Adding upstream version 6.1.76.upstream/6.1.76

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1690 insertions, 0 deletions

diff --git a/fs/smb/client/dfs_cache.c b/fs/smb/client/dfs_cache.c
new file mode 100644
index 000000000..3bc1d3494
--- /dev/null
+++ b/fs/smb/client/dfs_cache.c
@@ -0,0 +1,1690 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * DFS referral cache routines
+ *
+ * Copyright (c) 2018-2019 Paulo Alcantara <palcantara@suse.de>
+ */
+
+#include <linux/jhash.h>
+#include <linux/ktime.h>
+#include <linux/slab.h>
+#include <linux/proc_fs.h>
+#include <linux/nls.h>
+#include <linux/workqueue.h>
+#include <linux/uuid.h>
+#include "cifsglob.h"
+#include "smb2pdu.h"
+#include "smb2proto.h"
+#include "cifsproto.h"
+#include "cifs_debug.h"
+#include "cifs_unicode.h"
+#include "smb2glob.h"
+#include "dns_resolve.h"
+
+#include "dfs_cache.h"
+
+#define CACHE_HTABLE_SIZE 32
+#define CACHE_MAX_ENTRIES 64
+#define CACHE_MIN_TTL 120 /* 2 minutes */
+
+#define IS_DFS_INTERLINK(v) (((v) & DFSREF_REFERRAL_SERVER) && !((v) & DFSREF_STORAGE_SERVER))
+
+struct cache_dfs_tgt {
+	char *name;
+	int path_consumed;
+	struct list_head list;
+};
+
+struct cache_entry {
+	struct hlist_node hlist;
+	const char *path;
+	int hdr_flags; /* RESP_GET_DFS_REFERRAL.ReferralHeaderFlags */
+	int ttl; /* DFS_REREFERRAL_V3.TimeToLive */
+	int srvtype; /* DFS_REREFERRAL_V3.ServerType */
+	int ref_flags; /* DFS_REREFERRAL_V3.ReferralEntryFlags */
+	struct timespec64 etime;
+	int path_consumed; /* RESP_GET_DFS_REFERRAL.PathConsumed */
+	int numtgts;
+	struct list_head tlist;
+	struct cache_dfs_tgt *tgthint;
+};
+
+/* List of referral server sessions per dfs mount */
+struct mount_group {
+	struct list_head list;
+	uuid_t id;
+	struct cifs_ses *sessions[CACHE_MAX_ENTRIES];
+	int num_sessions;
+	spinlock_t lock;
+	struct list_head refresh_list;
+	struct kref refcount;
+};
+
+static struct kmem_cache *cache_slab __read_mostly;
+static struct workqueue_struct *dfscache_wq __read_mostly;
+
+static int cache_ttl;
+static DEFINE_SPINLOCK(cache_ttl_lock);
+
+static struct nls_table *cache_cp;
+
+/*
+ * Number of entries in the cache
+ */
+static atomic_t cache_count;
+
+static struct hlist_head cache_htable[CACHE_HTABLE_SIZE];
+static DECLARE_RWSEM(htable_rw_lock);
+
+static LIST_HEAD(mount_group_list);
+static DEFINE_MUTEX(mount_group_list_lock);
+
+static void refresh_cache_worker(struct work_struct *work);
+
+static DECLARE_DELAYED_WORK(refresh_task, refresh_cache_worker);
+
+static void get_ipc_unc(const char *ref_path, char *ipc, size_t ipclen)
+{
+	const char *host;
+	size_t len;
+
+	extract_unc_hostname(ref_path, &host, &len);
+	scnprintf(ipc, ipclen, "\\\\%.*s\\IPC$", (int)len, host);
+}
+
+static struct cifs_ses *find_ipc_from_server_path(struct cifs_ses **ses, const char *path)
+{
+	char unc[SERVER_NAME_LENGTH + sizeof("//x/IPC$")] = {0};
+
+	get_ipc_unc(path, unc, sizeof(unc));
+	for (; *ses; ses++) {
+		if (!strcasecmp(unc, (*ses)->tcon_ipc->tree_name))
+			return *ses;
+	}
+	return ERR_PTR(-ENOENT);
+}
+
+static void __mount_group_release(struct mount_group *mg)
+{
+	int i;
+
+	for (i = 0; i < mg->num_sessions; i++)
+		cifs_put_smb_ses(mg->sessions[i]);
+	kfree(mg);
+}
+
+static void mount_group_release(struct kref *kref)
+{
+	struct mount_group *mg = container_of(kref, struct mount_group, refcount);
+
+	mutex_lock(&mount_group_list_lock);
+	list_del(&mg->list);
+	mutex_unlock(&mount_group_list_lock);
+	__mount_group_release(mg);
+}
+
+static struct mount_group *find_mount_group_locked(const uuid_t *id)
+{
+	struct mount_group *mg;
+
+	list_for_each_entry(mg, &mount_group_list, list) {
+		if (uuid_equal(&mg->id, id))
+			return mg;
+	}
+	return ERR_PTR(-ENOENT);
+}
+
+static struct mount_group *__get_mount_group_locked(const uuid_t *id)
+{
+	struct mount_group *mg;
+
+	mg = find_mount_group_locked(id);
+	if (!IS_ERR(mg))
+		return mg;
+
+	mg = kmalloc(sizeof(*mg), GFP_KERNEL);
+	if (!mg)
+		return ERR_PTR(-ENOMEM);
+	kref_init(&mg->refcount);
+	uuid_copy(&mg->id, id);
+	mg->num_sessions = 0;
+	spin_lock_init(&mg->lock);
+	list_add(&mg->list, &mount_group_list);
+	return mg;
+}
+
+static struct mount_group *get_mount_group(const uuid_t *id)
+{
+	struct mount_group *mg;
+
+	mutex_lock(&mount_group_list_lock);
+	mg = __get_mount_group_locked(id);
+	if (!IS_ERR(mg))
+		kref_get(&mg->refcount);
+	mutex_unlock(&mount_group_list_lock);
+
+	return mg;
+}
+
+static void free_mount_group_list(void)
+{
+	struct mount_group *mg, *tmp_mg;
+
+	list_for_each_entry_safe(mg, tmp_mg, &mount_group_list, list) {
+		list_del_init(&mg->list);
+		__mount_group_release(mg);
+	}
+}
+
+/**
+ * dfs_cache_canonical_path - get a canonical DFS path
+ *
+ * @path: DFS path
+ * @cp: codepage
+ * @remap: mapping type
+ *
+ * Return canonical path if success, otherwise error.
