fs/cifs/dfs.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (c) 2022 Paulo Alcantara <palcantara@suse.de>
  */

 #include <linux/namei.h>
 #include "cifsproto.h"
 #include "cifs_debug.h"
 #include "dns_resolve.h"
 #include "fs_context.h"
 #include "dfs.h"

 /**
  * dfs_parse_target_referral - set fs context for dfs target referral
  *
  * @full_path: full path in UNC format.
  * @ref: dfs referral pointer.
  * @ctx: smb3 fs context pointer.
  *
  * Return zero if dfs referral was parsed correctly, otherwise non-zero.
  */
 int dfs_parse_target_referral(const char *full_path, const struct dfs_info3_param *ref,
 			      struct smb3_fs_context *ctx)
 {
 	int rc;
 	const char *prepath = NULL;
 	char *path;

 	if (!full_path || !*full_path || !ref || !ctx)
 		return -EINVAL;

 	if (WARN_ON_ONCE(!ref->node_name || ref->path_consumed < 0))
 		return -EINVAL;

 	if (strlen(full_path) - ref->path_consumed) {
 		prepath = full_path + ref->path_consumed;
 		/* skip initial delimiter */
 		if (*prepath == '/' || *prepath == '\\')
 			prepath++;
 	}

 	path = cifs_build_devname(ref->node_name, prepath);
 	if (IS_ERR(path))
 		return PTR_ERR(path);

 	rc = smb3_parse_devname(path, ctx);
 	if (rc)
 		goto out;

 	rc = dns_resolve_server_name_to_ip(path, (struct sockaddr *)&ctx->dstaddr, NULL);

 out:
 	kfree(path);
 	return rc;
 }

 /*
  * cifs_build_path_to_root returns full path to root when we do not have an
  * existing connection (tcon)
  */
 static char *build_unc_path_to_root(const struct smb3_fs_context *ctx,
 				    const struct cifs_sb_info *cifs_sb, bool useppath)
 {
 	char *full_path, *pos;
 	unsigned int pplen = useppath && ctx->prepath ? strlen(ctx->prepath) + 1 : 0;
 	unsigned int unc_len = strnlen(ctx->UNC, MAX_TREE_SIZE + 1);

 	if (unc_len > MAX_TREE_SIZE)
 		return ERR_PTR(-EINVAL);

 	full_path = kmalloc(unc_len + pplen + 1, GFP_KERNEL);
 	if (full_path == NULL)
 		return ERR_PTR(-ENOMEM);

 	memcpy(full_path, ctx->UNC, unc_len);
 	pos = full_path + unc_len;

 	if (pplen) {
 		*pos = CIFS_DIR_SEP(cifs_sb);
 		memcpy(pos + 1, ctx->prepath, pplen);
 		pos += pplen;
 	}

 	*pos = '\0'; /* add trailing null */
 	convert_delimiter(full_path, CIFS_DIR_SEP(cifs_sb));
 	cifs_dbg(FYI, "%s: full_path=%s\n", __func__, full_path);
 	return full_path;
 }

 static int get_session(struct cifs_mount_ctx *mnt_ctx, const char *full_path)
 {
 	struct smb3_fs_context *ctx = mnt_ctx->fs_ctx;
 	int rc;

 	ctx->leaf_fullpath = (char *)full_path;
 	rc = cifs_mount_get_session(mnt_ctx);
 	ctx->leaf_fullpath = NULL;

 	return rc;
 }

 static int get_root_smb_session(struct cifs_mount_ctx *mnt_ctx)
 {
 	struct smb3_fs_context *ctx = mnt_ctx->fs_ctx;
 	struct dfs_root_ses *root_ses;
 	struct cifs_ses *ses = mnt_ctx->ses;

 	if (ses) {
 		root_ses = kmalloc(sizeof(*root_ses), GFP_KERNEL);
 		if (!root_ses)
 			return -ENOMEM;

 		INIT_LIST_HEAD(&root_ses->list);

 		spin_lock(&cifs_tcp_ses_lock);
 		ses->ses_count++;
 		spin_unlock(&cifs_tcp_ses_lock);
 		root_ses->ses = ses;
 		list_add_tail(&root_ses->list, &mnt_ctx->dfs_ses_list);
 	}
 	ctx->dfs_root_ses = ses;
 	return 0;
 }

 static int get_dfs_conn(struct cifs_mount_ctx *mnt_ctx, const char *ref_path, const char *full_path,
 			const struct dfs_cache_tgt_iterator *tit)
 {
 	struct smb3_fs_context *ctx = mnt_ctx->fs_ctx;
 	struct dfs_info3_param ref = {};
 	bool is_refsrv = false;
 	int rc, rc2;

 	rc = dfs_cache_get_tgt_referral(ref_path + 1, tit, &ref);
 	if (rc)
 		return rc;

 	rc = dfs_parse_target_referral(full_path + 1, &ref, ctx);
 	if (rc)
 		goto out;

 	cifs_mount_put_conns(mnt_ctx);
 	rc = get_session(mnt_ctx, ref_path);
 	if (rc)
 		goto out;

 	is_refsrv = !!(ref.flags & DFSREF_REFERRAL_SERVER);

 	rc = -EREMOTE;
 	if (ref.flags & DFSREF_STORAGE_SERVER) {
 		rc = cifs_mount_get_tcon(mnt_ctx);
 		if (rc)
 			goto out;

