Forwarded: [PATCH] nfsd: fix out-of-bounds read of sv_permsocks when starting a thread

[syzbot <syzbot+561b859d032c8bf2fb53@syzkaller.appspotmail.com>]

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***

Subject: [PATCH] nfsd: fix out-of-bounds read of sv_permsocks when starting a thread
Author: kartikey406@gmail.com

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master


nfsd() derives its struct net from the first entry of
serv->sv_permsocks using list_entry() without checking that the list
is non-empty. If the list is empty, list_entry() returns a bogus
svc_xprt computed from the list head embedded in struct svc_serv, and
the following perm_sock->xpt_net load reads far past the end of the
svc_serv allocation:

  BUG: KASAN: slab-out-of-bounds in nfsd+0x118/0xbc0 fs/nfsd/nfssvc.c:894
  Read of size 8 at addr ffff88802d423f50 by task nfsd/5988

The list can be empty because nothing guarantees that a permanent
listener exists while a thread starts. With dynamic thread spawning, a
thread can begin running after the last listener has been closed and
removed.

Take sv_lock, which protects sv_permsocks, and check for an empty list
and read xpt_net in the same critical section. If there is no
permanent socket, report -ENOTCONN through svc_thread_init_status(),
which wakes the creator and exits the thread, instead of dereferencing
a bogus pointer.

Reported-by: syzbot+561b859d032c8bf2fb53@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=561b859d032c8bf2fb53
Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
---
 fs/nfsd/nfssvc.c      |   22 +-
 fs/nfsd/nfssvc.c.save | 1107 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 1125 insertions(+), 4 deletions(-)
 create mode 100644 fs/nfsd/nfssvc.c.save

diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c
index 2edf716ea022..da6fce79efae 100644
--- a/fs/nfsd/nfssvc.c
+++ b/fs/nfsd/nfssvc.c
@@ -890,17 +890,31 @@ nfsd(void *vrqstp)
 {
 	struct svc_rqst *rqstp = (struct svc_rqst *) vrqstp;
 	struct svc_pool *pool = rqstp->rq_pool;
-	struct svc_xprt *perm_sock = list_entry(rqstp->rq_server->sv_permsocks.next, typeof(struct svc_xprt), xpt_list);
-	struct net *net = perm_sock->xpt_net;
-	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
+	struct svc_serv *serv = rqstp->rq_server;
+	struct svc_xprt *perm_sock;
+	struct net *net = NULL;
+	struct nfsd_net *nn = NULL;
 	struct nfsd_thread_local_info ntli = { };
 	bool have_mutex = false;
+	int err = 0;
+
+	spin_lock_bh(&serv->sv_lock);
+	if (list_empty(&serv->sv_permsocks)) {
+		err = -ENOTCONN;
+	} else {
+		perm_sock = list_first_entry(&serv->sv_permsocks,
+				             struct svc_xprt, xpt_list);
+		net = perm_sock->xpt_net;
+	}
+	spin_unlock_bh(&serv->sv_lock);
 
+	if (!err)
+		nn = net_generic(net, nfsd_net_id);
 	/* At this point, the thread shares current->fs
 	 * with the init process. We need to create files with the
 	 * umask as defined by the client instead of init's umask.
 	 */
-	svc_thread_init_status(rqstp, unshare_fs_struct());
+	svc_thread_init_status(rqstp, err ?: unshare_fs_struct());
 
 	current->fs->umask = 0;
 
diff --git a/fs/nfsd/nfssvc.c.save b/fs/nfsd/nfssvc.c.save
new file mode 100644
index 000000000000..1df1bc79aaef
--- /dev/null
+++ b/fs/nfsd/nfssvc.c.save
@@ -0,0 +1,1107 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Central processing for nfsd.
+ *
+ * Authors:	Olaf Kirch (okir@monad.swb.de)
+ *
+ * Copyright (C) 1995, 1996, 1997 Olaf Kirch <okir@monad.swb.de>
+ */
+
+#include <linux/sched/signal.h>
+#include <linux/freezer.h>
+#include <linux/module.h>
+#include <linux/fs_struct.h>
+#include <linux/swap.h>
+#include <linux/siphash.h>
+
+#include <linux/sunrpc/stats.h>
+#include <linux/sunrpc/svcsock.h>
+#include <linux/sunrpc/svc_xprt.h>
+#include <linux/lockd/bind.h>
+#include <linux/nfsacl.h>
+#include <linux/nfslocalio.h>
+#include <linux/seq_file.h>
+#include <linux/inetdevice.h>
+#include <net/addrconf.h>
+#include <net/ipv6.h>
+#include <net/net_namespace.h>
+#include "nfsd.h"
+#include "cache.h"
+#include "vfs.h"
+#include "netns.h"
+#include "filecache.h"
+
+#include "trace.h"
+
+#define NFSDDBG_FACILITY	NFSDDBG_SVC
+
+atomic_t			nfsd_th_cnt = ATOMIC_INIT(0);
+static int			nfsd(void *vrqstp);
+#if defined(CONFIG_NFSD_V2_ACL) || defined(CONFIG_NFSD_V3_ACL)
+static int			nfsd_acl_rpcbind_set(struct net *,
+						     const struct svc_program *,
+						     u32, int,
+						     unsigned short,
+						     unsigned short);
+static __be32			nfsd_acl_init_request(struct svc_rqst *,
+						const struct svc_program *,
+						struct svc_process_info *);
+#endif
+static int			nfsd_rpcbind_set(struct net *,
+						 const struct svc_program *,
+						 u32, int,
+						 unsigned short,
+						 unsigned short);
+static __be32			nfsd_init_request(struct svc_rqst *,
+						const struct svc_program *,
+						struct svc_process_info *);
+
+/*
+ * nfsd_mutex protects nn->nfsd_serv -- both the pointer itself and some members
+ * of the svc_serv struct such as ->sv_temp_socks and ->sv_permsocks.
