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
27 static struct vfsmount *anon_inode_mnt __ro_after_init;
28 static struct inode *anon_inode_inode __ro_after_init;
29
30 /*
31 * anon_inodefs_dname() is called from d_path().
32 */
33 static 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
39 static const struct dentry_operations anon_inodefs_dentry_operations = {
40 .d_dname = anon_inodefs_dname,
41 };
42
43 static 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
52 static 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
58 static 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(inode))
68 return inode;
69 inode->i_flags &= ~S_PRIVATE;
70 error = security_inode_init_security_anon(inode, &qname, context_inode);
71 if (error) {
72 iput(inode);
73 return ERR_PTR(error);
74 }
75 return inode;
76 }
77
78 static 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(fops->owner))
88 return ERR_PTR(-ENOENT);
89
90 if (make_inode) {
91 inode = anon_inode_make_secure_inode(name, context_inode);
92 if (IS_ERR(inode)) {
93 file = ERR_CAST(inode);
94 goto err;
95 }
96 } else {
97 inode = anon_inode_inode;
98 if (IS_ERR(inode)) {
99 file = ERR_PTR(-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 & (O_ACCMODE | O_NONBLOCK), fops);
111 if (IS_ERR(file))
112 goto err_iput;
113
114 file->f_mapping = inode->i_mapping;
115
116 file->private_data = priv;
117
118 return file;
119
120 err_iput:
121 iput(inode);
122 err:
123 module_put(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 */
143 struct 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, false);
148 }
149 EXPORT_SYMBOL_GPL(anon_inode_getfile);
150
151 /**
152 * anon_inode_getfile_fmode - creates a new file instance by hooking it up to an
153 * anonymous inode, and a dentry that describe the "class"
154 * of the file
155 *
156 * @name: [in] name of the "class" of the new file
157 * @fops: [in] file operations for the new file
158 * @priv: [in] private data for the new file (will be file's private_data)
159 * @flags: [in] flags
160 * @f_mode: [in] fmode
161 *
162 * Creates a new file by hooking it on a single inode. This is useful for files
163 * that do not need to have a full-fledged inode in order to operate correctly.
164 * All the files created with anon_inode_getfile() will share a single inode,
165 * hence saving memory and avoiding code duplication for the file/inode/dentry
166 * setup. Allows setting the fmode. Returns the newly created file* or an error
167 * pointer.
168 */
169 struct file *anon_inode_getfile_fmode(const char *name,
170 const struct file_operations *fops,
171 void *priv, int flags, fmode_t f_mode)
172 {
173 struct file *file;
174
175 file = __anon_inode_getfile(name, fops, priv, flags, NULL, false);
176 if (!IS_ERR(file))
177 file->f_mode |= f_mode;
178
179 return file;
180 }
181 EXPORT_SYMBOL_GPL(anon_inode_getfile_fmode);
182
183 /**
184 * anon_inode_create_getfile - Like anon_inode_getfile(), but creates a new
185 * !S_PRIVATE anon inode rather than reuse the
186 * singleton anon inode and calls the
187 * inode_init_security_anon() LSM hook.
188 *
189 * @name: [in] name of the "class" of the new file
190 * @fops: [in] file operations for the new file
191 * @priv: [in] private data for the new file (will be file's private_data)
192 * @flags: [in] flags
193 * @context_inode:
194 * [in] the logical relationship with the new inode (optional)
195 *
196 * Create a new anonymous inode and file pair. This can be done for two
197 * reasons:
198 *
199 * - for the inode to have its own security context, so that LSMs can enforce
200 * policy on the inode's creation;
201 *
202 * - if the caller needs a unique inode, for example in order to customize
203 * the size returned by fstat()
204 *
205 * The LSM may use @context_inode in inode_init_security_anon(), but a
206 * reference to it is not held.
207 *
208 * Returns the newly created file* or an error pointer.
