linux-kernel - Re: [PATCH] NFSd: set nfsd_serv to NULL after service destruction

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Message-ID: <20120523215210.GA15910@fieldses.org>
Date:	Wed, 23 May 2012 17:52:10 -0400
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	Stanislav Kinsbursky <skinsbursky@...allels.com>
Cc:	linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org,
	devel@...nvz.org
Subject: Re: [PATCH] NFSd: set nfsd_serv to NULL after service destruction

On Fri, May 18, 2012 at 07:26:02PM +0400, Stanislav Kinsbursky wrote:
> Otherwise we will get NULL pointer dereference after
> svc_shutdown_net->sv_shutdown (nfsd_last_thread) call.
> This looks safe, because all such operations (svc_destroy) are performed with
> nfsd_mutex being held.
> 
> Signed-off-by: Stanislav Kinsbursky <skinsbursky@...allels.com>
> ---
>  fs/nfsd/nfsctl.c |    4 ++--
>  fs/nfsd/nfsd.h   |    6 ++++++
>  fs/nfsd/nfssvc.c |   10 ++++------
>  3 files changed, 12 insertions(+), 8 deletions(-)
> 
> diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
> index c55298e..82cca1e 100644
> --- a/fs/nfsd/nfsctl.c
> +++ b/fs/nfsd/nfsctl.c
> @@ -675,7 +675,7 @@ static ssize_t __write_ports_addfd(char *buf)
>  	if (err < 0) {
>  		if (nfsd_serv->sv_nrthreads == 1)
>  			svc_shutdown_net(nfsd_serv, net);
> -		svc_destroy(nfsd_serv);
> +		nfsd_destroy();

The server could still be running here.  We don't want to set nfsd_serv
to NULL.

--b.

>  		return err;
>  	}
>  
> @@ -746,7 +746,7 @@ out_close:
>  out_err:
>  	if (nfsd_serv->sv_nrthreads == 1)
>  		svc_shutdown_net(nfsd_serv, net);
> -	svc_destroy(nfsd_serv);
> +	nfsd_destroy();
>  	return err;
>  }
>  
> diff --git a/fs/nfsd/nfsd.h b/fs/nfsd/nfsd.h
> index 1671429..35db369 100644
> --- a/fs/nfsd/nfsd.h
> +++ b/fs/nfsd/nfsd.h
> @@ -73,6 +73,12 @@ int		nfsd_nrpools(void);
>  int		nfsd_get_nrthreads(int n, int *);
>  int		nfsd_set_nrthreads(int n, int *);
>  
> +static inline void nfsd_destroy(void)
> +{
> +	svc_destroy(nfsd_serv);
> +	nfsd_serv = NULL;
> +}
> +
>  #if defined(CONFIG_NFSD_V2_ACL) || defined(CONFIG_NFSD_V3_ACL)
>  #ifdef CONFIG_NFSD_V2_ACL
>  extern struct svc_version nfsd_acl_version2;
> diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c
> index ee709fc..ab89fe0 100644
> --- a/fs/nfsd/nfssvc.c
> +++ b/fs/nfsd/nfssvc.c
> @@ -254,8 +254,6 @@ static void nfsd_shutdown(void)
>  
>  static void nfsd_last_thread(struct svc_serv *serv, struct net *net)
>  {
> -	/* When last nfsd thread exits we need to do some clean-up */
> -	nfsd_serv = NULL;
>  	nfsd_shutdown();
>  
>  	svc_rpcb_cleanup(serv, net);
> @@ -348,7 +346,7 @@ int nfsd_create_serv(void)
>  
>  	error = svc_bind(nfsd_serv, current->nsproxy->net_ns);
>  	if (error < 0) {
> -		svc_destroy(nfsd_serv);
> +		nfsd_destroy();
>  		return error;
>  	}
>  
> @@ -430,7 +428,7 @@ int nfsd_set_nrthreads(int n, int *nthreads)
>  
>  	if (nfsd_serv->sv_nrthreads == 1)
>  		svc_shutdown_net(nfsd_serv, net);
> -	svc_destroy(nfsd_serv);
> +	nfsd_destroy();
>  
>  	return err;
>  }
> @@ -480,7 +478,7 @@ out_shutdown:
>  out_destroy:
>  	if (nfsd_serv->sv_nrthreads == 1)
>  		svc_shutdown_net(nfsd_serv, net);
> -	svc_destroy(nfsd_serv);		/* Release server */
> +	nfsd_destroy();		/* Release server */
>  out:
>  	mutex_unlock(&nfsd_mutex);
>  	return error;
> @@ -684,7 +682,7 @@ int nfsd_pool_stats_release(struct inode *inode, struct file *file)
>  	/* this function really, really should have been called svc_put() */
>  	if (nfsd_serv->sv_nrthreads == 1)
>  		svc_shutdown_net(nfsd_serv, net);
> -	svc_destroy(nfsd_serv);
> +	nfsd_destroy();
>  	mutex_unlock(&nfsd_mutex);
>  	return ret;
>  }
> 
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