linux-kernel - Re: [PATCH] [RFC] nfsd: fix possible dereference of static NULL nfsd

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Message-ID: <20120706172630.GA11193@fieldses.org>
Date:	Fri, 6 Jul 2012 13:26:30 -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] [RFC] nfsd: fix possible dereference of static NULL
 nfsd_serv pointer

On Fri, Jul 06, 2012 at 05:45:56PM +0400, Stanislav Kinsbursky wrote:
> This is a bug fix for 3.5 kernel.
> In case on NFSd service start failure svc_shutdown_net() will call svc_destroy
> callback and zeroize global nfsd_serv pointer, this in turn will lead to Oops
> in svc_destroy().
> 
> This patch is marked as RFC, because to many lines were changed. It can be
> easely simplified if requested.
> Moreover, NFSd service shutdown is going to be converted into csomething on
> per-net basis.

Doesn't this leave error paths in e.g. __write_ports_addfd() and
__write_ports_addxprt() unfixed?

I'm inclined to just submit your original fix (split up as in the last
version I sent) for 3.5 if you don't object.

--b.

> 
> Signed-off-by: Stanislav Kinsbursky <skinsbursky@...allels.com>
> ---
>  fs/nfsd/nfssvc.c |   14 ++++++++------
>  1 files changed, 8 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c
> index ee709fc..526a4aa 100644
> --- a/fs/nfsd/nfssvc.c
> +++ b/fs/nfsd/nfssvc.c
> @@ -446,6 +446,7 @@ nfsd_svc(unsigned short port, int nrservs)
>  	int	error;
>  	bool	nfsd_up_before;
>  	struct net *net = &init_net;
> +	struct svc_serv *serv = nfsd_serv;
>  
>  	mutex_lock(&nfsd_mutex);
>  	dprintk("nfsd: creating service\n");
> @@ -454,7 +455,7 @@ nfsd_svc(unsigned short port, int nrservs)
>  	if (nrservs > NFSD_MAXSERVS)
>  		nrservs = NFSD_MAXSERVS;
>  	error = 0;
> -	if (nrservs == 0 && nfsd_serv == NULL)
> +	if (nrservs == 0 && serv == NULL)
>  		goto out;
>  
>  	error = nfsd_create_serv();
> @@ -464,23 +465,24 @@ nfsd_svc(unsigned short port, int nrservs)
>  	nfsd_up_before = nfsd_up;
>  
>  	error = nfsd_startup(port, nrservs);
> +	error = -EINVAL;
>  	if (error)
>  		goto out_destroy;
> -	error = svc_set_num_threads(nfsd_serv, NULL, nrservs);
> +	error = svc_set_num_threads(serv, NULL, nrservs);
>  	if (error)
>  		goto out_shutdown;
>  	/* We are holding a reference to nfsd_serv which
>  	 * we don't want to count in the return value,
>  	 * so subtract 1
>  	 */
> -	error = nfsd_serv->sv_nrthreads - 1;
> +	error = serv->sv_nrthreads - 1;
>  out_shutdown:
>  	if (error < 0 && !nfsd_up_before)
>  		nfsd_shutdown();
>  out_destroy:
> -	if (nfsd_serv->sv_nrthreads == 1)
> -		svc_shutdown_net(nfsd_serv, net);
> -	svc_destroy(nfsd_serv);		/* Release server */
> +	if (serv->sv_nrthreads == 1)
> +		svc_shutdown_net(serv, net);
> +	svc_destroy(serv);		/* Release server */
>  out:
>  	mutex_unlock(&nfsd_mutex);
>  	return error;
> 
--
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