linux/fs/cifs/cifs_dfs_ref.c
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   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
  28static LIST_HEAD(cifs_dfs_automount_list);
  29
  30static void cifs_dfs_expire_automounts(struct work_struct *work);
  31static DECLARE_DELAYED_WORK(cifs_dfs_automount_task,
  32                            cifs_dfs_expire_automounts);
  33static int cifs_dfs_mountpoint_expiry_timeout = 500 * HZ;
  34
  35static 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
  45void 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 */
  63static char *
  64cifs_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 * @devname:            return the built cifs device name if passed pointer not NULL
 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, NULL);
 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, "cruid=", 6) == 0) {
 215                        off += noff;
 216                        continue;
 217                }
 218                if (strncasecmp(sb_mountdata + off, "unc=", 4) == 0) {
 219                        off += noff;
 220                        continue;
 221                }
 222                if (strncasecmp(sb_mountdata + off, "ip=", 3) == 0) {
 223                        off += noff;
 224                        continue;
 225                }
 226                if (strncasecmp(sb_mountdata + off, "prefixpath=", 11) == 0) {
 227                        off += noff;
 228                        continue;
 229                }
 230                strncat(mountdata, sb_mountdata + off, noff);
 231                off += noff;
 232        } while (tkn_e);
 233        strcat(mountdata, sb_mountdata + off);
 234        mountdata[md_len] = '\0';
 235
 236        /* copy new IP and ref share name */
 237        if (mountdata[strlen(mountdata) - 1] != sep)
 238                strncat(mountdata, &sep, 1);
 239        strcat(mountdata, "ip=");
 240        strcat(mountdata, srvIP);
 241
 242        if (devname)
 243                *devname = name;
 244        else
 245                kfree(name);
 246
 247        /*cifs_dbg(FYI, "%s: parent mountdata: %s\n", __func__, sb_mountdata);*/
 248        /*cifs_dbg(FYI, "%s: submount mountdata: %s\n", __func__, mountdata );*/
 249
 250compose_mount_options_out:
 251        kfree(srvIP);
 252        return mountdata;
 253
 254compose_mount_options_err:
 255        kfree(mountdata);
 256        mountdata = ERR_PTR(rc);
 257        kfree(name);
 258        goto compose_mount_options_out;
 259}
 260
 261/**
 262 * cifs_dfs_do_mount - mounts specified path using DFS full path
 263 *
 264 * Always pass down @fullpath to smb3_do_mount() so we can use the root server
 265 * to perform failover in case we failed to connect to the first target in the
 266 * referral.
 267 *
 268 * @mntpt:              directory entry for the path we are trying to automount
 269 * @cifs_sb:            parent/root superblock
 270 * @fullpath:           full path in UNC format
 271 */
 272static struct vfsmount *cifs_dfs_do_mount(struct dentry *mntpt,
 273                                          struct cifs_sb_info *cifs_sb,
 274                                          const char *fullpath)
 275{
 276        struct vfsmount *mnt;
 277        char *mountdata;
 278        char *devname;
 279
 280        devname = kstrdup(fullpath, GFP_KERNEL);
 281        if (!devname)
 282                return ERR_PTR(-ENOMEM);
 283
 284        convert_delimiter(devname, '/');
 285
 286        /* TODO: change to call fs_context_for_mount(), fill in context directly, call fc_mount */
 287
 288        /* See afs_mntpt_do_automount in fs/afs/mntpt.c for an example */
 289
 290        /* strip first '\' from fullpath */
 291        mountdata = cifs_compose_mount_options(cifs_sb->ctx->mount_options,
 292                                               fullpath + 1, NULL, NULL);
 293        if (IS_ERR(mountdata)) {
 294                kfree(devname);
 295                return (struct vfsmount *)mountdata;
 296        }
 297
 298        mnt = vfs_submount(mntpt, &cifs_fs_type, devname, mountdata);
 299        kfree(mountdata);
 300        kfree(devname);
 301        return mnt;
 302}
 303
 304/*
 305 * Create a vfsmount that we can automount
 306 */
 307static struct vfsmount *cifs_dfs_do_automount(struct dentry *mntpt)
 308{
 309        struct cifs_sb_info *cifs_sb;
 310        struct cifs_ses *ses;
 311        struct cifs_tcon *tcon;
 312        void *page;
 313        char *full_path, *root_path;
 314        unsigned int xid;
 315        int rc;
 316        struct vfsmount *mnt;
 317
 318        cifs_dbg(FYI, "in %s\n", __func__);
 319        BUG_ON(IS_ROOT(mntpt));
 320
 321        /*
 322         * The MSDFS spec states that paths in DFS referral requests and
 323         * responses must be prefixed by a single '\' character instead of
 324         * the double backslashes usually used in the UNC. This function
 325         * gives us the latter, so we must adjust the result.
