linux/fs/nfs/namespace.c
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   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#include "nfs.h"
  23
  24#define NFSDBG_FACILITY         NFSDBG_VFS
  25
  26static void nfs_expire_automounts(struct work_struct *work);
  27
  28static LIST_HEAD(nfs_automount_list);
  29static DECLARE_DELAYED_WORK(nfs_automount_task, nfs_expire_automounts);
  30int nfs_mountpoint_expiry_timeout = 500 * HZ;
  31
  32/*
  33 * nfs_path - reconstruct the path given an arbitrary dentry
  34 * @base - used to return pointer to the end of devname part of path
  35 * @dentry_in - pointer to dentry
  36 * @buffer - result buffer
  37 * @buflen_in - length of buffer
  38 * @flags - options (see below)
  39 *
  40 * Helper function for constructing the server pathname
  41 * by arbitrary hashed dentry.
  42 *
  43 * This is mainly for use in figuring out the path on the
  44 * server side when automounting on top of an existing partition
  45 * and in generating /proc/mounts and friends.
  46 *
  47 * Supported flags:
  48 * NFS_PATH_CANONICAL: ensure there is exactly one slash after
  49 *                     the original device (export) name
  50 *                     (if unset, the original name is returned verbatim)
  51 */
  52char *nfs_path(char **p, struct dentry *dentry_in, char *buffer,
  53               ssize_t buflen_in, unsigned flags)
  54{
  55        char *end;
  56        int namelen;
  57        unsigned seq;
  58        const char *base;
  59        struct dentry *dentry;
  60        ssize_t buflen;
  61
  62rename_retry:
  63        buflen = buflen_in;
  64        dentry = dentry_in;
  65        end = buffer+buflen;
  66        *--end = '\0';
  67        buflen--;
  68
  69        seq = read_seqbegin(&rename_lock);
  70        rcu_read_lock();
  71        while (1) {
  72                spin_lock(&dentry->d_lock);
  73                if (IS_ROOT(dentry))
  74                        break;
  75                namelen = dentry->d_name.len;
  76                buflen -= namelen + 1;
  77                if (buflen < 0)
  78                        goto Elong_unlock;
  79                end -= namelen;
  80                memcpy(end, dentry->d_name.name, namelen);
  81                *--end = '/';
  82                spin_unlock(&dentry->d_lock);
  83                dentry = dentry->d_parent;
  84        }
  85        if (read_seqretry(&rename_lock, seq)) {
  86                spin_unlock(&dentry->d_lock);
  87                rcu_read_unlock();
  88                goto rename_retry;
  89        }
  90        if ((flags & NFS_PATH_CANONICAL) && *end != '/') {
  91                if (--buflen < 0) {
  92                        spin_unlock(&dentry->d_lock);
  93                        rcu_read_unlock();
  94                        goto Elong;
  95                }
  96                *--end = '/';
  97        }
  98        *p = end;
  99        base = dentry->d_fsdata;
 100        if (!base) {
 101                spin_unlock(&dentry->d_lock);
 102                rcu_read_unlock();
 103                WARN_ON(1);
 104                return end;
 105        }
 106        namelen = strlen(base);
 107        if (*end == '/') {
 108                /* Strip off excess slashes in base string */
 109                while (namelen > 0 && base[namelen - 1] == '/')
 110                        namelen--;
 111        }
 112        buflen -= namelen;
 113        if (buflen < 0) {
 114                spin_unlock(&dentry->d_lock);
 115                rcu_read_unlock();
 116                goto Elong;
 117        }
 118        end -= namelen;
 119        memcpy(end, base, namelen);
 120        spin_unlock(&dentry->d_lock);
 121        rcu_read_unlock();
 122        return end;
 123Elong_unlock:
 124        spin_unlock(&dentry->d_lock);
 125        rcu_read_unlock();
 126        if (read_seqretry(&rename_lock, seq))
 127                goto rename_retry;
 128Elong:
 129        return ERR_PTR(-ENAMETOOLONG);
 130}
 131EXPORT_SYMBOL_GPL(nfs_path);
 132
 133/*
 134 * nfs_d_automount - Handle crossing a mountpoint on the server
 135 * @path - The mountpoint
 136 *
 137 * When we encounter a mountpoint on the server, we want to set up
 138 * a mountpoint on the client too, to prevent inode numbers from
 139 * colliding, and to allow "df" to work properly.
 140 * On NFSv4, we also want to allow for the fact that different
 141 * filesystems may be migrated to different servers in a failover
 142 * situation, and that different filesystems may want to use
 143 * different security flavours.
