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 {
 139         int rc;
 140         char *name;
 141         char *mountdata = NULL;
 142         const char *prepath = NULL;
 143         int md_len;
 144         char *tkn_e;
 145         char *srvIP = NULL;
 146         char sep = ',';
 147         int off, noff;
 148
 149         if (sb_mountdata == NULL)
 150                 return ERR_PTR(-EINVAL);
 151
 152         if (ref) {
 153                 if (strlen(fullpath) - ref->path_consumed) {
 154                         prepath = fullpath + ref->path_consumed;
 155                         /* skip initial delimiter */
 156                         if (*prepath == '/' || *prepath == '\\')
 157                                 prepath++;
 158                 }
 159
 160                 name = cifs_build_devname(ref->node_name, prepath);
 161                 if (IS_ERR(name)) {
 162                         rc = PTR_ERR(name);
 163                         name = NULL;
 164                         goto compose_mount_options_err;
 165                 }
 166         } else {
 167                 name = cifs_build_devname((char *)fullpath, NULL);
 168                 if (IS_ERR(name)) {
 169                         rc = PTR_ERR(name);
 170                         name = NULL;
 171                         goto compose_mount_options_err;
 172                 }
 173         }
 174
 175         rc = dns_resolve_server_name_to_ip(name, &srvIP);
 176         if (rc < 0) {
 177                 cifs_dbg(FYI, "%s: Failed to resolve server part of %s to IP: %d\n",
 178                          __func__, name, rc);
 179                 goto compose_mount_options_err;
 180         }
 181
 182         /*
 183          * In most cases, we'll be building a shorter string than the original,
 184          * but we do have to assume that the address in the ip= option may be
 185          * much longer than the original. Add the max length of an address
 186          * string to the length of the original string to allow for worst case.
 187          */
 188         md_len = strlen(sb_mountdata) + INET6_ADDRSTRLEN;
 189         mountdata = kzalloc(md_len + sizeof("ip=") + 1, GFP_KERNEL);
 190         if (mountdata == NULL) {
 191                 rc = -ENOMEM;
 192                 goto compose_mount_options_err;
 193         }
 194
 195         /* copy all options except of unc,ip,prefixpath */
 196         off = 0;
 197         if (strncmp(sb_mountdata, "sep=", 4) == 0) {
 198                         sep = sb_mountdata[4];
 199                         strncpy(mountdata, sb_mountdata, 5);
 200                         off += 5;
 201         }
 202
 203         do {
 204                 tkn_e = strchr(sb_mountdata + off, sep);
 205                 if (tkn_e == NULL)
 206                         noff = strlen(sb_mountdata + off);
 207                 else
 208                         noff = tkn_e - (sb_mountdata + off) + 1;
 209
 210                 if (strncasecmp(sb_mountdata + off, "unc=", 4) == 0) {
 211                         off += noff;
 212                         continue;
 213                 }
 214                 if (strncasecmp(sb_mountdata + off, "ip=", 3) == 0) {
 215                         off += noff;
 216                         continue;
 217                 }
 218                 if (strncasecmp(sb_mountdata + off, "prefixpath=", 11) == 0) {
 219                         off += noff;
 220                         continue;
 221                 }
 222                 strncat(mountdata, sb_mountdata + off, noff);
 223                 off += noff;
 224         } while (tkn_e);
 225         strcat(mountdata, sb_mountdata + off);
 226         mountdata[md_len] = '\0';
 227
 228         /* copy new IP and ref share name */
 229         if (mountdata[strlen(mountdata) - 1] != sep)
 230                 strncat(mountdata, &sep, 1);
 231         strcat(mountdata, "ip=");
 232         strcat(mountdata, srvIP);
 233
 234         kfree(name);
 235
 236         /*cifs_dbg(FYI, "%s: parent mountdata: %s\n", __func__, sb_mountdata);*/
 237         /*cifs_dbg(FYI, "%s: submount mountdata: %s\n", __func__, mountdata );*/
 238
 239 compose_mount_options_out:
 240         kfree(srvIP);
 241         return mountdata;
 242
 243 compose_mount_options_err:
 244         kfree(mountdata);
 245         mountdata = ERR_PTR(rc);
 246         kfree(name);
 247         goto compose_mount_options_out;
 248 }
 249
 250 /**
 251  * cifs_dfs_do_mount - mounts specified path using DFS full path
 252  *
 253  * Always pass down @fullpath to smb3_do_mount() so we can use the root server
 254  * to perform failover in case we failed to connect to the first target in the
 255  * referral.