+ */
+char *dfs_cache_canonical_path(const char *path, const struct nls_table *cp, int remap)
+{
+	char *tmp;
+	int plen = 0;
+	char *npath;
+
+	if (!path || strlen(path) < 3 || (*path != '\\' && *path != '/'))
+		return ERR_PTR(-EINVAL);
+
+	if (unlikely(strcmp(cp->charset, cache_cp->charset))) {
+		tmp = (char *)cifs_strndup_to_utf16(path, strlen(path), &plen, cp, remap);
+		if (!tmp) {
+			cifs_dbg(VFS, "%s: failed to convert path to utf16\n", __func__);
+			return ERR_PTR(-EINVAL);
+		}
+
+		npath = cifs_strndup_from_utf16(tmp, plen, true, cache_cp);
+		kfree(tmp);
+
+		if (!npath) {
+			cifs_dbg(VFS, "%s: failed to convert path from utf16\n", __func__);
+			return ERR_PTR(-EINVAL);
+		}
+	} else {
+		npath = kstrdup(path, GFP_KERNEL);
+		if (!npath)
+			return ERR_PTR(-ENOMEM);
+	}
+	convert_delimiter(npath, '\\');
+	return npath;
+}
+
+static inline bool cache_entry_expired(const struct cache_entry *ce)
+{
+	struct timespec64 ts;
+
+	ktime_get_coarse_real_ts64(&ts);
+	return timespec64_compare(&ts, &ce->etime) >= 0;
+}
+
+static inline void free_tgts(struct cache_entry *ce)
+{
+	struct cache_dfs_tgt *t, *n;
+
+	list_for_each_entry_safe(t, n, &ce->tlist, list) {
+		list_del(&t->list);
+		kfree(t->name);
+		kfree(t);
+	}
+}
+
+static inline void flush_cache_ent(struct cache_entry *ce)
+{
+	hlist_del_init(&ce->hlist);
+	kfree(ce->path);
+	free_tgts(ce);
+	atomic_dec(&cache_count);
+	kmem_cache_free(cache_slab, ce);
+}
+
+static void flush_cache_ents(void)
+{
+	int i;
+
+	for (i = 0; i < CACHE_HTABLE_SIZE; i++) {
+		struct hlist_head *l = &cache_htable[i];
+		struct hlist_node *n;
+		struct cache_entry *ce;
+
+		hlist_for_each_entry_safe(ce, n, l, hlist) {
+			if (!hlist_unhashed(&ce->hlist))
+				flush_cache_ent(ce);
+		}
+	}
+}
+
+/*
+ * dfs cache /proc file
+ */
+static int dfscache_proc_show(struct seq_file *m, void *v)
+{
+	int i;
+	struct cache_entry *ce;
+	struct cache_dfs_tgt *t;
+
+	seq_puts(m, "DFS cache\n---------\n");
+
+	down_read(&htable_rw_lock);
+	for (i = 0; i < CACHE_HTABLE_SIZE; i++) {
+		struct hlist_head *l = &cache_htable[i];
+
+		hlist_for_each_entry(ce, l, hlist) {
+			if (hlist_unhashed(&ce->hlist))
+				continue;
+
+			seq_printf(m,
+				   "cache entry: path=%s,type=%s,ttl=%d,etime=%ld,hdr_flags=0x%x,ref_flags=0x%x,interlink=%s,path_consumed=%d,expired=%s\n",
+				   ce->path, ce->srvtype == DFS_TYPE_ROOT ? "root" : "link",
+				   ce->ttl, ce->etime.tv_nsec, ce->hdr_flags, ce->ref_flags,
+				   IS_DFS_INTERLINK(ce->hdr_flags) ? "yes" : "no",
+				   ce->path_consumed, cache_entry_expired(ce) ? "yes" : "no");
+
+			list_for_each_entry(t, &ce->tlist, list) {
+				seq_printf(m, "  %s%s\n",
+					   t->name,
+					   ce->tgthint == t ? " (target hint)" : "");
+			}
+		}
+	}
+	up_read(&htable_rw_lock);
+
+	return 0;
+}
+
+static ssize_t dfscache_proc_write(struct file *file, const char __user *buffer,
+				   size_t count, loff_t *ppos)
+{
+	char c;
+	int rc;
+
+	rc = get_user(c, buffer);
+	if (rc)
+		return rc;
+
+	if (c != '0')
+		return -EINVAL;
+
+	cifs_dbg(FYI, "clearing dfs cache\n");
+
+	down_write(&htable_rw_lock);
+	flush_cache_ents();
+	up_write(&htable_rw_lock);
+
+	return count;
+}
+
+static int dfscache_proc_open(struct inode *inode, struct file *file)
+{
+	return single_open(file, dfscache_proc_show, NULL);
+}
+
+const struct proc_ops dfscache_proc_ops = {
+	.proc_open	= dfscache_proc_open,
+	.proc_read	= seq_read,
+	.proc_lseek	= seq_lseek,
+	.proc_release	= single_release,
+	.proc_write	= dfscache_proc_write,
+};
+
+#ifdef CONFIG_CIFS_DEBUG2
+static inline void dump_tgts(const struct cache_entry *ce)
+{
+	struct cache_dfs_tgt *t;
+
+	cifs_dbg(FYI, "target list:\n");
+	list_for_each_entry(t, &ce->tlist, list) {
+		cifs_dbg(FYI, "  %s%s\n", t->name,
+			 ce->tgthint == t ? " (target hint)" : "");
+	}
+}
+
+static inline void dump_ce(const struct cache_entry *ce)
+{
+	cifs_dbg(FYI, "cache entry: path=%s,type=%s,ttl=%d,etime=%ld,hdr_flags=0x%x,ref_flags=0x%x,interlink=%s,path_consumed=%d,expired=%s\n",
+		 ce->path,
+		 ce->srvtype == DFS_TYPE_ROOT ? "root" : "link", ce->ttl,
+		 ce->etime.tv_nsec,
+		 ce->hdr_flags, ce->ref_flags,
+		 IS_DFS_INTERLINK(ce->hdr_flags) ? "yes" : "no",
+		 ce->path_consumed,
+		 cache_entry_expired(ce) ? "yes" : "no");
+	dump_tgts(ce);
+}
+
+static inline void dump_refs(const struct dfs_info3_param *refs, int numrefs)
+{
+	int i;
+
+	cifs_dbg(FYI, "DFS referrals returned by the server:\n");
+	for (i = 0; i < numrefs; i++) {
+		const struct dfs_info3_param *ref = &refs[i];
+
+		cifs_dbg(FYI,
+			 "\n"
+			 "flags:         0x%x\n"
+			 "path_consumed: %d\n"
+			 "server_type:   0x%x\n"
+			 "ref_flag:      0x%x\n"
+			 "path_name:     %s\n"
+			 "node_name:     %s\n"
+			 "ttl:           %d (%dm)\n",
+			 ref->flags, ref->path_consumed, ref->server_type,
+			 ref->ref_flag, ref->path_name, ref->node_name,
+			 ref->ttl, ref->ttl / 60);
+	}
+}
+#else
+#define dump_tgts(e)
+#define dump_ce(e)
+#define dump_refs(r, n)
+#endif
+
+/**
+ * dfs_cache_init - Initialize DFS referral cache.
+ *
+ * Return zero if initialized successfully, otherwise non-zero.
