fs/nfs/callback.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0
 /*
  * linux/fs/nfs/callback.c
  *
  * Copyright (C) 2004 Trond Myklebust
  *
  * NFSv4 callback handling
  */

 #include <linux/completion.h>
 #include <linux/ip.h>
 #include <linux/module.h>
 #include <linux/sched/signal.h>
 #include <linux/sunrpc/svc.h>
 #include <linux/sunrpc/svcsock.h>
 #include <linux/nfs_fs.h>
 #include <linux/errno.h>
 #include <linux/mutex.h>
 #include <linux/freezer.h>
 #include <linux/sunrpc/svcauth_gss.h>
 #include <linux/sunrpc/bc_xprt.h>

 #include <net/inet_sock.h>

 #include "nfs4_fs.h"
 #include "callback.h"
 #include "internal.h"
 #include "netns.h"

 #define NFSDBG_FACILITY NFSDBG_CALLBACK

 struct nfs_callback_data {
 	unsigned int users;
 	struct svc_serv *serv;
 };

 static struct nfs_callback_data nfs_callback_info[NFS4_MAX_MINOR_VERSION + 1];
 static DEFINE_MUTEX(nfs_callback_mutex);
 static struct svc_program nfs4_callback_program;

 static int nfs4_callback_up_net(struct svc_serv *serv, struct net *net)
 {
 	const struct cred *cred = current_cred();
 	int ret;
 	struct nfs_net *nn = net_generic(net, nfs_net_id);

 	ret = svc_xprt_create(serv, "tcp", net, PF_INET,
 			      nfs_callback_set_tcpport, SVC_SOCK_ANONYMOUS,
 			      cred);
 	if (ret <= 0)
 		goto out_err;
 	nn->nfs_callback_tcpport = ret;
 	dprintk("NFS: Callback listener port = %u (af %u, net %x)\n",
 		nn->nfs_callback_tcpport, PF_INET, net->ns.inum);

 	ret = svc_xprt_create(serv, "tcp", net, PF_INET6,
 			      nfs_callback_set_tcpport, SVC_SOCK_ANONYMOUS,
 			      cred);
 	if (ret > 0) {
 		nn->nfs_callback_tcpport6 = ret;
 		dprintk("NFS: Callback listener port = %u (af %u, net %x)\n",
 			nn->nfs_callback_tcpport6, PF_INET6, net->ns.inum);
 	} else if (ret != -EAFNOSUPPORT)
 		goto out_err;
 	return 0;

 out_err:
 	return (ret) ? ret : -ENOMEM;
 }

 /*
  * This is the NFSv4 callback kernel thread.
  */
 static int
 nfs4_callback_svc(void *vrqstp)
 {
 	int err;
 	struct svc_rqst *rqstp = vrqstp;

 	set_freezable();

 	while (!kthread_freezable_should_stop(NULL)) {

 		if (signal_pending(current))
 			flush_signals(current);
 		/*
 		 * Listen for a request on the socket
 		 */
 		err = svc_recv(rqstp, MAX_SCHEDULE_TIMEOUT);
 		if (err == -EAGAIN || err == -EINTR)
 			continue;
 		svc_process(rqstp);
 	}

 	svc_exit_thread(rqstp);
 	return 0;
 }

 #if defined(CONFIG_NFS_V4_1)
 /*
  * The callback service for NFSv4.1 callbacks
  */
 static int
 nfs41_callback_svc(void *vrqstp)
 {
 	struct svc_rqst *rqstp = vrqstp;
 	struct svc_serv *serv = rqstp->rq_server;
 	struct rpc_rqst *req;
 	int error;
 	DEFINE_WAIT(wq);

 	set_freezable();

 	while (!kthread_freezable_should_stop(NULL)) {

 		if (signal_pending(current))
 			flush_signals(current);

