Merge tag 'timers_urgent_for_v6.13_rc1' of git://git.kernel.org/pub/scm/linux/kernel...

[drm/drm-misc.git] / fs / smb / client / dfs_cache.c

// 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.h"

#include "dfs_cache.h"

#define CACHE_HTABLE_SIZE       512
#define CACHE_MAX_ENTRIES       1024
#define CACHE_MIN_TTL           120 /* 2 minutes */
#define CACHE_DEFAULT_TTL       300 /* 5 minutes */

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;
};

static struct kmem_cache *cache_slab __read_mostly;
struct workqueue_struct *dfscache_wq;

atomic_t dfs_cache_ttl;

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);

/**
 * 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)
{
        cifs_dbg(FYI, "%s: %s\n", __func__, ce->path);
        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,
                                   str_yes_no(DFS_INTERLINK(ce->hdr_flags)),
                                   ce->path_consumed, str_yes_no(cache_entry_expired(ce)));

                        list_for_each_entry(t, &ce->tlist, list) {
                                seq_printf(m, "  %s%s\n",
                                           t->name,
                                           READ_ONCE(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,
                         READ_ONCE(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,
                 str_yes_no(DFS_INTERLINK(ce->hdr_flags)),
                 ce->path_consumed,
                 str_yes_no(cache_entry_expired(ce)));
        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_UNBOUND|WQ_FREEZABLE|WQ_MEM_RECLAIM,
                                      0);
        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);
        atomic_set(&dfs_cache_ttl, CACHE_DEFAULT_TTL);
        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 = READ_ONCE(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)
{
        struct cache_dfs_tgt *target;
        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++;
        }

        target = list_first_entry_or_null(&ce->tlist, struct cache_dfs_tgt,
                                          list);
        WRITE_ONCE(ce->tgthint, target);

        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;
}

/* Remove all referrals that have a single target or oldest entry */
static void purge_cache(void)
{
        int i;
        struct cache_entry *ce;
        struct cache_entry *oldest = NULL;

        for (i = 0; i < CACHE_HTABLE_SIZE; i++) {
                struct hlist_head *l = &cache_htable[i];
                struct hlist_node *n;

                hlist_for_each_entry_safe(ce, n, l, hlist) {
                        if (hlist_unhashed(&ce->hlist))
                                continue;
                        if (ce->numtgts == 1)
                                flush_cache_ent(ce);
                        else if (!oldest ||
                                 timespec64_compare(&ce->etime,
                                                    &oldest->etime) < 0)
                                oldest = ce;
                }
        }

        if (atomic_read(&cache_count) >= CACHE_MAX_ENTRIES && oldest)
                flush_cache_ent(oldest);
}

/* Add a new DFS cache entry */
static struct cache_entry *add_cache_entry_locked(struct dfs_info3_param *refs,
                                                  int numrefs)
{
        int rc;
        struct cache_entry *ce;
        unsigned int hash;
        int ttl;

        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);
                purge_cache();
        }

        rc = cache_entry_hash(refs[0].path_name, strlen(refs[0].path_name), &hash);
        if (rc)
                return ERR_PTR(rc);

        ce = alloc_cache_entry(refs, numrefs);
        if (IS_ERR(ce))
                return ce;

        ttl = min_t(int, atomic_read(&dfs_cache_ttl), ce->ttl);
        atomic_set(&dfs_cache_ttl, ttl);

        hlist_add_head(&ce->hlist, &cache_htable[hash]);
        dump_ce(ce);

        atomic_inc(&cache_count);

        return ce;
}

/* 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 cached entry if successful.
 * Return ERR_PTR(-ENOENT) if the entry is not found.
 * Return error ptr otherwise.
 */
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)
{
        unload_nls(cache_cp);
        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)
{
        struct cache_dfs_tgt *target;
        char *th = NULL;
        int rc;

        WARN_ON(!rwsem_is_locked(&htable_rw_lock));

        target = READ_ONCE(ce->tgthint);
        if (target) {
                th = kstrdup(target->name, 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;

        *refs = NULL;
        *numrefs = 0;

        if (!ses || !ses->server || !ses->server->ops->get_dfs_refer)
                return -EOPNOTSUPP;
        if (unlikely(!cache_cp))
                return -EINVAL;

        cifs_dbg(FYI, "%s: ipc=%s referral=%s\n", __func__, ses->tcon_ipc->tree_name, path);
        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.
 *
 * On success, return entry with acquired lock for reading, otherwise error ptr.
 */
static struct cache_entry *cache_refresh_path(const unsigned int xid,
                                              struct cifs_ses *ses,
                                              const char *path,
                                              bool force_refresh)
{
        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)) {
                if (!force_refresh && !cache_entry_expired(ce))
                        return ce;
        } else if (PTR_ERR(ce) != -ENOENT) {
                up_read(&htable_rw_lock);
                return ce;
        }

