summaryrefslogtreecommitdiff
path: root/fs/anon_inodes.c
blob: d26222b7eefe247f778d6b574873a9058d225146 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
// SPDX-License-Identifier: GPL-2.0-only
/*
 *  fs/anon_inodes.c
 *
 *  Copyright (C) 2007  Davide Libenzi <davidel@xmailserver.org>
 *
 *  Thanks to Arnd Bergmann for code review and suggestions.
 *  More changes for Thomas Gleixner suggestions.
 *
 */

#include <linux/cred.h>
#include <linux/file.h>
#include <linux/poll.h>
#include <linux/sched.h>
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/mount.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/magic.h>
#include <linux/anon_inodes.h>
#include <linux/pseudo_fs.h>

#include <linux/uaccess.h>

static struct vfsmount *anon_inode_mnt __ro_after_init;
static struct inode *anon_inode_inode __ro_after_init;

/*
 * anon_inodefs_dname() is called from d_path().
 */
static char *anon_inodefs_dname(struct dentry *dentry, char *buffer, int buflen)
{
	return dynamic_dname(buffer, buflen, "anon_inode:%s",
				dentry->d_name.name);
}

static const struct dentry_operations anon_inodefs_dentry_operations = {
	.d_dname	= anon_inodefs_dname,
};

static int anon_inodefs_init_fs_context(struct fs_context *fc)
{
	struct pseudo_fs_context *ctx = init_pseudo(fc, ANON_INODE_FS_MAGIC);
	if (!ctx)
		return -ENOMEM;
	ctx->dops = &anon_inodefs_dentry_operations;
	return 0;
}

static struct file_system_type anon_inode_fs_type = {
	.name		= "anon_inodefs",
	.init_fs_context = anon_inodefs_init_fs_context,
	.kill_sb	= kill_anon_super,
};

static struct inode *anon_inode_make_secure_inode(
	const char *name,
	const struct inode *context_inode)
{
	struct inode *inode;
	const struct qstr qname = QSTR_INIT(name, strlen(name));
	int error;

	inode = alloc_anon_inode(anon_inode_mnt->mnt_sb);
	if (IS_ERR(inode))
		return inode;
	inode->i_flags &= ~S_PRIVATE;
	error =	security_inode_init_security_anon(inode, &qname, context_inode);
	if (error) {
		iput(inode);
		return ERR_PTR(error);
	}
	return inode;
}

static struct file *__anon_inode_getfile(const char *name,
					 const struct file_operations *fops,
					 void *priv, int flags,
					 const struct inode *context_inode,
					 bool secure)
{
	struct inode *inode;
	struct file *file;

	if (fops->owner && !try_module_get(fops->owner))
		return ERR_PTR(-ENOENT);

	if (secure) {
		inode =	anon_inode_make_secure_inode(name, context_inode);
		if (IS_ERR(inode)) {
			file = ERR_CAST(inode);
			goto err;
		}
	} else {
		inode =	anon_inode_inode;
		if (IS_ERR(inode)) {
			file = ERR_PTR(-ENODEV);
			goto err;
		}
		/*
		 * We know the anon_inode inode count is always
		 * greater than zero, so ihold() is safe.
		 */
		ihold(inode);
	}

	file = alloc_file_pseudo(inode, anon_inode_mnt, name,
				 flags & (O_ACCMODE | O_NONBLOCK), fops);
	if (IS_ERR(file))
		goto err_iput;

	file->f_mapping = inode->i_mapping;

	file->private_data = priv;

	return file;

err_iput:
	iput(inode);
err:
	module_put(fops->owner);
	return file;
}

/**
 * anon_inode_getfile - creates a new file instance by hooking it up to an
 *                      anonymous inode, and a dentry that describe the "class"
 *                      of the file
 *
 * @name:    [in]    name of the "class" of the new file
 * @fops:    [in]    file operations for the new file
 * @priv:    [in]    private data for the new file (will be file's private_data)
 * @flags:   [in]    flags
 *
 * Creates a new file by hooking it on a single inode. This is useful for files
 * that do not need to have a full-fledged inode in order to operate correctly.
 * All the files created with anon_inode_getfile() will share a single inode,
 * hence saving memory and avoiding code duplication for the file/inode/dentry
 * setup.  Returns the newly created file* or an error pointer.
 */
struct file *anon_inode_getfile(const char *name,
				const struct file_operations *fops,
				void *priv, int flags)
{
	return __anon_inode_getfile(name, fops, priv, flags, NULL, false);
}
EXPORT_SYMBOL_GPL(anon_inode_getfile);