 		prepare_to_wait(&serv->sv_cb_waitq, &wq, TASK_INTERRUPTIBLE);
 		spin_lock_bh(&serv->sv_cb_lock);
 		if (!list_empty(&serv->sv_cb_list)) {
 			req = list_first_entry(&serv->sv_cb_list,
 					struct rpc_rqst, rq_bc_list);
 			list_del(&req->rq_bc_list);
 			spin_unlock_bh(&serv->sv_cb_lock);
 			finish_wait(&serv->sv_cb_waitq, &wq);
 			dprintk("Invoking bc_svc_process()\n");
 			error = bc_svc_process(serv, req, rqstp);
 			dprintk("bc_svc_process() returned w/ error code= %d\n",
 				error);
 		} else {
 			spin_unlock_bh(&serv->sv_cb_lock);
 			if (!kthread_should_stop())
 				schedule();
 			finish_wait(&serv->sv_cb_waitq, &wq);
 		}
 	}

 	svc_exit_thread(rqstp);
 	return 0;
 }

 static inline void nfs_callback_bc_serv(u32 minorversion, struct rpc_xprt *xprt,
 		struct svc_serv *serv)
 {
 	if (minorversion)
 		/*
 		 * Save the svc_serv in the transport so that it can
 		 * be referenced when the session backchannel is initialized
 		 */
 		xprt->bc_serv = serv;
 }
 #else
 static inline void nfs_callback_bc_serv(u32 minorversion, struct rpc_xprt *xprt,
 		struct svc_serv *serv)
 {
 }
 #endif /* CONFIG_NFS_V4_1 */

 static int nfs_callback_start_svc(int minorversion, struct rpc_xprt *xprt,
 				  struct svc_serv *serv)
 {
 	int nrservs = nfs_callback_nr_threads;
 	int ret;

 	nfs_callback_bc_serv(minorversion, xprt, serv);

 	if (nrservs < NFS4_MIN_NR_CALLBACK_THREADS)
 		nrservs = NFS4_MIN_NR_CALLBACK_THREADS;

 	if (serv->sv_nrthreads == nrservs)
 		return 0;

 	ret = svc_set_num_threads(serv, NULL, nrservs);
 	if (ret) {
 		svc_set_num_threads(serv, NULL, 0);
 		return ret;
 	}
 	dprintk("nfs_callback_up: service started\n");
 	return 0;
 }

 static void nfs_callback_down_net(u32 minorversion, struct svc_serv *serv, struct net *net)
 {
 	struct nfs_net *nn = net_generic(net, nfs_net_id);

 	if (--nn->cb_users[minorversion])
 		return;

 	dprintk("NFS: destroy per-net callback data; net=%x\n", net->ns.inum);
 	svc_xprt_destroy_all(serv, net);
 }

 static int nfs_callback_up_net(int minorversion, struct svc_serv *serv,
 			       struct net *net, struct rpc_xprt *xprt)
 {
 	struct nfs_net *nn = net_generic(net, nfs_net_id);
 	int ret;

 	if (nn->cb_users[minorversion]++)
 		return 0;

 	dprintk("NFS: create per-net callback data; net=%x\n", net->ns.inum);

 	ret = svc_bind(serv, net);
 	if (ret < 0) {
 		printk(KERN_WARNING "NFS: bind callback service failed\n");
 		goto err_bind;
 	}

 	ret = 0;
 	if (!IS_ENABLED(CONFIG_NFS_V4_1) || minorversion == 0)
 		ret = nfs4_callback_up_net(serv, net);
 	else if (xprt->ops->bc_setup)
 		set_bc_enabled(serv);
 	else
 		ret = -EPROTONOSUPPORT;

 	if (ret < 0) {
 		printk(KERN_ERR "NFS: callback service start failed\n");
 		goto err_socks;
 	}
 	return 0;

 err_socks:
 	svc_rpcb_cleanup(serv, net);
 err_bind:
 	nn->cb_users[minorversion]--;
 	dprintk("NFS: Couldn't create callback socket: err = %d; "
 			"net = %x\n", ret, net->ns.inum);
 	return ret;
 }

 static struct svc_serv *nfs_callback_create_svc(int minorversion)
 {
 	struct nfs_callback_data *cb_info = &nfs_callback_info[minorversion];
 	int (*threadfn)(void *data);
 	struct svc_serv *serv;

