fs/cifs/cifs_dfs_ref.c - third_party/kernel - Git at Google

 // SPDX-License-Identifier: GPL-2.0-or-later
 /*
  *   Contains the CIFS DFS referral mounting routines used for handling
  *   traversal via DFS junction point
  *
  *   Copyright (c) 2007 Igor Mammedov
  *   Copyright (C) International Business Machines  Corp., 2008
  *   Author(s): Igor Mammedov (niallain@gmail.com)
  *		Steve French (sfrench@us.ibm.com)
  */

 #include <linux/dcache.h>
 #include <linux/mount.h>
 #include <linux/namei.h>
 #include <linux/slab.h>
 #include <linux/vfs.h>
 #include <linux/fs.h>
 #include <linux/inet.h>
 #include "cifsglob.h"
 #include "cifsproto.h"
 #include "cifsfs.h"
 #include "dns_resolve.h"
 #include "cifs_debug.h"
 #include "cifs_unicode.h"
 #include "dfs_cache.h"

 static LIST_HEAD(cifs_dfs_automount_list);

 static void cifs_dfs_expire_automounts(struct work_struct *work);
 static DECLARE_DELAYED_WORK(cifs_dfs_automount_task,
 			    cifs_dfs_expire_automounts);
 static int cifs_dfs_mountpoint_expiry_timeout = 500 * HZ;

 static void cifs_dfs_expire_automounts(struct work_struct *work)
 {
 	struct list_head *list = &cifs_dfs_automount_list;

 	mark_mounts_for_expiry(list);
 	if (!list_empty(list))
 		schedule_delayed_work(&cifs_dfs_automount_task,
 				      cifs_dfs_mountpoint_expiry_timeout);
 }

 void cifs_dfs_release_automount_timer(void)
 {
 	BUG_ON(!list_empty(&cifs_dfs_automount_list));
 	cancel_delayed_work_sync(&cifs_dfs_automount_task);
 }

 /**
  * cifs_build_devname - build a devicename from a UNC and optional prepath
  * @nodename:	pointer to UNC string
  * @prepath:	pointer to prefixpath (or NULL if there isn't one)
  *
  * Build a new cifs devicename after chasing a DFS referral. Allocate a buffer
  * big enough to hold the final thing. Copy the UNC from the nodename, and
  * concatenate the prepath onto the end of it if there is one.
  *
  * Returns pointer to the built string, or a ERR_PTR. Caller is responsible
  * for freeing the returned string.
  */
 static char *
 cifs_build_devname(char *nodename, const char *prepath)
 {
 	size_t pplen;
 	size_t unclen;
 	char *dev;
 	char *pos;

 	/* skip over any preceding delimiters */
 	nodename += strspn(nodename, "\\");
 	if (!*nodename)
 		return ERR_PTR(-EINVAL);

 	/* get length of UNC and set pos to last char */
 	unclen = strlen(nodename);
 	pos = nodename + unclen - 1;

 	/* trim off any trailing delimiters */
 	while (*pos == '\\') {
 		--pos;
 		--unclen;
 	}

 	/* allocate a buffer:
 	 * +2 for preceding "//"
 	 * +1 for delimiter between UNC and prepath
 	 * +1 for trailing NULL
 	 */
 	pplen = prepath ? strlen(prepath) : 0;
 	dev = kmalloc(2 + unclen + 1 + pplen + 1, GFP_KERNEL);
 	if (!dev)
 		return ERR_PTR(-ENOMEM);

 	pos = dev;
 	/* add the initial "//" */
 	*pos = '/';
 	++pos;
 	*pos = '/';
 	++pos;

 	/* copy in the UNC portion from referral */
 	memcpy(pos, nodename, unclen);
 	pos += unclen;

 	/* copy the prefixpath remainder (if there is one) */
 	if (pplen) {
 		*pos = '/';
 		++pos;
 		memcpy(pos, prepath, pplen);
 		pos += pplen;
 	}