 326         */
 327        mnt = ERR_PTR(-ENOMEM);
 328
 329        cifs_sb = CIFS_SB(mntpt->d_sb);
 330        if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_NO_DFS) {
 331                mnt = ERR_PTR(-EREMOTE);
 332                goto cdda_exit;
 333        }
 334
 335        page = alloc_dentry_path();
 336        /* always use tree name prefix */
 337        full_path = build_path_from_dentry_optional_prefix(mntpt, page, true);
 338        if (IS_ERR(full_path)) {
 339                mnt = ERR_CAST(full_path);
 340                goto free_full_path;
 341        }
 342
 343        convert_delimiter(full_path, '\\');
 344
 345        cifs_dbg(FYI, "%s: full_path: %s\n", __func__, full_path);
 346
 347        if (!cifs_sb_master_tlink(cifs_sb)) {
 348                cifs_dbg(FYI, "%s: master tlink is NULL\n", __func__);
 349                goto free_full_path;
 350        }
 351
 352        tcon = cifs_sb_master_tcon(cifs_sb);
 353        if (!tcon) {
 354                cifs_dbg(FYI, "%s: master tcon is NULL\n", __func__);
 355                goto free_full_path;
 356        }
 357
 358        root_path = kstrdup(tcon->treeName, GFP_KERNEL);
 359        if (!root_path) {
 360                mnt = ERR_PTR(-ENOMEM);
 361                goto free_full_path;
 362        }
 363        cifs_dbg(FYI, "%s: root path: %s\n", __func__, root_path);
 364
 365        ses = tcon->ses;
 366        xid = get_xid();
 367
 368        /*
 369         * If DFS root has been expired, then unconditionally fetch it again to
 370         * refresh DFS referral cache.
 371         */
 372        rc = dfs_cache_find(xid, ses, cifs_sb->local_nls, cifs_remap(cifs_sb),
 373                            root_path + 1, NULL, NULL);
 374        if (!rc) {
 375                rc = dfs_cache_find(xid, ses, cifs_sb->local_nls,
 376                                    cifs_remap(cifs_sb), full_path + 1,
 377                                    NULL, NULL);
 378        }
 379
 380        free_xid(xid);
 381
 382        if (rc) {
 383                mnt = ERR_PTR(rc);
 384                goto free_root_path;
 385        }
 386        /*
 387         * OK - we were able to get and cache a referral for @full_path.
 388         *
 389         * Now, pass it down to cifs_mount() and it will retry every available
 390         * node server in case of failures - no need to do it here.
 391         */
 392        mnt = cifs_dfs_do_mount(mntpt, cifs_sb, full_path);
 393        cifs_dbg(FYI, "%s: cifs_dfs_do_mount:%s , mnt:%p\n", __func__,
 394                 full_path + 1, mnt);
 395
 396free_root_path:
 397        kfree(root_path);
 398free_full_path:
 399        free_dentry_path(page);
 400cdda_exit:
 401        cifs_dbg(FYI, "leaving %s\n" , __func__);
 402        return mnt;
 403}
 404
 405/*
 406 * Attempt to automount the referral
 407 */
 408struct vfsmount *cifs_dfs_d_automount(struct path *path)
 409{
 410        struct vfsmount *newmnt;
 411
 412        cifs_dbg(FYI, "in %s\n", __func__);
 413
 414        newmnt = cifs_dfs_do_automount(path->dentry);
 415        if (IS_ERR(newmnt)) {
 416                cifs_dbg(FYI, "leaving %s [automount failed]\n" , __func__);
 417                return newmnt;
 418        }
 419
 420        mntget(newmnt); /* prevent immediate expiration */
 421        mnt_set_expiry(newmnt, &cifs_dfs_automount_list);
 422        schedule_delayed_work(&cifs_dfs_automount_task,
 423                              cifs_dfs_mountpoint_expiry_timeout);
 424        cifs_dbg(FYI, "leaving %s [ok]\n" , __func__);
 425        return newmnt;
 426}
 427
 428const struct inode_operations cifs_dfs_referral_inode_operations = {
 429};
 430