        /*
         * 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, or it is a forced
         * refresh.
         * 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) {
                ce = ERR_PTR(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 (force_refresh || cache_entry_expired(ce)) {
                        rc = update_cache_entry_locked(ce, refs, numrefs);
                        if (rc)
                                ce = ERR_PTR(rc);
                }
        } else if (PTR_ERR(ce) == -ENOENT) {
                ce = add_cache_entry_locked(refs, numrefs);
        }

        if (IS_ERR(ce)) {
                up_write(&htable_rw_lock);
                goto out;
        }

        downgrade_write(&htable_rw_lock);
out:
        free_dfs_info_array(refs, numrefs);
        return ce;
}

/*
 * 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 (READ_ONCE(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);

        ce = cache_refresh_path(xid, ses, npath, false);
        if (IS_ERR(ce)) {
                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_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.
 */
void dfs_cache_noreq_update_tgthint(const char *path, const struct dfs_cache_tgt_iterator *it)
{
        struct cache_dfs_tgt *t;
        struct cache_entry *ce;

        if (!path || !it)
                return;

        cifs_dbg(FYI, "%s: path: %s\n", __func__, path);

        down_read(&htable_rw_lock);

        ce = lookup_cache_entry(path);
        if (IS_ERR(ce))
                goto out_unlock;

        t = READ_ONCE(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)) {
                        WRITE_ONCE(ce->tgthint, t);
                        cifs_dbg(FYI, "%s: new target hint: %s\n", __func__,
                                 it->it_name);
                        break;
                }
        }

out_unlock:
        up_read(&htable_rw_lock);
}

/**
 * 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;
}

/* 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 cifs_tcon *tcon, const char *s1)
{
        struct TCP_Server_Info *server = tcon->ses->server;
        struct sockaddr_storage ss;
        const char *host;
        const char *s2 = &tcon->tree_name[1];
        size_t hostlen;
        char unc[sizeof("\\\\") + SERVER_NAME_LENGTH] = {0};
        bool match;
        int rc;

        if (strcasecmp(s2, s1))
                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.
         */
        extract_unc_hostname(s1, &host, &hostlen);
        scnprintf(unc, sizeof(unc), "\\\\%.*s", (int)hostlen, host);

        rc = dns_resolve_server_name_to_ip(unc, (struct sockaddr *)&ss, NULL);
        if (rc < 0) {
                cifs_dbg(FYI, "%s: could not resolve %.*s. assuming server address matches.\n",
                         __func__, (int)hostlen, host);
                return true;
        }

        cifs_server_lock(server);
        match = cifs_match_ipaddr((struct sockaddr *)&server->dstaddr, (struct sockaddr *)&ss);
        cifs_server_unlock(server);

        return match;
}

static bool is_ses_good(struct cifs_ses *ses)
{
        struct TCP_Server_Info *server = ses->server;
        struct cifs_tcon *tcon = ses->tcon_ipc;
        bool ret;

        spin_lock(&ses->ses_lock);
        spin_lock(&ses->chan_lock);
        ret = !cifs_chan_needs_reconnect(ses, server) &&
                ses->ses_status == SES_GOOD &&
                !tcon->need_reconnect;
        spin_unlock(&ses->chan_lock);
        spin_unlock(&ses->ses_lock);
        return ret;
}

static char *get_ses_refpath(struct cifs_ses *ses)
{
        struct TCP_Server_Info *server = ses->server;
        char *path = ERR_PTR(-ENOENT);

        mutex_lock(&server->refpath_lock);
        if (server->leaf_fullpath) {
                path = kstrdup(server->leaf_fullpath + 1, GFP_ATOMIC);
                if (!path)
                        path = ERR_PTR(-ENOMEM);
        }
        mutex_unlock(&server->refpath_lock);
        return path;
}

