fs/nfs/namespace.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * linux/fs/nfs/namespace.c
   4  *
   5  * Copyright (C) 2005 Trond Myklebust <Trond.Myklebust@netapp.com>
   6  * - Modified by David Howells <dhowells@redhat.com>
   7  *
   8  * NFS namespace
   9  */
  10
  11 #include <linux/module.h>
  12 #include <linux/dcache.h>
  13 #include <linux/gfp.h>
  14 #include <linux/mount.h>
  15 #include <linux/namei.h>
  16 #include <linux/nfs_fs.h>
  17 #include <linux/string.h>
  18 #include <linux/sunrpc/clnt.h>
  19 #include <linux/vfs.h>
  20 #include <linux/sunrpc/gss_api.h>
  21 #include "internal.h"
  22
  23 #define NFSDBG_FACILITY         NFSDBG_VFS
  24
  25 static void nfs_expire_automounts(struct work_struct *work);
  26
  27 static LIST_HEAD(nfs_automount_list);
  28 static DECLARE_DELAYED_WORK(nfs_automount_task, nfs_expire_automounts);
  29 int nfs_mountpoint_expiry_timeout = 500 * HZ;
  30
  31 /*
  32  * nfs_path - reconstruct the path given an arbitrary dentry
  33  * @base - used to return pointer to the end of devname part of path
  34  * @dentry - pointer to dentry
  35  * @buffer - result buffer
  36  * @buflen - length of buffer
  37  * @flags - options (see below)
  38  *
  39  * Helper function for constructing the server pathname
  40  * by arbitrary hashed dentry.
  41  *
  42  * This is mainly for use in figuring out the path on the
  43  * server side when automounting on top of an existing partition
  44  * and in generating /proc/mounts and friends.
  45  *
  46  * Supported flags:
  47  * NFS_PATH_CANONICAL: ensure there is exactly one slash after
  48  *                     the original device (export) name
  49  *                     (if unset, the original name is returned verbatim)
  50  */
  51 char *nfs_path(char **p, struct dentry *dentry, char *buffer, ssize_t buflen,
  52                unsigned flags)
  53 {
  54         char *end;
  55         int namelen;
  56         unsigned seq;
  57         const char *base;
  58
  59 rename_retry:
  60         end = buffer+buflen;
  61         *--end = '\0';
  62         buflen--;
  63
  64         seq = read_seqbegin(&rename_lock);
  65         rcu_read_lock();
  66         while (1) {
  67                 spin_lock(&dentry->d_lock);
  68                 if (IS_ROOT(dentry))
  69                         break;
  70                 namelen = dentry->d_name.len;
  71                 buflen -= namelen + 1;
  72                 if (buflen < 0)
  73                         goto Elong_unlock;
  74                 end -= namelen;
  75                 memcpy(end, dentry->d_name.name, namelen);
  76                 *--end = '/';
  77                 spin_unlock(&dentry->d_lock);
  78                 dentry = dentry->d_parent;
  79         }
  80         if (read_seqretry(&rename_lock, seq)) {
  81                 spin_unlock(&dentry->d_lock);
  82                 rcu_read_unlock();
  83                 goto rename_retry;
  84         }
  85         if ((flags & NFS_PATH_CANONICAL) && *end != '/') {
  86                 if (--buflen < 0) {
  87                         spin_unlock(&dentry->d_lock);
  88                         rcu_read_unlock();
  89                         goto Elong;
  90                 }
  91                 *--end = '/';
  92         }
  93         *p = end;
  94         base = dentry->d_fsdata;
  95         if (!base) {
  96                 spin_unlock(&dentry->d_lock);
  97                 rcu_read_unlock();
  98                 WARN_ON(1);
  99                 return end;
 100         }
 101         namelen = strlen(base);
 102         if (*end == '/') {
 103                 /* Strip off excess slashes in base string */
 104                 while (namelen > 0 && base[namelen - 1] == '/')
 105                         namelen--;
 106         }
 107         buflen -= namelen;
 108         if (buflen < 0) {
 109                 spin_unlock(&dentry->d_lock);
 110                 rcu_read_unlock();
 111                 goto Elong;
 112         }
 113         end -= namelen;
 114         memcpy(end, base, namelen);
 115         spin_unlock(&dentry->d_lock);
 116         rcu_read_unlock();
 117         return end;
 118 Elong_unlock:
 119         spin_unlock(&dentry->d_lock);
 120         rcu_read_unlock();
 121         if (read_seqretry(&rename_lock, seq))
 122                 goto rename_retry;
 123 Elong:
 124         return ERR_PTR(-ENAMETOOLONG);
 125 }
 126 EXPORT_SYMBOL_GPL(nfs_path);
 127
 128 /*
 129  * nfs_d_automount - Handle crossing a mountpoint on the server
 130  * @path - The mountpoint
 131  *
 132  * When we encounter a mountpoint on the server, we want to set up
 133  * a mountpoint on the client too, to prevent inode numbers from
 134  * colliding, and to allow "df" to work properly.
 135  * On NFSv4, we also want to allow for the fact that different
 136  * filesystems may be migrated to different servers in a failover
 137  * situation, and that different filesystems may want to use
 138  * different security flavours.
