1// SPDX-License-Identifier: GPL-2.0-or-later
  2/*
  3 *   Contains the CIFS DFS referral mounting routines used for handling
  4 *   traversal via DFS junction point
  5 *
  6 *   Copyright (c) 2007 Igor Mammedov
  7 *   Copyright (C) International Business Machines  Corp., 2008
  8 *   Author(s): Igor Mammedov (niallain@gmail.com)
  9 *		Steve French (sfrench@us.ibm.com)
 10 */
 11
 12#include <linux/dcache.h>
 13#include <linux/mount.h>
 14#include <linux/namei.h>
 15#include <linux/slab.h>
 16#include <linux/vfs.h>
 17#include <linux/fs.h>
 18#include <linux/inet.h>
 19#include "cifsglob.h"
 20#include "cifsproto.h"
 21#include "cifsfs.h"
 22#include "dns_resolve.h"
 23#include "cifs_debug.h"
 24#include "cifs_unicode.h"
 25#include "dfs_cache.h"
 26
 27static LIST_HEAD(cifs_dfs_automount_list);
 28
 29static void cifs_dfs_expire_automounts(struct work_struct *work);
 30static DECLARE_DELAYED_WORK(cifs_dfs_automount_task,
 31			    cifs_dfs_expire_automounts);
 32static int cifs_dfs_mountpoint_expiry_timeout = 500 * HZ;
 33
 34static void cifs_dfs_expire_automounts(struct work_struct *work)
 35{
 36	struct list_head *list = &cifs_dfs_automount_list;
 37
 38	mark_mounts_for_expiry(list);
 39	if (!list_empty(list))
 40		schedule_delayed_work(&cifs_dfs_automount_task,
 41				      cifs_dfs_mountpoint_expiry_timeout);
 42}
 43
 44void cifs_dfs_release_automount_timer(void)
 45{
 46	BUG_ON(!list_empty(&cifs_dfs_automount_list));
 47	cancel_delayed_work_sync(&cifs_dfs_automount_task);
 48}
 49
 50/**
 51 * cifs_build_devname - build a devicename from a UNC and optional prepath
 52 * @nodename:	pointer to UNC string
 53 * @prepath:	pointer to prefixpath (or NULL if there isn't one)
 54 *
 55 * Build a new cifs devicename after chasing a DFS referral. Allocate a buffer
 56 * big enough to hold the final thing. Copy the UNC from the nodename, and
 57 * concatenate the prepath onto the end of it if there is one.
 58 *
 59 * Returns pointer to the built string, or a ERR_PTR. Caller is responsible
 60 * for freeing the returned string.
 61 */
 62static char *
 63cifs_build_devname(char *nodename, const char *prepath)
 64{
 65	size_t pplen;
 66	size_t unclen;
 67	char *dev;
 68	char *pos;
 69
 70	/* skip over any preceding delimiters */
 71	nodename += strspn(nodename, "\\");
 72	if (!*nodename)
 73		return ERR_PTR(-EINVAL);
 74
 75	/* get length of UNC and set pos to last char */
 76	unclen = strlen(nodename);
 77	pos = nodename + unclen - 1;
 78
 79	/* trim off any trailing delimiters */
 80	while (*pos == '\\') {
 81		--pos;
 82		--unclen;
 83	}
 84
 85	/* allocate a buffer:
 86	 * +2 for preceding "//"
 87	 * +1 for delimiter between UNC and prepath
 88	 * +1 for trailing NULL
 89	 */
 90	pplen = prepath ? strlen(prepath) : 0;
 91	dev = kmalloc(2 + unclen + 1 + pplen + 1, GFP_KERNEL);
 92	if (!dev)
 93		return ERR_PTR(-ENOMEM);
 94
 95	pos = dev;
 96	/* add the initial "//" */
 97	*pos = '/';
 98	++pos;
 99	*pos = '/';
100	++pos;
101
102	/* copy in the UNC portion from referral */
103	memcpy(pos, nodename, unclen);
104	pos += unclen;
105
106	/* copy the prefixpath remainder (if there is one) */
107	if (pplen) {
108		*pos = '/';
109		++pos;
110		memcpy(pos, prepath, pplen);
111		pos += pplen;
112	}
113
114	/* NULL terminator */
115	*pos = '\0';
116
117	convert_delimiter(dev, '/');
118	return dev;
119}
120
121
122/**
123 * cifs_compose_mount_options	-	creates mount options for referral
124 * @sb_mountdata:	parent/root DFS mount options (template)
125 * @fullpath:		full path in UNC format
126 * @ref:		optional server's referral
127 * @devname:		optional pointer for saving device name
128 *
129 * creates mount options for submount based on template options sb_mountdata
130 * and replacing unc,ip,prefixpath options with ones we've got form ref_unc.
131 *
132 * Returns: pointer to new mount options or ERR_PTR.
133 * Caller is responsible for freeing returned value if it is not error.
