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 secure)
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 (secure) {
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, secure: false);
148}
149EXPORT_SYMBOL_GPL(anon_inode_getfile);
150
151/**
152 * anon_inode_getfile_secure - 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. This
156 * allows for both the inode to have its own
157 * security context and for the LSM to enforce
158 * policy on the inode's creation.
159 *
160 * @name: [in] name of the "class" of the new file
161 * @fops: [in] file operations for the new file
162 * @priv: [in] private data for the new file (will be file's private_data)
163 * @flags: [in] flags
164 * @context_inode:
165 * [in] the logical relationship with the new inode (optional)
166 *
167 * The LSM may use @context_inode in inode_init_security_anon(), but a
168 * reference to it is not held. Returns the newly created file* or an error
169 * pointer. See the anon_inode_getfile() documentation for more information.
170 */
171struct file *anon_inode_getfile_secure(const char *name,
172 const struct file_operations *fops,
173 void *priv, int flags,
174 const struct inode *context_inode)
175{
176 return __anon_inode_getfile(name, fops, priv, flags,
177 context_inode, secure: true);
178}
179
180static int __anon_inode_getfd(const char *name,
181 const struct file_operations *fops,
182 void *priv, int flags,
183 const struct inode *context_inode,
184 bool secure)
185{
186 int error, fd;
187 struct file *file;
188
189 error = get_unused_fd_flags(flags);
190 if (error < 0)
191 return error;
192 fd = error;
193
194 file = __anon_inode_getfile(name, fops, priv, flags, context_inode,
195 secure);
196 if (IS_ERR(ptr: file)) {
197 error = PTR_ERR(ptr: file);
198 goto err_put_unused_fd;
199 }
200 fd_install(fd, file);
201
202 return fd;
203
204err_put_unused_fd:
205 put_unused_fd(fd);
206 return error;
207}
208
209/**
210 * anon_inode_getfd - creates a new file instance by hooking it up to
211 * an anonymous inode and a dentry that describe
212 * the "class" of the file
213 *
214 * @name: [in] name of the "class" of the new file
215 * @fops: [in] file operations for the new file
216 * @priv: [in] private data for the new file (will be file's private_data)
217 * @flags: [in] flags
218 *
219 * Creates a new file by hooking it on a single inode. This is
220 * useful for files that do not need to have a full-fledged inode in
221 * order to operate correctly. All the files created with
222 * anon_inode_getfd() will use the same singleton inode, reducing
223 * memory use and avoiding code duplication for the file/inode/dentry
224 * setup. Returns a newly created file descriptor or an error code.
225 */
226int anon_inode_getfd(const char *name, const struct file_operations *fops,
227 void *priv, int flags)
228{
229 return __anon_inode_getfd(name, fops, priv, flags, NULL, secure: false);
230}
231EXPORT_SYMBOL_GPL(anon_inode_getfd);
232
233/**
234 * anon_inode_getfd_secure - Like anon_inode_getfd(), but creates a new
235 * !S_PRIVATE anon inode rather than reuse the singleton anon inode, and calls
236 * the inode_init_security_anon() LSM hook. This allows the inode to have its
237 * own security context and for a LSM to reject creation of the inode.
238 *
239 * @name: [in] name of the "class" of the new file
240 * @fops: [in] file operations for the new file
241 * @priv: [in] private data for the new file (will be file's private_data)
242 * @flags: [in] flags
243 * @context_inode:
244 * [in] the logical relationship with the new inode (optional)
245 *
246 * The LSM may use @context_inode in inode_init_security_anon(), but a
247 * reference to it is not held.
248 */
249int anon_inode_getfd_secure(const char *name, const struct file_operations *fops,
250 void *priv, int flags,
251 const struct inode *context_inode)
252{
253 return __anon_inode_getfd(name, fops, priv, flags, context_inode, secure: true);
254}
255EXPORT_SYMBOL_GPL(anon_inode_getfd_secure);
256
257static int __init anon_inode_init(void)
258{
259 anon_inode_mnt = kern_mount(&anon_inode_fs_type);
260 if (IS_ERR(ptr: anon_inode_mnt))
261 panic(fmt: "anon_inode_init() kernel mount failed (%ld)\n", PTR_ERR(ptr: anon_inode_mnt));
262
263 anon_inode_inode = alloc_anon_inode(anon_inode_mnt->mnt_sb);
264 if (IS_ERR(ptr: anon_inode_inode))
265 panic(fmt: "anon_inode_init() inode allocation failed (%ld)\n", PTR_ERR(ptr: anon_inode_inode));
266
267 return 0;
268}
269
270fs_initcall(anon_inode_init);
271
272

source code of linux/fs/anon_inodes.c