releases/6.3.13/smb-client-fix-shared-dfs-root-mounts-with-different.patch

From 75074d4ebb2eec97e5da6c30c51dd714e8fc8099 Mon Sep 17 00:00:00 2001
From: Sasha Levin <sashal@kernel.org>
Date: Mon, 26 Jun 2023 16:04:17 -0300
Subject: smb: client: fix shared DFS root mounts with different prefixes

From: Paulo Alcantara <pc@manguebit.com>

[ Upstream commit 3ae872de410751fe5e629e04da491a632d95201c ]

When having two DFS root mounts that are connected to same namespace,
same mount options but different prefix paths, we can't really use the
shared @server->origin_fullpath when chasing DFS links in them.

Move the origin_fullpath field to cifs_tcon structure so when having
shared DFS root mounts with different prefix paths, and we need to
chase any DFS links, dfs_get_automount_devname() will pick up the
correct full path out of the @tcon that will be used for the new
mount.

Before patch

  mount.cifs //dom/dfs/dir /mnt/1 -o ...
  mount.cifs //dom/dfs /mnt/2 -o ...
  # shared server, ses, tcon
  # server: origin_fullpath=//dom/dfs/dir

  # @server->origin_fullpath + '/dir/link1'
  $ ls /mnt/2/dir/link1
  ls: cannot open directory '/mnt/2/dir/link1': No such file or directory

After patch

  mount.cifs //dom/dfs/dir /mnt/1 -o ...
  mount.cifs //dom/dfs /mnt/2 -o ...
  # shared server & ses
  # tcon_1: origin_fullpath=//dom/dfs/dir
  # tcon_2: origin_fullpath=//dom/dfs

  # @tcon_2->origin_fullpath + '/dir/link1'
  $ ls /mnt/2/dir/link1
  dir0  dir1  dir10  dir3  dir5  dir6  dir7  dir9  target2_file.txt  tsub

Fixes: 8e3554150d6c ("cifs: fix sharing of DFS connections")
Signed-off-by: Paulo Alcantara (SUSE) <pc@manguebit.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/cifs/cifs_debug.c | 16 +++++-----
 fs/cifs/cifsglob.h   | 10 +++----
 fs/cifs/cifsproto.h  |  2 +-
 fs/cifs/connect.c    | 70 +++++++++++++++++++++++++-------------------
 fs/cifs/dfs.c        | 55 +++++++++++++---------------------
 fs/cifs/dfs.h        | 19 ++++++------
 fs/cifs/dfs_cache.c  |  8 +++--
 fs/cifs/misc.c       | 38 ++++++++++++++++++------
 8 files changed, 118 insertions(+), 100 deletions(-)

diff --git a/fs/cifs/cifs_debug.c b/fs/cifs/cifs_debug.c
index d4ed200a94714..7e0667bdfba07 100644
--- a/fs/cifs/cifs_debug.c
+++ b/fs/cifs/cifs_debug.c
@@ -121,6 +121,12 @@ static void cifs_debug_tcon(struct seq_file *m, struct cifs_tcon *tcon)
 		seq_puts(m, " nosparse");
 	if (tcon->need_reconnect)
 		seq_puts(m, "\tDISCONNECTED ");
+	spin_lock(&tcon->tc_lock);
+	if (tcon->origin_fullpath) {
+		seq_printf(m, "\n\tDFS origin fullpath: %s",
+			   tcon->origin_fullpath);
+	}
+	spin_unlock(&tcon->tc_lock);
 	seq_putc(m, '\n');
 }
 
@@ -377,13 +383,9 @@ static int cifs_debug_data_proc_show(struct seq_file *m, void *v)
 		seq_printf(m, "\nIn Send: %d In MaxReq Wait: %d",
 				atomic_read(&server->in_send),
 				atomic_read(&server->num_waiters));
-		if (IS_ENABLED(CONFIG_CIFS_DFS_UPCALL)) {
-			if (server->origin_fullpath)
-				seq_printf(m, "\nDFS origin full path: %s",
-					   server->origin_fullpath);
-			if (server->leaf_fullpath)
-				seq_printf(m, "\nDFS leaf full path:   %s",
-					   server->leaf_fullpath);
+		if (server->leaf_fullpath) {
+			seq_printf(m, "\nDFS leaf full path: %s",
+				   server->leaf_fullpath);
 		}
 