 144 */
 145struct vfsmount *nfs_d_automount(struct path *path)
 146{
 147        struct nfs_fs_context *ctx;
 148        struct fs_context *fc;
 149        struct vfsmount *mnt = ERR_PTR(-ENOMEM);
 150        struct nfs_server *server = NFS_SERVER(d_inode(path->dentry));
 151        struct nfs_client *client = server->nfs_client;
 152        int timeout = READ_ONCE(nfs_mountpoint_expiry_timeout);
 153        int ret;
 154
 155        if (IS_ROOT(path->dentry))
 156                return ERR_PTR(-ESTALE);
 157
 158        /* Open a new filesystem context, transferring parameters from the
 159         * parent superblock, including the network namespace.
 160         */
 161        fc = fs_context_for_submount(path->mnt->mnt_sb->s_type, path->dentry);
 162        if (IS_ERR(fc))
 163                return ERR_CAST(fc);
 164
 165        ctx = nfs_fc2context(fc);
 166        ctx->clone_data.dentry  = path->dentry;
 167        ctx->clone_data.sb      = path->dentry->d_sb;
 168        ctx->clone_data.fattr   = nfs_alloc_fattr();
 169        if (!ctx->clone_data.fattr)
 170                goto out_fc;
 171
 172        if (fc->net_ns != client->cl_net) {
 173                put_net(fc->net_ns);
 174                fc->net_ns = get_net(client->cl_net);
 175        }
 176
 177        /* for submounts we want the same server; referrals will reassign */
 178        memcpy(&ctx->nfs_server.address, &client->cl_addr, client->cl_addrlen);
 179        ctx->nfs_server.addrlen = client->cl_addrlen;
 180        ctx->nfs_server.port    = server->port;
 181
 182        ctx->version            = client->rpc_ops->version;
 183        ctx->minorversion       = client->cl_minorversion;
 184        ctx->nfs_mod            = client->cl_nfs_mod;
 185        __module_get(ctx->nfs_mod->owner);
 186
 187        ret = client->rpc_ops->submount(fc, server);
 188        if (ret < 0) {
 189                mnt = ERR_PTR(ret);
 190                goto out_fc;
 191        }
 192
 193        up_write(&fc->root->d_sb->s_umount);
 194        mnt = vfs_create_mount(fc);
 195        if (IS_ERR(mnt))
 196                goto out_fc;
 197
 198        mntget(mnt); /* prevent immediate expiration */
 199        if (timeout <= 0)
 200                goto out_fc;
 201
 202        mnt_set_expiry(mnt, &nfs_automount_list);
 203        schedule_delayed_work(&nfs_automount_task, timeout);
 204
 205out_fc:
 206        put_fs_context(fc);
 207        return mnt;
 208}
 209
 210static int
 211nfs_namespace_getattr(struct user_namespace *mnt_userns,
 212                      const struct path *path, struct kstat *stat,
 213                      u32 request_mask, unsigned int query_flags)
 214{
 215        if (NFS_FH(d_inode(path->dentry))->size != 0)
 216                return nfs_getattr(mnt_userns, path, stat, request_mask,
 217                                   query_flags);
 218        generic_fillattr(&init_user_ns, d_inode(path->dentry), stat);
 219        return 0;
 220}
 221
 222static int
 223nfs_namespace_setattr(struct user_namespace *mnt_userns, struct dentry *dentry,
 224                      struct iattr *attr)
 225{
 226        if (NFS_FH(d_inode(dentry))->size != 0)
 227                return nfs_setattr(mnt_userns, dentry, attr);
 228        return -EACCES;
 229}
 230
 231const struct inode_operations nfs_mountpoint_inode_operations = {
 232        .getattr        = nfs_getattr,
 233        .setattr        = nfs_setattr,
 234};
 235
 236const struct inode_operations nfs_referral_inode_operations = {
 237        .getattr        = nfs_namespace_getattr,
 238        .setattr        = nfs_namespace_setattr,
 239};
 240
 241static void nfs_expire_automounts(struct work_struct *work)
 242{
 243        struct list_head *list = &nfs_automount_list;
 244        int timeout = READ_ONCE(nfs_mountpoint_expiry_timeout);
 245
 246        mark_mounts_for_expiry(list);
 247        if (!list_empty(list) && timeout > 0)
 248                schedule_delayed_work(&nfs_automount_task, timeout);
 249}
 250
 251void nfs_release_automount_timer(void)
 252{
 253        if (list_empty(&nfs_automount_list))
 254                cancel_delayed_work(&nfs_automount_task);
 255}
 256
 257/**
 258 * nfs_do_submount - set up mountpoint when crossing a filesystem boundary
