linux-kernel - Re: [PATCH] nfsd: don't ignore the return code of svc_proc

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Message-ID: <d6ecad5f-b2a5-435c-9209-d784a23b013c@oracle.com>
Date: Thu, 6 Feb 2025 13:17:24 -0500
From: Chuck Lever <chuck.lever@...cle.com>
To: Jeff Layton <jlayton@...nel.org>, Neil Brown <neilb@...e.de>,
        Olga Kornievskaia <okorniev@...hat.com>, Dai Ngo <Dai.Ngo@...cle.com>,
        Tom Talpey <tom@...pey.com>, Josef Bacik <josef@...icpanda.com>
Cc: linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org,
        syzbot+e34ad04f27991521104c@...kaller.appspotmail.com
Subject: Re: [PATCH] nfsd: don't ignore the return code of svc_proc_register()

On 2/6/25 1:12 PM, Jeff Layton wrote:
> Currently, nfsd_proc_stat_init() ignores the return value of
> svc_proc_register(). If the procfile creation fails, then the kernel
> will WARN when it tries to remove the entry later.
> 
> Fix nfsd_proc_stat_init() to return the same type of pointer as
> svc_proc_register(), and fix up nfsd_net_init() to check that and fail
> the nfsd_net construction if it occurs.
> 
> svc_proc_register() can fail if the dentry can't be allocated, or if an
> identical dentry already exists. The second case is pretty unlikely in
> the nfsd_net construction codepath, so if this happens, return -ENOMEM.
> 
> Fixes: 93483ac5fec6 ("nfsd: expose /proc/net/sunrpc/nfsd in net namespaces")
> Reported-by: syzbot+e34ad04f27991521104c@...kaller.appspotmail.com
> Closes: https://lore.kernel.org/linux-nfs/67a47501.050a0220.19061f.05f9.GAE@google.com/
> Signed-off-by: Jeff Layton <jlayton@...nel.org>
> ---
> I looked at the console log from the report, and syzkaller is doing
> fault injection on allocations. You can see the stack where the "nfsd"
> directory under /proc failed to be created due to one. This is a pretty
> unlikely bug under normal circumstances, but it's simple to fix. The
> problem predates the patch in Fixes:, but it's not worth the effort to
> backport this to anything earlier.

I'd prefer to document this by labeling the actual commit that
introduced the problem in the Fixes: tag, then using

"Cc: stable # vN.M"

to block automatic backporting to LTS kernels where this patch won't
apply cleanly. I can derive the values of N and M from the commit you
mention above, but do you happen to know the actual culprit commit?


> ---
>  fs/nfsd/nfsctl.c | 9 ++++++++-
>  fs/nfsd/stats.c  | 4 ++--
>  fs/nfsd/stats.h  | 2 +-
>  3 files changed, 11 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
> index 95ea4393305bd38493b640fbaba2e8f57f5a501d..583eda0df54dca394de4bbe8d148be2892df39cb 100644
> --- a/fs/nfsd/nfsctl.c
> +++ b/fs/nfsd/nfsctl.c
> @@ -2204,8 +2204,14 @@ static __net_init int nfsd_net_init(struct net *net)
>  					  NFSD_STATS_COUNTERS_NUM);
>  	if (retval)
>  		goto out_repcache_error;
> +
>  	memset(&nn->nfsd_svcstats, 0, sizeof(nn->nfsd_svcstats));
>  	nn->nfsd_svcstats.program = &nfsd_programs[0];
> +	if (!nfsd_proc_stat_init(net)) {
> +		retval = -ENOMEM;
> +		goto out_proc_error;
> +	}
> +
>  	for (i = 0; i < sizeof(nn->nfsd_versions); i++)
>  		nn->nfsd_versions[i] = nfsd_support_version(i);
>  	for (i = 0; i < sizeof(nn->nfsd4_minorversions); i++)
> @@ -2215,12 +2221,13 @@ static __net_init int nfsd_net_init(struct net *net)
>  	nfsd4_init_leases_net(nn);
>  	get_random_bytes(&nn->siphash_key, sizeof(nn->siphash_key));
>  	seqlock_init(&nn->writeverf_lock);
> -	nfsd_proc_stat_init(net);
>  #if IS_ENABLED(CONFIG_NFS_LOCALIO)
>  	INIT_LIST_HEAD(&nn->local_clients);
>  #endif
>  	return 0;
>  
> +out_proc_error:
> +	percpu_counter_destroy_many(nn->counter, NFSD_STATS_COUNTERS_NUM);
>  out_repcache_error:
>  	nfsd_idmap_shutdown(net);
>  out_idmap_error:
> diff --git a/fs/nfsd/stats.c b/fs/nfsd/stats.c
> index bb22893f1157e4c159e123b6d8e25b8eab52e187..f7eaf95e20fc8758566f469c6c2de79119fea070 100644
> --- a/fs/nfsd/stats.c
> +++ b/fs/nfsd/stats.c
> @@ -73,11 +73,11 @@ static int nfsd_show(struct seq_file *seq, void *v)
>  
>  DEFINE_PROC_SHOW_ATTRIBUTE(nfsd);
>  
> -void nfsd_proc_stat_init(struct net *net)
> +struct proc_dir_entry *nfsd_proc_stat_init(struct net *net)
>  {
>  	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
>  
> -	svc_proc_register(net, &nn->nfsd_svcstats, &nfsd_proc_ops);
> +	return svc_proc_register(net, &nn->nfsd_svcstats, &nfsd_proc_ops);
>  }
>  
>  void nfsd_proc_stat_shutdown(struct net *net)
> diff --git a/fs/nfsd/stats.h b/fs/nfsd/stats.h
> index 04aacb6c36e2576ba231ee481e3a3e9e9f255a61..e4efb0e4e56d467c13eaa5a1dd312c85dadeb4b8 100644
> --- a/fs/nfsd/stats.h
> +++ b/fs/nfsd/stats.h
> @@ -10,7 +10,7 @@
>  #include <uapi/linux/nfsd/stats.h>
>  #include <linux/percpu_counter.h>
>  
> -void nfsd_proc_stat_init(struct net *net);
> +struct proc_dir_entry *nfsd_proc_stat_init(struct net *net);
>  void nfsd_proc_stat_shutdown(struct net *net);
>  
>  static inline void nfsd_stats_rc_hits_inc(struct nfsd_net *nn)
> 
> ---
> base-commit: ebbdc9429c39336a406b191cfe84bca2c12c2f73
> change-id: 20250206-nfsd-fixes-8e61bdf66347
> 
> Best regards,


-- 
Chuck Lever