134 */
135char *cifs_compose_mount_options(const char *sb_mountdata,
136				   const char *fullpath,
137				   const struct dfs_info3_param *ref,
138				   char **devname)
139{
140	int rc;
141	char *name;
142	char *mountdata = NULL;
143	const char *prepath = NULL;
144	int md_len;
145	char *tkn_e;
146	char *srvIP = NULL;
147	char sep = ',';
148	int off, noff;
149
150	if (sb_mountdata == NULL)
151		return ERR_PTR(-EINVAL);
152
153	if (ref) {
154		if (strlen(fullpath) - ref->path_consumed) {
155			prepath = fullpath + ref->path_consumed;
156			/* skip initial delimiter */
157			if (*prepath == '/' || *prepath == '\\')
158				prepath++;
159		}
160
161		name = cifs_build_devname(ref->node_name, prepath);
162		if (IS_ERR(name)) {
163			rc = PTR_ERR(name);
164			name = NULL;
165			goto compose_mount_options_err;
166		}
167	} else {
168		name = cifs_build_devname((char *)fullpath, NULL);
169		if (IS_ERR(name)) {
170			rc = PTR_ERR(name);
171			name = NULL;
172			goto compose_mount_options_err;
173		}
174	}
175
176	rc = dns_resolve_server_name_to_ip(name, &srvIP);
177	if (rc < 0) {
178		cifs_dbg(FYI, "%s: Failed to resolve server part of %s to IP: %d\n",
179			 __func__, name, rc);
180		goto compose_mount_options_err;
181	}
182
183	/*
184	 * In most cases, we'll be building a shorter string than the original,
185	 * but we do have to assume that the address in the ip= option may be
186	 * much longer than the original. Add the max length of an address
187	 * string to the length of the original string to allow for worst case.
188	 */
189	md_len = strlen(sb_mountdata) + INET6_ADDRSTRLEN;
190	mountdata = kzalloc(md_len + sizeof("ip=") + 1, GFP_KERNEL);
191	if (mountdata == NULL) {
192		rc = -ENOMEM;
193		goto compose_mount_options_err;
194	}
195
196	/* copy all options except of unc,ip,prefixpath */
197	off = 0;
198	if (strncmp(sb_mountdata, "sep=", 4) == 0) {
199			sep = sb_mountdata[4];
200			strncpy(mountdata, sb_mountdata, 5);
201			off += 5;
202	}
203
204	do {
205		tkn_e = strchr(sb_mountdata + off, sep);
206		if (tkn_e == NULL)
207			noff = strlen(sb_mountdata + off);
208		else
209			noff = tkn_e - (sb_mountdata + off) + 1;
210
211		if (strncasecmp(sb_mountdata + off, "unc=", 4) == 0) {
212			off += noff;
213			continue;
214		}
215		if (strncasecmp(sb_mountdata + off, "ip=", 3) == 0) {
216			off += noff;
217			continue;
218		}
219		if (strncasecmp(sb_mountdata + off, "prefixpath=", 11) == 0) {
220			off += noff;
221			continue;
222		}
223		strncat(mountdata, sb_mountdata + off, noff);
224		off += noff;
225	} while (tkn_e);
226	strcat(mountdata, sb_mountdata + off);
227	mountdata[md_len] = '\0';
228
229	/* copy new IP and ref share name */
230	if (mountdata[strlen(mountdata) - 1] != sep)
231		strncat(mountdata, &sep, 1);
232	strcat(mountdata, "ip=");
233	strcat(mountdata, srvIP);
234
235	if (devname)
236		*devname = name;
237	else
238		kfree(name);
239
240	/*cifs_dbg(FYI, "%s: parent mountdata: %s\n", __func__, sb_mountdata);*/
241	/*cifs_dbg(FYI, "%s: submount mountdata: %s\n", __func__, mountdata );*/
242
243compose_mount_options_out:
244	kfree(srvIP);
245	return mountdata;
246
247compose_mount_options_err:
248	kfree(mountdata);
249	mountdata = ERR_PTR(rc);
250	kfree(name);
251	goto compose_mount_options_out;
252}
253
254/**
255 * cifs_dfs_do_mount - mounts specified path using DFS full path
256 *
257 * Always pass down @fullpath to smb3_do_mount() so we can use the root server
258 * to perform failover in case we failed to connect to the first target in the
259 * referral.