+ */
+int dfs_cache_init(void)
+{
+	int rc;
+	int i;
+
+	dfscache_wq = alloc_workqueue("cifs-dfscache", WQ_FREEZABLE | WQ_UNBOUND, 1);
+	if (!dfscache_wq)
+		return -ENOMEM;
+
+	cache_slab = kmem_cache_create("cifs_dfs_cache",
+				       sizeof(struct cache_entry), 0,
+				       SLAB_HWCACHE_ALIGN, NULL);
+	if (!cache_slab) {
+		rc = -ENOMEM;
+		goto out_destroy_wq;
+	}
+
+	for (i = 0; i < CACHE_HTABLE_SIZE; i++)
+		INIT_HLIST_HEAD(&cache_htable[i]);
+
+	atomic_set(&cache_count, 0);
+	cache_cp = load_nls("utf8");
+	if (!cache_cp)
+		cache_cp = load_nls_default();
+
+	cifs_dbg(FYI, "%s: initialized DFS referral cache\n", __func__);
+	return 0;
+
+out_destroy_wq:
+	destroy_workqueue(dfscache_wq);
+	return rc;
+}
+
+static int cache_entry_hash(const void *data, int size, unsigned int *hash)
+{
+	int i, clen;
+	const unsigned char *s = data;
+	wchar_t c;
+	unsigned int h = 0;
+
+	for (i = 0; i < size; i += clen) {
+		clen = cache_cp->char2uni(&s[i], size - i, &c);
+		if (unlikely(clen < 0)) {
+			cifs_dbg(VFS, "%s: can't convert char\n", __func__);
+			return clen;
+		}
+		c = cifs_toupper(c);
+		h = jhash(&c, sizeof(c), h);
+	}
+	*hash = h % CACHE_HTABLE_SIZE;
+	return 0;
+}
+
+/* Return target hint of a DFS cache entry */
+static inline char *get_tgt_name(const struct cache_entry *ce)
+{
+	struct cache_dfs_tgt *t = ce->tgthint;
+
+	return t ? t->name : ERR_PTR(-ENOENT);
+}
+
+/* Return expire time out of a new entry's TTL */
+static inline struct timespec64 get_expire_time(int ttl)
+{
+	struct timespec64 ts = {
+		.tv_sec = ttl,
+		.tv_nsec = 0,
+	};
+	struct timespec64 now;
+
+	ktime_get_coarse_real_ts64(&now);
+	return timespec64_add(now, ts);
+}
+
+/* Allocate a new DFS target */
+static struct cache_dfs_tgt *alloc_target(const char *name, int path_consumed)
+{
+	struct cache_dfs_tgt *t;
+
+	t = kmalloc(sizeof(*t), GFP_ATOMIC);
+	if (!t)
+		return ERR_PTR(-ENOMEM);
+	t->name = kstrdup(name, GFP_ATOMIC);
+	if (!t->name) {
+		kfree(t);
+		return ERR_PTR(-ENOMEM);
+	}
+	t->path_consumed = path_consumed;
+	INIT_LIST_HEAD(&t->list);
+	return t;
+}
+
+/*
+ * Copy DFS referral information to a cache entry and conditionally update
+ * target hint.
+ */
+static int copy_ref_data(const struct dfs_info3_param *refs, int numrefs,
+			 struct cache_entry *ce, const char *tgthint)
+{
+	int i;
+
+	ce->ttl = max_t(int, refs[0].ttl, CACHE_MIN_TTL);
+	ce->etime = get_expire_time(ce->ttl);
+	ce->srvtype = refs[0].server_type;
+	ce->hdr_flags = refs[0].flags;
+	ce->ref_flags = refs[0].ref_flag;
+	ce->path_consumed = refs[0].path_consumed;
+
+	for (i = 0; i < numrefs; i++) {
+		struct cache_dfs_tgt *t;
+
+		t = alloc_target(refs[i].node_name, refs[i].path_consumed);
+		if (IS_ERR(t)) {
+			free_tgts(ce);
+			return PTR_ERR(t);
+		}
+		if (tgthint && !strcasecmp(t->name, tgthint)) {
+			list_add(&t->list, &ce->tlist);
+			tgthint = NULL;
+		} else {
+			list_add_tail(&t->list, &ce->tlist);
+		}
+		ce->numtgts++;
+	}
+
+	ce->tgthint = list_first_entry_or_null(&ce->tlist,
+					       struct cache_dfs_tgt, list);
+
+	return 0;
+}
+
+/* Allocate a new cache entry */
+static struct cache_entry *alloc_cache_entry(struct dfs_info3_param *refs, int numrefs)
+{
+	struct cache_entry *ce;
+	int rc;
+
+	ce = kmem_cache_zalloc(cache_slab, GFP_KERNEL);
+	if (!ce)
+		return ERR_PTR(-ENOMEM);
+
+	ce->path = refs[0].path_name;
+	refs[0].path_name = NULL;
+
+	INIT_HLIST_NODE(&ce->hlist);
+	INIT_LIST_HEAD(&ce->tlist);
+
+	rc = copy_ref_data(refs, numrefs, ce, NULL);
+	if (rc) {
+		kfree(ce->path);
+		kmem_cache_free(cache_slab, ce);
+		ce = ERR_PTR(rc);
+	}
+	return ce;
+}
+
+static void remove_oldest_entry_locked(void)
+{
+	int i;
+	struct cache_entry *ce;
+	struct cache_entry *to_del = NULL;
+
+	WARN_ON(!rwsem_is_locked(&htable_rw_lock));
+
+	for (i = 0; i < CACHE_HTABLE_SIZE; i++) {
+		struct hlist_head *l = &cache_htable[i];
+
+		hlist_for_each_entry(ce, l, hlist) {
+			if (hlist_unhashed(&ce->hlist))
+				continue;
+			if (!to_del || timespec64_compare(&ce->etime,
+							  &to_del->etime) < 0)
+				to_del = ce;
+		}
+	}
+
+	if (!to_del) {
+		cifs_dbg(FYI, "%s: no entry to remove\n", __func__);
+		return;
+	}
+
+	cifs_dbg(FYI, "%s: removing entry\n", __func__);
+	dump_ce(to_del);
+	flush_cache_ent(to_del);
+}
+
+/* Add a new DFS cache entry */
+static int add_cache_entry_locked(struct dfs_info3_param *refs, int numrefs)
+{
+	int rc;
+	struct cache_entry *ce;
+	unsigned int hash;
+
+	WARN_ON(!rwsem_is_locked(&htable_rw_lock));
+
+	if (atomic_read(&cache_count) >= CACHE_MAX_ENTRIES) {
+		cifs_dbg(FYI, "%s: reached max cache size (%d)\n", __func__, CACHE_MAX_ENTRIES);
+		remove_oldest_entry_locked();
+	}
+
+	rc = cache_entry_hash(refs[0].path_name, strlen(refs[0].path_name), &hash);
+	if (rc)
+		return rc;
+
+	ce = alloc_cache_entry(refs, numrefs);
+	if (IS_ERR(ce))
+		return PTR_ERR(ce);
+
+	spin_lock(&cache_ttl_lock);
+	if (!cache_ttl) {
+		cache_ttl = ce->ttl;
+		queue_delayed_work(dfscache_wq, &refresh_task, cache_ttl * HZ);
+	} else {
+		cache_ttl = min_t(int, cache_ttl, ce->ttl);
+		mod_delayed_work(dfscache_wq, &refresh_task, cache_ttl * HZ);
+	}
+	spin_unlock(&cache_ttl_lock);
+
+	hlist_add_head(&ce->hlist, &cache_htable[hash]);
+	dump_ce(ce);
+
+	atomic_inc(&cache_count);
+
+	return 0;
+}
+
+/* Check if two DFS paths are equal.  @s1 and @s2 are expected to be in @cache_cp's charset */
+static bool dfs_path_equal(const char *s1, int len1, const char *s2, int len2)
+{
+	int i, l1, l2;
+	wchar_t c1, c2;
+
+	if (len1 != len2)
+		return false;
+
+	for (i = 0; i < len1; i += l1) {
+		l1 = cache_cp->char2uni(&s1[i], len1 - i, &c1);
+		l2 = cache_cp->char2uni(&s2[i], len2 - i, &c2);
+		if (unlikely(l1 < 0 && l2 < 0)) {
+			if (s1[i] != s2[i])
+				return false;
+			l1 = 1;
+			continue;
+		}
+		if (l1 != l2)
+			return false;
+		if (cifs_toupper(c1) != cifs_toupper(c2))
+			return false;
+	}
+	return true;
+}
+
+static struct cache_entry *__lookup_cache_entry(const char *path, unsigned int hash, int len)
+{
+	struct cache_entry *ce;
+
+	hlist_for_each_entry(ce, &cache_htable[hash], hlist) {
+		if (dfs_path_equal(ce->path, strlen(ce->path), path, len)) {
+			dump_ce(ce);
+			return ce;
+		}
+	}
+	return ERR_PTR(-ENOENT);
+}
+
+/*
+ * Find a DFS cache entry in hash table and optionally check prefix path against normalized @path.
