 17:20 +1000, NeilBrown wrote: > Writing to v4_end_grace can race with server shutdown and result in > memory being accessed after it was freed - reclaim_str_hashtbl in > particular. >=20 > We cannot hold nfsd_mutex across the nfsd4_end_grace() call as that is > held while client_tracking_op->init() is called and that can wait for > an upcall to nfsdcltrack which can write to v4_end_grace, resulting in a > deadlock. >=20 > nfsd4_end_grace() is also called by the landromat work queue and this > doesn't require locking as server shutdown will stop the work and wait > for it before freeing anything that nfsd4_end_grace() might access. >=20 > However, we must be sure that writing to v4_end_grace doesn't restart > the work item after shutdown has already waited for it. For this we add > a new flag protected with a spin_lock, and nn->client_lock is suitable. > It is set only while it is safe to make client tracking calls, and > v4_end_grace only schedules work while the flag is set and with the > spin_lock held. >=20 > So this patch adds an nfsd_net field "client_tracking_active" which is > set as described. Another field "grace_end_forced", is set when > v4_end_grace is written. After this is set, and providing > client_tracking_active is set, the laundromat is scheduled. > This "grace_end_forced" field bypasses other checks for whether the > grace period has finished. >=20 > This resolves a race which can result in use-after-free. >=20 > Reported-and-tested-by: Li Lingfeng > Closes: https://lore.kernel.org/linux-nfs/20250513074305.3362209-1-liling= feng3@huawei.com > Fixes: 7f5ef2e900d9 ("nfsd: add a v4_end_grace file to /proc/fs/nfsd") > Cc: stable@vger.kernel.org > Signed-off-by: NeilBrown > --- > fs/nfsd/netns.h | 2 ++ > fs/nfsd/nfs4state.c | 45 +++++++++++++++++++++++++++++++++++++++++++-- > fs/nfsd/nfsctl.c | 6 +++--- > fs/nfsd/state.h | 2 +- > 4 files changed, 49 insertions(+), 6 deletions(-) >=20 > diff --git a/fs/nfsd/netns.h b/fs/nfsd/netns.h > index 3e2d0fde80a7..fe8338735e7c 100644 > --- a/fs/nfsd/netns.h > +++ b/fs/nfsd/netns.h > @@ -66,6 +66,8 @@ struct nfsd_net { > =20 > struct lock_manager nfsd4_manager; > bool grace_ended; > + bool grace_end_forced; > + bool client_tracking_active; ISTM that the client_tracking_active bool is set and cleared similarly to the nn->client_tracking_ops pointer itself. It _might_ be possible to eliminate this bool and just use that pointer instead, though they are not exactly cleared at the same time. > time64_t boot_time; > =20 > struct dentry *nfsd_client_dir; > diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c > index d5694987f86f..124fe4f669aa 100644 > --- a/fs/nfsd/nfs4state.c > +++ b/fs/nfsd/nfs4state.c > @@ -84,7 +84,7 @@ static u64 current_sessionid =3D 1; > /* forward declarations */ > static bool check_for_locks(struct nfs4_file *fp, struct nfs4_lockowner = *lowner); > static void nfs4_free_ol_stateid(struct nfs4_stid *stid); > -void nfsd4_end_grace(struct nfsd_net *nn); > +static void nfsd4_end_grace(struct nfsd_net *nn); > static void _free_cpntf_state_locked(struct nfsd_net *nn, struct nfs4_cp= ntf_state *cps); > static void nfsd4_file_hash_remove(struct nfs4_file *fi); > static void deleg_reaper(struct nfsd_net *nn); > @@ -6458,7 +6458,7 @@ nfsd4_renew(struct svc_rqst *rqstp, struct nfsd4_co= mpound_state *cstate, > return nfs_ok; > } > =20 > -void > +static void > nfsd4_end_grace(struct nfsd_net *nn) > { > /* do nothing if grace period already ended */ > @@ -6491,6 +6491,36 @@ nfsd4_end_grace(struct nfsd_net *nn) > */ > } > =20 > +/** > + * nfsd4_force_end_grace - forcibly end the grace period > + * @nn: nfsd_net in which the grace period