260 *
261 * @cifs_sb:		parent/root superblock
262 * @fullpath:		full path in UNC format
263 */
264static struct vfsmount *cifs_dfs_do_mount(struct dentry *mntpt,
265					  struct cifs_sb_info *cifs_sb,
266					  const char *fullpath)
267{
268	struct vfsmount *mnt;
269	char *mountdata;
270	char *devname;
271
272	devname = kstrndup(fullpath, strlen(fullpath), GFP_KERNEL);
273	if (!devname)
274		return ERR_PTR(-ENOMEM);
275
276	convert_delimiter(devname, '/');
277
278	/* strip first '\' from fullpath */
279	mountdata = cifs_compose_mount_options(cifs_sb->mountdata,
280					       fullpath + 1, NULL, NULL);
281	if (IS_ERR(mountdata)) {
282		kfree(devname);
283		return (struct vfsmount *)mountdata;
284	}
285
286	mnt = vfs_submount(mntpt, &cifs_fs_type, devname, mountdata);
287	kfree(mountdata);
288	kfree(devname);
289	return mnt;
290}
291
292/*
293 * Create a vfsmount that we can automount
294 */
295static struct vfsmount *cifs_dfs_do_automount(struct dentry *mntpt)
296{
297	struct cifs_sb_info *cifs_sb;
298	struct cifs_ses *ses;
299	struct cifs_tcon *tcon;
300	char *full_path, *root_path;
301	unsigned int xid;
302	int rc;
303	struct vfsmount *mnt;
304
305	cifs_dbg(FYI, "in %s\n", __func__);
306	BUG_ON(IS_ROOT(mntpt));
307
308	/*
309	 * The MSDFS spec states that paths in DFS referral requests and
310	 * responses must be prefixed by a single '\' character instead of
311	 * the double backslashes usually used in the UNC. This function
312	 * gives us the latter, so we must adjust the result.
313	 */
314	mnt = ERR_PTR(-ENOMEM);
315
316	cifs_sb = CIFS_SB(mntpt->d_sb);
317	if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_NO_DFS) {
318		mnt = ERR_PTR(-EREMOTE);
319		goto cdda_exit;
320	}
321
322	/* always use tree name prefix */
323	full_path = build_path_from_dentry_optional_prefix(mntpt, true);
324	if (full_path == NULL)
325		goto cdda_exit;
326
327	convert_delimiter(full_path, '\\');
328
329	cifs_dbg(FYI, "%s: full_path: %s\n", __func__, full_path);
330
331	if (!cifs_sb_master_tlink(cifs_sb)) {
332		cifs_dbg(FYI, "%s: master tlink is NULL\n", __func__);
333		goto free_full_path;
334	}
335
336	tcon = cifs_sb_master_tcon(cifs_sb);
337	if (!tcon) {
338		cifs_dbg(FYI, "%s: master tcon is NULL\n", __func__);
339		goto free_full_path;
340	}
341
342	root_path = kstrdup(tcon->treeName, GFP_KERNEL);
343	if (!root_path) {
344		mnt = ERR_PTR(-ENOMEM);
345		goto free_full_path;
346	}
347	cifs_dbg(FYI, "%s: root path: %s\n", __func__, root_path);
348
349	ses = tcon->ses;
350	xid = get_xid();
351
352	/*
353	 * If DFS root has been expired, then unconditionally fetch it again to
354	 * refresh DFS referral cache.
355	 */
356	rc = dfs_cache_find(xid, ses, cifs_sb->local_nls, cifs_remap(cifs_sb),
357			    root_path + 1, NULL, NULL);
358	if (!rc) {
359		rc = dfs_cache_find(xid, ses, cifs_sb->local_nls,
360				    cifs_remap(cifs_sb), full_path + 1,
361				    NULL, NULL);
362	}
363
364	free_xid(xid);
365
366	if (rc) {
367		mnt = ERR_PTR(rc);
368		goto free_root_path;
369	}
370	/*
371	 * OK - we were able to get and cache a referral for @full_path.
372	 *
373	 * Now, pass it down to cifs_mount() and it will retry every available
374	 * node server in case of failures - no need to do it here.
375	 */
376	mnt = cifs_dfs_do_mount(mntpt, cifs_sb, full_path);
377	cifs_dbg(FYI, "%s: cifs_dfs_do_mount:%s , mnt:%p\n", __func__,
378		 full_path + 1, mnt);
379
380free_root_path:
381	kfree(root_path);
382free_full_path:
383	kfree(full_path);
384cdda_exit:
385	cifs_dbg(FYI, "leaving %s\n" , __func__);
386	return mnt;
387}
388
389/*
390 * Attempt to automount the referral
391 */
392struct vfsmount *cifs_dfs_d_automount(struct path *path)
393{
394	struct vfsmount *newmnt;
395
396	cifs_dbg(FYI, "in %s\n", __func__);
397
398	newmnt = cifs_dfs_do_automount(path->dentry);
399	if (IS_ERR(newmnt)) {
400		cifs_dbg(FYI, "leaving %s [automount failed]\n" , __func__);
401		return newmnt;
402	}
403
404	mntget(newmnt); /* prevent immediate expiration */
405	mnt_set_expiry(newmnt, &cifs_dfs_automount_list);
406	schedule_delayed_work(&cifs_dfs_automount_task,
407			      cifs_dfs_mountpoint_expiry_timeout);
408	cifs_dbg(FYI, "leaving %s [ok]\n" , __func__);
409	return newmnt;
410}
411
412const struct inode_operations cifs_dfs_referral_inode_operations = {
413};