anon_inodes.c

  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#include "internal.h"
 28
 29static struct vfsmount *anon_inode_mnt __ro_after_init;
 30static struct inode *anon_inode_inode __ro_after_init;
 31
 32/*
 33 * User space expects anonymous inodes to have no file type in st_mode.
 34 *
 35 * In particular, 'lsof' has this legacy logic:
 36 *
 37 *	type = s->st_mode & S_IFMT;
 38 *	switch (type) {
 39 *	  ...
 40 *	case 0:
 41 *		if (!strcmp(p, "anon_inode"))
 42 *			Lf->ntype = Ntype = N_ANON_INODE;
 43 *
 44 * to detect our old anon_inode logic.
 45 *
 46 * Rather than mess with our internal sane inode data, just fix it
 47 * up here in getattr() by masking off the format bits.
 48 */
 49int anon_inode_getattr(struct mnt_idmap *idmap, const struct path *path,
 50		       struct kstat *stat, u32 request_mask,
 51		       unsigned int query_flags)
 52{
 53	struct inode *inode = d_inode(path->dentry);
 54
 55	generic_fillattr(&nop_mnt_idmap, request_mask, inode, stat);
 56	stat->mode &= ~S_IFMT;
 57	return 0;
 58}
 59
 60int anon_inode_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
 61		       struct iattr *attr)
 62{
 63	return -EOPNOTSUPP;
 64}
 65
 66static const struct inode_operations anon_inode_operations = {
 67	.getattr = anon_inode_getattr,
 68	.setattr = anon_inode_setattr,
 69};
 70
 71/*
 72 * anon_inodefs_dname() is called from d_path().
 73 */
 74static char *anon_inodefs_dname(struct dentry *dentry, char *buffer, int buflen)
 75{
 76	return dynamic_dname(buffer, buflen, "anon_inode:%s",
 77				dentry->d_name.name);
 78}
 79
 80static const struct dentry_operations anon_inodefs_dentry_operations = {
 81	.d_dname	= anon_inodefs_dname,
 82};
 83
 84static int anon_inodefs_init_fs_context(struct fs_context *fc)
 85{
 86	struct pseudo_fs_context *ctx = init_pseudo(fc, ANON_INODE_FS_MAGIC);
 87	if (!ctx)
 88		return -ENOMEM;
 89	fc->s_iflags |= SB_I_NOEXEC;
 90	fc->s_iflags |= SB_I_NODEV;
 91	ctx->dops = &anon_inodefs_dentry_operations;
 92	return 0;
 93}
 94
 95static struct file_system_type anon_inode_fs_type = {
 96	.name		= "anon_inodefs",
 97	.init_fs_context = anon_inodefs_init_fs_context,
 98	.kill_sb	= kill_anon_super,
 99};
100
101/**
102 * anon_inode_make_secure_inode - allocate an anonymous inode with security context
103 * @sb:		[in]	Superblock to allocate from
104 * @name:	[in]	Name of the class of the newfile (e.g., "secretmem")
105 * @context_inode:
106 *		[in]	Optional parent inode for security inheritance
107 *
108 * The function ensures proper security initialization through the LSM hook
109 * security_inode_init_security_anon().
110 *
111 * Return:	Pointer to new inode on success, ERR_PTR on failure.
112 */
113struct inode *anon_inode_make_secure_inode(struct super_block *sb, const char *name,
114					   const struct inode *context_inode)
115{
116	struct inode *inode;
117	int error;
118
119	inode = alloc_anon_inode(sb);
120	if (IS_ERR(inode))
121		return inode;
122	inode->i_flags &= ~S_PRIVATE;
123	inode->i_op = &anon_inode_operations;
124	error =	security_inode_init_security_anon(inode, &QSTR(name),
125						  context_inode);
126	if (error) {
127		iput(inode);
128		return ERR_PTR(error);
129	}
130	return inode;
131}
132EXPORT_SYMBOL_FOR_MODULES(anon_inode_make_secure_inode, "kvm");
133
134static struct file *__anon_inode_getfile(const char *name,
135					 const struct file_operations *fops,
136					 void *priv, int flags,
137					 const struct inode *context_inode,
138					 bool make_inode)
139{
140	struct inode *inode;
141	struct file *file;
142
143	if (fops->owner && !try_module_get(fops->owner))
144		return ERR_PTR(-ENOENT);
145
146	if (make_inode) {
147		inode =	anon_inode_make_secure_inode(anon_inode_mnt->mnt_sb,
148						     name, context_inode);
149		if (IS_ERR(inode)) {
150			file = ERR_CAST(inode);
151			goto err;
152		}
153	} else {
154		inode =	anon_inode_inode;
155		if (IS_ERR(inode)) {
156			file = ERR_PTR(-ENODEV);
157			goto err;
158		}
159		/*
160		 * We know the anon_inode inode count is always
161		 * greater than zero, so ihold() is safe.
162		 */
163		ihold(inode);
164	}
165
166	file = alloc_file_pseudo(inode, anon_inode_mnt, name,
167				 flags & (O_ACCMODE | O_NONBLOCK), fops);
168	if (IS_ERR(file))
169		goto err_iput;
170
171	file->f_mapping = inode->i_mapping;
172
173	file->private_data = priv;
174
175	return file;
176
177err_iput:
178	iput(inode);
179err:
180	module_put(fops->owner);
181	return file;
182}
183
184/**
185 * anon_inode_getfile - creates a new file instance by hooking it up to an
186 *                      anonymous inode, and a dentry that describe the "class"
187 *                      of the file
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 *
194 * Creates a new file by hooking it on a single inode. This is useful for files
195 * that do not need to have a full-fledged inode in order to operate correctly.