 	/*
 	 * Check whether we're already up and running.
 	 */
 	if (cb_info->serv)
 		return svc_get(cb_info->serv);

 	/*
 	 * Sanity check: if there's no task,
 	 * we should be the first user ...
 	 */
 	if (cb_info->users)
 		printk(KERN_WARNING "nfs_callback_create_svc: no kthread, %d users??\n",
 			cb_info->users);

 	threadfn = nfs4_callback_svc;
 #if defined(CONFIG_NFS_V4_1)
 	if (minorversion)
 		threadfn = nfs41_callback_svc;
 #else
 	if (minorversion)
 		return ERR_PTR(-ENOTSUPP);
 #endif
 	serv = svc_create(&nfs4_callback_program, NFS4_CALLBACK_BUFSIZE,
 			  threadfn);
 	if (!serv) {
 		printk(KERN_ERR "nfs_callback_create_svc: create service failed\n");
 		return ERR_PTR(-ENOMEM);
 	}
 	cb_info->serv = serv;
 	/* As there is only one thread we need to over-ride the
 	 * default maximum of 80 connections
 	 */
 	serv->sv_maxconn = 1024;
 	dprintk("nfs_callback_create_svc: service created\n");
 	return serv;
 }

 /*
  * Bring up the callback thread if it is not already up.
  */
 int nfs_callback_up(u32 minorversion, struct rpc_xprt *xprt)
 {
 	struct svc_serv *serv;
 	struct nfs_callback_data *cb_info = &nfs_callback_info[minorversion];
 	int ret;
 	struct net *net = xprt->xprt_net;

 	mutex_lock(&nfs_callback_mutex);

 	serv = nfs_callback_create_svc(minorversion);
 	if (IS_ERR(serv)) {
 		ret = PTR_ERR(serv);
 		goto err_create;
 	}

 	ret = nfs_callback_up_net(minorversion, serv, net, xprt);
 	if (ret < 0)
 		goto err_net;

 	ret = nfs_callback_start_svc(minorversion, xprt, serv);
 	if (ret < 0)
 		goto err_start;

 	cb_info->users++;
 err_net:
 	if (!cb_info->users)
 		cb_info->serv = NULL;
 	svc_put(serv);
 err_create:
 	mutex_unlock(&nfs_callback_mutex);
 	return ret;

 err_start:
 	nfs_callback_down_net(minorversion, serv, net);
 	dprintk("NFS: Couldn't create server thread; err = %d\n", ret);
 	goto err_net;
 }

 /*
  * Kill the callback thread if it's no longer being used.
  */
 void nfs_callback_down(int minorversion, struct net *net)
 {
 	struct nfs_callback_data *cb_info = &nfs_callback_info[minorversion];
 	struct svc_serv *serv;

 	mutex_lock(&nfs_callback_mutex);
 	serv = cb_info->serv;
 	nfs_callback_down_net(minorversion, serv, net);
 	cb_info->users--;
 	if (cb_info->users == 0) {
 		svc_get(serv);
 		svc_set_num_threads(serv, NULL, 0);
 		svc_put(serv);
 		dprintk("nfs_callback_down: service destroyed\n");
 		cb_info->serv = NULL;
 	}
 	mutex_unlock(&nfs_callback_mutex);
 }

 /* Boolean check of RPC_AUTH_GSS principal */
 int
 check_gss_callback_principal(struct nfs_client *clp, struct svc_rqst *rqstp)
 {
 	char *p = rqstp->rq_cred.cr_principal;

 	if (rqstp->rq_authop->flavour != RPC_AUTH_GSS)
 		return 1;

 	/* No RPC_AUTH_GSS on NFSv4.1 back channel yet */
 	if (clp->cl_minorversion != 0)
 		return 0;
 	/*
 	 * It might just be a normal user principal, in which case
 	 * userspace won't bother to tell us the name at all.
 	 */
 	if (p == NULL)
 		return 0;

 	/*
 	 * Did we get the acceptor from userland during the SETCLIENID
 	 * negotiation?
 	 */
 	if (clp->cl_acceptor)
 		return !strcmp(p, clp->cl_acceptor);

