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 #include "fs_context.h"
  27
  28 static LIST_HEAD(cifs_dfs_automount_list);
  29
  30 static void cifs_dfs_expire_automounts(struct work_struct *work);
  31 static DECLARE_DELAYED_WORK(cifs_dfs_automount_task,
  32                             cifs_dfs_expire_automounts);
  33 static int cifs_dfs_mountpoint_expiry_timeout = 500 * HZ;
  34
  35 static void cifs_dfs_expire_automounts(struct work_struct *work)
  36 {
  37         struct list_head *list = &cifs_dfs_automount_list;
  38
  39         mark_mounts_for_expiry(list);
  40         if (!list_empty(list))
  41                 schedule_delayed_work(&cifs_dfs_automount_task,
  42                                       cifs_dfs_mountpoint_expiry_timeout);
  43 }
  44
  45 void cifs_dfs_release_automount_timer(void)
  46 {
  47         BUG_ON(!list_empty(&cifs_dfs_automount_list));
  48         cancel_delayed_work_sync(&cifs_dfs_automount_task);
  49 }
  50
  51 /**
  52  * cifs_build_devname - build a devicename from a UNC and optional prepath
  53  * @nodename:   pointer to UNC string
  54  * @prepath:    pointer to prefixpath (or NULL if there isn't one)
  55  *
  56  * Build a new cifs devicename after chasing a DFS referral. Allocate a buffer
  57  * big enough to hold the final thing. Copy the UNC from the nodename, and
  58  * concatenate the prepath onto the end of it if there is one.
  59  *
  60  * Returns pointer to the built string, or a ERR_PTR. Caller is responsible
  61  * for freeing the returned string.
  62  */
  63 static char *
  64 cifs_build_devname(char *nodename, const char *prepath)
  65 {
  66         size_t pplen;
  67         size_t unclen;
  68         char *dev;
  69         char *pos;
  70
  71         /* skip over any preceding delimiters */
  72         nodename += strspn(nodename, "\\");
  73         if (!*nodename)
  74                 return ERR_PTR(-EINVAL);
  75
  76         /* get length of UNC and set pos to last char */
  77         unclen = strlen(nodename);
  78         pos = nodename + unclen - 1;
  79
  80         /* trim off any trailing delimiters */
  81         while (*pos == '\\') {
  82                 --pos;
  83                 --unclen;
  84         }
  85
  86         /* allocate a buffer:
  87          * +2 for preceding "//"
  88          * +1 for delimiter between UNC and prepath
  89          * +1 for trailing NULL
  90          */
  91         pplen = prepath ? strlen(prepath) : 0;
  92         dev = kmalloc(2 + unclen + 1 + pplen + 1, GFP_KERNEL);
  93         if (!dev)
  94                 return ERR_PTR(-ENOMEM);
  95
  96         pos = dev;
  97         /* add the initial "//" */
  98         *pos = '/';
  99         ++pos;
 100         *pos = '/';
 101         ++pos;
 102
 103         /* copy in the UNC portion from referral */
 104         memcpy(pos, nodename, unclen);
 105         pos += unclen;
 106
 107         /* copy the prefixpath remainder (if there is one) */
 108         if (pplen) {
 109                 *pos = '/';
 110                 ++pos;
 111                 memcpy(pos, prepath, pplen);
 112                 pos += pplen;
 113         }
 114
 115         /* NULL terminator */
 116         *pos = '\0';
 117
 118         convert_delimiter(dev, '/');
 119         return dev;
 120 }
 121
 122
 123 /**
 124  * cifs_compose_mount_options   -       creates mount options for referral
 125  * @sb_mountdata:       parent/root DFS mount options (template)
 126  * @fullpath:           full path in UNC format
 127  * @ref:                optional server's referral
 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  * @mntpt:              directory entry for the path we are trying to automount
 262  * @cifs_sb:            parent/root superblock
 263  * @fullpath:           full path in UNC format
 264  */
 265 static struct vfsmount *cifs_dfs_do_mount(struct dentry *mntpt,
 266                                           struct cifs_sb_info *cifs_sb,
 267                                           const char *fullpath)
 268 {
 269         struct vfsmount *mnt;
 270         char *mountdata;
 271         char *devname;
 272
 273         devname = kstrndup(fullpath, strlen(fullpath), GFP_KERNEL);
 274         if (!devname)
 275                 return ERR_PTR(-ENOMEM);
 276
 277         convert_delimiter(devname, '/');
 278
 279         /* TODO: change to call fs_context_for_mount(), fill in context directly, call fc_mount */
 280
 281         /* See afs_mntpt_do_automount in fs/afs/mntpt.c for an example */
 282
 283         /* strip first '\' from fullpath */
 284         mountdata = cifs_compose_mount_options(cifs_sb->ctx->mount_options,
 285                                                fullpath + 1, NULL, NULL);
 286         if (IS_ERR(mountdata)) {
 287                 kfree(devname);
 288                 return (struct vfsmount *)mountdata;
 289         }
 290
 291         mnt = vfs_submount(mntpt, &cifs_fs_type, devname, mountdata);
 292         kfree(mountdata);
 293         kfree(devname);
 294         return mnt;
 295 }
 296
 297 /*
 298  * Create a vfsmount that we can automount
 299  */
 300 static struct vfsmount *cifs_dfs_do_automount(struct dentry *mntpt)
 301 {
 302         struct cifs_sb_info *cifs_sb;
 303         struct cifs_ses *ses;
 304         struct cifs_tcon *tcon;
 305         char *full_path, *root_path;
 306         unsigned int xid;
 307         int rc;
 308         struct vfsmount *mnt;
 309
 310         cifs_dbg(FYI, "in %s\n", __func__);
 311         BUG_ON(IS_ROOT(mntpt));
 312
 313         /*
 314          * The MSDFS spec states that paths in DFS referral requests and
 315          * responses must be prefixed by a single '\' character instead of
 316          * the double backslashes usually used in the UNC. This function
 317          * gives us the latter, so we must adjust the result.