+ *
+ * Use whole path components in the match.  Must be called with htable_rw_lock held.
+ *
+ * Return ERR_PTR(-ENOENT) if the entry is not found.
+ */
+static struct cache_entry *lookup_cache_entry(const char *path)
+{
+	struct cache_entry *ce;
+	int cnt = 0;
+	const char *s = path, *e;
+	char sep = *s;
+	unsigned int hash;
+	int rc;
+
+	while ((s = strchr(s, sep)) && ++cnt < 3)
+		s++;
+
+	if (cnt < 3) {
+		rc = cache_entry_hash(path, strlen(path), &hash);
+		if (rc)
+			return ERR_PTR(rc);
+		return __lookup_cache_entry(path, hash, strlen(path));
+	}
+	/*
+	 * Handle paths that have more than two path components and are a complete prefix of the DFS
+	 * referral request path (@path).
+	 *
+	 * See MS-DFSC 3.2.5.5 "Receiving a Root Referral Request or Link Referral Request".
+	 */
+	e = path + strlen(path) - 1;
+	while (e > s) {
+		int len;
+
+		/* skip separators */
+		while (e > s && *e == sep)
+			e--;
+		if (e == s)
+			break;
+
+		len = e + 1 - path;
+		rc = cache_entry_hash(path, len, &hash);
+		if (rc)
+			return ERR_PTR(rc);
+		ce = __lookup_cache_entry(path, hash, len);
+		if (!IS_ERR(ce))
+			return ce;
+
+		/* backward until separator */
+		while (e > s && *e != sep)
+			e--;
+	}
+	return ERR_PTR(-ENOENT);
+}
+
+/**
+ * dfs_cache_destroy - destroy DFS referral cache
+ */
+void dfs_cache_destroy(void)
+{
+	cancel_delayed_work_sync(&refresh_task);
+	unload_nls(cache_cp);
+	free_mount_group_list();
+	flush_cache_ents();
+	kmem_cache_destroy(cache_slab);
+	destroy_workqueue(dfscache_wq);
+
+	cifs_dbg(FYI, "%s: destroyed DFS referral cache\n", __func__);
+}
+
+/* Update a cache entry with the new referral in @refs */
+static int update_cache_entry_locked(struct cache_entry *ce, const struct dfs_info3_param *refs,
+				     int numrefs)
+{
+	int rc;
+	char *s, *th = NULL;
+
+	WARN_ON(!rwsem_is_locked(&htable_rw_lock));
+
+	if (ce->tgthint) {
+		s = ce->tgthint->name;
+		th = kstrdup(s, GFP_ATOMIC);
+		if (!th)
+			return -ENOMEM;
+	}
+
+	free_tgts(ce);
+	ce->numtgts = 0;
+
+	rc = copy_ref_data(refs, numrefs, ce, th);
+
+	kfree(th);
+
+	return rc;
+}
+
+static int get_dfs_referral(const unsigned int xid, struct cifs_ses *ses, const char *path,
+			    struct dfs_info3_param **refs, int *numrefs)
+{
+	int rc;
+	int i;
+
+	cifs_dbg(FYI, "%s: get an DFS referral for %s\n", __func__, path);
+
+	*refs = NULL;
+	*numrefs = 0;
+
+	if (!ses || !ses->server || !ses->server->ops->get_dfs_refer)
+		return -EOPNOTSUPP;
+	if (unlikely(!cache_cp))
+		return -EINVAL;
+
+	rc =  ses->server->ops->get_dfs_refer(xid, ses, path, refs, numrefs, cache_cp,
+					      NO_MAP_UNI_RSVD);
+	if (!rc) {
+		struct dfs_info3_param *ref = *refs;
+
+		for (i = 0; i < *numrefs; i++)
+			convert_delimiter(ref[i].path_name, '\\');
+	}
+	return rc;
+}
+
+/*
+ * Find, create or update a DFS cache entry.
+ *
+ * If the entry wasn't found, it will create a new one. Or if it was found but
+ * expired, then it will update the entry accordingly.
+ *
+ * For interlinks, cifs_mount() and expand_dfs_referral() are supposed to
+ * handle them properly.
+ */
+static int cache_refresh_path(const unsigned int xid, struct cifs_ses *ses, const char *path)
+{
+	struct dfs_info3_param *refs = NULL;
+	struct cache_entry *ce;
+	int numrefs = 0;
+	int rc;
+
+	cifs_dbg(FYI, "%s: search path: %s\n", __func__, path);
+
+	down_read(&htable_rw_lock);
+
+	ce = lookup_cache_entry(path);
+	if (!IS_ERR(ce) && !cache_entry_expired(ce)) {
+		up_read(&htable_rw_lock);
+		return 0;
+	}
+	/*
+	 * Unlock shared access as we don't want to hold any locks while getting
+	 * a new referral.  The @ses used for performing the I/O could be
+	 * reconnecting and it acquires @htable_rw_lock to look up the dfs cache
+	 * in order to failover -- if necessary.
+	 */
+	up_read(&htable_rw_lock);
+
+	/*
+	 * Either the entry was not found, or it is expired.
+	 * Request a new DFS referral in order to create or update a cache entry.
+	 */
+	rc = get_dfs_referral(xid, ses, path, &refs, &numrefs);
+	if (rc)
+		goto out;
+
+	dump_refs(refs, numrefs);
+
+	down_write(&htable_rw_lock);
+	/* Re-check as another task might have it added or refreshed already */
+	ce = lookup_cache_entry(path);
+	if (!IS_ERR(ce)) {
+		if (cache_entry_expired(ce))
+			rc = update_cache_entry_locked(ce, refs, numrefs);
+	} else {
+		rc = add_cache_entry_locked(refs, numrefs);
+	}
+
+	up_write(&htable_rw_lock);
+out:
+	free_dfs_info_array(refs, numrefs);
+	return rc;
+}
+
+/*
+ * Set up a DFS referral from a given cache entry.
+ *
+ * Must be called with htable_rw_lock held.