 	/*
 	 * Otherwise try to verify it using the cl_hostname. Note that this
 	 * doesn't work if a non-canonical hostname was used in the devname.
 	 */

 	/* Expect a GSS_C_NT_HOSTBASED_NAME like "nfs@serverhostname" */

 	if (memcmp(p, "nfs@", 4) != 0)
 		return 0;
 	p += 4;
 	if (strcmp(p, clp->cl_hostname) != 0)
 		return 0;
 	return 1;
 }

 /*
  * pg_authenticate method for nfsv4 callback threads.
  *
  * The authflavor has been negotiated, so an incorrect flavor is a server
  * bug. Deny packets with incorrect authflavor.
  *
  * All other checking done after NFS decoding where the nfs_client can be
  * found in nfs4_callback_compound
  */
 static int nfs_callback_authenticate(struct svc_rqst *rqstp)
 {
 	rqstp->rq_auth_stat = rpc_autherr_badcred;

 	switch (rqstp->rq_authop->flavour) {
 	case RPC_AUTH_NULL:
 		if (rqstp->rq_proc != CB_NULL)
 			return SVC_DENIED;
 		break;
 	case RPC_AUTH_GSS:
 		/* No RPC_AUTH_GSS support yet in NFSv4.1 */
 		 if (svc_is_backchannel(rqstp))
 			return SVC_DENIED;
 	}

 	rqstp->rq_auth_stat = rpc_auth_ok;
 	return SVC_OK;
 }

 /*
  * Define NFS4 callback program
  */
 static const struct svc_version *nfs4_callback_version[] = {
 	[1] = &nfs4_callback_version1,
 	[4] = &nfs4_callback_version4,
 };

 static struct svc_stat nfs4_callback_stats;

 static struct svc_program nfs4_callback_program = {
 	.pg_prog = NFS4_CALLBACK,			/* RPC service number */
 	.pg_nvers = ARRAY_SIZE(nfs4_callback_version),	/* Number of entries */
 	.pg_vers = nfs4_callback_version,		/* version table */
 	.pg_name = "NFSv4 callback",			/* service name */
 	.pg_class = "nfs",				/* authentication class */
 	.pg_stats = &nfs4_callback_stats,
 	.pg_authenticate = nfs_callback_authenticate,
 	.pg_init_request = svc_generic_init_request,
 	.pg_rpcbind_set	= svc_generic_rpcbind_set,
 };
	// SPDX-License-Identifier: GPL-2.0
	/*
	* linux/fs/nfs/callback.c
	*
	* Copyright (C) 2004 Trond Myklebust
	*
	* NFSv4 callback handling
	*/

	#include <linux/completion.h>
	#include <linux/ip.h>
	#include <linux/module.h>
	#include <linux/sched/signal.h>
	#include <linux/sunrpc/svc.h>
	#include <linux/sunrpc/svcsock.h>
	#include <linux/nfs_fs.h>
	#include <linux/errno.h>
	#include <linux/mutex.h>
	#include <linux/freezer.h>
	#include <linux/sunrpc/svcauth_gss.h>
	#include <linux/sunrpc/bc_xprt.h>

	#include <net/inet_sock.h>

	#include "nfs4_fs.h"
	#include "callback.h"
	#include "internal.h"
	#include "netns.h"

	#define NFSDBG_FACILITY NFSDBG_CALLBACK

	struct nfs_callback_data {
	unsigned int users;
	struct svc_serv *serv;
	};

	static struct nfs_callback_data nfs_callback_info[NFS4_MAX_MINOR_VERSION + 1];
	static DEFINE_MUTEX(nfs_callback_mutex);
	static struct svc_program nfs4_callback_program;

	static int nfs4_callback_up_net(struct svc_serv serv, struct net net)
	{
	const struct cred *cred = current_cred();
	int ret;
	struct nfs_net *nn = net_generic(net, nfs_net_id);

	ret = svc_xprt_create(serv, "tcp", net, PF_INET,
	nfs_callback_set_tcpport, SVC_SOCK_ANONYMOUS,
	cred);
	if (ret <= 0)
	goto out_err;
	nn->nfs_callback_tcpport = ret;
	dprintk("NFS: Callback listener port = %u (af %u, net %x)\n",
	nn->nfs_callback_tcpport, PF_INET, net->ns.inum);