 		/* some servers may not advertise referral capability under ref.flags */
 		is_refsrv |= is_tcon_dfs(mnt_ctx->tcon);

 		rc = cifs_is_path_remote(mnt_ctx);
 	}

 	if (rc == -EREMOTE && is_refsrv) {
 		rc2 = get_root_smb_session(mnt_ctx);
 		if (rc2)
 			rc = rc2;
 	}

 out:
 	free_dfs_info_param(&ref);
 	return rc;
 }

 static int __dfs_mount_share(struct cifs_mount_ctx *mnt_ctx)
 {
 	struct cifs_sb_info *cifs_sb = mnt_ctx->cifs_sb;
 	struct smb3_fs_context *ctx = mnt_ctx->fs_ctx;
 	char *ref_path = NULL, *full_path = NULL;
 	struct dfs_cache_tgt_iterator *tit;
 	struct TCP_Server_Info *server;
 	struct cifs_tcon *tcon;
 	char *origin_fullpath = NULL;
 	int num_links = 0;
 	int rc;

 	ref_path = dfs_get_path(cifs_sb, ctx->UNC);
 	if (IS_ERR(ref_path))
 		return PTR_ERR(ref_path);

 	full_path = build_unc_path_to_root(ctx, cifs_sb, true);
 	if (IS_ERR(full_path)) {
 		rc = PTR_ERR(full_path);
 		full_path = NULL;
 		goto out;
 	}

 	origin_fullpath = kstrdup(full_path, GFP_KERNEL);
 	if (!origin_fullpath) {
 		rc = -ENOMEM;
 		goto out;
 	}

 	do {
 		struct dfs_cache_tgt_list tl = DFS_CACHE_TGT_LIST_INIT(tl);

 		rc = dfs_get_referral(mnt_ctx, ref_path + 1, NULL, &tl);
 		if (rc)
 			break;

 		tit = dfs_cache_get_tgt_iterator(&tl);
 		if (!tit) {
 			cifs_dbg(VFS, "%s: dfs referral (%s) with no targets\n", __func__,
 				 ref_path + 1);
 			rc = -ENOENT;
 			dfs_cache_free_tgts(&tl);
 			break;
 		}

 		do {
 			rc = get_dfs_conn(mnt_ctx, ref_path, full_path, tit);
 			if (!rc)
 				break;
 			if (rc == -EREMOTE) {
 				if (++num_links > MAX_NESTED_LINKS) {
 					rc = -ELOOP;
 					break;
 				}
 				kfree(ref_path);
 				kfree(full_path);
 				ref_path = full_path = NULL;

 				full_path = build_unc_path_to_root(ctx, cifs_sb, true);
 				if (IS_ERR(full_path)) {
 					rc = PTR_ERR(full_path);
 					full_path = NULL;
 				} else {
 					ref_path = dfs_get_path(cifs_sb, full_path);
 					if (IS_ERR(ref_path)) {
 						rc = PTR_ERR(ref_path);
 						ref_path = NULL;
 					}
 				}
 				break;
 			}
 		} while ((tit = dfs_cache_get_next_tgt(&tl, tit)));
 		dfs_cache_free_tgts(&tl);
 	} while (rc == -EREMOTE);

 	if (!rc) {
 		server = mnt_ctx->server;
 		tcon = mnt_ctx->tcon;

 		mutex_lock(&server->refpath_lock);
 		if (!server->origin_fullpath) {
 			server->origin_fullpath = origin_fullpath;
 			server->current_fullpath = server->leaf_fullpath;
 			origin_fullpath = NULL;
 		}
 		mutex_unlock(&server->refpath_lock);

 		if (list_empty(&tcon->dfs_ses_list)) {
 			list_replace_init(&mnt_ctx->dfs_ses_list,
 					  &tcon->dfs_ses_list);
 		} else {
 			dfs_put_root_smb_sessions(&mnt_ctx->dfs_ses_list);
 		}
 	}

 out:
 	kfree(origin_fullpath);
 	kfree(ref_path);
 	kfree(full_path);
 	return rc;
 }

 int dfs_mount_share(struct cifs_mount_ctx *mnt_ctx, bool *isdfs)
 {
 	struct cifs_sb_info *cifs_sb = mnt_ctx->cifs_sb;
 	struct smb3_fs_context *ctx = mnt_ctx->fs_ctx;
 	int rc;