 	/* NULL terminator */
 	*pos = '\0';

 	convert_delimiter(dev, '/');
 	return dev;
 }


 /**
  * cifs_compose_mount_options	-	creates mount options for referral
  * @sb_mountdata:	parent/root DFS mount options (template)
  * @fullpath:		full path in UNC format
  * @ref:		optional server's referral
  * @devname:		optional pointer for saving device name
  *
  * creates mount options for submount based on template options sb_mountdata
  * and replacing unc,ip,prefixpath options with ones we've got form ref_unc.
  *
  * Returns: pointer to new mount options or ERR_PTR.
  * Caller is responsible for freeing returned value if it is not error.
  */
 char *cifs_compose_mount_options(const char *sb_mountdata,
 				   const char *fullpath,
 				   const struct dfs_info3_param *ref,
 				   char **devname)
 {
 	int rc;
 	char *name;
 	char *mountdata = NULL;
 	const char *prepath = NULL;
 	int md_len;
 	char *tkn_e;
 	char *srvIP = NULL;
 	char sep = ',';
 	int off, noff;

 	if (sb_mountdata == NULL)
 		return ERR_PTR(-EINVAL);

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

 		name = cifs_build_devname(ref->node_name, prepath);
 		if (IS_ERR(name)) {
 			rc = PTR_ERR(name);
 			name = NULL;
 			goto compose_mount_options_err;
 		}
 	} else {
 		name = cifs_build_devname((char *)fullpath, NULL);
 		if (IS_ERR(name)) {
 			rc = PTR_ERR(name);
 			name = NULL;
 			goto compose_mount_options_err;
 		}
 	}

 	rc = dns_resolve_server_name_to_ip(name, &srvIP);
 	if (rc < 0) {
 		cifs_dbg(FYI, "%s: Failed to resolve server part of %s to IP: %d\n",
 			 __func__, name, rc);
 		goto compose_mount_options_err;
 	}

 	/*
 	 * In most cases, we'll be building a shorter string than the original,
 	 * but we do have to assume that the address in the ip= option may be
 	 * much longer than the original. Add the max length of an address
 	 * string to the length of the original string to allow for worst case.
 	 */
 	md_len = strlen(sb_mountdata) + INET6_ADDRSTRLEN;
 	mountdata = kzalloc(md_len + sizeof("ip=") + 1, GFP_KERNEL);
 	if (mountdata == NULL) {
 		rc = -ENOMEM;
 		goto compose_mount_options_err;
 	}

 	/* copy all options except of unc,ip,prefixpath */
 	off = 0;
 	if (strncmp(sb_mountdata, "sep=", 4) == 0) {
 			sep = sb_mountdata[4];
 			strncpy(mountdata, sb_mountdata, 5);
 			off += 5;
 	}

 	do {
 		tkn_e = strchr(sb_mountdata + off, sep);
 		if (tkn_e == NULL)
 			noff = strlen(sb_mountdata + off);
 		else
 			noff = tkn_e - (sb_mountdata + off) + 1;

 		if (strncasecmp(sb_mountdata + off, "unc=", 4) == 0) {
 			off += noff;
 			continue;
 		}
 		if (strncasecmp(sb_mountdata + off, "ip=", 3) == 0) {
 			off += noff;
 			continue;
 		}
 		if (strncasecmp(sb_mountdata + off, "prefixpath=", 11) == 0) {
 			off += noff;
 			continue;
 		}
 		strncat(mountdata, sb_mountdata + off, noff);
 		off += noff;
 	} while (tkn_e);
 	strcat(mountdata, sb_mountdata + off);
 	mountdata[md_len] = '\0';

 	/* copy new IP and ref share name */
 	if (mountdata[strlen(mountdata) - 1] != sep)
 		strncat(mountdata, &sep, 1);
 	strcat(mountdata, "ip=");
 	strcat(mountdata, srvIP);

 	if (devname)
 		*devname = name;
 	else
 		kfree(name);

 	/*cifs_dbg(FYI, "%s: parent mountdata: %s\n", __func__, sb_mountdata);*/
 	/*cifs_dbg(FYI, "%s: submount mountdata: %s\n", __func__, mountdata );*/

 compose_mount_options_out:
 	kfree(srvIP);
 	return mountdata;

 compose_mount_options_err:
 	kfree(mountdata);
 	mountdata = ERR_PTR(rc);
 	kfree(name);
 	goto compose_mount_options_out;
 }

 /**
  * cifs_dfs_do_mount - mounts specified path using DFS full path
  *
  * Always pass down @fullpath to smb3_do_mount() so we can use the root server
  * to perform failover in case we failed to connect to the first target in the
  * referral.
  *
  * @cifs_sb:		parent/root superblock
  * @fullpath:		full path in UNC format
  */
 static struct vfsmount *cifs_dfs_do_mount(struct dentry *mntpt,
 					  struct cifs_sb_info *cifs_sb,
 					  const char *fullpath)
 {
 	struct vfsmount *mnt;
 	char *mountdata;
 	char *devname;

 	devname = kstrndup(fullpath, strlen(fullpath), GFP_KERNEL);
 	if (!devname)
 		return ERR_PTR(-ENOMEM);

 	convert_delimiter(devname, '/');

