fs/cifs/cifs_dfs_ref.c

   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
  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
  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 *
  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  */
 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 (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
 243 compose_mount_options_out:
 244         kfree(srvIP);
 245         return mountdata;
 246
 247 compose_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  */
 264 static 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  */
 295 static 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
 380 free_root_path:
 381         kfree(root_path);
 382 free_full_path:
 383         kfree(full_path);
 384 cdda_exit:
 385         cifs_dbg(FYI, "leaving %s\n" , __func__);
 386         return mnt;
 387 }
 388
 389 /*
 390  * Attempt to automount the referral
 391  */
 392 struct 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
 412 const struct inode_operations cifs_dfs_referral_inode_operations = {
 413 };