 	*isdfs = false;

 	rc = get_session(mnt_ctx, NULL);
 	if (rc)
 		return rc;
 	ctx->dfs_root_ses = mnt_ctx->ses;
 	/*
 	 * If called with 'nodfs' mount option, then skip DFS resolving.  Otherwise unconditionally
 	 * try to get an DFS referral (even cached) to determine whether it is an DFS mount.
 	 *
 	 * Skip prefix path to provide support for DFS referrals from w2k8 servers which don't seem
 	 * to respond with PATH_NOT_COVERED to requests that include the prefix.
 	 */
 	if ((cifs_sb->mnt_cifs_flags & CIFS_MOUNT_NO_DFS) ||
 	    dfs_get_referral(mnt_ctx, ctx->UNC + 1, NULL, NULL)) {
 		rc = cifs_mount_get_tcon(mnt_ctx);
 		if (rc)
 			return rc;

 		rc = cifs_is_path_remote(mnt_ctx);
 		if (!rc || rc != -EREMOTE)
 			return rc;
 	}

 	*isdfs = true;
 	rc = get_root_smb_session(mnt_ctx);
 	if (rc)
 		return rc;

 	return __dfs_mount_share(mnt_ctx);
 }

 /* Update dfs referral path of superblock */
 static int update_server_fullpath(struct TCP_Server_Info *server, struct cifs_sb_info *cifs_sb,
 				  const char *target)
 {
 	int rc = 0;
 	size_t len = strlen(target);
 	char *refpath, *npath;

 	if (unlikely(len < 2 || *target != '\\'))
 		return -EINVAL;

 	if (target[1] == '\\') {
 		len += 1;
 		refpath = kmalloc(len, GFP_KERNEL);
 		if (!refpath)
 			return -ENOMEM;

 		scnprintf(refpath, len, "%s", target);
 	} else {
 		len += sizeof("\\");
 		refpath = kmalloc(len, GFP_KERNEL);
 		if (!refpath)
 			return -ENOMEM;

 		scnprintf(refpath, len, "\\%s", target);
 	}

 	npath = dfs_cache_canonical_path(refpath, cifs_sb->local_nls, cifs_remap(cifs_sb));
 	kfree(refpath);

 	if (IS_ERR(npath)) {
 		rc = PTR_ERR(npath);
 	} else {
 		mutex_lock(&server->refpath_lock);
 		kfree(server->leaf_fullpath);
 		server->leaf_fullpath = npath;
 		mutex_unlock(&server->refpath_lock);
 		server->current_fullpath = server->leaf_fullpath;
 	}
 	return rc;
 }

 static int target_share_matches_server(struct TCP_Server_Info *server, char *share,
 				       bool *target_match)
 {
 	int rc = 0;
 	const char *dfs_host;
 	size_t dfs_host_len;

 	*target_match = true;
 	extract_unc_hostname(share, &dfs_host, &dfs_host_len);

 	/* Check if hostnames or addresses match */
 	cifs_server_lock(server);
 	if (dfs_host_len != strlen(server->hostname) ||
 	    strncasecmp(dfs_host, server->hostname, dfs_host_len)) {
 		cifs_dbg(FYI, "%s: %.*s doesn't match %s\n", __func__,
 			 (int)dfs_host_len, dfs_host, server->hostname);
 		rc = match_target_ip(server, dfs_host, dfs_host_len, target_match);
 		if (rc)
 			cifs_dbg(VFS, "%s: failed to match target ip: %d\n", __func__, rc);
 	}
 	cifs_server_unlock(server);
 	return rc;
 }

 static int __tree_connect_dfs_target(const unsigned int xid, struct cifs_tcon *tcon,
 				     struct cifs_sb_info *cifs_sb, char *tree, bool islink,
 				     struct dfs_cache_tgt_list *tl)
 {
 	int rc;
 	struct TCP_Server_Info *server = tcon->ses->server;
 	const struct smb_version_operations *ops = server->ops;
 	struct cifs_ses *root_ses = CIFS_DFS_ROOT_SES(tcon->ses);
 	struct cifs_tcon *ipc = root_ses->tcon_ipc;
 	char *share = NULL, *prefix = NULL;
 	struct dfs_cache_tgt_iterator *tit;
 	bool target_match;

 	tit = dfs_cache_get_tgt_iterator(tl);
 	if (!tit) {
 		rc = -ENOENT;
 		goto out;
 	}

 	/* Try to tree connect to all dfs targets */
 	for (; tit; tit = dfs_cache_get_next_tgt(tl, tit)) {
 		const char *target = dfs_cache_get_tgt_name(tit);
 		struct dfs_cache_tgt_list ntl = DFS_CACHE_TGT_LIST_INIT(ntl);

 		kfree(share);
 		kfree(prefix);
 		share = prefix = NULL;