 	/* strip first '\' from fullpath */
 	mountdata = cifs_compose_mount_options(cifs_sb->mountdata,
 					       fullpath + 1, NULL, NULL);
 	if (IS_ERR(mountdata)) {
 		kfree(devname);
 		return (struct vfsmount *)mountdata;
 	}

 	mnt = vfs_submount(mntpt, &cifs_fs_type, devname, mountdata);
 	kfree(mountdata);
 	kfree(devname);
 	return mnt;
 }

 /*
  * Create a vfsmount that we can automount
  */
 static struct vfsmount *cifs_dfs_do_automount(struct dentry *mntpt)
 {
 	struct cifs_sb_info *cifs_sb;
 	struct cifs_ses *ses;
 	struct cifs_tcon *tcon;
 	char *full_path, *root_path;
 	unsigned int xid;
 	int rc;
 	struct vfsmount *mnt;

 	cifs_dbg(FYI, "in %s\n", __func__);
 	BUG_ON(IS_ROOT(mntpt));

 	/*
 	 * The MSDFS spec states that paths in DFS referral requests and
 	 * responses must be prefixed by a single '\' character instead of
 	 * the double backslashes usually used in the UNC. This function
 	 * gives us the latter, so we must adjust the result.
 	 */
 	mnt = ERR_PTR(-ENOMEM);

 	cifs_sb = CIFS_SB(mntpt->d_sb);
 	if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_NO_DFS) {
 		mnt = ERR_PTR(-EREMOTE);
 		goto cdda_exit;
 	}

 	/* always use tree name prefix */
 	full_path = build_path_from_dentry_optional_prefix(mntpt, true);
 	if (full_path == NULL)
 		goto cdda_exit;

 	convert_delimiter(full_path, '\\');

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

 	if (!cifs_sb_master_tlink(cifs_sb)) {
 		cifs_dbg(FYI, "%s: master tlink is NULL\n", __func__);
 		goto free_full_path;
 	}

 	tcon = cifs_sb_master_tcon(cifs_sb);
 	if (!tcon) {
 		cifs_dbg(FYI, "%s: master tcon is NULL\n", __func__);
 		goto free_full_path;
 	}

 	root_path = kstrdup(tcon->treeName, GFP_KERNEL);
 	if (!root_path) {
 		mnt = ERR_PTR(-ENOMEM);
 		goto free_full_path;
 	}
 	cifs_dbg(FYI, "%s: root path: %s\n", __func__, root_path);

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

 	/*
 	 * If DFS root has been expired, then unconditionally fetch it again to
 	 * refresh DFS referral cache.
 	 */
 	rc = dfs_cache_find(xid, ses, cifs_sb->local_nls, cifs_remap(cifs_sb),
 			    root_path + 1, NULL, NULL);
 	if (!rc) {
 		rc = dfs_cache_find(xid, ses, cifs_sb->local_nls,
 				    cifs_remap(cifs_sb), full_path + 1,
 				    NULL, NULL);
 	}

 	free_xid(xid);

 	if (rc) {
 		mnt = ERR_PTR(rc);
 		goto free_root_path;
 	}
 	/*
 	 * OK - we were able to get and cache a referral for @full_path.
 	 *
 	 * Now, pass it down to cifs_mount() and it will retry every available
 	 * node server in case of failures - no need to do it here.
 	 */
 	mnt = cifs_dfs_do_mount(mntpt, cifs_sb, full_path);
 	cifs_dbg(FYI, "%s: cifs_dfs_do_mount:%s , mnt:%p\n", __func__,
 		 full_path + 1, mnt);

 free_root_path:
 	kfree(root_path);
 free_full_path:
 	kfree(full_path);
 cdda_exit:
 	cifs_dbg(FYI, "leaving %s\n" , __func__);
 	return mnt;
 }

 /*
  * Attempt to automount the referral
  */
 struct vfsmount *cifs_dfs_d_automount(struct path *path)
 {
 	struct vfsmount *newmnt;

