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  
26  static void nfs_expire_automounts(struct work_struct *work);
27  
28  static LIST_HEAD(nfs_automount_list);
29  static DECLARE_DELAYED_WORK(nfs_automount_task, nfs_expire_automounts);
30  int 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   */
nfs_path(char ** p,struct dentry * dentry_in,char * buffer,ssize_t buflen_in,unsigned flags)52  char *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  
62  rename_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;
123  Elong_unlock:
124  	spin_unlock(&dentry->d_lock);
125  	rcu_read_unlock();
126  	if (read_seqretry(&rename_lock, seq))
127  		goto rename_retry;
128  Elong:
129  	return ERR_PTR(-ENAMETOOLONG);
130  }
131  EXPORT_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   */
nfs_d_automount(struct path * path)145  struct 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_SB(path->dentry->d_sb);
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  
205  out_fc:
206  	put_fs_context(fc);
207  	return mnt;
208  }
209  
210  static int
nfs_namespace_getattr(struct mnt_idmap * idmap,const struct path * path,struct kstat * stat,u32 request_mask,unsigned int query_flags)211  nfs_namespace_getattr(struct mnt_idmap *idmap,
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(idmap, path, stat, request_mask,
217  				   query_flags);
218  	generic_fillattr(&nop_mnt_idmap, request_mask, d_inode(path->dentry),
219  			 stat);
220  	return 0;
221  }
222  
223  static int
nfs_namespace_setattr(struct mnt_idmap * idmap,struct dentry * dentry,struct iattr * attr)224  nfs_namespace_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
225  		      struct iattr *attr)
226  {
227  	if (NFS_FH(d_inode(dentry))->size != 0)
228  		return nfs_setattr(idmap, dentry, attr);
229  	return -EACCES;
230  }
231  
232  const struct inode_operations nfs_mountpoint_inode_operations = {
233  	.getattr	= nfs_getattr,
234  	.setattr	= nfs_setattr,
235  };
236  
237  const struct inode_operations nfs_referral_inode_operations = {
238  	.getattr	= nfs_namespace_getattr,
239  	.setattr	= nfs_namespace_setattr,
240  };
241  
nfs_expire_automounts(struct work_struct * work)242  static void nfs_expire_automounts(struct work_struct *work)
243  {
244  	struct list_head *list = &nfs_automount_list;
245  	int timeout = READ_ONCE(nfs_mountpoint_expiry_timeout);
246  
247  	mark_mounts_for_expiry(list);
248  	if (!list_empty(list) && timeout > 0)
249  		schedule_delayed_work(&nfs_automount_task, timeout);
250  }
251  
nfs_release_automount_timer(void)252  void nfs_release_automount_timer(void)
253  {
254  	if (list_empty(&nfs_automount_list))
255  		cancel_delayed_work(&nfs_automount_task);
256  }
257  
258  /**
259   * nfs_do_submount - set up mountpoint when crossing a filesystem boundary
260   * @fc: pointer to struct nfs_fs_context
261   *
262   */
nfs_do_submount(struct fs_context * fc)263  int nfs_do_submount(struct fs_context *fc)
264  {
265  	struct nfs_fs_context *ctx = nfs_fc2context(fc);
266  	struct dentry *dentry = ctx->clone_data.dentry;
267  	struct nfs_server *server;
268  	char *buffer, *p;
269  	int ret;
270  
271  	/* create a new volume representation */
272  	server = ctx->nfs_mod->rpc_ops->clone_server(NFS_SB(ctx->clone_data.sb),
273  						     ctx->mntfh,
274  						     ctx->clone_data.fattr,
275  						     ctx->selected_flavor);
276  
277  	if (IS_ERR(server))
278  		return PTR_ERR(server);
279  
280  	ctx->server = server;
281  
282  	buffer = kmalloc(4096, GFP_USER);
283  	if (!buffer)
284  		return -ENOMEM;
285  
286  	ctx->internal		= true;
287  	ctx->clone_data.inherited_bsize = ctx->clone_data.sb->s_blocksize_bits;
288  
289  	p = nfs_devname(dentry, buffer, 4096);
290  	if (IS_ERR(p)) {
291  		nfs_errorf(fc, "NFS: Couldn't determine submount pathname");
292  		ret = PTR_ERR(p);
293  	} else {
294  		ret = vfs_parse_fs_string(fc, "source", p, buffer + 4096 - p);
295  		if (!ret)
296  			ret = vfs_get_tree(fc);
297  	}
298  	kfree(buffer);
299  	return ret;
300  }
301  EXPORT_SYMBOL_GPL(nfs_do_submount);
302  
nfs_submount(struct fs_context * fc,struct nfs_server * server)303  int nfs_submount(struct fs_context *fc, struct nfs_server *server)
304  {
305  	struct nfs_fs_context *ctx = nfs_fc2context(fc);
306  	struct dentry *dentry = ctx->clone_data.dentry;
307  	struct dentry *parent = dget_parent(dentry);
308  	int err;
309  
310  	/* Look it up again to get its attributes */
311  	err = server->nfs_client->rpc_ops->lookup(d_inode(parent), dentry,
312  						  ctx->mntfh, ctx->clone_data.fattr);
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  }
320  EXPORT_SYMBOL_GPL(nfs_submount);
321  
param_set_nfs_timeout(const char * val,const struct kernel_param * kp)322  static 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  
param_get_nfs_timeout(char * buffer,const struct kernel_param * kp)347  static 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 sysfs_emit(buffer, "%li\n", num);
359  }
360  
361  static 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  
367  module_param(nfs_mountpoint_expiry_timeout, nfs_timeout, 0644);
368  MODULE_PARM_DESC(nfs_mountpoint_expiry_timeout,
369  		"Set the NFS automounted mountpoint timeout value (seconds)."
370  		"Values <= 0 turn expiration off.");
371