 		/* Check if share matches with tcp ses */
 		rc = dfs_cache_get_tgt_share(server->current_fullpath + 1, tit, &share, &prefix);
 		if (rc) {
 			cifs_dbg(VFS, "%s: failed to parse target share: %d\n", __func__, rc);
 			break;
 		}

 		rc = target_share_matches_server(server, share, &target_match);
 		if (rc)
 			break;
 		if (!target_match) {
 			rc = -EHOSTUNREACH;
 			continue;
 		}

 		dfs_cache_noreq_update_tgthint(server->current_fullpath + 1, tit);

 		if (ipc->need_reconnect) {
 			scnprintf(tree, MAX_TREE_SIZE, "\\\\%s\\IPC$", server->hostname);
 			rc = ops->tree_connect(xid, ipc->ses, tree, ipc, cifs_sb->local_nls);
 			cifs_dbg(FYI, "%s: reconnect ipc: %d\n", __func__, rc);
 		}

 		scnprintf(tree, MAX_TREE_SIZE, "\\%s", share);
 		if (!islink) {
 			rc = ops->tree_connect(xid, tcon->ses, tree, tcon, cifs_sb->local_nls);
 			break;
 		}
 		/*
 		 * If no dfs referrals were returned from link target, then just do a TREE_CONNECT
 		 * to it.  Otherwise, cache the dfs referral and then mark current tcp ses for
 		 * reconnect so either the demultiplex thread or the echo worker will reconnect to
 		 * newly resolved target.
 		 */
 		if (dfs_cache_find(xid, root_ses, cifs_sb->local_nls, cifs_remap(cifs_sb), target,
 				   NULL, &ntl)) {
 			rc = ops->tree_connect(xid, tcon->ses, tree, tcon, cifs_sb->local_nls);
 			if (rc)
 				continue;

 			rc = cifs_update_super_prepath(cifs_sb, prefix);
 		} else {
 			/* Target is another dfs share */
 			rc = update_server_fullpath(server, cifs_sb, target);
 			dfs_cache_free_tgts(tl);

 			if (!rc) {
 				rc = -EREMOTE;
 				list_replace_init(&ntl.tl_list, &tl->tl_list);
 			} else
 				dfs_cache_free_tgts(&ntl);
 		}
 		break;
 	}

 out:
 	kfree(share);
 	kfree(prefix);

 	return rc;
 }

 static int tree_connect_dfs_target(const unsigned int xid, struct cifs_tcon *tcon,
 				   struct cifs_sb_info *cifs_sb, char *tree, bool islink,
 				   struct dfs_cache_tgt_list *tl)
 {
 	int rc;
 	int num_links = 0;
 	struct TCP_Server_Info *server = tcon->ses->server;
 	char *old_fullpath = server->leaf_fullpath;

 	do {
 		rc = __tree_connect_dfs_target(xid, tcon, cifs_sb, tree, islink, tl);
 		if (!rc || rc != -EREMOTE)
 			break;
 	} while (rc = -ELOOP, ++num_links < MAX_NESTED_LINKS);
 	/*
 	 * If we couldn't tree connect to any targets from last referral path, then
 	 * retry it from newly resolved dfs referral.
 	 */
 	if (rc && server->leaf_fullpath != old_fullpath)
 		cifs_signal_cifsd_for_reconnect(server, true);

 	dfs_cache_free_tgts(tl);
 	return rc;
 }

 int cifs_tree_connect(const unsigned int xid, struct cifs_tcon *tcon, const struct nls_table *nlsc)
 {
 	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 dfs_info3_param ref = {0};

 	/* only send once per connect */
 	spin_lock(&tcon->tc_lock);
 	if (tcon->ses->ses_status != SES_GOOD ||
 	    (tcon->status != TID_NEW &&
 	    tcon->status != TID_NEED_TCON)) {
 		spin_unlock(&tcon->tc_lock);
 		return 0;
 	}
 	tcon->status = TID_IN_TCON;
 	spin_unlock(&tcon->tc_lock);

 	tree = kzalloc(MAX_TREE_SIZE, GFP_KERNEL);
 	if (!tree) {
 		rc = -ENOMEM;
 		goto out;
 	}

 	if (tcon->ipc) {
 		cifs_server_lock(server);
 		scnprintf(tree, MAX_TREE_SIZE, "\\\\%s\\IPC$", server->hostname);
 		cifs_server_unlock(server);
 		rc = ops->tree_connect(xid, tcon->ses, tree, tcon, nlsc);
 		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);