 		seq_printf(m, "\n\n\tSessions: ");
diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h
index 5f8fd20951af3..56d440772e029 100644
--- a/fs/cifs/cifsglob.h
+++ b/fs/cifs/cifsglob.h
@@ -736,23 +736,20 @@ struct TCP_Server_Info {
 #endif
 	struct mutex refpath_lock; /* protects leaf_fullpath */
 	/*
-	 * origin_fullpath: Canonical copy of smb3_fs_context::source.
-	 *                  It is used for matching existing DFS tcons.
-	 *
 	 * leaf_fullpath: Canonical DFS referral path related to this
 	 *                connection.
 	 *                It is used in DFS cache refresher, reconnect and may
 	 *                change due to nested DFS links.
 	 *
-	 * Both protected by @refpath_lock and @srv_lock.  The @refpath_lock is
-	 * mosly used for not requiring a copy of @leaf_fullpath when getting
+	 * Protected by @refpath_lock and @srv_lock.  The @refpath_lock is
+	 * mostly used for not requiring a copy of @leaf_fullpath when getting
 	 * cached or new DFS referrals (which might also sleep during I/O).
 	 * While @srv_lock is held for making string and NULL comparions against
 	 * both fields as in mount(2) and cache refresh.
 	 *
 	 * format: \\HOST\SHARE[\OPTIONAL PATH]
 	 */
-	char *origin_fullpath, *leaf_fullpath;
+	char *leaf_fullpath;
 };
 
 static inline bool is_smb1(struct TCP_Server_Info *server)
@@ -1242,6 +1239,7 @@ struct cifs_tcon {
 	struct delayed_work dfs_cache_work;
 #endif
 	struct delayed_work	query_interfaces; /* query interfaces workqueue job */
+	char *origin_fullpath; /* canonical copy of smb3_fs_context::source */
 };
 
 /*
diff --git a/fs/cifs/cifsproto.h b/fs/cifs/cifsproto.h
index c1c704990b986..16eac67fd48ac 100644
--- a/fs/cifs/cifsproto.h
+++ b/fs/cifs/cifsproto.h
@@ -649,7 +649,7 @@ int smb2_parse_query_directory(struct cifs_tcon *tcon, struct kvec *rsp_iov,
 			       int resp_buftype,
 			       struct cifs_search_info *srch_inf);
 
-struct super_block *cifs_get_tcp_super(struct TCP_Server_Info *server);
+struct super_block *cifs_get_dfs_tcon_super(struct cifs_tcon *tcon);
 void cifs_put_tcp_super(struct super_block *sb);
 int cifs_update_super_prepath(struct cifs_sb_info *cifs_sb, char *prefix);
 char *extract_hostname(const char *unc);
diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index 1250d156619b7..f0189afd940cf 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -996,7 +996,6 @@ static void clean_demultiplex_info(struct TCP_Server_Info *server)
 		 */
 	}
 
-	kfree(server->origin_fullpath);
 	kfree(server->leaf_fullpath);
 	kfree(server);
 
@@ -1386,7 +1385,9 @@ match_security(struct TCP_Server_Info *server, struct smb3_fs_context *ctx)
 }
 
 /* this function must be called with srv_lock held */
-static int match_server(struct TCP_Server_Info *server, struct smb3_fs_context *ctx)
+static int match_server(struct TCP_Server_Info *server,
+			struct smb3_fs_context *ctx,
+			bool match_super)
 {
 	struct sockaddr *addr = (struct sockaddr *)&ctx->dstaddr;
 