 259 * @fc: pointer to struct nfs_fs_context
 260 *
 261 */
 262int nfs_do_submount(struct fs_context *fc)
 263{
 264        struct nfs_fs_context *ctx = nfs_fc2context(fc);
 265        struct dentry *dentry = ctx->clone_data.dentry;
 266        struct nfs_server *server;
 267        char *buffer, *p;
 268        int ret;
 269
 270        /* create a new volume representation */
 271        server = ctx->nfs_mod->rpc_ops->clone_server(NFS_SB(ctx->clone_data.sb),
 272                                                     ctx->mntfh,
 273                                                     ctx->clone_data.fattr,
 274                                                     ctx->selected_flavor);
 275
 276        if (IS_ERR(server))
 277                return PTR_ERR(server);
 278
 279        ctx->server = server;
 280
 281        buffer = kmalloc(4096, GFP_USER);
 282        if (!buffer)
 283                return -ENOMEM;
 284
 285        ctx->internal           = true;
 286        ctx->clone_data.inherited_bsize = ctx->clone_data.sb->s_blocksize_bits;
 287
 288        p = nfs_devname(dentry, buffer, 4096);
 289        if (IS_ERR(p)) {
 290                nfs_errorf(fc, "NFS: Couldn't determine submount pathname");
 291                ret = PTR_ERR(p);
 292        } else {
 293                ret = vfs_parse_fs_string(fc, "source", p, buffer + 4096 - p);
 294                if (!ret)
 295                        ret = vfs_get_tree(fc);
 296        }
 297        kfree(buffer);
 298        return ret;
 299}
 300EXPORT_SYMBOL_GPL(nfs_do_submount);
 301
 302int nfs_submount(struct fs_context *fc, struct nfs_server *server)
 303{
 304        struct nfs_fs_context *ctx = nfs_fc2context(fc);
 305        struct dentry *dentry = ctx->clone_data.dentry;
 306        struct dentry *parent = dget_parent(dentry);
 307        int err;
 308
 309        /* Look it up again to get its attributes */
 310        err = server->nfs_client->rpc_ops->lookup(d_inode(parent), dentry,
 311                                                  ctx->mntfh, ctx->clone_data.fattr,
 312                                                  NULL);
 313        dput(parent);
 314        if (err != 0)
 315                return err;
 316
 317        ctx->selected_flavor = server->client->cl_auth->au_flavor;
 318        return nfs_do_submount(fc);
 319}
 320EXPORT_SYMBOL_GPL(nfs_submount);
 321
 322static int param_set_nfs_timeout(const char *val, const struct kernel_param *kp)
 323{
 324        long num;
 325        int ret;
 326
 327        if (!val)
 328                return -EINVAL;
 329        ret = kstrtol(val, 0, &num);
 330        if (ret)
 331                return -EINVAL;
 332        if (num > 0) {
 333                if (num >= INT_MAX / HZ)
 334                        num = INT_MAX;
 335                else
 336                        num *= HZ;
 337                *((int *)kp->arg) = num;
 338                if (!list_empty(&nfs_automount_list))
 339                        mod_delayed_work(system_wq, &nfs_automount_task, num);
 340        } else {
 341                *((int *)kp->arg) = -1*HZ;
 342                cancel_delayed_work(&nfs_automount_task);
 343        }
 344        return 0;
 345}
 346
 347static int param_get_nfs_timeout(char *buffer, const struct kernel_param *kp)
 348{
 349        long num = *((int *)kp->arg);
 350
 351        if (num > 0) {
 352                if (num >= INT_MAX - (HZ - 1))
 353                        num = INT_MAX / HZ;
 354                else
 355                        num = (num + (HZ - 1)) / HZ;
 356        } else
 357                num = -1;
 358        return scnprintf(buffer, PAGE_SIZE, "%li\n", num);
 359}
 360
 361static const struct kernel_param_ops param_ops_nfs_timeout = {
 362        .set = param_set_nfs_timeout,
 363        .get = param_get_nfs_timeout,
 364};
 365#define param_check_nfs_timeout(name, p) __param_check(name, p, int)
 366
 367module_param(nfs_mountpoint_expiry_timeout, nfs_timeout, 0644);
 368MODULE_PARM_DESC(nfs_mountpoint_expiry_timeout,
 369                "Set the NFS automounted mountpoint timeout value (seconds)."
 370                "Values <= 0 turn expiration off.");
 371
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