+ *
+ * Finally, the nfsd_mutex also protects some of the global variables that are
+ * accessed when nfsd starts and that are settable via the write_* routines in
+ * nfsctl.c. In particular:
+ *
+ *	user_recovery_dirname
+ *	user_lease_time
+ *	nfsd_versions
+ */
+DEFINE_MUTEX(nfsd_mutex);
+
+#if IS_ENABLED(CONFIG_NFS_LOCALIO)
+static const struct svc_version *localio_versions[] = {
+	[1] = &localio_version1,
+};
+
+#define NFSD_LOCALIO_NRVERS		ARRAY_SIZE(localio_versions)
+
+#endif /* CONFIG_NFS_LOCALIO */
+
+#if defined(CONFIG_NFSD_V2_ACL) || defined(CONFIG_NFSD_V3_ACL)
+static const struct svc_version *nfsd_acl_version[] = {
+# if defined(CONFIG_NFSD_V2_ACL)
+	[2] = &nfsd_acl_version2,
+# endif
+# if defined(CONFIG_NFSD_V3_ACL)
+	[3] = &nfsd_acl_version3,
+# endif
+};
+
+#define NFSD_ACL_MINVERS	2
+#define NFSD_ACL_NRVERS		ARRAY_SIZE(nfsd_acl_version)
+
+#endif /* defined(CONFIG_NFSD_V2_ACL) || defined(CONFIG_NFSD_V3_ACL) */
+
+static const struct svc_version *nfsd_version[NFSD_MAXVERS+1] = {
+#if defined(CONFIG_NFSD_V2)
+	[2] = &nfsd_version2,
+#endif
+	[3] = &nfsd_version3,
+#if defined(CONFIG_NFSD_V4)
+	[4] = &nfsd_version4,
+#endif
+};
+
+struct svc_program		nfsd_programs[] = {
+	{
+	.pg_prog		= NFS_PROGRAM,		/* program number */
+	.pg_nvers		= NFSD_MAXVERS+1,	/* nr of entries in nfsd_version */
+	.pg_vers		= nfsd_version,		/* version table */
+	.pg_name		= "nfsd",		/* program name */
+	.pg_class		= "nfsd",		/* authentication class */
+	.pg_authenticate	= svc_set_client,	/* export authentication */
+	.pg_init_request	= nfsd_init_request,
+	.pg_rpcbind_set		= nfsd_rpcbind_set,
+	},
+#if defined(CONFIG_NFSD_V2_ACL) || defined(CONFIG_NFSD_V3_ACL)
+	{
+	.pg_prog		= NFS_ACL_PROGRAM,
+	.pg_nvers		= NFSD_ACL_NRVERS,
+	.pg_vers		= nfsd_acl_version,
+	.pg_name		= "nfsacl",
+	.pg_class		= "nfsd",
+	.pg_authenticate	= svc_set_client,
+	.pg_init_request	= nfsd_acl_init_request,
+	.pg_rpcbind_set		= nfsd_acl_rpcbind_set,
+	},
+#endif /* defined(CONFIG_NFSD_V2_ACL) || defined(CONFIG_NFSD_V3_ACL) */
+#if IS_ENABLED(CONFIG_NFS_LOCALIO)
+	{
+	.pg_prog		= NFS_LOCALIO_PROGRAM,
+	.pg_nvers		= NFSD_LOCALIO_NRVERS,
+	.pg_vers		= localio_versions,
+	.pg_name		= "nfslocalio",
+	.pg_class		= "nfsd",
+	.pg_authenticate	= svc_set_client,
+	.pg_init_request	= svc_generic_init_request,
+	.pg_rpcbind_set		= svc_generic_rpcbind_set,
+	}
+#endif /* CONFIG_NFS_LOCALIO */
+};
+
+bool nfsd_support_version(int vers)
+{
+	if (vers >= NFSD_MINVERS && vers <= NFSD_MAXVERS)
+		return nfsd_version[vers] != NULL;
+	return false;
+}
+
+int nfsd_vers(struct nfsd_net *nn, int vers, enum vers_op change)
+{
+	if (vers < NFSD_MINVERS || vers > NFSD_MAXVERS)
+		return 0;
+	switch(change) {
+	case NFSD_SET:
+		nn->nfsd_versions[vers] = nfsd_support_version(vers);
+		break;
+	case NFSD_CLEAR:
+		nn->nfsd_versions[vers] = false;
+		break;
+	case NFSD_TEST:
+		return nn->nfsd_versions[vers];
+	case NFSD_AVAIL:
+		return nfsd_support_version(vers);
+	}
+	return 0;
+}
+
+static void
+nfsd_adjust_nfsd_versions4(struct nfsd_net *nn)
+{
+	unsigned i;
+
+	for (i = 0; i <= NFSD_SUPPORTED_MINOR_VERSION; i++) {
+		if (nn->nfsd4_minorversions[i])
+			return;
+	}
+	nfsd_vers(nn, 4, NFSD_CLEAR);
+}
+
+int nfsd_minorversion(struct nfsd_net *nn, u32 minorversion, enum vers_op change)
+{
+	if (minorversion > NFSD_SUPPORTED_MINOR_VERSION &&
+	    change != NFSD_AVAIL)
+		return -1;
+
+	switch(change) {
+	case NFSD_SET:
+		nfsd_vers(nn, 4, NFSD_SET);
+		nn->nfsd4_minorversions[minorversion] =
+			nfsd_vers(nn, 4, NFSD_TEST);
+		break;
+	case NFSD_CLEAR:
+		nn->nfsd4_minorversions[minorversion] = false;
+		nfsd_adjust_nfsd_versions4(nn);
+		break;
+	case NFSD_TEST:
+		return nn->nfsd4_minorversions[minorversion];
+	case NFSD_AVAIL:
+		return minorversion <= NFSD_SUPPORTED_MINOR_VERSION &&