+ */
+static int setup_referral(const char *path, struct cache_entry *ce,
+			  struct dfs_info3_param *ref, const char *target)
+{
+	int rc;
+
+	cifs_dbg(FYI, "%s: set up new ref\n", __func__);
+
+	memset(ref, 0, sizeof(*ref));
+
+	ref->path_name = kstrdup(path, GFP_ATOMIC);
+	if (!ref->path_name)
+		return -ENOMEM;
+
+	ref->node_name = kstrdup(target, GFP_ATOMIC);
+	if (!ref->node_name) {
+		rc = -ENOMEM;
+		goto err_free_path;
+	}
+
+	ref->path_consumed = ce->path_consumed;
+	ref->ttl = ce->ttl;
+	ref->server_type = ce->srvtype;
+	ref->ref_flag = ce->ref_flags;
+	ref->flags = ce->hdr_flags;
+
+	return 0;
+
+err_free_path:
+	kfree(ref->path_name);
+	ref->path_name = NULL;
+	return rc;
+}
+
+/* Return target list of a DFS cache entry */
+static int get_targets(struct cache_entry *ce, struct dfs_cache_tgt_list *tl)
+{
+	int rc;
+	struct list_head *head = &tl->tl_list;
+	struct cache_dfs_tgt *t;
+	struct dfs_cache_tgt_iterator *it, *nit;
+
+	memset(tl, 0, sizeof(*tl));
+	INIT_LIST_HEAD(head);
+
+	list_for_each_entry(t, &ce->tlist, list) {
+		it = kzalloc(sizeof(*it), GFP_ATOMIC);
+		if (!it) {
+			rc = -ENOMEM;
+			goto err_free_it;
+		}
+
+		it->it_name = kstrdup(t->name, GFP_ATOMIC);
+		if (!it->it_name) {
+			kfree(it);
+			rc = -ENOMEM;
+			goto err_free_it;
+		}
+		it->it_path_consumed = t->path_consumed;
+
+		if (ce->tgthint == t)
+			list_add(&it->it_list, head);
+		else
+			list_add_tail(&it->it_list, head);
+	}
+
+	tl->tl_numtgts = ce->numtgts;
+
+	return 0;
+
+err_free_it:
+	list_for_each_entry_safe(it, nit, head, it_list) {
+		list_del(&it->it_list);
+		kfree(it->it_name);
+		kfree(it);
+	}
+	return rc;
+}
+
+/**
+ * dfs_cache_find - find a DFS cache entry
+ *
+ * If it doesn't find the cache entry, then it will get a DFS referral
+ * for @path and create a new entry.
+ *
+ * In case the cache entry exists but expired, it will get a DFS referral
+ * for @path and then update the respective cache entry.
+ *
+ * These parameters are passed down to the get_dfs_refer() call if it
+ * needs to be issued:
+ * @xid: syscall xid
+ * @ses: smb session to issue the request on
+ * @cp: codepage
+ * @remap: path character remapping type
+ * @path: path to lookup in DFS referral cache.
+ *
+ * @ref: when non-NULL, store single DFS referral result in it.
+ * @tgt_list: when non-NULL, store complete DFS target list in it.
+ *
+ * Return zero if the target was found, otherwise non-zero.
+ */
+int dfs_cache_find(const unsigned int xid, struct cifs_ses *ses, const struct nls_table *cp,
+		   int remap, const char *path, struct dfs_info3_param *ref,
+		   struct dfs_cache_tgt_list *tgt_list)
+{
+	int rc;
+	const char *npath;
+	struct cache_entry *ce;
+
+	npath = dfs_cache_canonical_path(path, cp, remap);
+	if (IS_ERR(npath))
+		return PTR_ERR(npath);
+
+	rc = cache_refresh_path(xid, ses, npath);
+	if (rc)
+		goto out_free_path;
+
+	down_read(&htable_rw_lock);
+
+	ce = lookup_cache_entry(npath);
+	if (IS_ERR(ce)) {
+		up_read(&htable_rw_lock);
+		rc = PTR_ERR(ce);
+		goto out_free_path;
+	}
+
+	if (ref)
+		rc = setup_referral(path, ce, ref, get_tgt_name(ce));
+	else
+		rc = 0;
+	if (!rc && tgt_list)
+		rc = get_targets(ce, tgt_list);
+
+	up_read(&htable_rw_lock);
+
+out_free_path:
+	kfree(npath);
+	return rc;
+}
+
+/**
+ * dfs_cache_noreq_find - find a DFS cache entry without sending any requests to
+ * the currently connected server.
+ *
+ * NOTE: This function will neither update a cache entry in case it was
+ * expired, nor create a new cache entry if @path hasn't been found. It heavily
+ * relies on an existing cache entry.
+ *
+ * @path: canonical DFS path to lookup in the DFS referral cache.
+ * @ref: when non-NULL, store single DFS referral result in it.
+ * @tgt_list: when non-NULL, store complete DFS target list in it.
+ *
+ * Return 0 if successful.
+ * Return -ENOENT if the entry was not found.
+ * Return non-zero for other errors.
+ */
+int dfs_cache_noreq_find(const char *path, struct dfs_info3_param *ref,
+			 struct dfs_cache_tgt_list *tgt_list)
+{
+	int rc;
+	struct cache_entry *ce;
+
+	cifs_dbg(FYI, "%s: path: %s\n", __func__, path);
+
+	down_read(&htable_rw_lock);
+
+	ce = lookup_cache_entry(path);
+	if (IS_ERR(ce)) {
+		rc = PTR_ERR(ce);
+		goto out_unlock;
+	}
+
+	if (ref)
+		rc = setup_referral(path, ce, ref, get_tgt_name(ce));
+	else
+		rc = 0;
+	if (!rc && tgt_list)
+		rc = get_targets(ce, tgt_list);
+
+out_unlock:
+	up_read(&htable_rw_lock);
+	return rc;
+}
+
+/**
+ * dfs_cache_update_tgthint - update target hint of a DFS cache entry
+ *
+ * If it doesn't find the cache entry, then it will get a DFS referral for @path
+ * and create a new entry.
+ *
+ * In case the cache entry exists but expired, it will get a DFS referral
+ * for @path and then update the respective cache entry.
+ *
+ * @xid: syscall id
+ * @ses: smb session
+ * @cp: codepage
+ * @remap: type of character remapping for paths
+ * @path: path to lookup in DFS referral cache
+ * @it: DFS target iterator
+ *
+ * Return zero if the target hint was updated successfully, otherwise non-zero.
+ */
+int dfs_cache_update_tgthint(const unsigned int xid, struct cifs_ses *ses,
+			     const struct nls_table *cp, int remap, const char *path,
+			     const struct dfs_cache_tgt_iterator *it)
+{
+	struct cache_dfs_tgt *t;
+	struct cache_entry *ce;
+	const char *npath;
+	int rc = 0;
+
+	npath = dfs_cache_canonical_path(path, cp, remap);
+	if (IS_ERR(npath))
+		return PTR_ERR(npath);
+
+	cifs_dbg(FYI, "%s: update target hint - path: %s\n", __func__, npath);
+
+	rc = cache_refresh_path(xid, ses, npath);
+	if (rc)
+		goto out_free_path;
+
+	down_write(&htable_rw_lock);
+
+	ce = lookup_cache_entry(npath);
+	if (IS_ERR(ce)) {
+		rc = PTR_ERR(ce);
+		goto out_unlock;
+	}
+
+	t = ce->tgthint;
+
+	if (likely(!strcasecmp(it->it_name, t->name)))
+		goto out_unlock;
+
+	list_for_each_entry(t, &ce->tlist, list) {
+		if (!strcasecmp(t->name, it->it_name)) {
+			ce->tgthint = t;
+			cifs_dbg(FYI, "%s: new target hint: %s\n", __func__,
+				 it->it_name);
+			break;
+		}
+	}
+
+out_unlock:
+	up_write(&htable_rw_lock);
+out_free_path:
+	kfree(npath);
+	return rc;
+}
+
+/**
+ * dfs_cache_noreq_update_tgthint - update target hint of a DFS cache entry
+ * without sending any requests to the currently connected server.