/**
 * anon_inode_getfile_secure - Like anon_inode_getfile(), but creates a new
 *                             !S_PRIVATE anon inode rather than reuse the
 *                             singleton anon inode and calls the
 *                             inode_init_security_anon() LSM hook.  This
 *                             allows for both the inode to have its own
 *                             security context and for the LSM to enforce
 *                             policy on the inode's creation.
 *
 * @name:    [in]    name of the "class" of the new file
 * @fops:    [in]    file operations for the new file
 * @priv:    [in]    private data for the new file (will be file's private_data)
 * @flags:   [in]    flags
 * @context_inode:
 *           [in]    the logical relationship with the new inode (optional)
 *
 * The LSM may use @context_inode in inode_init_security_anon(), but a
 * reference to it is not held.  Returns the newly created file* or an error
 * pointer.  See the anon_inode_getfile() documentation for more information.
 */
struct file *anon_inode_getfile_secure(const char *name,
				       const struct file_operations *fops,
				       void *priv, int flags,
				       const struct inode *context_inode)
{
	return __anon_inode_getfile(name, fops, priv, flags,
				    context_inode, true);
}

static int __anon_inode_getfd(const char *name,
			      const struct file_operations *fops,
			      void *priv, int flags,
			      const struct inode *context_inode,
			      bool secure)
{
	int error, fd;
	struct file *file;

	error = get_unused_fd_flags(flags);
	if (error < 0)
		return error;
	fd = error;

	file = __anon_inode_getfile(name, fops, priv, flags, context_inode,
				    secure);
	if (IS_ERR(file)) {
		error = PTR_ERR(file);
		goto err_put_unused_fd;
	}
	fd_install(fd, file);

	return fd;

err_put_unused_fd:
	put_unused_fd(fd);
	return error;
}

/**
 * anon_inode_getfd - creates a new file instance by hooking it up to
 *                    an anonymous inode and a dentry that describe
 *                    the "class" of the file
 *
 * @name:    [in]    name of the "class" of the new file
 * @fops:    [in]    file operations for the new file
 * @priv:    [in]    private data for the new file (will be file's private_data)
 * @flags:   [in]    flags
 *
 * Creates a new file by hooking it on a single inode. This is
 * useful for files that do not need to have a full-fledged inode in
 * order to operate correctly.  All the files created with
 * anon_inode_getfd() will use the same singleton inode, reducing
 * memory use and avoiding code duplication for the file/inode/dentry
 * setup.  Returns a newly created file descriptor or an error code.
 */
int anon_inode_getfd(const char *name, const struct file_operations *fops,
		     void *priv, int flags)
{
	return __anon_inode_getfd(name, fops, priv, flags, NULL, false);
}
EXPORT_SYMBOL_GPL(anon_inode_getfd);

/**
 * anon_inode_getfd_secure - Like anon_inode_getfd(), but creates a new
 * !S_PRIVATE anon inode rather than reuse the singleton anon inode, and calls
 * the inode_init_security_anon() LSM hook. This allows the inode to have its
 * own security context and for a LSM to reject creation of the inode.
 *
 * @name:    [in]    name of the "class" of the new file
 * @fops:    [in]    file operations for the new file
 * @priv:    [in]    private data for the new file (will be file's private_data)
 * @flags:   [in]    flags
 * @context_inode:
 *           [in]    the logical relationship with the new inode (optional)
 *
 * The LSM may use @context_inode in inode_init_security_anon(), but a
 * reference to it is not held.
 */
int anon_inode_getfd_secure(const char *name, const struct file_operations *fops,
			    void *priv, int flags,
			    const struct inode *context_inode)
{
	return __anon_inode_getfd(name, fops, priv, flags, context_inode, true);
}
EXPORT_SYMBOL_GPL(anon_inode_getfd_secure);

static int __init anon_inode_init(void)
{
	anon_inode_mnt = kern_mount(&anon_inode_fs_type);
	if (IS_ERR(anon_inode_mnt))
		panic("anon_inode_init() kernel mount failed (%ld)\n", PTR_ERR(anon_inode_mnt));

	anon_inode_inode = alloc_anon_inode(anon_inode_mnt->mnt_sb);
	if (IS_ERR(anon_inode_inode))
		panic("anon_inode_init() inode allocation failed (%ld)\n", PTR_ERR(anon_inode_inode));

	return 0;
}

fs_initcall(anon_inode_init);