fs/cifs/cifs_dfs_ref.c

0001 // SPDX-License-Identifier: GPL-2.0-or-later
0002 /*
0003  *   Contains the CIFS DFS referral mounting routines used for handling
0004  *   traversal via DFS junction point
0005  *
0006  *   Copyright (c) 2007 Igor Mammedov
0007  *   Copyright (C) International Business Machines  Corp., 2008
0008  *   Author(s): Igor Mammedov (niallain@gmail.com)
0009  *      Steve French (sfrench@us.ibm.com)
0010  */
0011
0012 #include <linux/dcache.h>
0013 #include <linux/mount.h>
0014 #include <linux/namei.h>
0015 #include <linux/slab.h>
0016 #include <linux/vfs.h>
0017 #include <linux/fs.h>
0018 #include <linux/inet.h>
0019 #include "cifsglob.h"
0020 #include "cifsproto.h"
0021 #include "cifsfs.h"
0022 #include "dns_resolve.h"
0023 #include "cifs_debug.h"
0024 #include "cifs_unicode.h"
0025 #include "dfs_cache.h"
0026 #include "fs_context.h"
0027
0028 static LIST_HEAD(cifs_dfs_automount_list);
0029
0030 static void cifs_dfs_expire_automounts(struct work_struct *work);
0031 static DECLARE_DELAYED_WORK(cifs_dfs_automount_task,
0032                 cifs_dfs_expire_automounts);
0033 static int cifs_dfs_mountpoint_expiry_timeout = 500 * HZ;
0034
0035 static void cifs_dfs_expire_automounts(struct work_struct *work)
0036 {
0037     struct list_head *list = &cifs_dfs_automount_list;
0038
0039     mark_mounts_for_expiry(list);
0040     if (!list_empty(list))
0041         schedule_delayed_work(&cifs_dfs_automount_task,
0042                       cifs_dfs_mountpoint_expiry_timeout);
0043 }
0044
0045 void cifs_dfs_release_automount_timer(void)
0046 {
0047     BUG_ON(!list_empty(&cifs_dfs_automount_list));
0048     cancel_delayed_work_sync(&cifs_dfs_automount_task);
0049 }
0050
0051 /**
0052  * cifs_build_devname - build a devicename from a UNC and optional prepath
0053  * @nodename:   pointer to UNC string
0054  * @prepath:    pointer to prefixpath (or NULL if there isn't one)
0055  *
0056  * Build a new cifs devicename after chasing a DFS referral. Allocate a buffer
0057  * big enough to hold the final thing. Copy the UNC from the nodename, and
0058  * concatenate the prepath onto the end of it if there is one.
0059  *
0060  * Returns pointer to the built string, or a ERR_PTR. Caller is responsible
0061  * for freeing the returned string.
0062  */
0063 static char *
0064 cifs_build_devname(char *nodename, const char *prepath)
0065 {
0066     size_t pplen;
0067     size_t unclen;
0068     char *dev;
0069     char *pos;
0070
0071     /* skip over any preceding delimiters */
0072     nodename += strspn(nodename, "\\");
0073     if (!*nodename)
0074         return ERR_PTR(-EINVAL);
0075
0076     /* get length of UNC and set pos to last char */
0077     unclen = strlen(nodename);
0078     pos = nodename + unclen - 1;
0079
0080     /* trim off any trailing delimiters */
0081     while (*pos == '\\') {
0082         --pos;
0083         --unclen;
0084     }
0085
0086     /* allocate a buffer:
0087      * +2 for preceding "//"
0088      * +1 for delimiter between UNC and prepath
0089      * +1 for trailing NULL
0090      */
0091     pplen = prepath ? strlen(prepath) : 0;
0092     dev = kmalloc(2 + unclen + 1 + pplen + 1, GFP_KERNEL);
0093     if (!dev)
0094         return ERR_PTR(-ENOMEM);
0095
0096     pos = dev;
0097     /* add the initial "//" */
0098     *pos = '/';
0099     ++pos;
0100     *pos = '/';
0101     ++pos;
0102
0103     /* copy in the UNC portion from referral */
0104     memcpy(pos, nodename, unclen);
0105     pos += unclen;
0106
0107     /* copy the prefixpath remainder (if there is one) */
0108     if (pplen) {
0109         *pos = '/';
0110         ++pos;
0111         memcpy(pos, prepath, pplen);
0112         pos += pplen;
0113     }
0114
0115     /* NULL terminator */
0116     *pos = '\0';
0117
0118     convert_delimiter(dev, '/');
0119     return dev;
0120 }
0121
0122
0123 /**
0124  * cifs_compose_mount_options   -   creates mount options for referral
0125  * @sb_mountdata:   parent/root DFS mount options (template)
0126  * @fullpath:       full path in UNC format
0127  * @ref:        optional server's referral
0128  * @devname:        return the built cifs device name if passed pointer not NULL
0129  * creates mount options for submount based on template options sb_mountdata
0130  * and replacing unc,ip,prefixpath options with ones we've got form ref_unc.