must end. > + * > + * > + * An nfsv4 grace period can be terminated early if it is known that > + * no more client could reclaim state. Sometimes user-space can provide > + * that information - which will potentially be provided asychnronously > + * w.r.t. server startup or shutdown. > + * > + * nfsd4_force_end_grace() causing the grace period to end and takes > + * care to ensure races with server start/stop are not problematic. > + * > + * Return value: %false if the NFS server was not active and > + * %true if the server was, or may have been, active. > + */ > +bool > +nfsd4_force_end_grace(struct nfsd_net *nn) > +{ > + if (!nn->client_tracking_ops) > + return false; > + spin_lock(&nn->client_lock); > + if (nn->client_tracking_active) { > + nn->grace_end_forced =3D true; > + mod_delayed_work(laundry_wq, &nn->laundromat_work, 0); > + } > + spin_unlock(&nn->client_lock); > + return true; > +} > + > /* > * If we've waited a lease period but there are still clients trying to > * reclaim, wait a little longer to give them a chance to finish. > @@ -6500,6 +6530,8 @@ static bool clients_still_reclaiming(struct nfsd_ne= t *nn) > time64_t double_grace_period_end =3D nn->boot_time + > 2 * nn->nfsd4_lease; > =20 > + if (nn->grace_end_forced) > + return false; > if (nn->track_reclaim_completes && > atomic_read(&nn->nr_reclaim_complete) =3D=3D > nn->reclaim_str_hashtbl_size) > @@ -8807,6 +8839,8 @@ static int nfs4_state_create_net(struct net *net) > nn->unconf_name_tree =3D RB_ROOT; > nn->boot_time =3D ktime_get_real_seconds(); > nn->grace_ended =3D false; > + nn->grace_end_forced =3D false; > + nn->client_tracking_active =3D false; > nn->nfsd4_manager.block_opens =3D true; > INIT_LIST_HEAD(&nn->nfsd4_manager.list); > INIT_LIST_HEAD(&nn->client_lru); > @@ -8887,6 +8921,10 @@ nfs4_state_start_net(struct net *net) > return ret; > locks_start_grace(net, &nn->nfsd4_manager); > nfsd4_client_tracking_init(net); > + /* safe for laundromat to run now */ > + spin_lock(&nn->client_lock); > + nn->client_tracking_active =3D true; > + spin_unlock(&nn->client_lock); > if (nn->track_reclaim_completes && nn->reclaim_str_hashtbl_size =3D=3D = 0) > goto skip_grace; > printk(KERN_INFO "NFSD: starting %lld-second grace period (net %x)\n", > @@ -8935,6 +8973,9 @@ nfs4_state_shutdown_net(struct net *net) > =20 > shrinker_free(nn->nfsd_client_shrinker); > cancel_work_sync(&nn->nfsd_shrinker_work); > + spin_lock(&nn->client_lock); > + nn->client_tracking_active =3D false; > + spin_unlock(&nn->client_lock); > cancel_delayed_work_sync(&nn->laundromat_work); > locks_end_grace(&nn->nfsd4_manager); > =20 > diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c > index 3f3e9f6c4250..658f3f86a59f 100644 > --- a/fs/nfsd/nfsctl.c > +++ b/fs/nfsd/nfsctl.c > @@ -1082,10 +1082,10 @@ static ssize_t write_v4_end_grace(struct file *fi= le, char *buf, size_t size) > case 'Y': > case 'y': > case '1': > - if (!nn->nfsd_serv) > - return -EBUSY; > trace_nfsd_end_grace(netns(file)); > - nfsd4_end_grace(nn); > + if (!nfsd4_force_end_grace(nn)) > + return -EBUSY; > + > break; > default: > return -EINVAL; > diff --git a/fs/nfsd/state.h b/fs/nfsd/state.h > index 1995bca158b8..05eabc69de40 100644 > --- a/fs/nfsd/state.h > +++ b/fs/nfsd/state.h > @@ -836,7 +836,7 @@ static inline void nfsd4_revoke_states(struct net *ne= t, struct super_block *sb) > #endif > =20 > /* grace period management */ > -void nfsd4_end_grace(struct nfsd_net *nn); > +bool nfsd4_force_end_grace(struct nfsd_net *nn); > =20 > /* nfs4recover operations */ > extern int nfsd4_client_tracking_init(struct net *net); The patch itself and the new bool are fine though. Reviewed-by: Jeff Layton