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
27 static LIST_HEAD(cifs_dfs_automount_list);
28
29 static void cifs_dfs_expire_automounts(struct work_struct *work);
30 static DECLARE_DELAYED_WORK(cifs_dfs_automount_task,
31 cifs_dfs_expire_automounts);
32 static int cifs_dfs_mountpoint_expiry_timeout = 500 * HZ;
33
cifs_dfs_expire_automounts(struct work_struct * work)34 static 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
cifs_dfs_release_automount_timer(void)44 void 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 */
62 static char *
cifs_build_devname(char * nodename,const char * prepath)63 cifs_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 */
cifs_compose_mount_options(const char * sb_mountdata,const char * fullpath,const struct dfs_info3_param * ref,char ** devname)135 char *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
246 compose_mount_options_out:
247 kfree(srvIP);
248 return mountdata;
249
250 compose_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 */
cifs_dfs_do_mount(struct dentry * mntpt,struct cifs_sb_info * cifs_sb,const char * fullpath)267 static 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 */
cifs_dfs_do_automount(struct dentry * mntpt)298 static 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
383 free_root_path:
384 kfree(root_path);
385 free_full_path:
386 kfree(full_path);
387 cdda_exit:
388 cifs_dbg(FYI, "leaving %s\n" , __func__);
389 return mnt;
390 }
391
392 /*
393 * Attempt to automount the referral
394 */
cifs_dfs_d_automount(struct path * path)395 struct 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
415 const struct inode_operations cifs_dfs_referral_inode_operations = {
416 };
417