196 * All the files created with anon_inode_getfile() will share a single inode,
197 * hence saving memory and avoiding code duplication for the file/inode/dentry
198 * setup.  Returns the newly created file* or an error pointer.
199 */
200struct file *anon_inode_getfile(const char *name,
201				const struct file_operations *fops,
202				void *priv, int flags)
203{
204	return __anon_inode_getfile(name, fops, priv, flags, NULL, false);
205}
206EXPORT_SYMBOL_GPL(anon_inode_getfile);
207
208/**
209 * anon_inode_getfile_fmode - creates a new file instance by hooking it up to an
210 *                      anonymous inode, and a dentry that describe the "class"
211 *                      of the file
212 *
213 * @name:    [in]    name of the "class" of the new file
214 * @fops:    [in]    file operations for the new file
215 * @priv:    [in]    private data for the new file (will be file's private_data)
216 * @flags:   [in]    flags
217 * @f_mode:  [in]    fmode
218 *
219 * Creates a new file by hooking it on a single inode. This is useful for files
220 * that do not need to have a full-fledged inode in order to operate correctly.
221 * All the files created with anon_inode_getfile() will share a single inode,
222 * hence saving memory and avoiding code duplication for the file/inode/dentry
223 * setup. Allows setting the fmode. Returns the newly created file* or an error
224 * pointer.
225 */
226struct file *anon_inode_getfile_fmode(const char *name,
227				const struct file_operations *fops,
228				void *priv, int flags, fmode_t f_mode)
229{
230	struct file *file;
231
232	file = __anon_inode_getfile(name, fops, priv, flags, NULL, false);
233	if (!IS_ERR(file))
234		file->f_mode |= f_mode;
235
236	return file;
237}
238EXPORT_SYMBOL_GPL(anon_inode_getfile_fmode);
239
240/**
241 * anon_inode_create_getfile - Like anon_inode_getfile(), but creates a new
242 *                             !S_PRIVATE anon inode rather than reuse the
243 *                             singleton anon inode and calls the
244 *                             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 the newly created file* or an error pointer.
266 */
267struct file *anon_inode_create_getfile(const char *name,
268				       const struct file_operations *fops,
269				       void *priv, int flags,
270				       const struct inode *context_inode)
271{
272	return __anon_inode_getfile(name, fops, priv, flags,
273				    context_inode, true);
274}
275EXPORT_SYMBOL_GPL(anon_inode_create_getfile);
276
277static int __anon_inode_getfd(const char *name,
278			      const struct file_operations *fops,
279			      void *priv, int flags,
280			      const struct inode *context_inode,
281			      bool make_inode)
282{
283	return FD_ADD(flags, __anon_inode_getfile(name, fops, priv, flags,
284						  context_inode, make_inode));
285}
286
287/**
288 * anon_inode_getfd - creates a new file instance by hooking it up to
289 *                    an anonymous inode and a dentry that describe
290 *                    the "class" of the file
291 *
292 * @name:    [in]    name of the "class" of the new file
293 * @fops:    [in]    file operations for the new file
294 * @priv:    [in]    private data for the new file (will be file's private_data)
295 * @flags:   [in]    flags
296 *
297 * Creates a new file by hooking it on a single inode. This is
298 * useful for files that do not need to have a full-fledged inode in
299 * order to operate correctly.  All the files created with
300 * anon_inode_getfd() will use the same singleton inode, reducing
301 * memory use and avoiding code duplication for the file/inode/dentry
302 * setup.  Returns a newly created file descriptor or an error code.
303 */
304int anon_inode_getfd(const char *name, const struct file_operations *fops,
305		     void *priv, int flags)
306{
307	return __anon_inode_getfd(name, fops, priv, flags, NULL, false);
308}
309EXPORT_SYMBOL_GPL(anon_inode_getfd);
310
311/**
312 * anon_inode_create_getfd - Like anon_inode_getfd(), but creates a new
313 * !S_PRIVATE anon inode rather than reuse the singleton anon inode, and calls
314 * the inode_init_security_anon() LSM hook.
315 *
316 * @name:    [in]    name of the "class" of the new file
317 * @fops:    [in]    file operations for the new file
318 * @priv:    [in]    private data for the new file (will be file's private_data)
319 * @flags:   [in]    flags
320 * @context_inode:
321 *           [in]    the logical relationship with the new inode (optional)
322 *
323 * Create a new anonymous inode and file pair.  This can be done for two
324 * reasons:
325 *
326 * - for the inode to have its own security context, so that LSMs can enforce
327 *   policy on the inode's creation;
328 *
329 * - if the caller needs a unique inode, for example in order to customize
330 *   the size returned by fstat()
331 *
332 * The LSM may use @context_inode in inode_init_security_anon(), but a
333 * reference to it is not held.
334 *
335 * Returns a newly created file descriptor or an error code.
336 */
337int anon_inode_create_getfd(const char *name, const struct file_operations *fops,
338			    void *priv, int flags,
339			    const struct inode *context_inode)
340{
341	return __anon_inode_getfd(name, fops, priv, flags, context_inode, true);
342}
343
344
345static int __init anon_inode_init(void)
346{
347	anon_inode_mnt = kern_mount(&anon_inode_fs_type);
348	if (IS_ERR(anon_inode_mnt))
349		panic("anon_inode_init() kernel mount failed (%ld)\n", PTR_ERR(anon_inode_mnt));
350
351	anon_inode_inode = alloc_anon_inode(anon_inode_mnt->mnt_sb);
352	if (IS_ERR(anon_inode_inode))
353		panic("anon_inode_init() inode allocation failed (%ld)\n", PTR_ERR(anon_inode_inode));
354	anon_inode_inode->i_op = &anon_inode_operations;
355
356	return 0;
357}
358
359fs_initcall(anon_inode_init);
360