	ret = svc_xprt_create(serv, "tcp", net, PF_INET6,
	nfs_callback_set_tcpport, SVC_SOCK_ANONYMOUS,
	cred);
	if (ret > 0) {
	nn->nfs_callback_tcpport6 = ret;
	dprintk("NFS: Callback listener port = %u (af %u, net %x)\n",
	nn->nfs_callback_tcpport6, PF_INET6, net->ns.inum);
	} else if (ret != -EAFNOSUPPORT)
	goto out_err;
	return 0;

	out_err:
	return (ret) ? ret : -ENOMEM;
	}

	/*
	* This is the NFSv4 callback kernel thread.
	*/
	static int
	nfs4_callback_svc(void *vrqstp)
	{
	int err;
	struct svc_rqst *rqstp = vrqstp;

	set_freezable();

	while (!kthread_freezable_should_stop(NULL)) {

	if (signal_pending(current))
	flush_signals(current);
	/*
	* Listen for a request on the socket
	*/
	err = svc_recv(rqstp, MAX_SCHEDULE_TIMEOUT);
	if (err == -EAGAIN \|\| err == -EINTR)
	continue;
	svc_process(rqstp);
	}

	svc_exit_thread(rqstp);
	return 0;
	}

	#if defined(CONFIG_NFS_V4_1)
	/*
	* The callback service for NFSv4.1 callbacks
	*/
	static int
	nfs41_callback_svc(void *vrqstp)
	{
	struct svc_rqst *rqstp = vrqstp;
	struct svc_serv *serv = rqstp->rq_server;
	struct rpc_rqst *req;
	int error;
	DEFINE_WAIT(wq);

	set_freezable();

	while (!kthread_freezable_should_stop(NULL)) {

	if (signal_pending(current))
	flush_signals(current);

	prepare_to_wait(&serv->sv_cb_waitq, &wq, TASK_INTERRUPTIBLE);
	spin_lock_bh(&serv->sv_cb_lock);
	if (!list_empty(&serv->sv_cb_list)) {
	req = list_first_entry(&serv->sv_cb_list,
	struct rpc_rqst, rq_bc_list);
	list_del(&req->rq_bc_list);
	spin_unlock_bh(&serv->sv_cb_lock);
	finish_wait(&serv->sv_cb_waitq, &wq);
	dprintk("Invoking bc_svc_process()\n");
	error = bc_svc_process(serv, req, rqstp);
	dprintk("bc_svc_process() returned w/ error code= %d\n",
	error);
	} else {
	spin_unlock_bh(&serv->sv_cb_lock);
	if (!kthread_should_stop())
	schedule();
	finish_wait(&serv->sv_cb_waitq, &wq);
	}
	}

	svc_exit_thread(rqstp);
	return 0;
	}

	static inline void nfs_callback_bc_serv(u32 minorversion, struct rpc_xprt *xprt,
	struct svc_serv *serv)
	{
	if (minorversion)
	/*
	* Save the svc_serv in the transport so that it can
	* be referenced when the session backchannel is initialized
	*/
	xprt->bc_serv = serv;
	}
	#else
	static inline void nfs_callback_bc_serv(u32 minorversion, struct rpc_xprt *xprt,
	struct svc_serv *serv)
	{
	}
	#endif /* CONFIG_NFS_V4_1 */

	static int nfs_callback_start_svc(int minorversion, struct rpc_xprt *xprt,
	struct svc_serv *serv)
	{
	int nrservs = nfs_callback_nr_threads;
	int ret;

	nfs_callback_bc_serv(minorversion, xprt, serv);

	if (nrservs < NFS4_MIN_NR_CALLBACK_THREADS)
	nrservs = NFS4_MIN_NR_CALLBACK_THREADS;

	if (serv->sv_nrthreads == nrservs)
	return 0;