+			nfsd_vers(nn, 4, NFSD_AVAIL);
+	}
+	return 0;
+}
+
+bool nfsd_net_try_get(struct net *net) __must_hold(rcu)
+{
+	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
+
+	return (nn && percpu_ref_tryget_live(&nn->nfsd_net_ref));
+}
+
+void nfsd_net_put(struct net *net) __must_hold(rcu)
+{
+	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
+
+	percpu_ref_put(&nn->nfsd_net_ref);
+}
+
+static void nfsd_net_done(struct percpu_ref *ref)
+{
+	struct nfsd_net *nn = container_of(ref, struct nfsd_net, nfsd_net_ref);
+
+	complete(&nn->nfsd_net_confirm_done);
+}
+
+static void nfsd_net_free(struct percpu_ref *ref)
+{
+	struct nfsd_net *nn = container_of(ref, struct nfsd_net, nfsd_net_ref);
+
+	complete(&nn->nfsd_net_free_done);
+}
+
+/*
+ * Maximum number of nfsd processes
+ */
+#define	NFSD_MAXSERVS		8192
+
+/**
+ * nfsd_nrthreads - report a namespace's configured nfsd thread count
+ * @net: network namespace to query
+ *
+ * Return: the configured thread ceiling, or 0 when no service runs.
+ */
+int nfsd_nrthreads(struct net *net)
+{
+	int rv = 0;
+	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
+
+	/* nfsd_mutex keeps nn->nfsd_serv valid across the read. */
+	mutex_lock(&nfsd_mutex);
+	if (nn->nfsd_serv)
+		rv = svc_serv_maxthreads(nn->nfsd_serv);
+	mutex_unlock(&nfsd_mutex);
+	return rv;
+}
+
+static int nfsd_users = 0;
+
+static int nfsd_startup_generic(void)
+{
+	int ret;
+
+	if (nfsd_users++)
+		return 0;
+
+	ret = nfsd_file_cache_init();
+	if (ret)
+		goto dec_users;
+
+	ret = nfs4_state_start();
+	if (ret)
+		goto out_file_cache;
+	return 0;
+
+out_file_cache:
+	nfsd_file_cache_shutdown();
+dec_users:
+	nfsd_users--;
+	return ret;
+}
+
+static void nfsd_shutdown_generic(void)
+{
+	if (--nfsd_users)
+		return;
+
+	nfs4_state_shutdown();
+	nfsd_file_cache_shutdown();
+}
+
+static bool nfsd_needs_lockd(struct nfsd_net *nn)
+{
+	return nfsd_vers(nn, 2, NFSD_TEST) || nfsd_vers(nn, 3, NFSD_TEST);
+}
+
+/**
+ * nfsd_copy_write_verifier - Atomically copy a write verifier
+ * @verf: buffer in which to receive the verifier cookie
+ * @nn: NFS net namespace
+ *
+ * This function provides a wait-free mechanism for copying the
+ * namespace's write verifier without tearing it.
+ */
+void nfsd_copy_write_verifier(__be32 verf[2], struct nfsd_net *nn)
+{
+	unsigned int seq;
+
+	do {
+		seq = read_seqbegin(&nn->writeverf_lock);
+		memcpy(verf, nn->writeverf, sizeof(nn->writeverf));
+	} while (read_seqretry(&nn->writeverf_lock, seq));
+}
+
+static void nfsd_reset_write_verifier_locked(struct nfsd_net *nn)
+{
+	struct timespec64 now;
+	u64 verf;
+
+	/*
+	 * Because the time value is hashed, y2038 time_t overflow
+	 * is irrelevant in this usage.
+	 */
+	ktime_get_raw_ts64(&now);
+	verf = siphash_2u64(now.tv_sec, now.tv_nsec, &nn->siphash_key);
+	memcpy(nn->writeverf, &verf, sizeof(nn->writeverf));
+}
+
+/**
+ * nfsd_reset_write_verifier - Generate a new write verifier
+ * @nn: NFS net namespace
+ *
+ * This function updates the ->writeverf field of @nn. This field
+ * contains an opaque cookie that, according to Section 18.32.3 of
+ * RFC 8881, "the client can use to determine whether a server has
+ * changed instance state (e.g., server restart) between a call to
+ * WRITE and a subsequent call to either WRITE or COMMIT.  This
+ * cookie MUST be unchanged during a single instance of the NFSv4.1
+ * server and MUST be unique between instances of the NFSv4.1
+ * server."
+ */
+void nfsd_reset_write_verifier(struct nfsd_net *nn)
+{
+	write_seqlock(&nn->writeverf_lock);
+	nfsd_reset_write_verifier_locked(nn);
+	write_sequnlock(&nn->writeverf_lock);
+}
+
+/*
+ * Crank up a set of per-namespace resources for a new NFSD instance,
+ * including lockd, a duplicate reply cache, an open file cache
+ * instance, and a cache of NFSv4 state objects.
