xref: /kernel/linux/linux-5.10/fs/cifs/cifs_dfs_ref.c (revision 8c2ecf20) 
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 (WARN_ON_ONCE(!ref->node_name || ref->path_consumed < 0))
155			return ERR_PTR(-EINVAL);
156
157		if (strlen(fullpath) - ref->path_consumed) {
158			prepath = fullpath + ref->path_consumed;
159			/* skip initial delimiter */
160			if (*prepath == '/' || *prepath == '\\')
161				prepath++;
162		}
163
164		name = cifs_build_devname(ref->node_name, prepath);
165		if (IS_ERR(name)) {
166			rc = PTR_ERR(name);
167			name = NULL;
168			goto compose_mount_options_err;
169		}
170	} else {
171		name = cifs_build_devname((char *)fullpath, NULL);
172		if (IS_ERR(name)) {
173			rc = PTR_ERR(name);
174			name = NULL;
175			goto compose_mount_options_err;
176		}
177	}
178
179	rc = dns_resolve_server_name_to_ip(name, &srvIP);
180	if (rc < 0) {
181		cifs_dbg(FYI, "%s: Failed to resolve server part of %s to IP: %d\n",
182			 __func__, name, rc);
183		goto compose_mount_options_err;
184	}
185
186	/*
187	 * In most cases, we'll be building a shorter string than the original,
188	 * but we do have to assume that the address in the ip= option may be
189	 * much longer than the original. Add the max length of an address
190	 * string to the length of the original string to allow for worst case.
191	 */
192	md_len = strlen(sb_mountdata) + INET6_ADDRSTRLEN;
193	mountdata = kzalloc(md_len + sizeof("ip=") + 1, GFP_KERNEL);
194	if (mountdata == NULL) {
195		rc = -ENOMEM;
196		goto compose_mount_options_err;
197	}
198
199	/* copy all options except of unc,ip,prefixpath */
200	off = 0;
201	if (strncmp(sb_mountdata, "sep=", 4) == 0) {
202			sep = sb_mountdata[4];
203			strncpy(mountdata, sb_mountdata, 5);
204			off += 5;
205	}
206
207	do {
208		tkn_e = strchr(sb_mountdata + off, sep);
209		if (tkn_e == NULL)
210			noff = strlen(sb_mountdata + off);
211		else
212			noff = tkn_e - (sb_mountdata + off) + 1;
213
214		if (strncasecmp(sb_mountdata + off, "unc=", 4) == 0) {
215			off += noff;
216			continue;
217		}
218		if (strncasecmp(sb_mountdata + off, "ip=", 3) == 0) {
219			off += noff;
220			continue;
221		}
222		if (strncasecmp(sb_mountdata + off, "prefixpath=", 11) == 0) {
223			off += noff;
224			continue;
225		}
226		strncat(mountdata, sb_mountdata + off, noff);
227		off += noff;
228	} while (tkn_e);
229	strcat(mountdata, sb_mountdata + off);
230	mountdata[md_len] = '\0';
231
232	/* copy new IP and ref share name */
233	if (mountdata[strlen(mountdata) - 1] != sep)
234		strncat(mountdata, &sep, 1);
235	strcat(mountdata, "ip=");
236	strcat(mountdata, srvIP);
237
238	if (devname)
239		*devname = name;
240	else
241		kfree(name);
242
243	/*cifs_dbg(FYI, "%s: parent mountdata: %s\n", __func__, sb_mountdata);*/
244	/*cifs_dbg(FYI, "%s: submount mountdata: %s\n", __func__, mountdata );*/
245
246compose_mount_options_out:
247	kfree(srvIP);
248	return mountdata;
249
250compose_mount_options_err:
251	kfree(mountdata);
252	mountdata = ERR_PTR(rc);
253	kfree(name);
254	goto compose_mount_options_out;
255}
256
257/**
258 * cifs_dfs_do_mount - mounts specified path using DFS full path
259 *
260 * Always pass down @fullpath to smb3_do_mount() so we can use the root server
261 * to perform failover in case we failed to connect to the first target in the
262 * referral.