 	/* If it is not dfs or there was no cached dfs referral, then reconnect to same share */
 	if (!server->current_fullpath ||
 	    dfs_cache_noreq_find(server->current_fullpath + 1, &ref, &tl)) {
 		rc = ops->tree_connect(xid, tcon->ses, tcon->tree_name, tcon, cifs_sb->local_nls);
 		goto out;
 	}

 	rc = tree_connect_dfs_target(xid, tcon, cifs_sb, tree, ref.server_type == DFS_TYPE_LINK,
 				     &tl);
 	free_dfs_info_param(&ref);

 out:
 	kfree(tree);
 	cifs_put_tcp_super(sb);

 	if (rc) {
 		spin_lock(&tcon->tc_lock);
 		if (tcon->status == TID_IN_TCON)
 			tcon->status = TID_NEED_TCON;
 		spin_unlock(&tcon->tc_lock);
 	} else {
 		spin_lock(&tcon->tc_lock);
 		if (tcon->status == TID_IN_TCON)
 			tcon->status = TID_GOOD;
 		spin_unlock(&tcon->tc_lock);
 		tcon->need_reconnect = false;
 	}

 	return rc;
 }
	// SPDX-License-Identifier: GPL-2.0
	/*
	* Copyright (c) 2022 Paulo Alcantara <palcantara@suse.de>
	*/

	#include <linux/namei.h>
	#include "cifsproto.h"
	#include "cifs_debug.h"
	#include "dns_resolve.h"
	#include "fs_context.h"
	#include "dfs.h"

	/**
	* dfs_parse_target_referral - set fs context for dfs target referral
	*
	* @full_path: full path in UNC format.
	* @ref: dfs referral pointer.
	* @ctx: smb3 fs context pointer.
	*
	* Return zero if dfs referral was parsed correctly, otherwise non-zero.
	*/
	int dfs_parse_target_referral(const char full_path, const struct dfs_info3_param ref,
	struct smb3_fs_context *ctx)
	{
	int rc;
	const char *prepath = NULL;
	char *path;

	if (!full_path \|\| !*full_path \|\| !ref \|\| !ctx)
	return -EINVAL;

	if (WARN_ON_ONCE(!ref->node_name \|\| ref->path_consumed < 0))
	return -EINVAL;

	if (strlen(full_path) - ref->path_consumed) {
	prepath = full_path + ref->path_consumed;
	/* skip initial delimiter */
	if (prepath == '/' \|\| prepath == '\\')
	prepath++;
	}

	path = cifs_build_devname(ref->node_name, prepath);
	if (IS_ERR(path))
	return PTR_ERR(path);

	rc = smb3_parse_devname(path, ctx);
	if (rc)
	goto out;

	rc = dns_resolve_server_name_to_ip(path, (struct sockaddr *)&ctx->dstaddr, NULL);

	out:
	kfree(path);
	return rc;
	}

	/*
	* cifs_build_path_to_root returns full path to root when we do not have an
	* existing connection (tcon)
	*/
	static char build_unc_path_to_root(const struct smb3_fs_context ctx,
	const struct cifs_sb_info *cifs_sb, bool useppath)
	{
	char full_path, pos;
	unsigned int pplen = useppath && ctx->prepath ? strlen(ctx->prepath) + 1 : 0;
	unsigned int unc_len = strnlen(ctx->UNC, MAX_TREE_SIZE + 1);

	if (unc_len > MAX_TREE_SIZE)
	return ERR_PTR(-EINVAL);

	full_path = kmalloc(unc_len + pplen + 1, GFP_KERNEL);
	if (full_path == NULL)
	return ERR_PTR(-ENOMEM);

	memcpy(full_path, ctx->UNC, unc_len);
	pos = full_path + unc_len;

	if (pplen) {
	*pos = CIFS_DIR_SEP(cifs_sb);
	memcpy(pos + 1, ctx->prepath, pplen);
	pos += pplen;
	}

	pos = '\0'; / add trailing null */
	convert_delimiter(full_path, CIFS_DIR_SEP(cifs_sb));
	cifs_dbg(FYI, "%s: full_path=%s\n", __func__, full_path);
	return full_path;
	}

	static int get_session(struct cifs_mount_ctx mnt_ctx, const char full_path)
	{
	struct smb3_fs_context *ctx = mnt_ctx->fs_ctx;
	int rc;

	ctx->leaf_fullpath = (char *)full_path;
	rc = cifs_mount_get_session(mnt_ctx);
	ctx->leaf_fullpath = NULL;

	return rc;
	}

	static int get_root_smb_session(struct cifs_mount_ctx *mnt_ctx)
	{
	struct smb3_fs_context *ctx = mnt_ctx->fs_ctx;
	struct dfs_root_ses *root_ses;
	struct cifs_ses *ses = mnt_ctx->ses;

	if (ses) {
	root_ses = kmalloc(sizeof(*root_ses), GFP_KERNEL);
	if (!root_ses)
	return -ENOMEM;