 318          */
 319         mnt = ERR_PTR(-ENOMEM);
 320
 321         cifs_sb = CIFS_SB(mntpt->d_sb);
 322         if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_NO_DFS) {
 323                 mnt = ERR_PTR(-EREMOTE);
 324                 goto cdda_exit;
 325         }
 326
 327         /* always use tree name prefix */
 328         full_path = build_path_from_dentry_optional_prefix(mntpt, true);
 329         if (full_path == NULL)
 330                 goto cdda_exit;
 331
 332         convert_delimiter(full_path, '\\');
 333
 334         cifs_dbg(FYI, "%s: full_path: %s\n", __func__, full_path);
 335
 336         if (!cifs_sb_master_tlink(cifs_sb)) {
 337                 cifs_dbg(FYI, "%s: master tlink is NULL\n", __func__);
 338                 goto free_full_path;
 339         }
 340
 341         tcon = cifs_sb_master_tcon(cifs_sb);
 342         if (!tcon) {
 343                 cifs_dbg(FYI, "%s: master tcon is NULL\n", __func__);
 344                 goto free_full_path;
 345         }
 346
 347         root_path = kstrdup(tcon->treeName, GFP_KERNEL);
 348         if (!root_path) {
 349                 mnt = ERR_PTR(-ENOMEM);
 350                 goto free_full_path;
 351         }
 352         cifs_dbg(FYI, "%s: root path: %s\n", __func__, root_path);
 353
 354         ses = tcon->ses;
 355         xid = get_xid();
 356
 357         /*
 358          * If DFS root has been expired, then unconditionally fetch it again to
 359          * refresh DFS referral cache.
 360          */
 361         rc = dfs_cache_find(xid, ses, cifs_sb->local_nls, cifs_remap(cifs_sb),
 362                             root_path + 1, NULL, NULL);
 363         if (!rc) {
 364                 rc = dfs_cache_find(xid, ses, cifs_sb->local_nls,
 365                                     cifs_remap(cifs_sb), full_path + 1,
 366                                     NULL, NULL);
 367         }
 368
 369         free_xid(xid);
 370
 371         if (rc) {
 372                 mnt = ERR_PTR(rc);
 373                 goto free_root_path;
 374         }
 375         /*
 376          * OK - we were able to get and cache a referral for @full_path.
 377          *
 378          * Now, pass it down to cifs_mount() and it will retry every available
 379          * node server in case of failures - no need to do it here.
 380          */
 381         mnt = cifs_dfs_do_mount(mntpt, cifs_sb, full_path);
 382         cifs_dbg(FYI, "%s: cifs_dfs_do_mount:%s , mnt:%p\n", __func__,
 383                  full_path + 1, mnt);
 384
 385 free_root_path:
 386         kfree(root_path);
 387 free_full_path:
 388         kfree(full_path);
 389 cdda_exit:
 390         cifs_dbg(FYI, "leaving %s\n" , __func__);
 391         return mnt;
 392 }
 393
 394 /*
 395  * Attempt to automount the referral
 396  */
 397 struct vfsmount *cifs_dfs_d_automount(struct path *path)
 398 {
 399         struct vfsmount *newmnt;
 400
 401         cifs_dbg(FYI, "in %s\n", __func__);
 402
 403         newmnt = cifs_dfs_do_automount(path->dentry);
 404         if (IS_ERR(newmnt)) {
 405                 cifs_dbg(FYI, "leaving %s [automount failed]\n" , __func__);
 406                 return newmnt;
 407         }
 408
 409         mntget(newmnt); /* prevent immediate expiration */
 410         mnt_set_expiry(newmnt, &cifs_dfs_automount_list);
 411         schedule_delayed_work(&cifs_dfs_automount_task,
 412                               cifs_dfs_mountpoint_expiry_timeout);
 413         cifs_dbg(FYI, "leaving %s [ok]\n" , __func__);
 414         return newmnt;
 415 }
 416
 417 const struct inode_operations cifs_dfs_referral_inode_operations = {
 418 };