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

 	newmnt = cifs_dfs_do_automount(path->dentry);
 	if (IS_ERR(newmnt)) {
 		cifs_dbg(FYI, "leaving %s [automount failed]\n" , __func__);
 		return newmnt;
 	}

 	mntget(newmnt); /* prevent immediate expiration */
 	mnt_set_expiry(newmnt, &cifs_dfs_automount_list);
 	schedule_delayed_work(&cifs_dfs_automount_task,
 			      cifs_dfs_mountpoint_expiry_timeout);
 	cifs_dbg(FYI, "leaving %s [ok]\n" , __func__);
 	return newmnt;
 }

 const struct inode_operations cifs_dfs_referral_inode_operations = {
 };
	// SPDX-License-Identifier: GPL-2.0-or-later
	/*
	* Contains the CIFS DFS referral mounting routines used for handling
	* traversal via DFS junction point
	*
	* Copyright (c) 2007 Igor Mammedov
	* Copyright (C) International Business Machines Corp., 2008
	* Author(s): Igor Mammedov (niallain@gmail.com)
	* Steve French (sfrench@us.ibm.com)
	*/

	#include <linux/dcache.h>
	#include <linux/mount.h>
	#include <linux/namei.h>
	#include <linux/slab.h>
	#include <linux/vfs.h>
	#include <linux/fs.h>
	#include <linux/inet.h>
	#include "cifsglob.h"
	#include "cifsproto.h"
	#include "cifsfs.h"
	#include "dns_resolve.h"
	#include "cifs_debug.h"
	#include "cifs_unicode.h"
	#include "dfs_cache.h"

	static LIST_HEAD(cifs_dfs_automount_list);

	static void cifs_dfs_expire_automounts(struct work_struct *work);
	static DECLARE_DELAYED_WORK(cifs_dfs_automount_task,
	cifs_dfs_expire_automounts);
	static int cifs_dfs_mountpoint_expiry_timeout = 500 * HZ;

	static void cifs_dfs_expire_automounts(struct work_struct *work)
	{
	struct list_head *list = &cifs_dfs_automount_list;

	mark_mounts_for_expiry(list);
	if (!list_empty(list))
	schedule_delayed_work(&cifs_dfs_automount_task,
	cifs_dfs_mountpoint_expiry_timeout);
	}

	void cifs_dfs_release_automount_timer(void)
	{
	BUG_ON(!list_empty(&cifs_dfs_automount_list));
	cancel_delayed_work_sync(&cifs_dfs_automount_task);
	}

	/**
	* cifs_build_devname - build a devicename from a UNC and optional prepath
	* @nodename: pointer to UNC string
	* @prepath: pointer to prefixpath (or NULL if there isn't one)
	*
	* Build a new cifs devicename after chasing a DFS referral. Allocate a buffer
	* big enough to hold the final thing. Copy the UNC from the nodename, and
	* concatenate the prepath onto the end of it if there is one.
	*
	* Returns pointer to the built string, or a ERR_PTR. Caller is responsible
	* for freeing the returned string.
	*/
	static char *
	cifs_build_devname(char nodename, const char prepath)
	{
	size_t pplen;
	size_t unclen;
	char *dev;
	char *pos;

	/* skip over any preceding delimiters */
	nodename += strspn(nodename, "\\");
	if (!*nodename)
	return ERR_PTR(-EINVAL);

	/* get length of UNC and set pos to last char */
	unclen = strlen(nodename);
	pos = nodename + unclen - 1;

	/* trim off any trailing delimiters */
	while (*pos == '\\') {
	--pos;
	--unclen;
	}

	/* allocate a buffer:
	* +2 for preceding "//"
	* +1 for delimiter between UNC and prepath
	* +1 for trailing NULL
	*/
	pplen = prepath ? strlen(prepath) : 0;
	dev = kmalloc(2 + unclen + 1 + pplen + 1, GFP_KERNEL);
	if (!dev)
	return ERR_PTR(-ENOMEM);

	pos = dev;
	/* add the initial "//" */
	*pos = '/';
	++pos;
	*pos = '/';
	++pos;

	/* copy in the UNC portion from referral */
	memcpy(pos, nodename, unclen);
	pos += unclen;

	/* copy the prefixpath remainder (if there is one) */
	if (pplen) {
	*pos = '/';
	++pos;
	memcpy(pos, prepath, pplen);
	pos += pplen;
	}