+ */
+static int nfsd_startup_net(struct net *net, const struct cred *cred)
+{
+	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
+	int ret;
+
+	if (test_bit(NFSD_NET_UP, &nn->flags))
+		return 0;
+
+	ret = nfsd_startup_generic();
+	if (ret)
+		return ret;
+
+	if (list_empty(&nn->nfsd_serv->sv_permsocks)) {
+		pr_warn("NFSD: Failed to start, no listeners configured.\n");
+		ret = -EIO;
+		goto out_socks;
+	}
+
+	if (nfsd_needs_lockd(nn) && !test_bit(NFSD_NET_LOCKD_UP, &nn->flags)) {
+		ret = lockd_up(net, cred);
+		if (ret)
+			goto out_socks;
+		set_bit(NFSD_NET_LOCKD_UP, &nn->flags);
+	}
+
+	ret = nfsd_file_cache_start_net(net);
+	if (ret)
+		goto out_lockd;
+
+	ret = nfsd_reply_cache_init(nn);
+	if (ret)
+		goto out_filecache;
+
+#ifdef CONFIG_NFSD_V4_2_INTER_SSC
+	nfsd4_ssc_init_umount_work(nn);
+#endif
+	ret = nfs4_state_start_net(net);
+	if (ret)
+		goto out_reply_cache;
+
+	set_bit(NFSD_NET_UP, &nn->flags);
+	return 0;
+
+out_reply_cache:
+	nfsd_reply_cache_shutdown(nn);
+out_filecache:
+	nfsd_file_cache_shutdown_net(net);
+out_lockd:
+	if (test_bit(NFSD_NET_LOCKD_UP, &nn->flags)) {
+		lockd_down(net);
+		clear_bit(NFSD_NET_LOCKD_UP, &nn->flags);
+	}
+out_socks:
+	nfsd_shutdown_generic();
+	return ret;
+}
+
+static void nfsd_shutdown_net(struct net *net)
+{
+	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
+
+	if (test_bit(NFSD_NET_UP, &nn->flags)) {
+		percpu_ref_kill_and_confirm(&nn->nfsd_net_ref, nfsd_net_done);
+		wait_for_completion(&nn->nfsd_net_confirm_done);
+
+		nfsd_export_flush(net);
+		nfs4_state_shutdown_net(net);
+		nfsd_reply_cache_shutdown(nn);
+		nfsd_file_cache_shutdown_net(net);
+		if (test_bit(NFSD_NET_LOCKD_UP, &nn->flags)) {
+			lockd_down(net);
+			clear_bit(NFSD_NET_LOCKD_UP, &nn->flags);
+		}
+		wait_for_completion(&nn->nfsd_net_free_done);
+	}
+
+	percpu_ref_exit(&nn->nfsd_net_ref);
+
+	if (test_bit(NFSD_NET_UP, &nn->flags))
+		nfsd_shutdown_generic();
+	clear_bit(NFSD_NET_UP, &nn->flags);
+}
+
+static DEFINE_SPINLOCK(nfsd_notifier_lock);
+static int nfsd_inetaddr_event(struct notifier_block *this, unsigned long event,
+	void *ptr)
+{
+	struct in_ifaddr *ifa = (struct in_ifaddr *)ptr;
+	struct net_device *dev = ifa->ifa_dev->dev;
+	struct net *net = dev_net(dev);
+	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
+	struct sockaddr_in sin;
+
+	if (event != NETDEV_DOWN || !nn->nfsd_serv)
+		goto out;
+
+	spin_lock(&nfsd_notifier_lock);
+	if (nn->nfsd_serv) {
+		dprintk("nfsd_inetaddr_event: removed %pI4\n", &ifa->ifa_local);
+		sin.sin_family = AF_INET;
+		sin.sin_addr.s_addr = ifa->ifa_local;
+		svc_age_temp_xprts_now(nn->nfsd_serv, (struct sockaddr *)&sin);
+	}
+	spin_unlock(&nfsd_notifier_lock);
+
+out:
+	return NOTIFY_DONE;
+}
+
+static struct notifier_block nfsd_inetaddr_notifier = {
+	.notifier_call = nfsd_inetaddr_event,
+};
+
+#if IS_ENABLED(CONFIG_IPV6)
+static int nfsd_inet6addr_event(struct notifier_block *this,
+	unsigned long event, void *ptr)
+{
+	struct inet6_ifaddr *ifa = (struct inet6_ifaddr *)ptr;
+	struct net_device *dev = ifa->idev->dev;
+	struct net *net = dev_net(dev);
+	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
+	struct sockaddr_in6 sin6;
+
+	if (event != NETDEV_DOWN || !nn->nfsd_serv)
+		goto out;
+
+	spin_lock(&nfsd_notifier_lock);
+	if (nn->nfsd_serv) {
+		dprintk("nfsd_inet6addr_event: removed %pI6\n", &ifa->addr);
+		sin6.sin6_family = AF_INET6;
+		sin6.sin6_addr = ifa->addr;
+		if (ipv6_addr_type(&sin6.sin6_addr) & IPV6_ADDR_LINKLOCAL)
+			sin6.sin6_scope_id = ifa->idev->dev->ifindex;
+		svc_age_temp_xprts_now(nn->nfsd_serv, (struct sockaddr *)&sin6);
+	}
+	spin_unlock(&nfsd_notifier_lock);
+
+out:
+	return NOTIFY_DONE;
+}
+
+static struct notifier_block nfsd_inet6addr_notifier = {
+	.notifier_call = nfsd_inet6addr_event,
+};
+#endif
+
+/* Only used under nfsd_mutex, so this atomic may be overkill: */
+static atomic_t nfsd_notifier_refcount = ATOMIC_INIT(0);
+
+/**
+ * nfsd_destroy_serv - tear down NFSD's svc_serv for a namespace
+ * @net: network namespace the NFS service is associated with
+ */
+void nfsd_destroy_serv(struct net *net)
+{
+	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
+	struct svc_serv *serv = nn->nfsd_serv;
+
+	lockdep_assert_held(&nfsd_mutex);
+
+	spin_lock(&nfsd_notifier_lock);
+	nn->nfsd_serv = NULL;
+	spin_unlock(&nfsd_notifier_lock);
+
+	/* check if the notifier still has clients */
+	if (atomic_dec_return(&nfsd_notifier_refcount) == 0) {
+		unregister_inetaddr_notifier(&nfsd_inetaddr_notifier);
+#if IS_ENABLED(CONFIG_IPV6)
+		unregister_inet6addr_notifier(&nfsd_inet6addr_notifier);
+#endif
+	}
+
+	/*
+	 * write_ports can create the server without actually starting
+	 * any threads.  If we get shut down before any threads are
+	 * started, then nfsd_destroy_serv will be run before any of this
+	 * other initialization has been done except the rpcb information.