	INIT_LIST_HEAD(&root_ses->list);

	spin_lock(&cifs_tcp_ses_lock);
	ses->ses_count++;
	spin_unlock(&cifs_tcp_ses_lock);
	root_ses->ses = ses;
	list_add_tail(&root_ses->list, &mnt_ctx->dfs_ses_list);
	}
	ctx->dfs_root_ses = ses;
	return 0;
	}

	static int get_dfs_conn(struct cifs_mount_ctx mnt_ctx, const char ref_path, const char *full_path,
	const struct dfs_cache_tgt_iterator *tit)
	{
	struct smb3_fs_context *ctx = mnt_ctx->fs_ctx;
	struct dfs_info3_param ref = {};
	bool is_refsrv = false;
	int rc, rc2;

	rc = dfs_cache_get_tgt_referral(ref_path + 1, tit, &ref);
	if (rc)
	return rc;

	rc = dfs_parse_target_referral(full_path + 1, &ref, ctx);
	if (rc)
	goto out;

	cifs_mount_put_conns(mnt_ctx);
	rc = get_session(mnt_ctx, ref_path);
	if (rc)
	goto out;

	is_refsrv = !!(ref.flags & DFSREF_REFERRAL_SERVER);

	rc = -EREMOTE;
	if (ref.flags & DFSREF_STORAGE_SERVER) {
	rc = cifs_mount_get_tcon(mnt_ctx);
	if (rc)
	goto out;

	/* some servers may not advertise referral capability under ref.flags */
	is_refsrv \|= is_tcon_dfs(mnt_ctx->tcon);

	rc = cifs_is_path_remote(mnt_ctx);
	}

	if (rc == -EREMOTE && is_refsrv) {
	rc2 = get_root_smb_session(mnt_ctx);
	if (rc2)
	rc = rc2;
	}

	out:
	free_dfs_info_param(&ref);
	return rc;
	}

	static int __dfs_mount_share(struct cifs_mount_ctx *mnt_ctx)
	{
	struct cifs_sb_info *cifs_sb = mnt_ctx->cifs_sb;
	struct smb3_fs_context *ctx = mnt_ctx->fs_ctx;
	char ref_path = NULL, full_path = NULL;
	struct dfs_cache_tgt_iterator *tit;
	struct TCP_Server_Info *server;
	struct cifs_tcon *tcon;
	char *origin_fullpath = NULL;
	int num_links = 0;
	int rc;

	ref_path = dfs_get_path(cifs_sb, ctx->UNC);
	if (IS_ERR(ref_path))
	return PTR_ERR(ref_path);

	full_path = build_unc_path_to_root(ctx, cifs_sb, true);
	if (IS_ERR(full_path)) {
	rc = PTR_ERR(full_path);
	full_path = NULL;
	goto out;
	}

	origin_fullpath = kstrdup(full_path, GFP_KERNEL);
	if (!origin_fullpath) {
	rc = -ENOMEM;
	goto out;
	}

	do {
	struct dfs_cache_tgt_list tl = DFS_CACHE_TGT_LIST_INIT(tl);

	rc = dfs_get_referral(mnt_ctx, ref_path + 1, NULL, &tl);
	if (rc)
	break;

	tit = dfs_cache_get_tgt_iterator(&tl);
	if (!tit) {
	cifs_dbg(VFS, "%s: dfs referral (%s) with no targets\n", __func__,
	ref_path + 1);
	rc = -ENOENT;
	dfs_cache_free_tgts(&tl);
	break;
	}

	do {
	rc = get_dfs_conn(mnt_ctx, ref_path, full_path, tit);
	if (!rc)
	break;
	if (rc == -EREMOTE) {
	if (++num_links > MAX_NESTED_LINKS) {
	rc = -ELOOP;
	break;
	}
	kfree(ref_path);
	kfree(full_path);
	ref_path = full_path = NULL;

	full_path = build_unc_path_to_root(ctx, cifs_sb, true);
	if (IS_ERR(full_path)) {
	rc = PTR_ERR(full_path);
	full_path = NULL;
	} else {
	ref_path = dfs_get_path(cifs_sb, full_path);
	if (IS_ERR(ref_path)) {
	rc = PTR_ERR(ref_path);
	ref_path = NULL;
	}
	}
	break;
	}
	} while ((tit = dfs_cache_get_next_tgt(&tl, tit)));
	dfs_cache_free_tgts(&tl);
	} while (rc == -EREMOTE);

	if (!rc) {
	server = mnt_ctx->server;
	tcon = mnt_ctx->tcon;

	mutex_lock(&server->refpath_lock);
	if (!server->origin_fullpath) {
	server->origin_fullpath = origin_fullpath;
	server->current_fullpath = server->leaf_fullpath;
	origin_fullpath = NULL;
	}
	mutex_unlock(&server->refpath_lock);

	if (list_empty(&tcon->dfs_ses_list)) {
	list_replace_init(&mnt_ctx->dfs_ses_list,
	&tcon->dfs_ses_list);
	} else {
	dfs_put_root_smb_sessions(&mnt_ctx->dfs_ses_list);
	}
	}

	out:
	kfree(origin_fullpath);
	kfree(ref_path);
	kfree(full_path);
	return rc;
	}

	int dfs_mount_share(struct cifs_mount_ctx mnt_ctx, bool isdfs)
	{
	struct cifs_sb_info *cifs_sb = mnt_ctx->cifs_sb;
	struct smb3_fs_context *ctx = mnt_ctx->fs_ctx;
	int rc;