@@ -1417,36 +1418,38 @@ static int match_server(struct TCP_Server_Info *server, struct smb3_fs_context *
 			       (struct sockaddr *)&server->srcaddr))
 		return 0;
 	/*
-	 * - Match for an DFS tcon (@server->origin_fullpath).
-	 * - Match for an DFS root server connection (@server->leaf_fullpath).
-	 * - If none of the above and @ctx->leaf_fullpath is set, then
-	 *   it is a new DFS connection.
-	 * - If 'nodfs' mount option was passed, then match only connections
-	 *   that have no DFS referrals set
-	 *   (e.g. can't failover to other targets).
+	 * When matching cifs.ko superblocks (@match_super == true), we can't
+	 * really match either @server->leaf_fullpath or @server->dstaddr
+	 * directly since this @server might belong to a completely different
+	 * server -- in case of domain-based DFS referrals or DFS links -- as
+	 * provided earlier by mount(2) through 'source' and 'ip' options.
+	 *
+	 * Otherwise, match the DFS referral in @server->leaf_fullpath or the
+	 * destination address in @server->dstaddr.
+	 *
+	 * When using 'nodfs' mount option, we avoid sharing it with DFS
+	 * connections as they might failover.
 	 */
-	if (!ctx->nodfs) {
-		if (ctx->source && server->origin_fullpath) {
-			if (!dfs_src_pathname_equal(ctx->source,
-						    server->origin_fullpath))
+	if (!match_super) {
+		if (!ctx->nodfs) {
+			if (server->leaf_fullpath) {
+				if (!ctx->leaf_fullpath ||
+				    strcasecmp(server->leaf_fullpath,
+					       ctx->leaf_fullpath))
+					return 0;
+			} else if (ctx->leaf_fullpath) {
 				return 0;
+			}
 		} else if (server->leaf_fullpath) {
-			if (!ctx->leaf_fullpath ||
-			    strcasecmp(server->leaf_fullpath,
-				       ctx->leaf_fullpath))
-				return 0;
-		} else if (ctx->leaf_fullpath) {
 			return 0;
 		}
-	} else if (server->origin_fullpath || server->leaf_fullpath) {
-		return 0;
 	}
 
 	/*
 	 * Match for a regular connection (address/hostname/port) which has no
 	 * DFS referrals set.
 	 */
-	if (!server->origin_fullpath && !server->leaf_fullpath &&
+	if (!server->leaf_fullpath &&
 	    (strcasecmp(server->hostname, ctx->server_hostname) ||
 	     !match_server_address(server, addr) ||
 	     !match_port(server, addr)))
@@ -1482,7 +1485,8 @@ cifs_find_tcp_session(struct smb3_fs_context *ctx)
 		 * Skip ses channels since they're only handled in lower layers
 		 * (e.g. cifs_send_recv).
 		 */
-		if (CIFS_SERVER_IS_CHAN(server) || !match_server(server, ctx)) {
+		if (CIFS_SERVER_IS_CHAN(server) ||
+		    !match_server(server, ctx, false)) {
 			spin_unlock(&server->srv_lock);
 			continue;
 		}
@@ -2270,10 +2274,16 @@ static int match_tcon(struct cifs_tcon *tcon, struct smb3_fs_context *ctx)
 
 	if (tcon->status == TID_EXITING)
 		return 0;
-	/* Skip UNC validation when matching DFS connections or superblocks */
-	if (!server->origin_fullpath && !server->leaf_fullpath &&
-	    strncmp(tcon->tree_name, ctx->UNC, MAX_TREE_SIZE))
+
+	if (tcon->origin_fullpath) {
+		if (!ctx->source ||
+		    !dfs_src_pathname_equal(ctx->source,
+					    tcon->origin_fullpath))
+			return 0;
+	} else if (!server->leaf_fullpath &&
+		   strncmp(tcon->tree_name, ctx->UNC, MAX_TREE_SIZE)) {
 		return 0;
+	}
 	if (tcon->seal != ctx->seal)
 		return 0;
 	if (tcon->snapshot_time != ctx->snapshot_time)
@@ -2672,7 +2682,7 @@ compare_mount_options(struct super_block *sb, struct cifs_mnt_data *mnt_data)
 }
 
 static int match_prepath(struct super_block *sb,
-			 struct TCP_Server_Info *server,
+			 struct cifs_tcon *tcon,
 			 struct cifs_mnt_data *mnt_data)
 {
 	struct smb3_fs_context *ctx = mnt_data->ctx;
@@ -2683,8 +2693,8 @@ static int match_prepath(struct super_block *sb,
 	bool new_set = (new->mnt_cifs_flags & CIFS_MOUNT_USE_PREFIX_PATH) &&
 		new->prepath;
 