+ *
+ * NOTE: This function will neither update a cache entry in case it was
+ * expired, nor create a new cache entry if @path hasn't been found. It heavily
+ * relies on an existing cache entry.
+ *
+ * @path: canonical DFS path to lookup in DFS referral cache.
+ * @it: target iterator which contains the target hint to update the cache
+ * entry with.
+ *
+ * Return zero if the target hint was updated successfully, otherwise non-zero.
+ */
+int dfs_cache_noreq_update_tgthint(const char *path, const struct dfs_cache_tgt_iterator *it)
+{
+	int rc;
+	struct cache_entry *ce;
+	struct cache_dfs_tgt *t;
+
+	if (!it)
+		return -EINVAL;
+
+	cifs_dbg(FYI, "%s: path: %s\n", __func__, path);
+
+	down_write(&htable_rw_lock);
+
+	ce = lookup_cache_entry(path);
+	if (IS_ERR(ce)) {
+		rc = PTR_ERR(ce);
+		goto out_unlock;
+	}
+
+	rc = 0;
+	t = ce->tgthint;
+
+	if (unlikely(!strcasecmp(it->it_name, t->name)))
+		goto out_unlock;
+
+	list_for_each_entry(t, &ce->tlist, list) {
+		if (!strcasecmp(t->name, it->it_name)) {
+			ce->tgthint = t;
+			cifs_dbg(FYI, "%s: new target hint: %s\n", __func__,
+				 it->it_name);
+			break;
+		}
+	}
+
+out_unlock:
+	up_write(&htable_rw_lock);
+	return rc;
+}
+
+/**
+ * dfs_cache_get_tgt_referral - returns a DFS referral (@ref) from a given
+ * target iterator (@it).
+ *
+ * @path: canonical DFS path to lookup in DFS referral cache.
+ * @it: DFS target iterator.
+ * @ref: DFS referral pointer to set up the gathered information.
+ *
+ * Return zero if the DFS referral was set up correctly, otherwise non-zero.
+ */
+int dfs_cache_get_tgt_referral(const char *path, const struct dfs_cache_tgt_iterator *it,
+			       struct dfs_info3_param *ref)
+{
+	int rc;
+	struct cache_entry *ce;
+
+	if (!it || !ref)
+		return -EINVAL;
+
+	cifs_dbg(FYI, "%s: path: %s\n", __func__, path);
+
+	down_read(&htable_rw_lock);
+
+	ce = lookup_cache_entry(path);
+	if (IS_ERR(ce)) {
+		rc = PTR_ERR(ce);
+		goto out_unlock;
+	}
+
+	cifs_dbg(FYI, "%s: target name: %s\n", __func__, it->it_name);
+
+	rc = setup_referral(path, ce, ref, it->it_name);
+
+out_unlock:
+	up_read(&htable_rw_lock);
+	return rc;
+}
+
+/**
+ * dfs_cache_add_refsrv_session - add SMB session of referral server
+ *
+ * @mount_id: mount group uuid to lookup.
+ * @ses: reference counted SMB session of referral server.
+ */
+void dfs_cache_add_refsrv_session(const uuid_t *mount_id, struct cifs_ses *ses)
+{
+	struct mount_group *mg;
+
+	if (WARN_ON_ONCE(!mount_id || uuid_is_null(mount_id) || !ses))
+		return;
+
+	mg = get_mount_group(mount_id);
+	if (WARN_ON_ONCE(IS_ERR(mg)))
+		return;
+
+	spin_lock(&mg->lock);
+	if (mg->num_sessions < ARRAY_SIZE(mg->sessions))
+		mg->sessions[mg->num_sessions++] = ses;
+	spin_unlock(&mg->lock);
+	kref_put(&mg->refcount, mount_group_release);
+}
+
+/**
+ * dfs_cache_put_refsrv_sessions - put all referral server sessions
+ *
+ * Put all SMB sessions from the given mount group id.
+ *
+ * @mount_id: mount group uuid to lookup.
+ */
+void dfs_cache_put_refsrv_sessions(const uuid_t *mount_id)
+{
+	struct mount_group *mg;
+
+	if (!mount_id || uuid_is_null(mount_id))
+		return;
+
+	mutex_lock(&mount_group_list_lock);
+	mg = find_mount_group_locked(mount_id);
+	if (IS_ERR(mg)) {
+		mutex_unlock(&mount_group_list_lock);
+		return;
+	}
+	mutex_unlock(&mount_group_list_lock);
+	kref_put(&mg->refcount, mount_group_release);
+}
+
+/* Extract share from DFS target and return a pointer to prefix path or NULL */
+static const char *parse_target_share(const char *target, char **share)
+{
+	const char *s, *seps = "/\\";
+	size_t len;
+
+	s = strpbrk(target + 1, seps);
+	if (!s)
+		return ERR_PTR(-EINVAL);
+
+	len = strcspn(s + 1, seps);
+	if (!len)
+		return ERR_PTR(-EINVAL);
+	s += len;
+
+	len = s - target + 1;
+	*share = kstrndup(target, len, GFP_KERNEL);
+	if (!*share)
+		return ERR_PTR(-ENOMEM);
+
+	s = target + len;
+	return s + strspn(s, seps);
+}
+
+/**
+ * dfs_cache_get_tgt_share - parse a DFS target
+ *
+ * @path: DFS full path
+ * @it: DFS target iterator.
+ * @share: tree name.
+ * @prefix: prefix path.
+ *
+ * Return zero if target was parsed correctly, otherwise non-zero.
+ */
+int dfs_cache_get_tgt_share(char *path, const struct dfs_cache_tgt_iterator *it, char **share,
+			    char **prefix)
+{
+	char sep;
+	char *target_share;
+	char *ppath = NULL;
+	const char *target_ppath, *dfsref_ppath;
+	size_t target_pplen, dfsref_pplen;
+	size_t len, c;
+
+	if (!it || !path || !share || !prefix || strlen(path) < it->it_path_consumed)
+		return -EINVAL;
+
+	sep = it->it_name[0];
+	if (sep != '\\' && sep != '/')
+		return -EINVAL;
+
+	target_ppath = parse_target_share(it->it_name, &target_share);
+	if (IS_ERR(target_ppath))
+		return PTR_ERR(target_ppath);
+
+	/* point to prefix in DFS referral path */
+	dfsref_ppath = path + it->it_path_consumed;
+	dfsref_ppath += strspn(dfsref_ppath, "/\\");
+
+	target_pplen = strlen(target_ppath);
+	dfsref_pplen = strlen(dfsref_ppath);
+
+	/* merge prefix paths from DFS referral path and target node */
+	if (target_pplen || dfsref_pplen) {
+		len = target_pplen + dfsref_pplen + 2;
+		ppath = kzalloc(len, GFP_KERNEL);
+		if (!ppath) {
+			kfree(target_share);
+			return -ENOMEM;
+		}
+		c = strscpy(ppath, target_ppath, len);
+		if (c && dfsref_pplen)
+			ppath[c] = sep;
+		strlcat(ppath, dfsref_ppath, len);
+	}
+	*share = target_share;
+	*prefix = ppath;
+	return 0;
+}
+
+static bool target_share_equal(struct TCP_Server_Info *server, const char *s1, const char *s2)
+{
+	char unc[sizeof("\\\\") + SERVER_NAME_LENGTH] = {0};
+	const char *host;
+	size_t hostlen;
+	char *ip = NULL;
+	struct sockaddr sa;
+	bool match;
+	int rc;
+
+	if (strcasecmp(s1, s2))
+		return false;
+
+	/*
+	 * Resolve share's hostname and check if server address matches.  Otherwise just ignore it
+	 * as we could not have upcall to resolve hostname or failed to convert ip address.
