fs/anon_inodes.c - linux - Git at Google

 // 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 make_inode)
 {
 	struct inode *inode;
 	struct file *file;

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

 	if (make_inode) {
 		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_create_getfile - 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.
  *
  * @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)
  *
  * Create a new anonymous inode and file pair.  This can be done for two
  * reasons:
  *
  * - for the inode to have its own security context, so that LSMs can enforce
  *   policy on the inode's creation;
  *
  * - if the caller needs a unique inode, for example in order to customize
  *   the size returned by fstat()
  *
  * 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.
  */
 struct file *anon_inode_create_getfile(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);
 }
 EXPORT_SYMBOL_GPL(anon_inode_create_getfile);

 static int __anon_inode_getfd(const char *name,
 			      const struct file_operations *fops,
 			      void *priv, int flags,
 			      const struct inode *context_inode,
 			      bool make_inode)
 {
 	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,
 				    make_inode);
 	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_create_getfd - 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.
  *
  * @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)
  *
  * Create a new anonymous inode and file pair.  This can be done for two
  * reasons:
  *
  * - for the inode to have its own security context, so that LSMs can enforce
  *   policy on the inode's creation;
  *
  * - if the caller needs a unique inode, for example in order to customize
  *   the size returned by fstat()
  *
  * The LSM may use @context_inode in inode_init_security_anon(), but a
  * reference to it is not held.
  *
  * Returns a newly created file descriptor or an error code.
  */
 int anon_inode_create_getfd(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);
 }

 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);
	// 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 make_inode)
	{
	struct inode *inode;
	struct file *file;

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

	if (make_inode) {
	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_create_getfile - 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.
	*
	* @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)
	*
	* Create a new anonymous inode and file pair. This can be done for two
	* reasons:
	*
	* - for the inode to have its own security context, so that LSMs can enforce
	* policy on the inode's creation;
	*
	* - if the caller needs a unique inode, for example in order to customize
	* the size returned by fstat()
	*
	* 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.
	*/
	struct file anon_inode_create_getfile(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);
	}
	EXPORT_SYMBOL_GPL(anon_inode_create_getfile);

	static int __anon_inode_getfd(const char *name,
	const struct file_operations *fops,
	void *priv, int flags,
	const struct inode *context_inode,
	bool make_inode)
	{
	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,
	make_inode);
	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_create_getfd - 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.
	*
	* @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)
	*
	* Create a new anonymous inode and file pair. This can be done for two
	* reasons:
	*
	* - for the inode to have its own security context, so that LSMs can enforce
	* policy on the inode's creation;
	*
	* - if the caller needs a unique inode, for example in order to customize
	* the size returned by fstat()
	*
	* The LSM may use @context_inode in inode_init_security_anon(), but a
	* reference to it is not held.
	*
	* Returns a newly created file descriptor or an error code.
	*/
	int anon_inode_create_getfd(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);
	}

	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);