	ret = svc_set_num_threads(serv, NULL, nrservs);
	if (ret) {
	svc_set_num_threads(serv, NULL, 0);
	return ret;
	}
	dprintk("nfs_callback_up: service started\n");
	return 0;
	}

	static void nfs_callback_down_net(u32 minorversion, struct svc_serv serv, struct net net)
	{
	struct nfs_net *nn = net_generic(net, nfs_net_id);

	if (--nn->cb_users[minorversion])
	return;

	dprintk("NFS: destroy per-net callback data; net=%x\n", net->ns.inum);
	svc_xprt_destroy_all(serv, net);
	}

	static int nfs_callback_up_net(int minorversion, struct svc_serv *serv,
	struct net net, struct rpc_xprt xprt)
	{
	struct nfs_net *nn = net_generic(net, nfs_net_id);
	int ret;

	if (nn->cb_users[minorversion]++)
	return 0;

	dprintk("NFS: create per-net callback data; net=%x\n", net->ns.inum);

	ret = svc_bind(serv, net);
	if (ret < 0) {
	printk(KERN_WARNING "NFS: bind callback service failed\n");
	goto err_bind;
	}

	ret = 0;
	if (!IS_ENABLED(CONFIG_NFS_V4_1) \|\| minorversion == 0)
	ret = nfs4_callback_up_net(serv, net);
	else if (xprt->ops->bc_setup)
	set_bc_enabled(serv);
	else
	ret = -EPROTONOSUPPORT;

	if (ret < 0) {
	printk(KERN_ERR "NFS: callback service start failed\n");
	goto err_socks;
	}
	return 0;

	err_socks:
	svc_rpcb_cleanup(serv, net);
	err_bind:
	nn->cb_users[minorversion]--;
	dprintk("NFS: Couldn't create callback socket: err = %d; "
	"net = %x\n", ret, net->ns.inum);
	return ret;
	}

	static struct svc_serv *nfs_callback_create_svc(int minorversion)
	{
	struct nfs_callback_data *cb_info = &nfs_callback_info[minorversion];
	int (threadfn)(void data);
	struct svc_serv *serv;

	/*
	* Check whether we're already up and running.
	*/
	if (cb_info->serv)
	return svc_get(cb_info->serv);

	/*
	* Sanity check: if there's no task,
	* we should be the first user ...
	*/
	if (cb_info->users)
	printk(KERN_WARNING "nfs_callback_create_svc: no kthread, %d users??\n",
	cb_info->users);

	threadfn = nfs4_callback_svc;
	#if defined(CONFIG_NFS_V4_1)
	if (minorversion)
	threadfn = nfs41_callback_svc;
	#else
	if (minorversion)
	return ERR_PTR(-ENOTSUPP);
	#endif
	serv = svc_create(&nfs4_callback_program, NFS4_CALLBACK_BUFSIZE,
	threadfn);
	if (!serv) {
	printk(KERN_ERR "nfs_callback_create_svc: create service failed\n");
	return ERR_PTR(-ENOMEM);
	}
	cb_info->serv = serv;
	/* As there is only one thread we need to over-ride the
	* default maximum of 80 connections
	*/
	serv->sv_maxconn = 1024;
	dprintk("nfs_callback_create_svc: service created\n");
	return serv;
	}

	/*
	* Bring up the callback thread if it is not already up.
	*/
	int nfs_callback_up(u32 minorversion, struct rpc_xprt *xprt)
	{
	struct svc_serv *serv;
	struct nfs_callback_data *cb_info = &nfs_callback_info[minorversion];
	int ret;
	struct net *net = xprt->xprt_net;

	mutex_lock(&nfs_callback_mutex);

	serv = nfs_callback_create_svc(minorversion);
	if (IS_ERR(serv)) {
	ret = PTR_ERR(serv);
	goto err_create;
	}

	ret = nfs_callback_up_net(minorversion, serv, net, xprt);
	if (ret < 0)
	goto err_net;

	ret = nfs_callback_start_svc(minorversion, xprt, serv);
	if (ret < 0)
	goto err_start;

	cb_info->users++;
	err_net:
	if (!cb_info->users)
	cb_info->serv = NULL;
	svc_put(serv);
	err_create:
	mutex_unlock(&nfs_callback_mutex);
	return ret;

	err_start:
	nfs_callback_down_net(minorversion, serv, net);
	dprintk("NFS: Couldn't create server thread; err = %d\n", ret);
	goto err_net;
	}