0131  *
0132  * Returns: pointer to new mount options or ERR_PTR.
0133  * Caller is responsible for freeing returned value if it is not error.
0134  */
0135 char *cifs_compose_mount_options(const char *sb_mountdata,
0136                  const char *fullpath,
0137                  const struct dfs_info3_param *ref,
0138                  char **devname)
0139 {
0140     int rc;
0141     char *name;
0142     char *mountdata = NULL;
0143     const char *prepath = NULL;
0144     int md_len;
0145     char *tkn_e;
0146     char *srvIP = NULL;
0147     char sep = ',';
0148     int off, noff;
0149
0150     if (sb_mountdata == NULL)
0151         return ERR_PTR(-EINVAL);
0152
0153     if (ref) {
0154         if (WARN_ON_ONCE(!ref->node_name || ref->path_consumed < 0))
0155             return ERR_PTR(-EINVAL);
0156
0157         if (strlen(fullpath) - ref->path_consumed) {
0158             prepath = fullpath + ref->path_consumed;
0159             /* skip initial delimiter */
0160             if (*prepath == '/' || *prepath == '\\')
0161                 prepath++;
0162         }
0163
0164         name = cifs_build_devname(ref->node_name, prepath);
0165         if (IS_ERR(name)) {
0166             rc = PTR_ERR(name);
0167             name = NULL;
0168             goto compose_mount_options_err;
0169         }
0170     } else {
0171         name = cifs_build_devname((char *)fullpath, NULL);
0172         if (IS_ERR(name)) {
0173             rc = PTR_ERR(name);
0174             name = NULL;
0175             goto compose_mount_options_err;
0176         }
0177     }
0178
0179     rc = dns_resolve_server_name_to_ip(name, &srvIP, NULL);
0180     if (rc < 0) {
0181         cifs_dbg(FYI, "%s: Failed to resolve server part of %s to IP: %d\n",
0182              __func__, name, rc);
0183         goto compose_mount_options_err;
0184     }
0185
0186     /*
0187      * In most cases, we'll be building a shorter string than the original,
0188      * but we do have to assume that the address in the ip= option may be
0189      * much longer than the original. Add the max length of an address
0190      * string to the length of the original string to allow for worst case.
0191      */
0192     md_len = strlen(sb_mountdata) + INET6_ADDRSTRLEN;
0193     mountdata = kzalloc(md_len + sizeof("ip=") + 1, GFP_KERNEL);
0194     if (mountdata == NULL) {
0195         rc = -ENOMEM;
0196         goto compose_mount_options_err;
0197     }
0198
0199     /* copy all options except of unc,ip,prefixpath */
0200     off = 0;
0201     if (strncmp(sb_mountdata, "sep=", 4) == 0) {
0202             sep = sb_mountdata[4];
0203             strncpy(mountdata, sb_mountdata, 5);
0204             off += 5;
0205     }
0206
0207     do {
0208         tkn_e = strchr(sb_mountdata + off, sep);
0209         if (tkn_e == NULL)
0210             noff = strlen(sb_mountdata + off);
0211         else
0212             noff = tkn_e - (sb_mountdata + off) + 1;
0213
0214         if (strncasecmp(sb_mountdata + off, "cruid=", 6) == 0) {
0215             off += noff;
0216             continue;
0217         }
0218         if (strncasecmp(sb_mountdata + off, "unc=", 4) == 0) {
0219             off += noff;
0220             continue;
0221         }
0222         if (strncasecmp(sb_mountdata + off, "ip=", 3) == 0) {
0223             off += noff;
0224             continue;
0225         }
0226         if (strncasecmp(sb_mountdata + off, "prefixpath=", 11) == 0) {
0227             off += noff;
0228             continue;
0229         }
0230         strncat(mountdata, sb_mountdata + off, noff);
0231         off += noff;
0232     } while (tkn_e);
0233     strcat(mountdata, sb_mountdata + off);
0234     mountdata[md_len] = '\0';
0235
0236     /* copy new IP and ref share name */
0237     if (mountdata[strlen(mountdata) - 1] != sep)
0238         strncat(mountdata, &sep, 1);
0239     strcat(mountdata, "ip=");
0240     strcat(mountdata, srvIP);
0241
0242     if (devname)
0243         *devname = name;
0244     else
0245         kfree(name);
0246
0247     /*cifs_dbg(FYI, "%s: parent mountdata: %s\n", __func__, sb_mountdata);*/
0248     /*cifs_dbg(FYI, "%s: submount mountdata: %s\n", __func__, mountdata );*/
0249
0250 compose_mount_options_out:
0251     kfree(srvIP);
0252     return mountdata;
0253
0254 compose_mount_options_err:
0255     kfree(mountdata);
0256     mountdata = ERR_PTR(rc);
0257     kfree(name);
0258     goto compose_mount_options_out;
0259 }
0260
0261 /**
0262  * cifs_dfs_do_mount - mounts specified path using DFS full path
0263  *
0264  * Always pass down @fullpath to smb3_do_mount() so we can use the root server
0265  * to perform failover in case we failed to connect to the first target in the
0266  * referral.
