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 // 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->treeName))
             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)
 {
     int rc;
     struct cache_entry *ce;
     struct dfs_info3_param *refs = NULL;
     int numrefs = 0;
     bool newent = false;
 
     cifs_dbg(FYI, "%s: search path: %s\n", __func__, path);
 
     down_write(&htable_rw_lock);
 
     ce = lookup_cache_entry(path);
     if (!IS_ERR(ce)) {
         if (!cache_entry_expired(ce)) {
             dump_ce(ce);
             up_write(&htable_rw_lock);
             return 0;
         }
     } else {
         newent = true;
     }
 
     /*
      * 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_unlock;
 
     dump_refs(refs, numrefs);
 
     if (!newent) {
         rc = update_cache_entry_locked(ce, refs, numrefs);
         goto out_unlock;
     }
 
     rc = add_cache_entry_locked(refs, numrefs);
 
 out_unlock:
     up_write(&htable_rw_lock);
     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)
 {
     int rc;
     const char *npath;
     struct cache_entry *ce;
     struct cache_dfs_tgt *t;
 
     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);
 }

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