Re: [PATCH] add securityfs for all LSMs to use

[Mike Waychison <mike@waychison.com>]

Greg KH wrote:
> Here's a small patch against 2.6.13-rc2 that adds securityfs, a virtual
> fs that all LSMs can use instead of creating their own.  The fs should
> be mounted at /sys/kernel/security, and the fs creates that mount point.
> This will make the LSB people happy that we aren't creating a new
> /my_lsm_fs directory in the root for every different LSM.

How are LSM modules supposed to use these files?  or is that forthcoming?

Comments inline:

> 
> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
>  
>  include/linux/security.h |    5 
>  security/Makefile        |    2 
>  security/inode.c         |  344 +++++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 350 insertions(+), 1 deletion(-)
> 
> ---
> --- gregkh-2.6.orig/security/Makefile	2005-06-17 12:48:29.000000000 -0700
> +++ gregkh-2.6/security/Makefile	2005-07-06 01:05:56.000000000 -0700
> @@ -11,7 +11,7 @@
>  endif
>  
>  # Object file lists
> -obj-$(CONFIG_SECURITY)			+= security.o dummy.o
> +obj-$(CONFIG_SECURITY)			+= security.o dummy.o inode.o
>  # Must precede capability.o in order to stack properly.
>  obj-$(CONFIG_SECURITY_SELINUX)		+= selinux/built-in.o
>  obj-$(CONFIG_SECURITY_CAPABILITIES)	+= commoncap.o capability.o
> --- /dev/null	1970-01-01 00:00:00.000000000 +0000
> +++ gregkh-2.6/security/inode.c	2005-07-06 01:08:12.000000000 -0700
> @@ -0,0 +1,344 @@
> +/*
> + *  inode.c - securityfs
> + *
> + *  Copyright (C) 2005 Greg Kroah-Hartman <gregkh@suse.de>
> + *
> + *	This program is free software; you can redistribute it and/or
> + *	modify it under the terms of the GNU General Public License version
> + *	2 as published by the Free Software Foundation.
> + *
> + *  Based on fs/debugfs/inode.c which had the following copyright notice:
> + *    Copyright (C) 2004 Greg Kroah-Hartman <greg@kroah.com>
> + *    Copyright (C) 2004 IBM Inc.
> + */
> +
> +/* #define DEBUG */
> +#include <linux/config.h>
> +#include <linux/module.h>
> +#include <linux/fs.h>
> +#include <linux/mount.h>
> +#include <linux/pagemap.h>
> +#include <linux/init.h>
> +#include <linux/namei.h>
> +#include <linux/security.h>
> +
> +#define SECURITYFS_MAGIC	0x73636673
> +
> +static struct vfsmount *mount;
> +static int mount_count;
> +
> +/*
> + * TODO:
> + *   I think I can get rid of these default_file_ops, but not quite sure...
> + */
> +static ssize_t default_read_file(struct file *file, char __user *buf,
> +				 size_t count, loff_t *ppos)
> +{
> +	return 0;
> +}
> +
> +static ssize_t default_write_file(struct file *file, const char __user *buf,
> +				   size_t count, loff_t *ppos)
> +{
> +	return count;
> +}
> +
> +static int default_open(struct inode *inode, struct file *file)
> +{
> +	if (inode->u.generic_ip)
> +		file->private_data = inode->u.generic_ip;
> +
> +	return 0;
> +}
> +
> +static struct file_operations default_file_ops = {
> +	.read =		default_read_file,
> +	.write =	default_write_file,
> +	.open =		default_open,
> +};
> +
> +static struct inode *get_inode(struct super_block *sb, int mode, dev_t dev)
> +{
> +	struct inode *inode = new_inode(sb);
> +
> +	if (inode) {
> +		inode->i_mode = mode;
> +		inode->i_uid = 0;
> +		inode->i_gid = 0;
> +		inode->i_blksize = PAGE_CACHE_SIZE;
> +		inode->i_blocks = 0;
> +		inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
> +		switch (mode & S_IFMT) {
> +		default:
> +			init_special_inode(inode, mode, dev);
> +			break;
> +		case S_IFREG:
> +			inode->i_fop = &default_file_ops;
> +			break;
> +		case S_IFDIR:
> +			inode->i_op = &simple_dir_inode_operations;
> +			inode->i_fop = &simple_dir_operations;
> +
> +			/* directory inodes start off with i_nlink == 2 (for "." entry) */
> +			inode->i_nlink++;
> +			break;
> +		}
> +	}
> +	return inode;
> +}
> +
> +/* SMP-safe */
> +static int mknod(struct inode *dir, struct dentry *dentry,
> +			 int mode, dev_t dev)
> +{
> +	struct inode *inode = get_inode(dir->i_sb, mode, dev);
> +	int error = -EPERM;
> +
> +	if (dentry->d_inode)

You leak an inode here.