/* Refresh dfs referral of @ses */
static void refresh_ses_referral(struct cifs_ses *ses)
{
        struct cache_entry *ce;
        unsigned int xid;
        char *path;
        int rc = 0;

        xid = get_xid();

        path = get_ses_refpath(ses);
        if (IS_ERR(path)) {
                rc = PTR_ERR(path);
                path = NULL;
                goto out;
        }

        ses = CIFS_DFS_ROOT_SES(ses);
        if (!is_ses_good(ses)) {
                cifs_dbg(FYI, "%s: skip cache refresh due to disconnected ipc\n",
                         __func__);
                goto out;
        }

        ce = cache_refresh_path(xid, ses, path, false);
        if (!IS_ERR(ce))
                up_read(&htable_rw_lock);
        else
                rc = PTR_ERR(ce);

out:
        free_xid(xid);
        kfree(path);
}

static int __refresh_tcon_referral(struct cifs_tcon *tcon,
                                   const char *path,
                                   struct dfs_info3_param *refs,
                                   int numrefs, bool force_refresh)
{
        struct cache_entry *ce;
        bool reconnect = force_refresh;
        int rc = 0;
        int i;

        if (unlikely(!numrefs))
                return 0;

        if (force_refresh) {
                for (i = 0; i < numrefs; i++) {
                        /* TODO: include prefix paths in the matching */
                        if (target_share_equal(tcon, refs[i].node_name)) {
                                reconnect = false;
                                break;
                        }
                }
        }

        down_write(&htable_rw_lock);
        ce = lookup_cache_entry(path);
        if (!IS_ERR(ce)) {
                if (force_refresh || cache_entry_expired(ce))
                        rc = update_cache_entry_locked(ce, refs, numrefs);
        } else if (PTR_ERR(ce) == -ENOENT) {
                ce = add_cache_entry_locked(refs, numrefs);
        }
        up_write(&htable_rw_lock);

        if (IS_ERR(ce))
                rc = PTR_ERR(ce);
        if (reconnect) {
                cifs_tcon_dbg(FYI, "%s: mark for reconnect\n", __func__);
                cifs_signal_cifsd_for_reconnect(tcon->ses->server, true);
        }
        return rc;
}

static void refresh_tcon_referral(struct cifs_tcon *tcon, bool force_refresh)
{
        struct dfs_info3_param *refs = NULL;
        struct cache_entry *ce;
        struct cifs_ses *ses;
        unsigned int xid;
        bool needs_refresh;
        char *path;
        int numrefs = 0;
        int rc = 0;

        xid = get_xid();
        ses = tcon->ses;

        path = get_ses_refpath(ses);
        if (IS_ERR(path)) {
                rc = PTR_ERR(path);
                path = NULL;
                goto out;
        }

        down_read(&htable_rw_lock);
        ce = lookup_cache_entry(path);
        needs_refresh = force_refresh || IS_ERR(ce) || cache_entry_expired(ce);
        if (!needs_refresh) {
                up_read(&htable_rw_lock);
                goto out;
        }
        up_read(&htable_rw_lock);

        ses = CIFS_DFS_ROOT_SES(ses);
        if (!is_ses_good(ses)) {
                cifs_dbg(FYI, "%s: skip cache refresh due to disconnected ipc\n",
                         __func__);
                goto out;
        }

        rc = get_dfs_referral(xid, ses, path, &refs, &numrefs);
        if (!rc) {
                rc = __refresh_tcon_referral(tcon, path, refs,
                                             numrefs, force_refresh);
        }

out:
        free_xid(xid);
        kfree(path);
        free_dfs_info_array(refs, numrefs);
}

/**
 * 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;

        if (!cifs_sb || !cifs_sb->master_tlink)
                return -EINVAL;

        tcon = cifs_sb_master_tcon(cifs_sb);

        spin_lock(&tcon->tc_lock);
        if (!tcon->origin_fullpath) {
                spin_unlock(&tcon->tc_lock);
                cifs_dbg(FYI, "%s: not a dfs mount\n", __func__);
                return 0;
        }
        spin_unlock(&tcon->tc_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;

        refresh_tcon_referral(tcon, true);
        return 0;
}

/* Refresh all DFS referrals related to DFS tcon */
void dfs_cache_refresh(struct work_struct *work)
{
        struct cifs_tcon *tcon;
        struct cifs_ses *ses;

        tcon = container_of(work, struct cifs_tcon, dfs_cache_work.work);

        list_for_each_entry(ses, &tcon->dfs_ses_list, dlist)
                refresh_ses_referral(ses);
        refresh_tcon_referral(tcon, false);

        queue_delayed_work(dfscache_wq, &tcon->dfs_cache_work,
                           atomic_read(&dfs_cache_ttl) * HZ);
}