209 */
210 struct file *anon_inode_create_getfile(const char *name,
211 const struct file_operations *fops,
212 void *priv, int flags,
213 const struct inode *context_inode)
214 {
215 return __anon_inode_getfile(name, fops, priv, flags,
216 context_inode, true);
217 }
218 EXPORT_SYMBOL_GPL(anon_inode_create_getfile);
219
220 static int __anon_inode_getfd(const char *name,
221 const struct file_operations *fops,
222 void *priv, int flags,
223 const struct inode *context_inode,
224 bool make_inode)
225 {
226 int error, fd;
227 struct file *file;
228
229 error = get_unused_fd_flags(flags);
230 if (error < 0)
231 return error;
232 fd = error;
233
234 file = __anon_inode_getfile(name, fops, priv, flags, context_inode,
235 make_inode);
236 if (IS_ERR(file)) {
237 error = PTR_ERR(file);
238 goto err_put_unused_fd;
239 }
240 fd_install(fd, file);
241
242 return fd;
243
244 err_put_unused_fd:
245 put_unused_fd(fd);
246 return error;
247 }
248
249 /**
250 * anon_inode_getfd - creates a new file instance by hooking it up to
251 * an anonymous inode and a dentry that describe
252 * the "class" of the file
253 *
254 * @name: [in] name of the "class" of the new file
255 * @fops: [in] file operations for the new file
256 * @priv: [in] private data for the new file (will be file's private_data)
257 * @flags: [in] flags
258 *
259 * Creates a new file by hooking it on a single inode. This is
260 * useful for files that do not need to have a full-fledged inode in
261 * order to operate correctly. All the files created with
262 * anon_inode_getfd() will use the same singleton inode, reducing
263 * memory use and avoiding code duplication for the file/inode/dentry
264 * setup. Returns a newly created file descriptor or an error code.
265 */
266 int anon_inode_getfd(const char *name, const struct file_operations *fops,
267 void *priv, int flags)
268 {
269 return __anon_inode_getfd(name, fops, priv, flags, NULL, false);
270 }
271 EXPORT_SYMBOL_GPL(anon_inode_getfd);
272
273 /**
274 * anon_inode_create_getfd - Like anon_inode_getfd(), but creates a new
275 * !S_PRIVATE anon inode rather than reuse the singleton anon inode, and calls
276 * the inode_init_security_anon() LSM hook.
277 *
278 * @name: [in] name of the "class" of the new file
279 * @fops: [in] file operations for the new file
280 * @priv: [in] private data for the new file (will be file's private_data)
281 * @flags: [in] flags
282 * @context_inode:
283 * [in] the logical relationship with the new inode (optional)
284 *
285 * Create a new anonymous inode and file pair. This can be done for two
286 * reasons:
287 *
288 * - for the inode to have its own security context, so that LSMs can enforce
289 * policy on the inode's creation;
290 *
291 * - if the caller needs a unique inode, for example in order to customize
292 * the size returned by fstat()
293 *
294 * The LSM may use @context_inode in inode_init_security_anon(), but a
295 * reference to it is not held.
296 *
297 * Returns a newly created file descriptor or an error code.
298 */
299 int anon_inode_create_getfd(const char *name, const struct file_operations *fops,
300 void *priv, int flags,
301 const struct inode *context_inode)
302 {
303 return __anon_inode_getfd(name, fops, priv, flags, context_inode, true);
304 }
305
306
307 static int __init anon_inode_init(void)
308 {
309 anon_inode_mnt = kern_mount(&anon_inode_fs_type);
310 if (IS_ERR(anon_inode_mnt))
311 panic("anon_inode_init() kernel mount failed (%ld)\n", PTR_ERR(anon_inode_mnt));
312
313 anon_inode_inode = alloc_anon_inode(anon_inode_mnt->mnt_sb);
314 if (IS_ERR(anon_inode_inode))
315 panic("anon_inode_init() inode allocation failed (%ld)\n", PTR_ERR(anon_inode_inode));
316
317 return 0;
318 }
319
320 fs_initcall(anon_inode_init);
321
322
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