	*isdfs = false;

	rc = get_session(mnt_ctx, NULL);
	if (rc)
	return rc;
	ctx->dfs_root_ses = mnt_ctx->ses;
	/*
	* If called with 'nodfs' mount option, then skip DFS resolving. Otherwise unconditionally
	* try to get an DFS referral (even cached) to determine whether it is an DFS mount.
	*
	* Skip prefix path to provide support for DFS referrals from w2k8 servers which don't seem
	* to respond with PATH_NOT_COVERED to requests that include the prefix.
	*/
	if ((cifs_sb->mnt_cifs_flags & CIFS_MOUNT_NO_DFS) \|\|
	dfs_get_referral(mnt_ctx, ctx->UNC + 1, NULL, NULL)) {
	rc = cifs_mount_get_tcon(mnt_ctx);
	if (rc)
	return rc;

	rc = cifs_is_path_remote(mnt_ctx);
	if (!rc \|\| rc != -EREMOTE)
	return rc;
	}

	*isdfs = true;
	rc = get_root_smb_session(mnt_ctx);
	if (rc)
	return rc;

	return __dfs_mount_share(mnt_ctx);
	}

	/* Update dfs referral path of superblock */
	static int update_server_fullpath(struct TCP_Server_Info server, struct cifs_sb_info cifs_sb,
	const char *target)
	{
	int rc = 0;
	size_t len = strlen(target);
	char refpath, npath;

	if (unlikely(len < 2 \|\| *target != '\\'))
	return -EINVAL;

	if (target[1] == '\\') {
	len += 1;
	refpath = kmalloc(len, GFP_KERNEL);
	if (!refpath)
	return -ENOMEM;

	scnprintf(refpath, len, "%s", target);
	} else {
	len += sizeof("\\");
	refpath = kmalloc(len, GFP_KERNEL);
	if (!refpath)
	return -ENOMEM;

	scnprintf(refpath, len, "\\%s", target);
	}

	npath = dfs_cache_canonical_path(refpath, cifs_sb->local_nls, cifs_remap(cifs_sb));
	kfree(refpath);

	if (IS_ERR(npath)) {
	rc = PTR_ERR(npath);
	} else {
	mutex_lock(&server->refpath_lock);
	kfree(server->leaf_fullpath);
	server->leaf_fullpath = npath;
	mutex_unlock(&server->refpath_lock);
	server->current_fullpath = server->leaf_fullpath;
	}
	return rc;
	}

	static int target_share_matches_server(struct TCP_Server_Info server, char share,
	bool *target_match)
	{
	int rc = 0;
	const char *dfs_host;
	size_t dfs_host_len;

	*target_match = true;
	extract_unc_hostname(share, &dfs_host, &dfs_host_len);

	/* Check if hostnames or addresses match */
	cifs_server_lock(server);
	if (dfs_host_len != strlen(server->hostname) \|\|
	strncasecmp(dfs_host, server->hostname, dfs_host_len)) {
	cifs_dbg(FYI, "%s: %.*s doesn't match %s\n", __func__,
	(int)dfs_host_len, dfs_host, server->hostname);
	rc = match_target_ip(server, dfs_host, dfs_host_len, target_match);
	if (rc)
	cifs_dbg(VFS, "%s: failed to match target ip: %d\n", __func__, rc);
	}
	cifs_server_unlock(server);
	return rc;
	}

	static int __tree_connect_dfs_target(const unsigned int xid, struct cifs_tcon *tcon,
	struct cifs_sb_info cifs_sb, char tree, bool islink,
	struct dfs_cache_tgt_list *tl)
	{
	int rc;
	struct TCP_Server_Info *server = tcon->ses->server;
	const struct smb_version_operations *ops = server->ops;
	struct cifs_ses *root_ses = CIFS_DFS_ROOT_SES(tcon->ses);
	struct cifs_tcon *ipc = root_ses->tcon_ipc;
	char share = NULL, prefix = NULL;
	struct dfs_cache_tgt_iterator *tit;
	bool target_match;

	tit = dfs_cache_get_tgt_iterator(tl);
	if (!tit) {
	rc = -ENOENT;
	goto out;
	}

	/* Try to tree connect to all dfs targets */
	for (; tit; tit = dfs_cache_get_next_tgt(tl, tit)) {
	const char *target = dfs_cache_get_tgt_name(tit);
	struct dfs_cache_tgt_list ntl = DFS_CACHE_TGT_LIST_INIT(ntl);

	kfree(share);
	kfree(prefix);
	share = prefix = NULL;

