1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * fs/anon_inodes.c
4 *
5 * Copyright (C) 2007 Davide Libenzi <davidel@xmailserver.org>
6 *
7 * Thanks to Arnd Bergmann for code review and suggestions.
8 * More changes for Thomas Gleixner suggestions.
9 *
10 */
11
12#include <linux/cred.h>
13#include <linux/file.h>
14#include <linux/poll.h>
15#include <linux/sched.h>
16#include <linux/init.h>
17#include <linux/fs.h>
18#include <linux/mount.h>
19#include <linux/module.h>
20#include <linux/kernel.h>
21#include <linux/magic.h>
22#include <linux/anon_inodes.h>
23#include <linux/pseudo_fs.h>
24
25#include <linux/uaccess.h>
26
27static struct vfsmount *anon_inode_mnt __ro_after_init;
28static struct inode *anon_inode_inode __ro_after_init;
29
30/*
31 * anon_inodefs_dname() is called from d_path().
32 */
33static char *anon_inodefs_dname(struct dentry *dentry, char *buffer, int buflen)
34{
35 return dynamic_dname(buffer, buflen, "anon_inode:%s",
36 dentry->d_name.name);
37}
38
39static const struct dentry_operations anon_inodefs_dentry_operations = {
40 .d_dname = anon_inodefs_dname,
41};
42
43static int anon_inodefs_init_fs_context(struct fs_context *fc)
44{
45 struct pseudo_fs_context *ctx = init_pseudo(fc, ANON_INODE_FS_MAGIC);
46 if (!ctx)
47 return -ENOMEM;
48 ctx->dops = &anon_inodefs_dentry_operations;
49 return 0;
50}
51
52static struct file_system_type anon_inode_fs_type = {
53 .name = "anon_inodefs",
54 .init_fs_context = anon_inodefs_init_fs_context,
55 .kill_sb = kill_anon_super,
56};
57
58static struct inode *anon_inode_make_secure_inode(
59 const char *name,
60 const struct inode *context_inode)
61{
62 struct inode *inode;
63 const struct qstr qname = QSTR_INIT(name, strlen(name));
64 int error;
65
66 inode = alloc_anon_inode(anon_inode_mnt->mnt_sb);
67 if (IS_ERR(ptr: inode))
68 return inode;
69 inode->i_flags &= ~S_PRIVATE;
70 error = security_inode_init_security_anon(inode, name: &qname, context_inode);
71 if (error) {
72 iput(inode);
73 return ERR_PTR(error);
74 }
75 return inode;
76}
77
78static struct file *__anon_inode_getfile(const char *name,
79 const struct file_operations *fops,
80 void *priv, int flags,
81 const struct inode *context_inode,
82 bool make_inode)
83{
84 struct inode *inode;
85 struct file *file;
86
87 if (fops->owner && !try_module_get(module: fops->owner))
88 return ERR_PTR(error: -ENOENT);
89
90 if (make_inode) {
91 inode = anon_inode_make_secure_inode(name, context_inode);
92 if (IS_ERR(ptr: inode)) {
93 file = ERR_CAST(ptr: inode);
94 goto err;
95 }
96 } else {
97 inode = anon_inode_inode;
98 if (IS_ERR(ptr: inode)) {
99 file = ERR_PTR(error: -ENODEV);
100 goto err;
101 }
102 /*
103 * We know the anon_inode inode count is always
104 * greater than zero, so ihold() is safe.
105 */
106 ihold(inode);
107 }
108
109 file = alloc_file_pseudo(inode, anon_inode_mnt, name,
110 flags: flags & (O_ACCMODE | O_NONBLOCK), fops);
111 if (IS_ERR(ptr: file))
112 goto err_iput;
113
114 file->f_mapping = inode->i_mapping;
115
116 file->private_data = priv;
117
118 return file;
119
120err_iput:
121 iput(inode);
122err:
123 module_put(module: fops->owner);
124 return file;
125}
126
127/**
128 * anon_inode_getfile - creates a new file instance by hooking it up to an
129 * anonymous inode, and a dentry that describe the "class"
130 * of the file
131 *
132 * @name: [in] name of the "class" of the new file
133 * @fops: [in] file operations for the new file
134 * @priv: [in] private data for the new file (will be file's private_data)
135 * @flags: [in] flags
136 *
137 * Creates a new file by hooking it on a single inode. This is useful for files
138 * that do not need to have a full-fledged inode in order to operate correctly.
139 * All the files created with anon_inode_getfile() will share a single inode,
140 * hence saving memory and avoiding code duplication for the file/inode/dentry
141 * setup. Returns the newly created file* or an error pointer.
142 */
143struct file *anon_inode_getfile(const char *name,
144 const struct file_operations *fops,
145 void *priv, int flags)
146{
147 return __anon_inode_getfile(name, fops, priv, flags, NULL, make_inode: false);
148}
149EXPORT_SYMBOL_GPL(anon_inode_getfile);
150
151/**
152 * anon_inode_create_getfile - Like anon_inode_getfile(), but creates a new
153 * !S_PRIVATE anon inode rather than reuse the
154 * singleton anon inode and calls the
155 * inode_init_security_anon() LSM hook.
