SUNRPC: NULL utsname dereference on NFS umount during namespace cleanup

Fix an Oopsable condition when nsm_mon_unmon is called as part of the
namespace cleanup, which now apparently happens after the utsname
has been freed.

Link: http://lkml.kernel.org/r/20150125220604.090121ae@neptune.home
Reported-by: Bruno Prémont <bonbons@linux-vserver.org>
Cc: stable@vger.kernel.org # 3.18
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

fs/lockd/mon.c

@@ -65,7 +65,7 @@ static inline struct sockaddr *nsm_addr(const struct nsm_handle *nsm)
 	return (struct sockaddr *)&nsm->sm_addr;
 }
 
-static struct rpc_clnt *nsm_create(struct net *net)
+static struct rpc_clnt *nsm_create(struct net *net, const char *nodename)
 {
 	struct sockaddr_in sin = {
 		.sin_family		= AF_INET,
@@ -77,6 +77,7 @@ static struct rpc_clnt *nsm_create(struct net *net)
 		.address		= (struct sockaddr *)&sin,
 		.addrsize		= sizeof(sin),
 		.servername		= "rpc.statd",
+		.nodename		= nodename,
 		.program		= &nsm_program,
 		.version		= NSM_VERSION,
 		.authflavor		= RPC_AUTH_NULL,
@@ -102,7 +103,7 @@ out:
 	return clnt;
 }
 
-static struct rpc_clnt *nsm_client_get(struct net *net)
+static struct rpc_clnt *nsm_client_get(struct net *net, const char *nodename)
 {
 	struct rpc_clnt	*clnt, *new;
 	struct lockd_net *ln = net_generic(net, lockd_net_id);
@@ -111,7 +112,7 @@ static struct rpc_clnt *nsm_client_get(struct net *net)
 	if (clnt != NULL)
 		goto out;
 
-	clnt = new = nsm_create(net);
+	clnt = new = nsm_create(net, nodename);
 	if (IS_ERR(clnt))
 		goto out;
 
@@ -190,19 +191,23 @@ int nsm_monitor(const struct nlm_host *host)
 	struct nsm_res	res;
 	int		status;
 	struct rpc_clnt *clnt;
+	const char *nodename = NULL;
 
 	dprintk("lockd: nsm_monitor(%s)\n", nsm->sm_name);
 
 	if (nsm->sm_monitored)
 		return 0;
 
+	if (host->h_rpcclnt)
+		nodename = host->h_rpcclnt->cl_nodename;
+
 	/*
 	 * Choose whether to record the caller_name or IP address of
 	 * this peer in the local rpc.statd's database.
 	 */
 	nsm->sm_mon_name = nsm_use_hostnames ? nsm->sm_name : nsm->sm_addrbuf;
 
-	clnt = nsm_client_get(host->net);
+	clnt = nsm_client_get(host->net, nodename);
 	if (IS_ERR(clnt)) {
 		status = PTR_ERR(clnt);
 		dprintk("lockd: failed to create NSM upcall transport, "

include/linux/sunrpc/clnt.h

@@ -57,7 +57,7 @@ struct rpc_clnt {
 	const struct rpc_timeout *cl_timeout;	/* Timeout strategy */
 
 	int			cl_nodelen;	/* nodename length */
-	char 			cl_nodename[UNX_MAXNODENAME];
+	char 			cl_nodename[UNX_MAXNODENAME+1];
 	struct rpc_pipe_dir_head cl_pipedir_objects;
 	struct rpc_clnt *	cl_parent;	/* Points to parent of clones */
 	struct rpc_rtt		cl_rtt_default;
@@ -112,6 +112,7 @@ struct rpc_create_args {
 	struct sockaddr		*saddress;
 	const struct rpc_timeout *timeout;
 	const char		*servername;
+	const char		*nodename;
 	const struct rpc_program *program;
 	u32			prognumber;	/* overrides program->number */
 	u32			version;

net/sunrpc/clnt.c

@@ -286,10 +286,8 @@ static struct rpc_xprt *rpc_clnt_set_transport(struct rpc_clnt *clnt,
 
 static void rpc_clnt_set_nodename(struct rpc_clnt *clnt, const char *nodename)
 {
-	clnt->cl_nodelen = strlen(nodename);
-	if (clnt->cl_nodelen > UNX_MAXNODENAME)
-		clnt->cl_nodelen = UNX_MAXNODENAME;
-	memcpy(clnt->cl_nodename, nodename, clnt->cl_nodelen);
+	clnt->cl_nodelen = strlcpy(clnt->cl_nodename,
+			nodename, sizeof(clnt->cl_nodename));
 }
 
 static int rpc_client_register(struct rpc_clnt *clnt,
@@ -365,6 +363,7 @@ static struct rpc_clnt * rpc_new_client(const struct rpc_create_args *args,
 	const struct rpc_version *version;
 	struct rpc_clnt *clnt = NULL;
 	const struct rpc_timeout *timeout;
+	const char *nodename = args->nodename;
 	int err;
 
 	/* sanity check the name before trying to print it */
@@ -420,8 +419,10 @@ static struct rpc_clnt * rpc_new_client(const struct rpc_create_args *args,
 
 	atomic_set(&clnt->cl_count, 1);
 
+	if (nodename == NULL)
+		nodename = utsname()->nodename;
 	/* save the nodename */
-	rpc_clnt_set_nodename(clnt, utsname()->nodename);
+	rpc_clnt_set_nodename(clnt, nodename);
 
 	err = rpc_client_register(clnt, args->authflavor, args->client_name);
 	if (err)
@@ -576,6 +577,7 @@ static struct rpc_clnt *__rpc_clone_client(struct rpc_create_args *args,
 	if (xprt == NULL)
 		goto out_err;
 	args->servername = xprt->servername;
+	args->nodename = clnt->cl_nodename;
 
 	new = rpc_new_client(args, xprt, clnt);
 	if (IS_ERR(new)) {

net/sunrpc/rpcb_clnt.c

@@ -355,7 +355,8 @@ out:
 	return result;
 }
 
-static struct rpc_clnt *rpcb_create(struct net *net, const char *hostname,
+static struct rpc_clnt *rpcb_create(struct net *net, const char *nodename,
+				    const char *hostname,
 				    struct sockaddr *srvaddr, size_t salen,
 				    int proto, u32 version)
 {
@@ -365,6 +366,7 @@ static struct rpc_clnt *rpcb_create(struct net *net, const char *hostname,
 		.address	= srvaddr,
 		.addrsize	= salen,
 		.servername	= hostname,
+		.nodename	= nodename,
 		.program	= &rpcb_program,
 		.version	= version,
 		.authflavor	= RPC_AUTH_UNIX,
@@ -740,7 +742,9 @@ void rpcb_getport_async(struct rpc_task *task)
 	dprintk("RPC: %5u %s: trying rpcbind version %u\n",
 		task->tk_pid, __func__, bind_version);
 
-	rpcb_clnt = rpcb_create(xprt->xprt_net, xprt->servername, sap, salen,
+	rpcb_clnt = rpcb_create(xprt->xprt_net,
+				clnt->cl_nodename,
+				xprt->servername, sap, salen,
 				xprt->prot, bind_version);
 	if (IS_ERR(rpcb_clnt)) {
 		status = PTR_ERR(rpcb_clnt);