	/* Check if share matches with tcp ses */
	rc = dfs_cache_get_tgt_share(server->current_fullpath + 1, tit, &share, &prefix);
	if (rc) {
	cifs_dbg(VFS, "%s: failed to parse target share: %d\n", __func__, rc);
	break;
	}

	rc = target_share_matches_server(server, share, &target_match);
	if (rc)
	break;
	if (!target_match) {
	rc = -EHOSTUNREACH;
	continue;
	}

	dfs_cache_noreq_update_tgthint(server->current_fullpath + 1, tit);

	if (ipc->need_reconnect) {
	scnprintf(tree, MAX_TREE_SIZE, "\\\\%s\\IPC$", server->hostname);
	rc = ops->tree_connect(xid, ipc->ses, tree, ipc, cifs_sb->local_nls);
	cifs_dbg(FYI, "%s: reconnect ipc: %d\n", __func__, rc);
	}

	scnprintf(tree, MAX_TREE_SIZE, "\\%s", share);
	if (!islink) {
	rc = ops->tree_connect(xid, tcon->ses, tree, tcon, cifs_sb->local_nls);
	break;
	}
	/*
	* If no dfs referrals were returned from link target, then just do a TREE_CONNECT
	* to it. Otherwise, cache the dfs referral and then mark current tcp ses for
	* reconnect so either the demultiplex thread or the echo worker will reconnect to
	* newly resolved target.
	*/
	if (dfs_cache_find(xid, root_ses, cifs_sb->local_nls, cifs_remap(cifs_sb), target,
	NULL, &ntl)) {
	rc = ops->tree_connect(xid, tcon->ses, tree, tcon, cifs_sb->local_nls);
	if (rc)
	continue;

	rc = cifs_update_super_prepath(cifs_sb, prefix);
	} else {
	/* Target is another dfs share */
	rc = update_server_fullpath(server, cifs_sb, target);
	dfs_cache_free_tgts(tl);

	if (!rc) {
	rc = -EREMOTE;
	list_replace_init(&ntl.tl_list, &tl->tl_list);
	} else
	dfs_cache_free_tgts(&ntl);
	}
	break;
	}

	out:
	kfree(share);
	kfree(prefix);

	return rc;
	}

	static int tree_connect_dfs_target(const unsigned int xid, struct cifs_tcon *tcon,
	struct cifs_sb_info cifs_sb, char tree, bool islink,
	struct dfs_cache_tgt_list *tl)
	{
	int rc;
	int num_links = 0;
	struct TCP_Server_Info *server = tcon->ses->server;
	char *old_fullpath = server->leaf_fullpath;

	do {
	rc = __tree_connect_dfs_target(xid, tcon, cifs_sb, tree, islink, tl);
	if (!rc \|\| rc != -EREMOTE)
	break;
	} while (rc = -ELOOP, ++num_links < MAX_NESTED_LINKS);
	/*
	* If we couldn't tree connect to any targets from last referral path, then
	* retry it from newly resolved dfs referral.
	*/
	if (rc && server->leaf_fullpath != old_fullpath)
	cifs_signal_cifsd_for_reconnect(server, true);

	dfs_cache_free_tgts(tl);
	return rc;
	}

	int cifs_tree_connect(const unsigned int xid, struct cifs_tcon tcon, const struct nls_table nlsc)
	{
	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 dfs_info3_param ref = {0};

	/* only send once per connect */
	spin_lock(&tcon->tc_lock);
	if (tcon->ses->ses_status != SES_GOOD \|\|
	(tcon->status != TID_NEW &&
	tcon->status != TID_NEED_TCON)) {
	spin_unlock(&tcon->tc_lock);
	return 0;
	}
	tcon->status = TID_IN_TCON;
	spin_unlock(&tcon->tc_lock);

	tree = kzalloc(MAX_TREE_SIZE, GFP_KERNEL);
	if (!tree) {
	rc = -ENOMEM;
	goto out;
	}

	if (tcon->ipc) {
	cifs_server_lock(server);
	scnprintf(tree, MAX_TREE_SIZE, "\\\\%s\\IPC$", server->hostname);
	cifs_server_unlock(server);
	rc = ops->tree_connect(xid, tcon->ses, tree, tcon, nlsc);
	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);

	/* If it is not dfs or there was no cached dfs referral, then reconnect to same share */
	if (!server->current_fullpath \|\|
	dfs_cache_noreq_find(server->current_fullpath + 1, &ref, &tl)) {
	rc = ops->tree_connect(xid, tcon->ses, tcon->tree_name, tcon, cifs_sb->local_nls);
	goto out;
	}

	rc = tree_connect_dfs_target(xid, tcon, cifs_sb, tree, ref.server_type == DFS_TYPE_LINK,
	&tl);
	free_dfs_info_param(&ref);

	out:
	kfree(tree);
	cifs_put_tcp_super(sb);

	if (rc) {
	spin_lock(&tcon->tc_lock);
	if (tcon->status == TID_IN_TCON)
	tcon->status = TID_NEED_TCON;
	spin_unlock(&tcon->tc_lock);
	} else {
	spin_lock(&tcon->tc_lock);
	if (tcon->status == TID_IN_TCON)
	tcon->status = TID_GOOD;
	spin_unlock(&tcon->tc_lock);
	tcon->need_reconnect = false;
	}

	return rc;
	}