> +		return -EEXIST;
> +
> +	if (inode) {
> +		d_instantiate(dentry, inode);
> +		dget(dentry);
> +		error = 0;
> +	}
> +	return error;
> +}
> +
> +static int mkdir(struct inode *dir, struct dentry *dentry, int mode)
> +{
> +	int res;
> +
> +	mode = (mode & (S_IRWXUGO | S_ISVTX)) | S_IFDIR;
> +	res = mknod(dir, dentry, mode, 0);
> +	if (!res)
> +		dir->i_nlink++;
> +	return res;
> +}
> +
> +static int create(struct inode *dir, struct dentry *dentry, int mode)
> +{
> +	mode = (mode & S_IALLUGO) | S_IFREG;
> +	return mknod(dir, dentry, mode, 0);
> +}
> +
> +static inline int positive(struct dentry *dentry)
> +{
> +	return dentry->d_inode && !d_unhashed(dentry);
> +}
> +
> +static int fill_super(struct super_block *sb, void *data, int silent)
> +{
> +	static struct tree_descr files[] = {{""}};
> +
> +	return simple_fill_super(sb, SECURITYFS_MAGIC, files);
> +}
> +
> +static struct super_block *get_sb(struct file_system_type *fs_type,
> +				        int flags, const char *dev_name,
> +					void *data)
> +{
> +	return get_sb_single(fs_type, flags, data, fill_super);
> +}
> +
> +static struct file_system_type fs_type = {
> +	.owner =	THIS_MODULE,
> +	.name =		"securityfs",
> +	.get_sb =	get_sb,
> +	.kill_sb =	kill_litter_super,
> +};
> +
> +static int create_by_name(const char *name, mode_t mode,
> +			  struct dentry *parent,
> +			  struct dentry **dentry)
> +{
> +	int error = 0;
> +
> +	/* If the parent is not specified, we create it in the root.
> +	 * We need the root dentry to do this, which is in the super
> +	 * block. A pointer to that is in the struct vfsmount that we
> +	 * have around.
> +	 */
> +	if (!parent ) {
> +		if (mount && mount->mnt_sb) {
> +			parent = mount->mnt_sb->s_root;
> +		}
> +	}

You should be guaranteed by here that mount is valid due to the
simple_pin_fs().

> +	if (!parent) {
> +		pr_debug("securityfs: Ah! can not find a parent!\n");
> +		return -EFAULT;
> +	}
> +
> +	*dentry = NULL;

Not needed?

> +	down(&parent->d_inode->i_sem);
> +	*dentry = lookup_one_len(name, parent, strlen(name));
> +	if (!IS_ERR(dentry)) {
> +		if ((mode & S_IFMT) == S_IFDIR)
> +			error = mkdir(parent->d_inode, *dentry, mode);
> +		else
> +			error = create(parent->d_inode, *dentry, mode);
> +	} else

} else {

> +		error = PTR_ERR(dentry);

}

> +	up(&parent->d_inode->i_sem);
> +
> +	return error;
> +}
> +
> +/**
> + * securityfs_create_file - create a file in the securityfs filesystem
> + *
> + * @name: a pointer to a string containing the name of the file to create.
> + * @mode: the permission that the file should have
> + * @parent: a pointer to the parent dentry for this file.  This should be a
> + *          directory dentry if set.  If this paramater is NULL, then the
> + *          file will be created in the root of the securityfs filesystem.
> + * @data: a pointer to something that the caller will want to get to later
> + *        on.  The inode.u.generic_ip pointer will point to this value on
> + *        the open() call.
> + * @fops: a pointer to a struct file_operations that should be used for
> + *        this file.
> + *
> + * This is the basic "create a file" function for securityfs.  It allows for a
> + * wide range of flexibility in createing a file, or a directory (if you
> + * want to create a directory, the securityfs_create_dir() function is
> + * recommended to be used instead.)
> + *
> + * This function will return a pointer to a dentry if it succeeds.  This
> + * pointer must be passed to the securityfs_remove() function when the file is
> + * to be removed (no automatic cleanup happens if your module is unloaded,
> + * you are responsible here.)  If an error occurs, NULL will be returned.
> + *
> + * If securityfs is not enabled in the kernel, the value -ENODEV will be
> + * returned.  It is not wise to check for this value, but rather, check for
> + * NULL or !NULL instead as to eliminate the need for #ifdef in the calling
> + * code.
> + */
> +struct dentry *securityfs_create_file(const char *name, mode_t mode,
> +				   struct dentry *parent, void *data,
> +				   struct file_operations *fops)
> +{
> +	struct dentry *dentry = NULL;
> +	int error;
> +
> +	pr_debug("securityfs: creating file '%s'\n",name);
> +
> +	error = simple_pin_fs("securityfs", &mount, &mount_count);
> +	if (error) {
> +		dentry = ERR_PTR(error);
> +		goto exit;
> +	}
> +
> +	error = create_by_name(name, mode, parent, &dentry);
> +	if (error) {
> +		dentry = ERR_PTR(error);

