[PATCH] [RFC] nfsd: fix possible dereference of static NULL nfsd_serv pointer

[Stanislav Kinsbursky <skinsbursky@parallels.com>]

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.

Signed-off-by: Stanislav Kinsbursky <skinsbursky@parallels.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;