	/*
	* Kill the callback thread if it's no longer being used.
	*/
	void nfs_callback_down(int minorversion, struct net *net)
	{
	struct nfs_callback_data *cb_info = &nfs_callback_info[minorversion];
	struct svc_serv *serv;

	mutex_lock(&nfs_callback_mutex);
	serv = cb_info->serv;
	nfs_callback_down_net(minorversion, serv, net);
	cb_info->users--;
	if (cb_info->users == 0) {
	svc_get(serv);
	svc_set_num_threads(serv, NULL, 0);
	svc_put(serv);
	dprintk("nfs_callback_down: service destroyed\n");
	cb_info->serv = NULL;
	}
	mutex_unlock(&nfs_callback_mutex);
	}

	/* Boolean check of RPC_AUTH_GSS principal */
	int
	check_gss_callback_principal(struct nfs_client clp, struct svc_rqst rqstp)
	{
	char *p = rqstp->rq_cred.cr_principal;

	if (rqstp->rq_authop->flavour != RPC_AUTH_GSS)
	return 1;

	/* No RPC_AUTH_GSS on NFSv4.1 back channel yet */
	if (clp->cl_minorversion != 0)
	return 0;
	/*
	* It might just be a normal user principal, in which case
	* userspace won't bother to tell us the name at all.
	*/
	if (p == NULL)
	return 0;

	/*
	* Did we get the acceptor from userland during the SETCLIENID
	* negotiation?
	*/
	if (clp->cl_acceptor)
	return !strcmp(p, clp->cl_acceptor);

	/*
	* Otherwise try to verify it using the cl_hostname. Note that this
	* doesn't work if a non-canonical hostname was used in the devname.
	*/

	/* Expect a GSS_C_NT_HOSTBASED_NAME like "nfs@serverhostname" */

	if (memcmp(p, "nfs@", 4) != 0)
	return 0;
	p += 4;
	if (strcmp(p, clp->cl_hostname) != 0)
	return 0;
	return 1;
	}

	/*
	* pg_authenticate method for nfsv4 callback threads.
	*
	* The authflavor has been negotiated, so an incorrect flavor is a server
	* bug. Deny packets with incorrect authflavor.
	*
	* All other checking done after NFS decoding where the nfs_client can be
	* found in nfs4_callback_compound
	*/
	static int nfs_callback_authenticate(struct svc_rqst *rqstp)
	{
	rqstp->rq_auth_stat = rpc_autherr_badcred;

	switch (rqstp->rq_authop->flavour) {
	case RPC_AUTH_NULL:
	if (rqstp->rq_proc != CB_NULL)
	return SVC_DENIED;
	break;
	case RPC_AUTH_GSS:
	/* No RPC_AUTH_GSS support yet in NFSv4.1 */
	if (svc_is_backchannel(rqstp))
	return SVC_DENIED;
	}

	rqstp->rq_auth_stat = rpc_auth_ok;
	return SVC_OK;
	}

	/*
	* Define NFS4 callback program
	*/
	static const struct svc_version *nfs4_callback_version[] = {
	[1] = &nfs4_callback_version1,
	[4] = &nfs4_callback_version4,
	};

	static struct svc_stat nfs4_callback_stats;

	static struct svc_program nfs4_callback_program = {
	.pg_prog = NFS4_CALLBACK, /* RPC service number */
	.pg_nvers = ARRAY_SIZE(nfs4_callback_version), /* Number of entries */
	.pg_vers = nfs4_callback_version, /* version table */
	.pg_name = "NFSv4 callback", /* service name */
	.pg_class = "nfs", /* authentication class */
	.pg_stats = &nfs4_callback_stats,
	.pg_authenticate = nfs_callback_authenticate,
	.pg_init_request = svc_generic_init_request,
	.pg_rpcbind_set = svc_generic_rpcbind_set,
	};