 256  *
 257  * @mntpt:              directory entry for the path we are trying to automount
 258  * @cifs_sb:            parent/root superblock
 259  * @fullpath:           full path in UNC format
 260  */
 261 static struct vfsmount *cifs_dfs_do_mount(struct dentry *mntpt,
 262                                           struct cifs_sb_info *cifs_sb,
 263                                           const char *fullpath)
 264 {
 265         struct vfsmount *mnt;
 266         char *mountdata;
 267         char *devname;
 268
 269         devname = kstrndup(fullpath, strlen(fullpath), GFP_KERNEL);
 270         if (!devname)
 271                 return ERR_PTR(-ENOMEM);
 272
 273         convert_delimiter(devname, '/');
 274
 275         /* TODO: change to call fs_context_for_mount(), fill in context directly, call fc_mount */
 276
 277         /* See afs_mntpt_do_automount in fs/afs/mntpt.c for an example */
 278
 279         /* strip first '\' from fullpath */
 280         mountdata = cifs_compose_mount_options(cifs_sb->ctx->mount_options,
 281                                                fullpath + 1, NULL);
 282         if (IS_ERR(mountdata)) {
 283                 kfree(devname);
 284                 return (struct vfsmount *)mountdata;
 285         }
 286
 287         mnt = vfs_submount(mntpt, &cifs_fs_type, devname, mountdata);
 288         kfree(mountdata);
 289         kfree(devname);
 290         return mnt;
 291 }
 292
 293 /*
 294  * Create a vfsmount that we can automount
 295  */
 296 static struct vfsmount *cifs_dfs_do_automount(struct dentry *mntpt)
 297 {
 298         struct cifs_sb_info *cifs_sb;
 299         struct cifs_ses *ses;
 300         struct cifs_tcon *tcon;
 301         char *full_path, *root_path;
 302         unsigned int xid;
 303         int rc;
 304         struct vfsmount *mnt;
 305
 306         cifs_dbg(FYI, "in %s\n", __func__);
 307         BUG_ON(IS_ROOT(mntpt));
 308
 309         /*
 310          * The MSDFS spec states that paths in DFS referral requests and
 311          * responses must be prefixed by a single '\' character instead of
 312          * the double backslashes usually used in the UNC. This function
 313          * gives us the latter, so we must adjust the result.
 314          */
 315         mnt = ERR_PTR(-ENOMEM);
 316
 317         cifs_sb = CIFS_SB(mntpt->d_sb);
 318         if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_NO_DFS) {
 319                 mnt = ERR_PTR(-EREMOTE);
 320                 goto cdda_exit;
 321         }
 322
 323         /* always use tree name prefix */
 324         full_path = build_path_from_dentry_optional_prefix(mntpt, true);
 325         if (full_path == NULL)
 326                 goto cdda_exit;
 327
 328         convert_delimiter(full_path, '\\');
 329
 330         cifs_dbg(FYI, "%s: full_path: %s\n", __func__, full_path);
 331
 332         if (!cifs_sb_master_tlink(cifs_sb)) {
 333                 cifs_dbg(FYI, "%s: master tlink is NULL\n", __func__);
 334                 goto free_full_path;
 335         }
 336
 337         tcon = cifs_sb_master_tcon(cifs_sb);
 338         if (!tcon) {
 339                 cifs_dbg(FYI, "%s: master tcon is NULL\n", __func__);
 340                 goto free_full_path;
 341         }
 342
 343         root_path = kstrdup(tcon->treeName, GFP_KERNEL);
 344         if (!root_path) {
 345                 mnt = ERR_PTR(-ENOMEM);
 346                 goto free_full_path;
 347         }
 348         cifs_dbg(FYI, "%s: root path: %s\n", __func__, root_path);
 349
 350         ses = tcon->ses;
 351         xid = get_xid();
 352
 353         /*
 354          * If DFS root has been expired, then unconditionally fetch it again to
 355          * refresh DFS referral cache.
 356          */
 357         rc = dfs_cache_find(xid, ses, cifs_sb->local_nls, cifs_remap(cifs_sb),
 358                             root_path + 1, NULL, NULL);
 359         if (!rc) {
 360                 rc = dfs_cache_find(xid, ses, cifs_sb->local_nls,
 361                                     cifs_remap(cifs_sb), full_path + 1,
 362                                     NULL, NULL);
 363         }
 364
 365         free_xid(xid);
 366
 367         if (rc) {
 368                 mnt = ERR_PTR(rc);
 369                 goto free_root_path;
 370         }
 371         /*
 372          * OK - we were able to get and cache a referral for @full_path.
 373          *
 374          * Now, pass it down to cifs_mount() and it will retry every available
 375          * node server in case of failures - no need to do it here.
 376          */
 377         mnt = cifs_dfs_do_mount(mntpt, cifs_sb, full_path);
 378         cifs_dbg(FYI, "%s: cifs_dfs_do_mount:%s , mnt:%p\n", __func__,
 379                  full_path + 1, mnt);
 380
 381 free_root_path:
 382         kfree(root_path);
 383 free_full_path:
 384         kfree(full_path);
 385 cdda_exit:
 386         cifs_dbg(FYI, "leaving %s\n" , __func__);
 387         return mnt;
 388 }
 389
 390 /*
 391  * Attempt to automount the referral
 392  */
 393 struct vfsmount *cifs_dfs_d_automount(struct path *path)
 394 {
 395         struct vfsmount *newmnt;
 396
 397         cifs_dbg(FYI, "in %s\n", __func__);
 398
 399         newmnt = cifs_dfs_do_automount(path->dentry);
 400         if (IS_ERR(newmnt)) {
 401                 cifs_dbg(FYI, "leaving %s [automount failed]\n" , __func__);
 402                 return newmnt;
 403         }
 404
 405         mntget(newmnt); /* prevent immediate expiration */
 406         mnt_set_expiry(newmnt, &cifs_dfs_automount_list);
 407         schedule_delayed_work(&cifs_dfs_automount_task,
 408                               cifs_dfs_mountpoint_expiry_timeout);
 409         cifs_dbg(FYI, "leaving %s [ok]\n" , __func__);
 410         return newmnt;
 411 }
 412
 413 const struct inode_operations cifs_dfs_referral_inode_operations = {
 414 };