156 *
157 * @name: [in] name of the "class" of the new file
158 * @fops: [in] file operations for the new file
159 * @priv: [in] private data for the new file (will be file's private_data)
160 * @flags: [in] flags
161 * @context_inode:
162 * [in] the logical relationship with the new inode (optional)
163 *
164 * Create a new anonymous inode and file pair. This can be done for two
165 * reasons:
166 *
167 * - for the inode to have its own security context, so that LSMs can enforce
168 * policy on the inode's creation;
169 *
170 * - if the caller needs a unique inode, for example in order to customize
171 * the size returned by fstat()
172 *
173 * The LSM may use @context_inode in inode_init_security_anon(), but a
174 * reference to it is not held.
175 *
176 * Returns the newly created file* or an error pointer.
177 */
178struct file *anon_inode_create_getfile(const char *name,
179 const struct file_operations *fops,
180 void *priv, int flags,
181 const struct inode *context_inode)
182{
183 return __anon_inode_getfile(name, fops, priv, flags,
184 context_inode, make_inode: true);
185}
186EXPORT_SYMBOL_GPL(anon_inode_create_getfile);
187
188static int __anon_inode_getfd(const char *name,
189 const struct file_operations *fops,
190 void *priv, int flags,
191 const struct inode *context_inode,
192 bool make_inode)
193{
194 int error, fd;
195 struct file *file;
196
197 error = get_unused_fd_flags(flags);
198 if (error < 0)
199 return error;
200 fd = error;
201
202 file = __anon_inode_getfile(name, fops, priv, flags, context_inode,
203 make_inode);
204 if (IS_ERR(ptr: file)) {
205 error = PTR_ERR(ptr: file);
206 goto err_put_unused_fd;
207 }
208 fd_install(fd, file);
209
210 return fd;
211
212err_put_unused_fd:
213 put_unused_fd(fd);
214 return error;
215}
216
217/**
218 * anon_inode_getfd - creates a new file instance by hooking it up to
219 * an anonymous inode and a dentry that describe
220 * the "class" of the file
221 *
222 * @name: [in] name of the "class" of the new file
223 * @fops: [in] file operations for the new file
224 * @priv: [in] private data for the new file (will be file's private_data)
225 * @flags: [in] flags
226 *
227 * Creates a new file by hooking it on a single inode. This is
228 * useful for files that do not need to have a full-fledged inode in
229 * order to operate correctly. All the files created with
230 * anon_inode_getfd() will use the same singleton inode, reducing
231 * memory use and avoiding code duplication for the file/inode/dentry
232 * setup. Returns a newly created file descriptor or an error code.
233 */
234int anon_inode_getfd(const char *name, const struct file_operations *fops,
235 void *priv, int flags)
236{
237 return __anon_inode_getfd(name, fops, priv, flags, NULL, make_inode: false);
238}
239EXPORT_SYMBOL_GPL(anon_inode_getfd);
240
241/**
242 * anon_inode_create_getfd - Like anon_inode_getfd(), but creates a new
243 * !S_PRIVATE anon inode rather than reuse the singleton anon inode, and calls
244 * the inode_init_security_anon() LSM hook.
245 *
246 * @name: [in] name of the "class" of the new file
247 * @fops: [in] file operations for the new file
248 * @priv: [in] private data for the new file (will be file's private_data)
249 * @flags: [in] flags
250 * @context_inode:
251 * [in] the logical relationship with the new inode (optional)
252 *
253 * Create a new anonymous inode and file pair. This can be done for two
254 * reasons:
255 *
256 * - for the inode to have its own security context, so that LSMs can enforce
257 * policy on the inode's creation;
258 *
259 * - if the caller needs a unique inode, for example in order to customize
260 * the size returned by fstat()
261 *
262 * The LSM may use @context_inode in inode_init_security_anon(), but a
263 * reference to it is not held.
264 *
265 * Returns a newly created file descriptor or an error code.
266 */
267int anon_inode_create_getfd(const char *name, const struct file_operations *fops,
268 void *priv, int flags,
269 const struct inode *context_inode)
270{
271 return __anon_inode_getfd(name, fops, priv, flags, context_inode, make_inode: true);
272}
273
274static int __init anon_inode_init(void)
275{
276 anon_inode_mnt = kern_mount(&anon_inode_fs_type);
277 if (IS_ERR(ptr: anon_inode_mnt))
278 panic(fmt: "anon_inode_init() kernel mount failed (%ld)\n", PTR_ERR(ptr: anon_inode_mnt));
279
280 anon_inode_inode = alloc_anon_inode(anon_inode_mnt->mnt_sb);
281 if (IS_ERR(ptr: anon_inode_inode))
282 panic(fmt: "anon_inode_init() inode allocation failed (%ld)\n", PTR_ERR(ptr: anon_inode_inode));
283
284 return 0;
285}
286
287fs_initcall(anon_inode_init);
288
289

source code of linux/fs/anon_inodes.c