-	if (server->origin_fullpath &&
-	    dfs_src_pathname_equal(server->origin_fullpath, ctx->source))
+	if (tcon->origin_fullpath &&
+	    dfs_src_pathname_equal(tcon->origin_fullpath, ctx->source))
 		return 1;
 
 	if (old_set && new_set && !strcmp(new->prepath, old->prepath))
@@ -2732,10 +2742,10 @@ cifs_match_super(struct super_block *sb, void *data)
 	spin_lock(&ses->ses_lock);
 	spin_lock(&ses->chan_lock);
 	spin_lock(&tcon->tc_lock);
-	if (!match_server(tcp_srv, ctx) ||
+	if (!match_server(tcp_srv, ctx, true) ||
 	    !match_session(ses, ctx) ||
 	    !match_tcon(tcon, ctx) ||
-	    !match_prepath(sb, tcp_srv, mnt_data)) {
+	    !match_prepath(sb, tcon, mnt_data)) {
 		rc = 0;
 		goto out;
 	}
diff --git a/fs/cifs/dfs.c b/fs/cifs/dfs.c
index 2390b2fedd6a3..267536a7531df 100644
--- a/fs/cifs/dfs.c
+++ b/fs/cifs/dfs.c
@@ -249,14 +249,12 @@ static int __dfs_mount_share(struct cifs_mount_ctx *mnt_ctx)
 		server = mnt_ctx->server;
 		tcon = mnt_ctx->tcon;
 
-		mutex_lock(&server->refpath_lock);
-		spin_lock(&server->srv_lock);
-		if (!server->origin_fullpath) {
-			server->origin_fullpath = origin_fullpath;
+		spin_lock(&tcon->tc_lock);
+		if (!tcon->origin_fullpath) {
+			tcon->origin_fullpath = origin_fullpath;
 			origin_fullpath = NULL;
 		}
-		spin_unlock(&server->srv_lock);
-		mutex_unlock(&server->refpath_lock);
+		spin_unlock(&tcon->tc_lock);
 
 		if (list_empty(&tcon->dfs_ses_list)) {
 			list_replace_init(&mnt_ctx->dfs_ses_list,
@@ -279,18 +277,13 @@ int dfs_mount_share(struct cifs_mount_ctx *mnt_ctx, bool *isdfs)
 {
 	struct smb3_fs_context *ctx = mnt_ctx->fs_ctx;
 	struct cifs_ses *ses;
-	char *source = ctx->source;
 	bool nodfs = ctx->nodfs;
 	int rc;
 
 	*isdfs = false;
-	/* Temporarily set @ctx->source to NULL as we're not matching DFS
-	 * superblocks yet.  See cifs_match_super() and match_server().
-	 */
-	ctx->source = NULL;
 	rc = get_session(mnt_ctx, NULL);
 	if (rc)
-		goto out;
+		return rc;
 
 	ctx->dfs_root_ses = mnt_ctx->ses;
 	/*
@@ -304,7 +297,7 @@ int dfs_mount_share(struct cifs_mount_ctx *mnt_ctx, bool *isdfs)
 		rc = dfs_get_referral(mnt_ctx, ctx->UNC + 1, NULL, NULL);
 		if (rc) {
 			if (rc != -ENOENT && rc != -EOPNOTSUPP && rc != -EIO)
-				goto out;
+				return rc;
 			nodfs = true;
 		}
 	}
@@ -312,7 +305,7 @@ int dfs_mount_share(struct cifs_mount_ctx *mnt_ctx, bool *isdfs)
 		rc = cifs_mount_get_tcon(mnt_ctx);
 		if (!rc)
 			rc = cifs_is_path_remote(mnt_ctx);
-		goto out;
+		return rc;
 	}
 
 	*isdfs = true;
@@ -328,12 +321,7 @@ int dfs_mount_share(struct cifs_mount_ctx *mnt_ctx, bool *isdfs)
 	rc = __dfs_mount_share(mnt_ctx);
 	if (ses == ctx->dfs_root_ses)
 		cifs_put_smb_ses(ses);
-out:
-	/*
-	 * Restore previous value of @ctx->source so DFS superblock can be
-	 * matched in cifs_match_super().
-	 */
-	ctx->source = source;
+
 	return rc;
 }
 
@@ -567,11 +555,11 @@ int cifs_tree_connect(const unsigned int xid, struct cifs_tcon *tcon, const stru
 	int rc;
 	struct TCP_Server_Info *server = tcon->ses->server;
 	const struct smb_version_operations *ops = server->ops;
-	struct super_block *sb = NULL;
-	struct cifs_sb_info *cifs_sb;
 	struct dfs_cache_tgt_list tl = DFS_CACHE_TGT_LIST_INIT(tl);
-	char *tree;
+	struct cifs_sb_info *cifs_sb = NULL;
+	struct super_block *sb = NULL;
 	struct dfs_info3_param ref = {0};
+	char *tree;
 