	/* NULL terminator */
	*pos = '\0';

	convert_delimiter(dev, '/');
	return dev;
	}


	/**
	* cifs_compose_mount_options - creates mount options for referral
	* @sb_mountdata: parent/root DFS mount options (template)
	* @fullpath: full path in UNC format
	* @ref: optional server's referral
	* @devname: optional pointer for saving device name
	*
	* creates mount options for submount based on template options sb_mountdata
	* and replacing unc,ip,prefixpath options with ones we've got form ref_unc.
	*
	* Returns: pointer to new mount options or ERR_PTR.
	* Caller is responsible for freeing returned value if it is not error.
	*/
	char cifs_compose_mount_options(const char sb_mountdata,
	const char *fullpath,
	const struct dfs_info3_param *ref,
	char **devname)
	{
	int rc;
	char *name;
	char *mountdata = NULL;
	const char *prepath = NULL;
	int md_len;
	char *tkn_e;
	char *srvIP = NULL;
	char sep = ',';
	int off, noff;

	if (sb_mountdata == NULL)
	return ERR_PTR(-EINVAL);

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

	name = cifs_build_devname(ref->node_name, prepath);
	if (IS_ERR(name)) {
	rc = PTR_ERR(name);
	name = NULL;
	goto compose_mount_options_err;
	}
	} else {
	name = cifs_build_devname((char *)fullpath, NULL);
	if (IS_ERR(name)) {
	rc = PTR_ERR(name);
	name = NULL;
	goto compose_mount_options_err;
	}
	}

	rc = dns_resolve_server_name_to_ip(name, &srvIP);
	if (rc < 0) {
	cifs_dbg(FYI, "%s: Failed to resolve server part of %s to IP: %d\n",
	__func__, name, rc);
	goto compose_mount_options_err;
	}

	/*
	* In most cases, we'll be building a shorter string than the original,
	* but we do have to assume that the address in the ip= option may be
	* much longer than the original. Add the max length of an address
	* string to the length of the original string to allow for worst case.
	*/
	md_len = strlen(sb_mountdata) + INET6_ADDRSTRLEN;
	mountdata = kzalloc(md_len + sizeof("ip=") + 1, GFP_KERNEL);
	if (mountdata == NULL) {
	rc = -ENOMEM;
	goto compose_mount_options_err;
	}

	/* copy all options except of unc,ip,prefixpath */
	off = 0;
	if (strncmp(sb_mountdata, "sep=", 4) == 0) {
	sep = sb_mountdata[4];
	strncpy(mountdata, sb_mountdata, 5);
	off += 5;
	}

	do {
	tkn_e = strchr(sb_mountdata + off, sep);
	if (tkn_e == NULL)
	noff = strlen(sb_mountdata + off);
	else
	noff = tkn_e - (sb_mountdata + off) + 1;

	if (strncasecmp(sb_mountdata + off, "unc=", 4) == 0) {
	off += noff;
	continue;
	}
	if (strncasecmp(sb_mountdata + off, "ip=", 3) == 0) {
	off += noff;
	continue;
	}
	if (strncasecmp(sb_mountdata + off, "prefixpath=", 11) == 0) {
	off += noff;
	continue;
	}
	strncat(mountdata, sb_mountdata + off, noff);
	off += noff;
	} while (tkn_e);
	strcat(mountdata, sb_mountdata + off);
	mountdata[md_len] = '\0';

	/* copy new IP and ref share name */
	if (mountdata[strlen(mountdata) - 1] != sep)
	strncat(mountdata, &sep, 1);
	strcat(mountdata, "ip=");
	strcat(mountdata, srvIP);

	if (devname)
	*devname = name;
	else
	kfree(name);

	/cifs_dbg(FYI, "%s: parent mountdata: %s\n", __func__, sb_mountdata);/
	/cifs_dbg(FYI, "%s: submount mountdata: %s\n", __func__, mountdata );/

	compose_mount_options_out:
	kfree(srvIP);
	return mountdata;

	compose_mount_options_err:
	kfree(mountdata);
	mountdata = ERR_PTR(rc);
	kfree(name);
	goto compose_mount_options_out;
	}

	/**
	* cifs_dfs_do_mount - mounts specified path using DFS full path
	*
	* Always pass down @fullpath to smb3_do_mount() so we can use the root server
	* to perform failover in case we failed to connect to the first target in the
	* referral.
	*
	* @cifs_sb: parent/root superblock
	* @fullpath: full path in UNC format
	*/
	static struct vfsmount cifs_dfs_do_mount(struct dentry mntpt,
	struct cifs_sb_info *cifs_sb,
	const char *fullpath)
	{
	struct vfsmount *mnt;
	char *mountdata;
	char *devname;

	devname = kstrndup(fullpath, strlen(fullpath), GFP_KERNEL);
	if (!devname)
	return ERR_PTR(-ENOMEM);

	convert_delimiter(devname, '/');

