linux-kernel - Re: [PATCH v2] nfsd: remove long-standing revoked delegations by force

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <837da22b428e5a7cbda1f56868cbfe23e89dccf7.camel@kernel.org>
Date: Wed, 03 Sep 2025 08:15:16 -0400
From: Jeff Layton <jlayton@...nel.org>
To: Li Lingfeng <lilingfeng3@...wei.com>, chuck.lever@...cle.com, 
	neil@...wn.name, okorniev@...hat.com, Dai.Ngo@...cle.com, tom@...pey.com, 
	linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: yukuai1@...weicloud.com, houtao1@...wei.com, yi.zhang@...wei.com, 
	yangerkun@...wei.com, lilingfeng@...weicloud.com, zhangjian496@...wei.com, 
	bcodding@...hat.com
Subject: Re: [PATCH v2] nfsd: remove long-standing revoked delegations by
 force

On Wed, 2025-09-03 at 19:59 +0800, Li Lingfeng wrote:
> When file access conflicts occur between clients, the server recalls
> delegations. If the client holding delegation fails to return it after
> a recall, nfs4_laundromat adds the delegation to cl_revoked list.
> This causes subsequent SEQUENCE operations to set the
> SEQ4_STATUS_RECALLABLE_STATE_REVOKED flag, forcing the client to
> validate all delegations and return the revoked one.
> 
> However, if the client fails to return the delegation like this:
> nfs4_laundromat                       nfsd4_delegreturn
>  unhash_delegation_locked
>  list_add // add dp to reaplist
>           // by dl_recall_lru
>  list_del_init // delete dp from
>                // reaplist
>                                        destroy_delegation
>                                         unhash_delegation_locked
>                                          // do nothing but return false
>  revoke_delegation
>  list_add // add dp to cl_revoked
>           // by dl_recall_lru
> 
> The delegation will remain in the server's cl_revoked list while the
> client marks it revoked and won't find it upon detecting
> SEQ4_STATUS_RECALLABLE_STATE_REVOKED.
> This leads to a loop:
> the server persistently sets SEQ4_STATUS_RECALLABLE_STATE_REVOKED, and the
> client repeatedly tests all delegations, severely impacting performance
> when numerous delegations exist.
> 
> Since abnormal delegations are removed from flc_lease via nfs4_laundromat
> --> revoke_delegation --> destroy_unhashed_deleg -->
> nfs4_unlock_deleg_lease --> kernel_setlease, and do not block new open
> requests indefinitely, retaining such a delegation on the server is
> unnecessary.
> 
> Reported-by: Zhang Jian <zhangjian496@...wei.com>
> Fixes: 3bd64a5ba171 ("nfsd4: implement SEQ4_STATUS_RECALLABLE_STATE_REVOKED")
> Closes: https://lore.kernel.org/all/ff8debe9-6877-4cf7-ba29-fc98eae0ffa0@huawei.com/
> Signed-off-by: Li Lingfeng <lilingfeng3@...wei.com>
> ---
>   Changes in v2:
>   1) Set SC_STATUS_CLOSED unconditionally in destroy_delegation();
>   2) Determine whether to remove the delegation based on SC_STATUS_CLOSED,
>      rather than by timeout;
>   3) Modify the commit message.
>  fs/nfsd/nfs4state.c | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
> 
> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> index 88c347957da5..bb9e1df4e41f 100644
> --- a/fs/nfsd/nfs4state.c
> +++ b/fs/nfsd/nfs4state.c
> @@ -1336,6 +1336,11 @@ static void destroy_delegation(struct nfs4_delegation *dp)
>  
>  	spin_lock(&state_lock);
>  	unhashed = unhash_delegation_locked(dp, SC_STATUS_CLOSED);
> +	/*
> +	 * Unconditionally set SC_STATUS_CLOSED, regardless of whether the
> +	 * delegation is hashed, to mark the current delegation as invalid.
> +	 */
> +	dp->dl_stid.sc_status |= SC_STATUS_CLOSED;
>  	spin_unlock(&state_lock);
>  	if (unhashed)
>  		destroy_unhashed_deleg(dp);
> @@ -4326,6 +4331,8 @@ nfsd4_sequence(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
>  	int buflen;
>  	struct net *net = SVC_NET(rqstp);
>  	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
> +	struct list_head *pos, *next;
> +	struct nfs4_delegation *dp;
>  

nit: These could be moved inside the if statement below.

>  	if (resp->opcnt != 1)
>  		return nfserr_sequence_pos;
> @@ -4470,6 +4477,19 @@ nfsd4_sequence(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
>  	default:
>  		seq->status_flags = 0;
>  	}

I wouldn't mind a comment here that explains why we have to do this.
This is the sort of thing that will have us all scratching our heads in
a few years.

> +	if (!list_empty(&clp->cl_revoked)) {
> +		spin_lock(&clp->cl_lock);
> +		list_for_each_safe(pos, next, &clp->cl_revoked) {
> +			dp = list_entry(pos, struct nfs4_delegation, dl_recall_lru);
> +			if (dp->dl_stid.sc_status & SC_STATUS_CLOSED) {
> +				list_del_init(&dp->dl_recall_lru);
> +				spin_unlock(&clp->cl_lock);
> +				nfs4_put_stid(&dp->dl_stid);
> +				spin_lock(&clp->cl_lock);
> +			}
> +		}
> +		spin_unlock(&clp->cl_lock);
> +	}

nit: I'd move the if statement below inside the above if statement. No
need to check list_empty() twice if it was empty the first time. Maybe
the compiler papers over this and only does it once?

>  	if (!list_empty(&clp->cl_revoked))
>  		seq->status_flags |= SEQ4_STATUS_RECALLABLE_STATE_REVOKED;
>  	if (atomic_read(&clp->cl_admin_revoked))

Otherwise, this looks great. Thanks for the patch!

Reviewed-by: Jeff Layton <jlayton@...nel.org>