 	/* only send once per connect */
 	spin_lock(&tcon->tc_lock);
@@ -603,19 +591,18 @@ int cifs_tree_connect(const unsigned int xid, struct cifs_tcon *tcon, const stru
 		goto out;
 	}
 
-	sb = cifs_get_tcp_super(server);
-	if (IS_ERR(sb)) {
-		rc = PTR_ERR(sb);
-		cifs_dbg(VFS, "%s: could not find superblock: %d\n", __func__, rc);
-		goto out;
-	}
-
-	cifs_sb = CIFS_SB(sb);
+	sb = cifs_get_dfs_tcon_super(tcon);
+	if (!IS_ERR(sb))
+		cifs_sb = CIFS_SB(sb);
 
-	/* If it is not dfs or there was no cached dfs referral, then reconnect to same share */
-	if (!server->leaf_fullpath ||
+	/*
+	 * Tree connect to last share in @tcon->tree_name whether dfs super or
+	 * cached dfs referral was not found.
+	 */
+	if (!cifs_sb || !server->leaf_fullpath ||
 	    dfs_cache_noreq_find(server->leaf_fullpath + 1, &ref, &tl)) {
-		rc = ops->tree_connect(xid, tcon->ses, tcon->tree_name, tcon, cifs_sb->local_nls);
+		rc = ops->tree_connect(xid, tcon->ses, tcon->tree_name, tcon,
+				       cifs_sb ? cifs_sb->local_nls : nlsc);
 		goto out;
 	}
 
diff --git a/fs/cifs/dfs.h b/fs/cifs/dfs.h
index 1c90df5ecfbda..98e9d2aca6a7a 100644
--- a/fs/cifs/dfs.h
+++ b/fs/cifs/dfs.h
@@ -39,16 +39,15 @@ static inline char *dfs_get_automount_devname(struct dentry *dentry, void *page)
 {
 	struct cifs_sb_info *cifs_sb = CIFS_SB(dentry->d_sb);
 	struct cifs_tcon *tcon = cifs_sb_master_tcon(cifs_sb);
-	struct TCP_Server_Info *server = tcon->ses->server;
 	size_t len;
 	char *s;
 
-	spin_lock(&server->srv_lock);
-	if (unlikely(!server->origin_fullpath)) {
-		spin_unlock(&server->srv_lock);
+	spin_lock(&tcon->tc_lock);
+	if (unlikely(!tcon->origin_fullpath)) {
+		spin_unlock(&tcon->tc_lock);
 		return ERR_PTR(-EREMOTE);
 	}
-	spin_unlock(&server->srv_lock);
+	spin_unlock(&tcon->tc_lock);
 
 	s = dentry_path_raw(dentry, page, PATH_MAX);
 	if (IS_ERR(s))
@@ -57,16 +56,16 @@ static inline char *dfs_get_automount_devname(struct dentry *dentry, void *page)
 	if (!s[1])
 		s++;
 
-	spin_lock(&server->srv_lock);
-	len = strlen(server->origin_fullpath);
+	spin_lock(&tcon->tc_lock);
+	len = strlen(tcon->origin_fullpath);
 	if (s < (char *)page + len) {
-		spin_unlock(&server->srv_lock);
+		spin_unlock(&tcon->tc_lock);
 		return ERR_PTR(-ENAMETOOLONG);
 	}
 
 	s -= len;
-	memcpy(s, server->origin_fullpath, len);
-	spin_unlock(&server->srv_lock);
+	memcpy(s, tcon->origin_fullpath, len);
+	spin_unlock(&tcon->tc_lock);
 	convert_delimiter(s, '/');
 
 	return s;
diff --git a/fs/cifs/dfs_cache.c b/fs/cifs/dfs_cache.c
index 1513b2709889b..33adf43a01f1d 100644
--- a/fs/cifs/dfs_cache.c
+++ b/fs/cifs/dfs_cache.c
@@ -1248,18 +1248,20 @@ static int refresh_tcon(struct cifs_tcon *tcon, bool force_refresh)
 int dfs_cache_remount_fs(struct cifs_sb_info *cifs_sb)
 {
 	struct cifs_tcon *tcon;
-	struct TCP_Server_Info *server;
 
 	if (!cifs_sb || !cifs_sb->master_tlink)
 		return -EINVAL;
 
 	tcon = cifs_sb_master_tcon(cifs_sb);
-	server = tcon->ses->server;
 