+	 */
+	svc_xprt_destroy_all(serv, net, true);
+	nfsd_shutdown_net(net);
+	svc_destroy(&serv);
+}
+
+void nfsd_reset_versions(struct nfsd_net *nn)
+{
+	int i;
+
+	for (i = 0; i <= NFSD_MAXVERS; i++)
+		if (nfsd_vers(nn, i, NFSD_TEST))
+			return;
+
+	for (i = 0; i <= NFSD_MAXVERS; i++)
+		if (i != 4)
+			nfsd_vers(nn, i, NFSD_SET);
+		else {
+			int minor = 0;
+			while (nfsd_minorversion(nn, minor, NFSD_SET) >= 0)
+				minor++;
+		}
+}
+
+static int nfsd_get_default_max_blksize(void)
+{
+	struct sysinfo i;
+	unsigned long long target;
+	unsigned long ret;
+
+	si_meminfo(&i);
+	target = (i.totalram - i.totalhigh) << PAGE_SHIFT;
+	/*
+	 * Aim for 1/4096 of memory per thread This gives 1MB on 4Gig
+	 * machines, but only uses 32K on 128M machines.  Bottom out at
+	 * 8K on 32M and smaller.  Of course, this is only a default.
+	 */
+	target >>= 12;
+
+	ret = NFSSVC_DEFBLKSIZE;
+	while (ret > target && ret >= 8*1024*2)
+		ret /= 2;
+	return ret;
+}
+
+void nfsd_shutdown_threads(struct net *net)
+{
+	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
+	struct svc_serv *serv;
+
+	mutex_lock(&nfsd_mutex);
+	serv = nn->nfsd_serv;
+	if (serv == NULL) {
+		mutex_unlock(&nfsd_mutex);
+		return;
+	}
+
+	/* Kill outstanding nfsd threads */
+	svc_set_num_threads(serv, 0, 0);
+	nfsd_destroy_serv(net);
+	mutex_unlock(&nfsd_mutex);
+}
+
+struct svc_rqst *nfsd_current_rqst(void)
+{
+	if (kthread_func(current) == nfsd)
+		return kthread_data(current);
+	return NULL;
+}
+
+int nfsd_create_serv(struct net *net)
+{
+	int error;
+	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
+	struct svc_serv *serv;
+
+	WARN_ON(!mutex_is_locked(&nfsd_mutex));
+	if (nn->nfsd_serv)
+		return 0;
+
+	error = percpu_ref_init(&nn->nfsd_net_ref, nfsd_net_free,
+				0, GFP_KERNEL);
+	if (error)
+		return error;
+	init_completion(&nn->nfsd_net_free_done);
+	init_completion(&nn->nfsd_net_confirm_done);
+
+	if (nfsd_max_blksize == 0)
+		nfsd_max_blksize = nfsd_get_default_max_blksize();
+	nfsd_reset_versions(nn);
+	serv = svc_create_pooled(nfsd_programs, ARRAY_SIZE(nfsd_programs),
+				 &nn->nfsd_svcstats,
+				 nfsd_max_blksize, nfsd);
+	if (serv == NULL) {
+		percpu_ref_exit(&nn->nfsd_net_ref);
+		return -ENOMEM;
+	}
+
+	error = svc_bind(serv, net);
+	if (error < 0) {
+		svc_destroy(&serv);
+		percpu_ref_exit(&nn->nfsd_net_ref);
+		return error;
+	}
+	spin_lock(&nfsd_notifier_lock);
+	nn->nfsd_serv = serv;
+	spin_unlock(&nfsd_notifier_lock);
+
+	/* check if the notifier is already set */
+	if (atomic_inc_return(&nfsd_notifier_refcount) == 1) {
+		register_inetaddr_notifier(&nfsd_inetaddr_notifier);
+#if IS_ENABLED(CONFIG_IPV6)
+		register_inet6addr_notifier(&nfsd_inet6addr_notifier);
+#endif
+	}
+	nfsd_reset_write_verifier(nn);
+	return 0;
+}
+
+int nfsd_nrpools(struct net *net)
+{
+	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
+
+	if (nn->nfsd_serv == NULL)
+		return 0;
+	else
+		return svc_serv_nrpools(nn->nfsd_serv);
+}
+
+int nfsd_get_nrthreads(int n, int *nthreads, struct net *net)
+{
+	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
+	struct svc_serv *serv = nn->nfsd_serv;
+	int i;
+
+	if (serv)
+		for (i = 0; i < svc_serv_nrpools(serv) && i < n; i++)
+			nthreads[i] = serv->sv_pools[i].sp_nrthrmax;
+	return 0;
+}
+
+/**
+ * nfsd_set_nrthreads - set the number of running threads in the net's service
+ * @n: number of array members in @nthreads
+ * @nthreads: array of thread counts for each pool
+ * @net: network namespace to operate within
+ *
+ * This function alters the number of running threads for the given network
+ * namespace in each pool. If passed an array longer then the number of pools
+ * the extra pool settings are ignored. If passed an array shorter than the
+ * number of pools, the missing values are interpreted as 0's.
