xref: /kernel/linux/linux-5.10/fs/nfs/namespace.c (revision 8c2ecf20) 
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_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
205out_fc:
206	put_fs_context(fc);
207	return mnt;
208}
209
210static int
211nfs_namespace_getattr(const struct path *path, struct kstat *stat,
212			u32 request_mask, unsigned int query_flags)
213{
214	if (NFS_FH(d_inode(path->dentry))->size != 0)
215		return nfs_getattr(path, stat, request_mask, query_flags);
216	generic_fillattr(d_inode(path->dentry), stat);
217	return 0;
218}
219
220static int
221nfs_namespace_setattr(struct dentry *dentry, struct iattr *attr)
222{
223	if (NFS_FH(d_inode(dentry))->size != 0)
224		return nfs_setattr(dentry, attr);
225	return -EACCES;
226}
227
228const struct inode_operations nfs_mountpoint_inode_operations = {
229	.getattr	= nfs_getattr,
230	.setattr	= nfs_setattr,
231};
232
233const struct inode_operations nfs_referral_inode_operations = {
234	.getattr	= nfs_namespace_getattr,
235	.setattr	= nfs_namespace_setattr,
236};
237
238static void nfs_expire_automounts(struct work_struct *work)
239{
240	struct list_head *list = &nfs_automount_list;
241	int timeout = READ_ONCE(nfs_mountpoint_expiry_timeout);
242
243	mark_mounts_for_expiry(list);
244	if (!list_empty(list) && timeout > 0)
245		schedule_delayed_work(&nfs_automount_task, timeout);
246}
247
248void nfs_release_automount_timer(void)
249{
250	if (list_empty(&nfs_automount_list))
251		cancel_delayed_work(&nfs_automount_task);
252}
253
254/**
255 * nfs_do_submount - set up mountpoint when crossing a filesystem boundary
256 * @fc: pointer to struct nfs_fs_context
257 *
258 */
259int nfs_do_submount(struct fs_context *fc)
260{
261	struct nfs_fs_context *ctx = nfs_fc2context(fc);
262	struct dentry *dentry = ctx->clone_data.dentry;
263	struct nfs_server *server;
264	char *buffer, *p;
265	int ret;
266
267	/* create a new volume representation */
268	server = ctx->nfs_mod->rpc_ops->clone_server(NFS_SB(ctx->clone_data.sb),
269						     ctx->mntfh,
270						     ctx->clone_data.fattr,
271						     ctx->selected_flavor);
272
273	if (IS_ERR(server))
274		return PTR_ERR(server);
275
276	ctx->server = server;
277
278	buffer = kmalloc(4096, GFP_USER);
279	if (!buffer)
280		return -ENOMEM;
281
282	ctx->internal		= true;
283	ctx->clone_data.inherited_bsize = ctx->clone_data.sb->s_blocksize_bits;
284
285	p = nfs_devname(dentry, buffer, 4096);
286	if (IS_ERR(p)) {
287		nfs_errorf(fc, "NFS: Couldn't determine submount pathname");
288		ret = PTR_ERR(p);
289	} else {
290		ret = vfs_parse_fs_string(fc, "source", p, buffer + 4096 - p);
291		if (!ret)
292			ret = vfs_get_tree(fc);
293	}
294	kfree(buffer);
295	return ret;
296}
297EXPORT_SYMBOL_GPL(nfs_do_submount);
298
299int nfs_submount(struct fs_context *fc, struct nfs_server *server)
300{
301	struct nfs_fs_context *ctx = nfs_fc2context(fc);
302	struct dentry *dentry = ctx->clone_data.dentry;
303	struct dentry *parent = dget_parent(dentry);
304	int err;
305
306	/* Look it up again to get its attributes */
307	err = server->nfs_client->rpc_ops->lookup(d_inode(parent), dentry,
308						  ctx->mntfh, ctx->clone_data.fattr,
309						  NULL);
310	dput(parent);
311	if (err != 0)
312		return err;
313
314	ctx->selected_flavor = server->client->cl_auth->au_flavor;
315	return nfs_do_submount(fc);
316}
317EXPORT_SYMBOL_GPL(nfs_submount);
318
319static int param_set_nfs_timeout(const char *val, const struct kernel_param *kp)
320{
321	long num;
322	int ret;
323
324	if (!val)
325		return -EINVAL;
326	ret = kstrtol(val, 0, &num);
327	if (ret)
328		return -EINVAL;
329	if (num > 0) {
330		if (num >= INT_MAX / HZ)
331			num = INT_MAX;
332		else
333			num *= HZ;
334		*((int *)kp->arg) = num;
335		if (!list_empty(&nfs_automount_list))
336			mod_delayed_work(system_wq, &nfs_automount_task, num);
337	} else {
338		*((int *)kp->arg) = -1*HZ;
339		cancel_delayed_work(&nfs_automount_task);
340	}
341	return 0;
342}
343
344static int param_get_nfs_timeout(char *buffer, const struct kernel_param *kp)
345{
346	long num = *((int *)kp->arg);
347
348	if (num > 0) {
349		if (num >= INT_MAX - (HZ - 1))
350			num = INT_MAX / HZ;
351		else
352			num = (num + (HZ - 1)) / HZ;
353	} else
354		num = -1;
355	return scnprintf(buffer, PAGE_SIZE, "%li\n", num);
356}
357
358static const struct kernel_param_ops param_ops_nfs_timeout = {
359	.set = param_set_nfs_timeout,
360	.get = param_get_nfs_timeout,
361};
362#define param_check_nfs_timeout(name, p) __param_check(name, p, int);
363
364module_param(nfs_mountpoint_expiry_timeout, nfs_timeout, 0644);
365MODULE_PARM_DESC(nfs_mountpoint_expiry_timeout,
366		"Set the NFS automounted mountpoint timeout value (seconds)."
367		"Values <= 0 turn expiration off.");
368