-	if (!server->origin_fullpath) {
+	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).
diff --git a/fs/cifs/misc.c b/fs/cifs/misc.c
index cd914be905b24..b0dedc26643b6 100644
--- a/fs/cifs/misc.c
+++ b/fs/cifs/misc.c
@@ -156,6 +156,7 @@ tconInfoFree(struct cifs_tcon *tcon)
 #ifdef CONFIG_CIFS_DFS_UPCALL
 	dfs_put_root_smb_sessions(&tcon->dfs_ses_list);
 #endif
+	kfree(tcon->origin_fullpath);
 	kfree(tcon);
 }
 
@@ -1106,20 +1107,25 @@ struct super_cb_data {
 	struct super_block *sb;
 };
 
-static void tcp_super_cb(struct super_block *sb, void *arg)
+static void tcon_super_cb(struct super_block *sb, void *arg)
 {
 	struct super_cb_data *sd = arg;
-	struct TCP_Server_Info *server = sd->data;
 	struct cifs_sb_info *cifs_sb;
-	struct cifs_tcon *tcon;
+	struct cifs_tcon *t1 = sd->data, *t2;
 
 	if (sd->sb)
 		return;
 
 	cifs_sb = CIFS_SB(sb);
-	tcon = cifs_sb_master_tcon(cifs_sb);
-	if (tcon->ses->server == server)
+	t2 = cifs_sb_master_tcon(cifs_sb);
+
+	spin_lock(&t2->tc_lock);
+	if (t1->ses == t2->ses &&
+	    t1->ses->server == t2->ses->server &&
+	    t2->origin_fullpath &&
+	    dfs_src_pathname_equal(t2->origin_fullpath, t1->origin_fullpath))
 		sd->sb = sb;
+	spin_unlock(&t2->tc_lock);
 }
 
 static struct super_block *__cifs_get_super(void (*f)(struct super_block *, void *),
@@ -1145,6 +1151,7 @@ static struct super_block *__cifs_get_super(void (*f)(struct super_block *, void
 			return sd.sb;
 		}
 	}
+	pr_warn_once("%s: could not find dfs superblock\n", __func__);
 	return ERR_PTR(-EINVAL);
 }
 
@@ -1154,9 +1161,15 @@ static void __cifs_put_super(struct super_block *sb)
 		cifs_sb_deactive(sb);
 }
 
-struct super_block *cifs_get_tcp_super(struct TCP_Server_Info *server)
+struct super_block *cifs_get_dfs_tcon_super(struct cifs_tcon *tcon)
 {
-	return __cifs_get_super(tcp_super_cb, server);
+	spin_lock(&tcon->tc_lock);
+	if (!tcon->origin_fullpath) {
+		spin_unlock(&tcon->tc_lock);
+		return ERR_PTR(-ENOENT);
+	}
+	spin_unlock(&tcon->tc_lock);
+	return __cifs_get_super(tcon_super_cb, tcon);
 }
 
 void cifs_put_tcp_super(struct super_block *sb)
@@ -1238,9 +1251,16 @@ int cifs_inval_name_dfs_link_error(const unsigned int xid,
 	 */
 	if (strlen(full_path) < 2 || !cifs_sb ||
 	    (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_NO_DFS) ||
-	    !is_tcon_dfs(tcon) || !ses->server->origin_fullpath)
+	    !is_tcon_dfs(tcon))
 		return 0;
 
+	spin_lock(&tcon->tc_lock);
+	if (!tcon->origin_fullpath) {
+		spin_unlock(&tcon->tc_lock);
+		return 0;
+	}
+	spin_unlock(&tcon->tc_lock);
+
 	/*
 	 * Slow path - tcon is DFS and @full_path has prefix path, so attempt
 	 * to get a referral to figure out whether it is an DFS link.
@@ -1264,7 +1284,7 @@ int cifs_inval_name_dfs_link_error(const unsigned int xid,
 
 		/*
 		 * XXX: we are not using dfs_cache_find() here because we might
-		 * end filling all the DFS cache and thus potentially
+		 * end up filling all the DFS cache and thus potentially
 		 * removing cached DFS targets that the client would eventually
 		 * need during failover.
 		 */
-- 
2.39.2