+ *
+ * Returns 0 on success or a negative errno on error.
+ */
+int nfsd_set_nrthreads(int n, int *nthreads, struct net *net)
+{
+	int i = 0;
+	int tot = 0;
+	int err = 0;
+	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
+
+	lockdep_assert_held(&nfsd_mutex);
+
+	if (nn->nfsd_serv == NULL || n <= 0)
+		return 0;
+
+	/* Special case: When n == 1, distribute threads equally among pools. */
+	if (n == 1)
+		return svc_set_num_threads(nn->nfsd_serv, nn->min_threads, nthreads[0]);
+
+	if (n > svc_serv_nrpools(nn->nfsd_serv))
+		n = svc_serv_nrpools(nn->nfsd_serv);
+
+	/* enforce a global maximum number of threads */
+	tot = 0;
+	for (i = 0; i < n; i++) {
+		nthreads[i] = min(nthreads[i], NFSD_MAXSERVS);
+		tot += nthreads[i];
+	}
+	if (tot > NFSD_MAXSERVS) {
+		/* total too large: scale down requested numbers */
+		for (i = 0; i < n && tot > 0; i++) {
+			int new = nthreads[i] * NFSD_MAXSERVS / tot;
+			tot -= (nthreads[i] - new);
+			nthreads[i] = new;
+		}
+		for (i = 0; i < n && tot > 0; i++) {
+			nthreads[i]--;
+			tot--;
+		}
+	}
+
+	/* apply the new numbers */
+	for (i = 0; i < n; i++) {
+		err = svc_set_pool_threads(nn->nfsd_serv,
+					   &nn->nfsd_serv->sv_pools[i],
+					   nn->min_threads, nthreads[i]);
+		if (err)
+			goto out;
+	}
+
+	/* Anything undefined in array is considered to be 0 */
+	for (i = n; i < svc_serv_nrpools(nn->nfsd_serv); ++i) {
+		err = svc_set_pool_threads(nn->nfsd_serv,
+					   &nn->nfsd_serv->sv_pools[i],
+					   0, 0);
+		if (err)
+			goto out;
+	}
+out:
+	return err;
+}
+
+/**
+ * nfsd_svc: start up or shut down the nfsd server
+ * @n: number of array members in @nthreads
+ * @nthreads: array of thread counts for each pool
+ * @net: network namespace to operate within
+ * @cred: credentials to use for xprt creation
+ * @scope: server scope value (defaults to nodename)
+ *
+ * Adjust the number of threads in each pool and return the new
+ * total number of threads in the service.
+ */
+int
+nfsd_svc(int n, int *nthreads, struct net *net, const struct cred *cred, const char *scope)
+{
+	int	error;
+	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
+	struct svc_serv *serv;
+
+	lockdep_assert_held(&nfsd_mutex);
+
+	dprintk("nfsd: creating service\n");
+
+	strscpy(nn->nfsd_name, scope ? scope : utsname()->nodename,
+		sizeof(nn->nfsd_name));
+
+	error = nfsd_create_serv(net);
+	if (error)
+		goto out;
+	serv = nn->nfsd_serv;
+
+	error = nfsd_startup_net(net, cred);
+	if (error)
+		goto out_put;
+	error = nfsd_set_nrthreads(n, nthreads, net);
+	if (error)
+		goto out_put;
+	error = serv->sv_nrthreads;
+out_put:
+	if (serv->sv_nrthreads == 0)
+		nfsd_destroy_serv(net);
+out:
+	return error;
+}
+
+#if defined(CONFIG_NFSD_V2_ACL) || defined(CONFIG_NFSD_V3_ACL)
+static bool
+nfsd_support_acl_version(int vers)
+{
+	if (vers >= NFSD_ACL_MINVERS && vers < NFSD_ACL_NRVERS)
+		return nfsd_acl_version[vers] != NULL;
+	return false;
+}
+
+static int
+nfsd_acl_rpcbind_set(struct net *net, const struct svc_program *progp,
+		     u32 version, int family, unsigned short proto,
+		     unsigned short port)
+{
+	if (!nfsd_support_acl_version(version) ||
+	    !nfsd_vers(net_generic(net, nfsd_net_id), version, NFSD_TEST))
+		return 0;
+	return svc_generic_rpcbind_set(net, progp, version, family,
+			proto, port);
+}
+
+static __be32
+nfsd_acl_init_request(struct svc_rqst *rqstp,
+		      const struct svc_program *progp,
+		      struct svc_process_info *ret)
+{
+	struct nfsd_net *nn = net_generic(SVC_NET(rqstp), nfsd_net_id);
+	int i;
+
+	if (likely(nfsd_support_acl_version(rqstp->rq_vers) &&
+	    nfsd_vers(nn, rqstp->rq_vers, NFSD_TEST)))
+		return svc_generic_init_request(rqstp, progp, ret);
+
+	ret->mismatch.lovers = NFSD_ACL_NRVERS;
+	for (i = NFSD_ACL_MINVERS; i < NFSD_ACL_NRVERS; i++) {
+		if (nfsd_support_acl_version(i) &&
+		    nfsd_vers(nn, i, NFSD_TEST)) {
+			ret->mismatch.lovers = i;
+			break;
+		}
+	}
+	if (ret->mismatch.lovers == NFSD_ACL_NRVERS)
+		return rpc_prog_unavail;
+	ret->mismatch.hivers = NFSD_ACL_MINVERS;
+	for (i = NFSD_ACL_NRVERS - 1; i >= NFSD_ACL_MINVERS; i--) {
+		if (nfsd_support_acl_version(i) &&
+		    nfsd_vers(nn, i, NFSD_TEST)) {