0267  *
0268  * @mntpt:      directory entry for the path we are trying to automount
0269  * @cifs_sb:        parent/root superblock
0270  * @fullpath:       full path in UNC format
0271  */
0272 static struct vfsmount *cifs_dfs_do_mount(struct dentry *mntpt,
0273                       struct cifs_sb_info *cifs_sb,
0274                       const char *fullpath)
0275 {
0276     struct vfsmount *mnt;
0277     char *mountdata;
0278     char *devname;
0279
0280     devname = kstrdup(fullpath, GFP_KERNEL);
0281     if (!devname)
0282         return ERR_PTR(-ENOMEM);
0283
0284     convert_delimiter(devname, '/');
0285
0286     /* TODO: change to call fs_context_for_mount(), fill in context directly, call fc_mount */
0287
0288     /* See afs_mntpt_do_automount in fs/afs/mntpt.c for an example */
0289
0290     /* strip first '\' from fullpath */
0291     mountdata = cifs_compose_mount_options(cifs_sb->ctx->mount_options,
0292                            fullpath + 1, NULL, NULL);
0293     if (IS_ERR(mountdata)) {
0294         kfree(devname);
0295         return (struct vfsmount *)mountdata;
0296     }
0297
0298     mnt = vfs_submount(mntpt, &cifs_fs_type, devname, mountdata);
0299     kfree(mountdata);
0300     kfree(devname);
0301     return mnt;
0302 }
0303
0304 /*
0305  * Create a vfsmount that we can automount
0306  */
0307 static struct vfsmount *cifs_dfs_do_automount(struct dentry *mntpt)
0308 {
0309     struct cifs_sb_info *cifs_sb;
0310     void *page;
0311     char *full_path;
0312     struct vfsmount *mnt;
0313
0314     cifs_dbg(FYI, "in %s\n", __func__);
0315     BUG_ON(IS_ROOT(mntpt));
0316
0317     /*
0318      * The MSDFS spec states that paths in DFS referral requests and
0319      * responses must be prefixed by a single '\' character instead of
0320      * the double backslashes usually used in the UNC. This function
0321      * gives us the latter, so we must adjust the result.
0322      */
0323     cifs_sb = CIFS_SB(mntpt->d_sb);
0324     if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_NO_DFS) {
0325         mnt = ERR_PTR(-EREMOTE);
0326         goto cdda_exit;
0327     }
0328
0329     page = alloc_dentry_path();
0330     /* always use tree name prefix */
0331     full_path = build_path_from_dentry_optional_prefix(mntpt, page, true);
0332     if (IS_ERR(full_path)) {
0333         mnt = ERR_CAST(full_path);
0334         goto free_full_path;
0335     }
0336
0337     convert_delimiter(full_path, '\\');
0338     cifs_dbg(FYI, "%s: full_path: %s\n", __func__, full_path);
0339
0340     mnt = cifs_dfs_do_mount(mntpt, cifs_sb, full_path);
0341     cifs_dbg(FYI, "%s: cifs_dfs_do_mount:%s , mnt:%p\n", __func__, full_path + 1, mnt);
0342
0343 free_full_path:
0344     free_dentry_path(page);
0345 cdda_exit:
0346     cifs_dbg(FYI, "leaving %s\n" , __func__);
0347     return mnt;
0348 }
0349
0350 /*
0351  * Attempt to automount the referral
0352  */
0353 struct vfsmount *cifs_dfs_d_automount(struct path *path)
0354 {
0355     struct vfsmount *newmnt;
0356
0357     cifs_dbg(FYI, "in %s\n", __func__);
0358
0359     newmnt = cifs_dfs_do_automount(path->dentry);
0360     if (IS_ERR(newmnt)) {
0361         cifs_dbg(FYI, "leaving %s [automount failed]\n" , __func__);
0362         return newmnt;
0363     }
0364
0365     mntget(newmnt); /* prevent immediate expiration */
0366     mnt_set_expiry(newmnt, &cifs_dfs_automount_list);
0367     schedule_delayed_work(&cifs_dfs_automount_task,
0368                   cifs_dfs_mountpoint_expiry_timeout);
0369     cifs_dbg(FYI, "leaving %s [ok]\n" , __func__);
0370     return newmnt;
0371 }
0372
0373 const struct inode_operations cifs_dfs_referral_inode_operations = {
0374 };