263 *
264 * @cifs_sb:		parent/root superblock
265 * @fullpath:		full path in UNC format
266 */
267static struct vfsmount *cifs_dfs_do_mount(struct dentry *mntpt,
268					  struct cifs_sb_info *cifs_sb,
269					  const char *fullpath)
270{
271	struct vfsmount *mnt;
272	char *mountdata;
273	char *devname;
274
275	devname = kstrndup(fullpath, strlen(fullpath), GFP_KERNEL);
276	if (!devname)
277		return ERR_PTR(-ENOMEM);
278
279	convert_delimiter(devname, '/');
280
281	/* strip first '\' from fullpath */
282	mountdata = cifs_compose_mount_options(cifs_sb->mountdata,
283					       fullpath + 1, NULL, NULL);
284	if (IS_ERR(mountdata)) {
285		kfree(devname);
286		return (struct vfsmount *)mountdata;
287	}
288
289	mnt = vfs_submount(mntpt, &cifs_fs_type, devname, mountdata);
290	kfree(mountdata);
291	kfree(devname);
292	return mnt;
293}
294
295/*
296 * Create a vfsmount that we can automount
297 */
298static struct vfsmount *cifs_dfs_do_automount(struct dentry *mntpt)
299{
300	struct cifs_sb_info *cifs_sb;
301	struct cifs_ses *ses;
302	struct cifs_tcon *tcon;
303	char *full_path, *root_path;
304	unsigned int xid;
305	int rc;
306	struct vfsmount *mnt;
307
308	cifs_dbg(FYI, "in %s\n", __func__);
309	BUG_ON(IS_ROOT(mntpt));
310
311	/*
312	 * The MSDFS spec states that paths in DFS referral requests and
313	 * responses must be prefixed by a single '\' character instead of
314	 * the double backslashes usually used in the UNC. This function
315	 * gives us the latter, so we must adjust the result.
316	 */
317	mnt = ERR_PTR(-ENOMEM);
318
319	cifs_sb = CIFS_SB(mntpt->d_sb);
320	if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_NO_DFS) {
321		mnt = ERR_PTR(-EREMOTE);
322		goto cdda_exit;
323	}
324
325	/* always use tree name prefix */
326	full_path = build_path_from_dentry_optional_prefix(mntpt, true);
327	if (full_path == NULL)
328		goto cdda_exit;
329
330	convert_delimiter(full_path, '\\');
331
332	cifs_dbg(FYI, "%s: full_path: %s\n", __func__, full_path);
333
334	if (!cifs_sb_master_tlink(cifs_sb)) {
335		cifs_dbg(FYI, "%s: master tlink is NULL\n", __func__);
336		goto free_full_path;
337	}
338
339	tcon = cifs_sb_master_tcon(cifs_sb);
340	if (!tcon) {
341		cifs_dbg(FYI, "%s: master tcon is NULL\n", __func__);
342		goto free_full_path;
343	}
344
345	root_path = kstrdup(tcon->treeName, GFP_KERNEL);
346	if (!root_path) {
347		mnt = ERR_PTR(-ENOMEM);
348		goto free_full_path;
349	}
350	cifs_dbg(FYI, "%s: root path: %s\n", __func__, root_path);
351
352	ses = tcon->ses;
353	xid = get_xid();
354
355	/*
356	 * If DFS root has been expired, then unconditionally fetch it again to
357	 * refresh DFS referral cache.
358	 */
359	rc = dfs_cache_find(xid, ses, cifs_sb->local_nls, cifs_remap(cifs_sb),
360			    root_path + 1, NULL, NULL);
361	if (!rc) {
362		rc = dfs_cache_find(xid, ses, cifs_sb->local_nls,
363				    cifs_remap(cifs_sb), full_path + 1,
364				    NULL, NULL);
365	}
366
367	free_xid(xid);
368
369	if (rc) {
370		mnt = ERR_PTR(rc);
371		goto free_root_path;
372	}
373	/*
374	 * OK - we were able to get and cache a referral for @full_path.
375	 *
376	 * Now, pass it down to cifs_mount() and it will retry every available
377	 * node server in case of failures - no need to do it here.
378	 */
379	mnt = cifs_dfs_do_mount(mntpt, cifs_sb, full_path);
380	cifs_dbg(FYI, "%s: cifs_dfs_do_mount:%s , mnt:%p\n", __func__,
381		 full_path + 1, mnt);
382
383free_root_path:
384	kfree(root_path);
385free_full_path:
386	kfree(full_path);
387cdda_exit:
388	cifs_dbg(FYI, "leaving %s\n" , __func__);
389	return mnt;
390}
391
392/*
393 * Attempt to automount the referral
394 */
395struct vfsmount *cifs_dfs_d_automount(struct path *path)
396{
397	struct vfsmount *newmnt;
398
399	cifs_dbg(FYI, "in %s\n", __func__);
400
401	newmnt = cifs_dfs_do_automount(path->dentry);
402	if (IS_ERR(newmnt)) {
403		cifs_dbg(FYI, "leaving %s [automount failed]\n" , __func__);
404		return newmnt;
405	}
406
407	mntget(newmnt); /* prevent immediate expiration */
408	mnt_set_expiry(newmnt, &cifs_dfs_automount_list);
409	schedule_delayed_work(&cifs_dfs_automount_task,
410			      cifs_dfs_mountpoint_expiry_timeout);
411	cifs_dbg(FYI, "leaving %s [ok]\n" , __func__);
412	return newmnt;
413}
414
415const struct inode_operations cifs_dfs_referral_inode_operations = {
416};
417