+			ret->mismatch.hivers = i;
+			break;
+		}
+	}
+	return rpc_prog_mismatch;
+}
+#endif
+
+static int
+nfsd_rpcbind_set(struct net *net, const struct svc_program *progp,
+		 u32 version, int family, unsigned short proto,
+		 unsigned short port)
+{
+	if (!nfsd_vers(net_generic(net, nfsd_net_id), version, NFSD_TEST))
+		return 0;
+	return svc_generic_rpcbind_set(net, progp, version, family,
+			proto, port);
+}
+
+static __be32
+nfsd_init_request(struct svc_rqst *rqstp,
+		  const struct svc_program *progp,
+		  struct svc_process_info *ret)
+{
+	struct nfsd_net *nn = net_generic(SVC_NET(rqstp), nfsd_net_id);
+	int i;
+
+	if (likely(nfsd_vers(nn, rqstp->rq_vers, NFSD_TEST)))
+		return svc_generic_init_request(rqstp, progp, ret);
+
+	ret->mismatch.lovers = NFSD_MAXVERS + 1;
+	for (i = NFSD_MINVERS; i <= NFSD_MAXVERS; i++) {
+		if (nfsd_vers(nn, i, NFSD_TEST)) {
+			ret->mismatch.lovers = i;
+			break;
+		}
+	}
+	if (ret->mismatch.lovers > NFSD_MAXVERS)
+		return rpc_prog_unavail;
+	ret->mismatch.hivers = NFSD_MINVERS;
+	for (i = NFSD_MAXVERS; i >= NFSD_MINVERS; i--) {
+		if (nfsd_vers(nn, i, NFSD_TEST)) {
+			ret->mismatch.hivers = i;
+			break;
+		}
+	}
+	return rpc_prog_mismatch;
+}
+
+/*
+ * This is the NFS server kernel thread
+ */
+static int
+nfsd(void *vrqstp)
+{
+	struct svc_rqst *rqstp = (struct svc_rqst *) vrqstp;
+	struct svc_pool *pool = rqstp->rq_pool;
+	struct svc_xprt *perm_sock;
+	struct net *net;
+	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
+	struct nfsd_thread_local_info ntli = { };
+	bool have_mutex = false;
+
+	spin_lock_bh(&serv->sv_lock);
+	if (list_empty(&serv->sv_permsocks)) {
+		err = -ENOTCONN;
+	} else {
+		perm_sock = list_first_entry(&serv->sv_permsocks,
+                                             struct svc_xprt, xpt_list);
+		net = perm_sock->xpt_net;
+	}
+	spin_unlock_bh(&serv->sv_lock);
+
+
+
+	/* At this point, the thread shares current->fs
+	 * with the init process. We need to create files with the
+	 * umask as defined by the client instead of init's umask.
+	 */
+	svc_thread_init_status(rqstp, unshare_fs_struct());
+
+	current->fs->umask = 0;
+
+	atomic_inc(&nfsd_th_cnt);
+
+	set_freezable();
+
+	/* use dynamic allocation if ntli should ever become large */
+	static_assert(sizeof(struct nfsd_thread_local_info) < 256);
+	rqstp->rq_private = &ntli;
+
+	/*
+	 * The main request loop
+	 */
+	while (!svc_thread_should_stop(rqstp)) {
+		switch (svc_recv(rqstp, 5 * HZ)) {
+		case -ETIMEDOUT:
+			/* No work arrived within the timeout window */
+			if (mutex_trylock(&nfsd_mutex)) {
+				if (pool->sp_nrthreads > pool->sp_nrthrmin) {
+					trace_nfsd_dynthread_kill(net, pool);
+					set_bit(RQ_VICTIM, &rqstp->rq_flags);
+					have_mutex = true;
+				} else {
+					mutex_unlock(&nfsd_mutex);
+				}
+			} else {
+				trace_nfsd_dynthread_trylock_fail(net, pool);
+			}
+			break;
+		case -EBUSY:
+			/* No idle threads; consider spawning another */
+			if (pool->sp_nrthreads < pool->sp_nrthrmax) {
+				if (mutex_trylock(&nfsd_mutex)) {
+					if (pool->sp_nrthreads < pool->sp_nrthrmax) {
+						int ret;
+
+						trace_nfsd_dynthread_start(net, pool);
+						ret = svc_new_thread(rqstp->rq_server, pool);
+						if (ret)
+							pr_notice_ratelimited("%s: unable to spawn new thread: %d\n",
+									      __func__, ret);
+					}
+					mutex_unlock(&nfsd_mutex);
+				} else {
+					trace_nfsd_dynthread_trylock_fail(net, pool);
+				}
+			}
+			clear_bit(SP_TASK_STARTING, &pool->sp_flags);
+			break;
+		default:
+			break;
+		}
+		nfsd_file_net_dispose(nn);
+	}
+
+	atomic_dec(&nfsd_th_cnt);
+
+	/* Release the thread */
+	svc_exit_thread(rqstp);
+	if (have_mutex)
+		mutex_unlock(&nfsd_mutex);
+	return 0;
+}
+
+/*
+ * Set rq_status_counter back to an even value, indicating that the rqstp
+ * fields are no longer meaningful to a lockless reader. This pairs with the
+ * odd-valued store made once the request has been decoded, and must run on
+ * every return path that follows it so that the seq-lock like protocol used
+ * by nfsd_nl_rpc_status_get_dumpit() is not left permanently odd. The store
+ * also advances the counter so a concurrent reader detects the transition.