	/* strip first '\' from fullpath */
	mountdata = cifs_compose_mount_options(cifs_sb->mountdata,
	fullpath + 1, NULL, NULL);
	if (IS_ERR(mountdata)) {
	kfree(devname);
	return (struct vfsmount *)mountdata;
	}

	mnt = vfs_submount(mntpt, &cifs_fs_type, devname, mountdata);
	kfree(mountdata);
	kfree(devname);
	return mnt;
	}

	/*
	* Create a vfsmount that we can automount
	*/
	static struct vfsmount cifs_dfs_do_automount(struct dentry mntpt)
	{
	struct cifs_sb_info *cifs_sb;
	struct cifs_ses *ses;
	struct cifs_tcon *tcon;
	char full_path, root_path;
	unsigned int xid;
	int rc;
	struct vfsmount *mnt;

	cifs_dbg(FYI, "in %s\n", __func__);
	BUG_ON(IS_ROOT(mntpt));

	/*
	* The MSDFS spec states that paths in DFS referral requests and
	* responses must be prefixed by a single '\' character instead of
	* the double backslashes usually used in the UNC. This function
	* gives us the latter, so we must adjust the result.
	*/
	mnt = ERR_PTR(-ENOMEM);

	cifs_sb = CIFS_SB(mntpt->d_sb);
	if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_NO_DFS) {
	mnt = ERR_PTR(-EREMOTE);
	goto cdda_exit;
	}

	/* always use tree name prefix */
	full_path = build_path_from_dentry_optional_prefix(mntpt, true);
	if (full_path == NULL)
	goto cdda_exit;

	convert_delimiter(full_path, '\\');

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

	if (!cifs_sb_master_tlink(cifs_sb)) {
	cifs_dbg(FYI, "%s: master tlink is NULL\n", __func__);
	goto free_full_path;
	}

	tcon = cifs_sb_master_tcon(cifs_sb);
	if (!tcon) {
	cifs_dbg(FYI, "%s: master tcon is NULL\n", __func__);
	goto free_full_path;
	}

	root_path = kstrdup(tcon->treeName, GFP_KERNEL);
	if (!root_path) {
	mnt = ERR_PTR(-ENOMEM);
	goto free_full_path;
	}
	cifs_dbg(FYI, "%s: root path: %s\n", __func__, root_path);

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

	/*
	* If DFS root has been expired, then unconditionally fetch it again to
	* refresh DFS referral cache.
	*/
	rc = dfs_cache_find(xid, ses, cifs_sb->local_nls, cifs_remap(cifs_sb),
	root_path + 1, NULL, NULL);
	if (!rc) {
	rc = dfs_cache_find(xid, ses, cifs_sb->local_nls,
	cifs_remap(cifs_sb), full_path + 1,
	NULL, NULL);
	}

	free_xid(xid);

	if (rc) {
	mnt = ERR_PTR(rc);
	goto free_root_path;
	}
	/*
	* OK - we were able to get and cache a referral for @full_path.
	*
	* Now, pass it down to cifs_mount() and it will retry every available
	* node server in case of failures - no need to do it here.
	*/
	mnt = cifs_dfs_do_mount(mntpt, cifs_sb, full_path);
	cifs_dbg(FYI, "%s: cifs_dfs_do_mount:%s , mnt:%p\n", __func__,
	full_path + 1, mnt);

	free_root_path:
	kfree(root_path);
	free_full_path:
	kfree(full_path);
	cdda_exit:
	cifs_dbg(FYI, "leaving %s\n" , __func__);
	return mnt;
	}

	/*
	* Attempt to automount the referral
	*/
	struct vfsmount cifs_dfs_d_automount(struct path path)
	{
	struct vfsmount *newmnt;

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

	newmnt = cifs_dfs_do_automount(path->dentry);
	if (IS_ERR(newmnt)) {
	cifs_dbg(FYI, "leaving %s [automount failed]\n" , __func__);
	return newmnt;
	}

	mntget(newmnt); /* prevent immediate expiration */
	mnt_set_expiry(newmnt, &cifs_dfs_automount_list);
	schedule_delayed_work(&cifs_dfs_automount_task,
	cifs_dfs_mountpoint_expiry_timeout);
	cifs_dbg(FYI, "leaving %s [ok]\n" , __func__);
	return newmnt;
	}

	const struct inode_operations cifs_dfs_referral_inode_operations = {
	};