 139  */
 140 struct vfsmount *nfs_d_automount(struct path *path)
 141 {
 142         struct vfsmount *mnt;
 143         struct nfs_server *server = NFS_SERVER(d_inode(path->dentry));
 144         struct nfs_fh *fh = NULL;
 145         struct nfs_fattr *fattr = NULL;
 146
 147         if (IS_ROOT(path->dentry))
 148                 return ERR_PTR(-ESTALE);
 149
 150         mnt = ERR_PTR(-ENOMEM);
 151         fh = nfs_alloc_fhandle();
 152         fattr = nfs_alloc_fattr();
 153         if (fh == NULL || fattr == NULL)
 154                 goto out;
 155
 156         mnt = server->nfs_client->rpc_ops->submount(server, path->dentry, fh, fattr);
 157         if (IS_ERR(mnt))
 158                 goto out;
 159
 160         mntget(mnt); /* prevent immediate expiration */
 161         mnt_set_expiry(mnt, &nfs_automount_list);
 162         schedule_delayed_work(&nfs_automount_task, nfs_mountpoint_expiry_timeout);
 163
 164 out:
 165         nfs_free_fattr(fattr);
 166         nfs_free_fhandle(fh);
 167         return mnt;
 168 }
 169
 170 static int
 171 nfs_namespace_getattr(const struct path *path, struct kstat *stat,
 172                         u32 request_mask, unsigned int query_flags)
 173 {
 174         if (NFS_FH(d_inode(path->dentry))->size != 0)
 175                 return nfs_getattr(path, stat, request_mask, query_flags);
 176         generic_fillattr(d_inode(path->dentry), stat);
 177         return 0;
 178 }
 179
 180 static int
 181 nfs_namespace_setattr(struct dentry *dentry, struct iattr *attr)
 182 {
 183         if (NFS_FH(d_inode(dentry))->size != 0)
 184                 return nfs_setattr(dentry, attr);
 185         return -EACCES;
 186 }
 187
 188 const struct inode_operations nfs_mountpoint_inode_operations = {
 189         .getattr        = nfs_getattr,
 190         .setattr        = nfs_setattr,
 191 };
 192
 193 const struct inode_operations nfs_referral_inode_operations = {
 194         .getattr        = nfs_namespace_getattr,
 195         .setattr        = nfs_namespace_setattr,
 196 };
 197
 198 static void nfs_expire_automounts(struct work_struct *work)
 199 {
 200         struct list_head *list = &nfs_automount_list;
 201
 202         mark_mounts_for_expiry(list);
 203         if (!list_empty(list))
 204                 schedule_delayed_work(&nfs_automount_task, nfs_mountpoint_expiry_timeout);
 205 }
 206
 207 void nfs_release_automount_timer(void)
 208 {
 209         if (list_empty(&nfs_automount_list))
 210                 cancel_delayed_work(&nfs_automount_task);
 211 }
 212
 213 /*
 214  * Clone a mountpoint of the appropriate type
 215  */
 216 static struct vfsmount *nfs_do_clone_mount(struct nfs_server *server,
 217                                            const char *devname,
 218                                            struct nfs_clone_mount *mountdata)
 219 {
 220         return vfs_submount(mountdata->dentry, &nfs_xdev_fs_type, devname, mountdata);
 221 }
 222
 223 /**
 224  * nfs_do_submount - set up mountpoint when crossing a filesystem boundary
 225  * @dentry: parent directory
 226  * @fh: filehandle for new root dentry
 227  * @fattr: attributes for new root inode
 228  * @authflavor: security flavor to use when performing the mount
 229  *
 230  */
 231 struct vfsmount *nfs_do_submount(struct dentry *dentry, struct nfs_fh *fh,
 232                                  struct nfs_fattr *fattr, rpc_authflavor_t authflavor)
 233 {
 234         struct nfs_clone_mount mountdata = {
 235                 .sb = dentry->d_sb,
 236                 .dentry = dentry,
 237                 .fh = fh,
 238                 .fattr = fattr,
 239                 .authflavor = authflavor,
 240         };
 241         struct vfsmount *mnt;
 242         char *page = (char *) __get_free_page(GFP_USER);
 243         char *devname;
 244
 245         if (page == NULL)
 246                 return ERR_PTR(-ENOMEM);
 247
 248         devname = nfs_devname(dentry, page, PAGE_SIZE);
 249         if (IS_ERR(devname))
 250                 mnt = ERR_CAST(devname);
 251         else
 252                 mnt = nfs_do_clone_mount(NFS_SB(dentry->d_sb), devname, &mountdata);
 253
 254         free_page((unsigned long)page);
 255         return mnt;
 256 }
 257 EXPORT_SYMBOL_GPL(nfs_do_submount);
 258
 259 struct vfsmount *nfs_submount(struct nfs_server *server, struct dentry *dentry,
 260                               struct nfs_fh *fh, struct nfs_fattr *fattr)
 261 {
 262         int err;
 263         struct dentry *parent = dget_parent(dentry);
 264
 265         /* Look it up again to get its attributes */
 266         err = server->nfs_client->rpc_ops->lookup(d_inode(parent), &dentry->d_name, fh, fattr, NULL);
 267         dput(parent);
 268         if (err != 0)
 269                 return ERR_PTR(err);
 270
 271         return nfs_do_submount(dentry, fh, fattr, server->client->cl_auth->au_flavor);
 272 }
 273 EXPORT_SYMBOL_GPL(nfs_submount);