+ */
+static void nfsd_status_counter_set_idle(struct svc_rqst *rqstp)
+{
+	smp_store_release(&rqstp->rq_status_counter,
+			  (rqstp->rq_status_counter | 1) + 1);
+}
+
+/**
+ * nfsd_dispatch - Process an NFS or NFSACL or LOCALIO Request
+ * @rqstp: incoming request
+ *
+ * This RPC dispatcher integrates the NFS server's duplicate reply cache.
+ *
+ * Return values:
+ *  %0: Processing complete; do not send a Reply
+ *  %1: Processing complete; send Reply in rqstp->rq_res
+ */
+int nfsd_dispatch(struct svc_rqst *rqstp)
+{
+	struct nfsd_thread_local_info *ntli = rqstp->rq_private;
+	const struct svc_procedure *proc = rqstp->rq_procinfo;
+	__be32 *statp = rqstp->rq_accept_statp;
+	struct nfsd_cacherep *rp;
+	unsigned int start, len;
+	__be32 *nfs_reply;
+
+	/*
+	 * Give the xdr decoder a chance to change this if it wants
+	 * (necessary in the NFSv4.0 compound case)
+	 */
+	ntli->ntli_cachetype = proc->pc_cachetype;
+
+	/*
+	 * ->pc_decode advances the argument stream past the NFS
+	 * Call header, so grab the header's starting location and
+	 * size now for the call to nfsd_cache_lookup().
+	 */
+	start = xdr_stream_pos(&rqstp->rq_arg_stream);
+	len = xdr_stream_remaining(&rqstp->rq_arg_stream);
+	if (!proc->pc_decode(rqstp, &rqstp->rq_arg_stream))
+		goto out_decode_err;
+
+	/*
+	 * Release rq_status_counter setting it to an odd value after the rpc
+	 * request has been properly parsed. rq_status_counter is used to
+	 * notify the consumers if the rqstp fields are stable
+	 * (rq_status_counter is odd) or not meaningful (rq_status_counter
+	 * is even).
+	 */
+	smp_store_release(&rqstp->rq_status_counter, rqstp->rq_status_counter | 1);
+
+	rp = NULL;
+	switch (nfsd_cache_lookup(rqstp, start, len, &rp)) {
+	case RC_DOIT:
+		break;
+	case RC_REPLY:
+		goto out_cached_reply;
+	case RC_DROPIT:
+		goto out_dropit;
+	}
+
+	nfs_reply = xdr_inline_decode(&rqstp->rq_res_stream, 0);
+	*statp = proc->pc_func(rqstp);
+	if (test_bit(RQ_DROPME, &rqstp->rq_flags))
+		goto out_update_drop;
+
+	if (!proc->pc_encode(rqstp, &rqstp->rq_res_stream))
+		goto out_encode_err;
+
+	nfsd_cache_update(rqstp, rp, ntli->ntli_cachetype, nfs_reply);
+out_cached_reply:
+	nfsd_status_counter_set_idle(rqstp);
+	return 1;
+
+out_decode_err:
+	trace_nfsd_garbage_args_err(rqstp);
+	*statp = rpc_garbage_args;
+	return 1;
+
+out_update_drop:
+	nfsd_cache_update(rqstp, rp, RC_NOCACHE, NULL);
+out_dropit:
+	nfsd_status_counter_set_idle(rqstp);
+	return 0;
+
+out_encode_err:
+	trace_nfsd_cant_encode_err(rqstp);
+	nfsd_cache_update(rqstp, rp, RC_NOCACHE, NULL);
+	*statp = rpc_system_err;
+	nfsd_status_counter_set_idle(rqstp);
+	return 1;
+}
+
+/**
+ * nfssvc_decode_voidarg - Decode void arguments
+ * @rqstp: Server RPC transaction context
+ * @xdr: XDR stream positioned at arguments to decode
+ *
+ * Return values:
+ *   %false: Arguments were not valid
+ *   %true: Decoding was successful
+ */
+bool nfssvc_decode_voidarg(struct svc_rqst *rqstp, struct xdr_stream *xdr)
+{
+	return true;
+}
+
+/**
+ * nfssvc_encode_voidres - Encode void results
+ * @rqstp: Server RPC transaction context
+ * @xdr: XDR stream into which to encode results
+ *
+ * Return values:
+ *   %false: Local error while encoding
+ *   %true: Encoding was successful
+ */
+bool nfssvc_encode_voidres(struct svc_rqst *rqstp, struct xdr_stream *xdr)
+{
+	return true;
+}
-- 
2.43.0