simple_release_fs

> +		goto exit;
> +	}
> +
> +	if (dentry->d_inode) {
> +		if (fops)
> +			dentry->d_inode->i_fop = fops;
> +		if (data)
> +			dentry->d_inode->u.generic_ip = data;
> +	}
> +exit:
> +	return dentry;
> +}
> +EXPORT_SYMBOL_GPL(securityfs_create_file);
> +
> +/**
> + * securityfs_create_dir - create a directory in the securityfs filesystem
> + *
> + * @name: a pointer to a string containing the name of the directory to
> + *        create.
> + * @parent: a pointer to the parent dentry for this file.  This should be a
> + *          directory dentry if set.  If this paramater is NULL, then the
> + *          directory will be created in the root of the securityfs filesystem.
> + *
> + * This function creates a directory in securityfs with the given name.
> + *
> + * This function will return a pointer to a dentry if it succeeds.  This
> + * pointer must be passed to the securityfs_remove() function when the file is
> + * to be removed (no automatic cleanup happens if your module is unloaded,
> + * you are responsible here.)  If an error occurs, NULL will be returned.
> + *
> + * If securityfs is not enabled in the kernel, the value -ENODEV will be
> + * returned.  It is not wise to check for this value, but rather, check for
> + * NULL or !NULL instead as to eliminate the need for #ifdef in the calling
> + * code.
> + */
> +struct dentry *securityfs_create_dir(const char *name, struct dentry *parent)
> +{
> +	return securityfs_create_file(name,
> +				      S_IFDIR | S_IRWXU | S_IRUGO | S_IXUGO,
> +				      parent, NULL, NULL);
> +}
> +EXPORT_SYMBOL_GPL(securityfs_create_dir);
> +
> +/**
> + * securityfs_remove - removes a file or directory from the securityfs filesystem
> + *
> + * @dentry: a pointer to a the dentry of the file or directory to be
> + *          removed.
> + *
> + * This function removes a file or directory in securityfs that was previously
> + * created with a call to another securityfs function (like
> + * securityfs_create_file() or variants thereof.)
> + *
> + * This function is required to be called in order for the file to be
> + * removed, no automatic cleanup of files will happen when a module is
> + * removed, you are responsible here.
> + */

Is this true?  It would appear that this module can't be unloaded until
all files are _remove'd, no? (due to mount pinning).

> +void securityfs_remove(struct dentry *dentry)
> +{
> +	struct dentry *parent;
> +
> +	if (!dentry)
> +		return;
> +
> +	parent = dentry->d_parent;
> +	if (!parent || !parent->d_inode)
> +		return;
> +
> +	down(&parent->d_inode->i_sem);
> +	if (positive(dentry)) {
> +		if (dentry->d_inode) {
> +			if (S_ISDIR(dentry->d_inode->i_mode))
> +				simple_rmdir(parent->d_inode, dentry);
> +			else
> +				simple_unlink(parent->d_inode, dentry);
> +		dput(dentry);

Indentation?

> +		}
> +	}
> +	up(&parent->d_inode->i_sem);
> +	simple_release_fs(&mount, &mount_count);
> +}
> +EXPORT_SYMBOL_GPL(securityfs_remove);

Does EXPORT_SYMBOL(_GPL) even work from a module?   I must be behind the
times.


> +
> +static decl_subsys(security, NULL, NULL);
> +
> +static int __init securityfs_init(void)
> +{
> +	int retval;
> +
> +	kset_set_kset_s(&security_subsys, kernel_subsys);
> +	retval = subsystem_register(&security_subsys);
> +	if (retval)
> +		return retval;
> +
> +	retval = register_filesystem(&fs_type);
> +	if (retval)
> +		subsystem_unregister(&security_subsys);
> +	return retval;
> +}
> +
> +static void __exit securityfs_exit(void)
> +{
> +	simple_release_fs(&mount, &mount_count);
> +	unregister_filesystem(&fs_type);
> +	subsystem_unregister(&security_subsys);
> +}
> +
> +core_initcall(securityfs_init);
> +module_exit(securityfs_exit);
> +MODULE_LICENSE("GPL");
> +
> --- gregkh-2.6.orig/include/linux/security.h	2005-06-17 12:48:29.000000000 -0700
> +++ gregkh-2.6/include/linux/security.h	2005-07-06 01:05:56.000000000 -0700
> @@ -1983,6 +1983,11 @@
>  extern int unregister_security	(struct security_operations *ops);
>  extern int mod_reg_security	(const char *name, struct security_operations *ops);
>  extern int mod_unreg_security	(const char *name, struct security_operations *ops);
> +extern struct dentry *securityfs_create_file(const char *name, mode_t mode,
> +					     struct dentry *parent, void *data,
> +					     struct file_operations *fops);
> +extern struct dentry *securityfs_create_dir(const char *name, struct dentry *parent);
> +extern void securityfs_remove(struct dentry *dentry);
>  
>  
>  #else /* CONFIG_SECURITY */
> 

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