+	 */
+	match = true;
+	extract_unc_hostname(s1, &host, &hostlen);
+	scnprintf(unc, sizeof(unc), "\\\\%.*s", (int)hostlen, host);
+
+	rc = dns_resolve_server_name_to_ip(unc, &ip, NULL);
+	if (rc < 0) {
+		cifs_dbg(FYI, "%s: could not resolve %.*s. assuming server address matches.\n",
+			 __func__, (int)hostlen, host);
+		return true;
+	}
+
+	if (!cifs_convert_address(&sa, ip, strlen(ip))) {
+		cifs_dbg(VFS, "%s: failed to convert address \'%s\'. skip address matching.\n",
+			 __func__, ip);
+	} else {
+		cifs_server_lock(server);
+		match = cifs_match_ipaddr((struct sockaddr *)&server->dstaddr, &sa);
+		cifs_server_unlock(server);
+	}
+
+	kfree(ip);
+	return match;
+}
+
+/*
+ * Mark dfs tcon for reconnecting when the currently connected tcon does not match any of the new
+ * target shares in @refs.
+ */
+static void mark_for_reconnect_if_needed(struct cifs_tcon *tcon, struct dfs_cache_tgt_list *tl,
+					 const struct dfs_info3_param *refs, int numrefs)
+{
+	struct dfs_cache_tgt_iterator *it;
+	int i;
+
+	for (it = dfs_cache_get_tgt_iterator(tl); it; it = dfs_cache_get_next_tgt(tl, it)) {
+		for (i = 0; i < numrefs; i++) {
+			if (target_share_equal(tcon->ses->server, dfs_cache_get_tgt_name(it),
+					       refs[i].node_name))
+				return;
+		}
+	}
+
+	cifs_dbg(FYI, "%s: no cached or matched targets. mark dfs share for reconnect.\n", __func__);
+	cifs_signal_cifsd_for_reconnect(tcon->ses->server, true);
+}
+
+/* Refresh dfs referral of tcon and mark it for reconnect if needed */
+static int __refresh_tcon(const char *path, struct cifs_ses **sessions, struct cifs_tcon *tcon,
+			  bool force_refresh)
+{
+	struct cifs_ses *ses;
+	struct cache_entry *ce;
+	struct dfs_info3_param *refs = NULL;
+	int numrefs = 0;
+	bool needs_refresh = false;
+	struct dfs_cache_tgt_list tl = DFS_CACHE_TGT_LIST_INIT(tl);
+	int rc = 0;
+	unsigned int xid;
+
+	ses = find_ipc_from_server_path(sessions, path);
+	if (IS_ERR(ses)) {
+		cifs_dbg(FYI, "%s: could not find ipc session\n", __func__);
+		return PTR_ERR(ses);
+	}
+
+	down_read(&htable_rw_lock);
+	ce = lookup_cache_entry(path);
+	needs_refresh = force_refresh || IS_ERR(ce) || cache_entry_expired(ce);
+	if (!IS_ERR(ce)) {
+		rc = get_targets(ce, &tl);
+		if (rc)
+			cifs_dbg(FYI, "%s: could not get dfs targets: %d\n", __func__, rc);
+	}
+	up_read(&htable_rw_lock);
+
+	if (!needs_refresh) {
+		rc = 0;
+		goto out;
+	}
+
+	xid = get_xid();
+	rc = get_dfs_referral(xid, ses, path, &refs, &numrefs);
+	free_xid(xid);
+
+	/* Create or update a cache entry with the new referral */
+	if (!rc) {
+		dump_refs(refs, numrefs);
+
+		down_write(&htable_rw_lock);
+		ce = lookup_cache_entry(path);
+		if (IS_ERR(ce))
+			add_cache_entry_locked(refs, numrefs);
+		else if (force_refresh || cache_entry_expired(ce))
+			update_cache_entry_locked(ce, refs, numrefs);
+		up_write(&htable_rw_lock);
+
+		mark_for_reconnect_if_needed(tcon, &tl, refs, numrefs);
+	}
+
+out:
+	dfs_cache_free_tgts(&tl);
+	free_dfs_info_array(refs, numrefs);
+	return rc;
+}
+
+static int refresh_tcon(struct cifs_ses **sessions, struct cifs_tcon *tcon, bool force_refresh)
+{
+	struct TCP_Server_Info *server = tcon->ses->server;
+
+	mutex_lock(&server->refpath_lock);
+	if (server->origin_fullpath) {
+		if (server->leaf_fullpath && strcasecmp(server->leaf_fullpath,
+							server->origin_fullpath))
+			__refresh_tcon(server->leaf_fullpath + 1, sessions, tcon, force_refresh);
+		__refresh_tcon(server->origin_fullpath + 1, sessions, tcon, force_refresh);
+	}
+	mutex_unlock(&server->refpath_lock);
+
+	return 0;
+}
+
+/**
+ * dfs_cache_remount_fs - remount a DFS share
+ *
+ * Reconfigure dfs mount by forcing a new DFS referral and if the currently cached targets do not
+ * match any of the new targets, mark it for reconnect.
+ *
+ * @cifs_sb: cifs superblock.
+ *
+ * Return zero if remounted, otherwise non-zero.
+ */
+int dfs_cache_remount_fs(struct cifs_sb_info *cifs_sb)
+{
+	struct cifs_tcon *tcon;
+	struct TCP_Server_Info *server;
+	struct mount_group *mg;
+	struct cifs_ses *sessions[CACHE_MAX_ENTRIES + 1] = {NULL};
+	int rc;
+
+	if (!cifs_sb || !cifs_sb->master_tlink)
+		return -EINVAL;
+
+	tcon = cifs_sb_master_tcon(cifs_sb);
+	server = tcon->ses->server;
+
+	if (!server->origin_fullpath) {
+		cifs_dbg(FYI, "%s: not a dfs mount\n", __func__);
+		return 0;
+	}
+
+	if (uuid_is_null(&cifs_sb->dfs_mount_id)) {
+		cifs_dbg(FYI, "%s: no dfs mount group id\n", __func__);
+		return -EINVAL;
+	}
+
+	mutex_lock(&mount_group_list_lock);
+	mg = find_mount_group_locked(&cifs_sb->dfs_mount_id);
+	if (IS_ERR(mg)) {
+		mutex_unlock(&mount_group_list_lock);
+		cifs_dbg(FYI, "%s: no ipc session for refreshing referral\n", __func__);
+		return PTR_ERR(mg);
+	}
+	kref_get(&mg->refcount);
+	mutex_unlock(&mount_group_list_lock);
+
+	spin_lock(&mg->lock);
+	memcpy(&sessions, mg->sessions, mg->num_sessions * sizeof(mg->sessions[0]));
+	spin_unlock(&mg->lock);
+
+	/*
+	 * After reconnecting to a different server, unique ids won't match anymore, so we disable
+	 * serverino. This prevents dentry revalidation to think the dentry are stale (ESTALE).
+	 */
+	cifs_autodisable_serverino(cifs_sb);
+	/*
+	 * Force the use of prefix path to support failover on DFS paths that resolve to targets
+	 * that have different prefix paths.
+	 */
+	cifs_sb->mnt_cifs_flags |= CIFS_MOUNT_USE_PREFIX_PATH;
+	rc = refresh_tcon(sessions, tcon, true);
+
+	kref_put(&mg->refcount, mount_group_release);
+	return rc;
+}
+
+/*
+ * Refresh all active dfs mounts regardless of whether they are in cache or not.
+ * (cache can be cleared)
+ */
+static void refresh_mounts(struct cifs_ses **sessions)
+{
+	struct TCP_Server_Info *server;
+	struct cifs_ses *ses;
+	struct cifs_tcon *tcon, *ntcon;
+	struct list_head tcons;
+
+	INIT_LIST_HEAD(&tcons);
+
+	spin_lock(&cifs_tcp_ses_lock);
+	list_for_each_entry(server, &cifs_tcp_ses_list, tcp_ses_list) {
+		spin_lock(&server->srv_lock);
+		if (!server->is_dfs_conn) {
+			spin_unlock(&server->srv_lock);
+			continue;
+		}
+		spin_unlock(&server->srv_lock);
+
+		list_for_each_entry(ses, &server->smb_ses_list, smb_ses_list) {
+			list_for_each_entry(tcon, &ses->tcon_list, tcon_list) {
+				spin_lock(&tcon->tc_lock);
+				if (!tcon->ipc && !tcon->need_reconnect) {
+					tcon->tc_count++;
+					list_add_tail(&tcon->ulist, &tcons);
+				}
+				spin_unlock(&tcon->tc_lock);
+			}
+		}
+	}
+	spin_unlock(&cifs_tcp_ses_lock);
+
+	list_for_each_entry_safe(tcon, ntcon, &tcons, ulist) {
+		struct TCP_Server_Info *server = tcon->ses->server;
+
+		list_del_init(&tcon->ulist);
+
+		mutex_lock(&server->refpath_lock);
+		if (server->origin_fullpath) {
+			if (server->leaf_fullpath && strcasecmp(server->leaf_fullpath,
+								server->origin_fullpath))
+				__refresh_tcon(server->leaf_fullpath + 1, sessions, tcon, false);
+			__refresh_tcon(server->origin_fullpath + 1, sessions, tcon, false);
+		}
+		mutex_unlock(&server->refpath_lock);
+
+		cifs_put_tcon(tcon);
+	}
+}
+
+static void refresh_cache(struct cifs_ses **sessions)
+{
+	int i;
+	struct cifs_ses *ses;
+	unsigned int xid;
+	char *ref_paths[CACHE_MAX_ENTRIES];
+	int count = 0;
+	struct cache_entry *ce;
+
+	/*
+	 * Refresh all cached entries.  Get all new referrals outside critical section to avoid
+	 * starvation while performing SMB2 IOCTL on broken or slow connections.
+
+	 * The cache entries may cover more paths than the active mounts
+	 * (e.g. domain-based DFS referrals or multi tier DFS setups).
+	 */
+	down_read(&htable_rw_lock);
+	for (i = 0; i < CACHE_HTABLE_SIZE; i++) {
+		struct hlist_head *l = &cache_htable[i];
+
+		hlist_for_each_entry(ce, l, hlist) {
+			if (count == ARRAY_SIZE(ref_paths))
+				goto out_unlock;
+			if (hlist_unhashed(&ce->hlist) || !cache_entry_expired(ce) ||
+			    IS_ERR(find_ipc_from_server_path(sessions, ce->path)))
+				continue;
+			ref_paths[count++] = kstrdup(ce->path, GFP_ATOMIC);
+		}
+	}
+
+out_unlock:
+	up_read(&htable_rw_lock);
+
+	for (i = 0; i < count; i++) {
+		char *path = ref_paths[i];
+		struct dfs_info3_param *refs = NULL;
+		int numrefs = 0;
+		int rc = 0;
+
+		if (!path)
+			continue;
+
+		ses = find_ipc_from_server_path(sessions, path);
+		if (IS_ERR(ses))
+			goto next_referral;
+
+		xid = get_xid();
+		rc = get_dfs_referral(xid, ses, path, &refs, &numrefs);
+		free_xid(xid);
+
+		if (!rc) {
+			down_write(&htable_rw_lock);
+			ce = lookup_cache_entry(path);
+			/*
+			 * We need to re-check it because other tasks might have it deleted or
+			 * updated.
+			 */
+			if (!IS_ERR(ce) && cache_entry_expired(ce))
+				update_cache_entry_locked(ce, refs, numrefs);
+			up_write(&htable_rw_lock);
+		}
+
+next_referral:
+		kfree(path);
+		free_dfs_info_array(refs, numrefs);
+	}
+}
+
+/*
+ * Worker that will refresh DFS cache and active mounts based on lowest TTL value from a DFS
+ * referral.
+ */
+static void refresh_cache_worker(struct work_struct *work)
+{
+	struct list_head mglist;
+	struct mount_group *mg, *tmp_mg;
+	struct cifs_ses *sessions[CACHE_MAX_ENTRIES + 1] = {NULL};
+	int max_sessions = ARRAY_SIZE(sessions) - 1;
+	int i = 0, count;
+
+	INIT_LIST_HEAD(&mglist);
+
+	/* Get refereces of mount groups */
+	mutex_lock(&mount_group_list_lock);
+	list_for_each_entry(mg, &mount_group_list, list) {
+		kref_get(&mg->refcount);
+		list_add(&mg->refresh_list, &mglist);
+	}
+	mutex_unlock(&mount_group_list_lock);
+
+	/* Fill in local array with an NULL-terminated list of all referral server sessions */
+	list_for_each_entry(mg, &mglist, refresh_list) {
+		if (i >= max_sessions)
+			break;
+
+		spin_lock(&mg->lock);
+		if (i + mg->num_sessions > max_sessions)
+			count = max_sessions - i;
+		else
+			count = mg->num_sessions;
+		memcpy(&sessions[i], mg->sessions, count * sizeof(mg->sessions[0]));
+		spin_unlock(&mg->lock);
+		i += count;
+	}
+
+	if (sessions[0]) {
+		/* Refresh all active mounts and cached entries */
+		refresh_mounts(sessions);
+		refresh_cache(sessions);
+	}
+
+	list_for_each_entry_safe(mg, tmp_mg, &mglist, refresh_list) {
+		list_del_init(&mg->refresh_list);
+		kref_put(&mg->refcount, mount_group_release);
+	}
+
+	spin_lock(&cache_ttl_lock);
+	queue_delayed_work(dfscache_wq, &refresh_task, cache_ttl * HZ);
+	spin_unlock(&cache_ttl_lock);
+}