linux/fs/configfs/configfs_internal.h
Louis Rilling 2a109f2a41 [PATCH] configfs: Prevent userspace from creating new entries under attaching directories
process 1: 					process 2:
configfs_mkdir("A")
  attach_group("A")
    attach_item("A")
      d_instantiate("A")
    populate_groups("A")
      mutex_lock("A")
      attach_group("A/B")
        attach_item("A")
          d_instantiate("A/B")
						mkdir("A/B/C")
						  do_path_lookup("A/B/C", LOOKUP_PARENT)
						    ok
						  lookup_create("A/B/C")
						    mutex_lock("A/B")
						    ok
						  configfs_mkdir("A/B/C")
						    ok
      attach_group("A/C")
        attach_item("A/C")
          d_instantiate("A/C")
        populate_groups("A/C")
          mutex_lock("A/C")
          attach_group("A/C/D")
            attach_item("A/C/D")
              failure
          mutex_unlock("A/C")
          detach_groups("A/C")
            nothing to do
						mkdir("A/C/E")
						  do_path_lookup("A/C/E", LOOKUP_PARENT)
						    ok
						  lookup_create("A/C/E")
						    mutex_lock("A/C")
						    ok
						  configfs_mkdir("A/C/E")
						    ok
        detach_item("A/C")
        d_delete("A/C")
      mutex_unlock("A")
      detach_groups("A")
        mutex_lock("A/B")
        detach_group("A/B")
	  detach_groups("A/B")
	    nothing since no _default_ group
          detach_item("A/B")
        mutex_unlock("A/B")
        d_delete("A/B")
    detach_item("A")
    d_delete("A")

Two bugs:

1/ "A/B/C" and "A/C/E" are created, but never removed while their parent are
removed in the end. The same could happen with symlink() instead of mkdir().

2/ "A" and "A/C" inodes are not locked while detach_item() is called on them,
   which may probably confuse VFS.

This commit fixes 1/, tagging new directories with CONFIGFS_USET_CREATING before
building the inode and instantiating the dentry, and validating the whole
group+default groups hierarchy in a second pass by clearing
CONFIGFS_USET_CREATING.
	mkdir(), symlink(), lookup(), and dir_open() simply return -ENOENT if
called in (or linking to) a directory tagged with CONFIGFS_USET_CREATING. This
does not prevent userspace from calling stat() successfuly on such directories,
but this prevents userspace from adding (children to | symlinking from/to |
read/write attributes of | listing the contents of) not validated items. In
other words, userspace will not interact with the subsystem on a new item until
the new item creation completes correctly.
	It was first proposed to re-use CONFIGFS_USET_IN_MKDIR instead of a new
flag CONFIGFS_USET_CREATING, but this generated conflicts when checking the
target of a new symlink: a valid target directory in the middle of attaching
a new user-created child item could be wrongly detected as being attached.

2/ is fixed by next commit.

Signed-off-by: Louis Rilling <louis.rilling@kerlabs.com>
Signed-off-by: Joel Becker <joel.becker@oracle.com>
Signed-off-by: Mark Fasheh <mfasheh@suse.com>
2008-07-31 16:21:13 -07:00

157 lines
4.9 KiB
C

/* -*- mode: c; c-basic-offset:8; -*-
* vim: noexpandtab sw=8 ts=8 sts=0:
*
* configfs_internal.h - Internal stuff for configfs
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public
* License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*
* You should have received a copy of the GNU General Public
* License along with this program; if not, write to the
* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
* Boston, MA 021110-1307, USA.
*
* Based on sysfs:
* sysfs is Copyright (C) 2001, 2002, 2003 Patrick Mochel
*
* configfs Copyright (C) 2005 Oracle. All rights reserved.
*/
#include <linux/slab.h>
#include <linux/list.h>
#include <linux/spinlock.h>
struct configfs_dirent {
atomic_t s_count;
int s_dependent_count;
struct list_head s_sibling;
struct list_head s_children;
struct list_head s_links;
void * s_element;
int s_type;
umode_t s_mode;
struct dentry * s_dentry;
struct iattr * s_iattr;
};
#define CONFIGFS_ROOT 0x0001
#define CONFIGFS_DIR 0x0002
#define CONFIGFS_ITEM_ATTR 0x0004
#define CONFIGFS_ITEM_LINK 0x0020
#define CONFIGFS_USET_DIR 0x0040
#define CONFIGFS_USET_DEFAULT 0x0080
#define CONFIGFS_USET_DROPPING 0x0100
#define CONFIGFS_USET_IN_MKDIR 0x0200
#define CONFIGFS_USET_CREATING 0x0400
#define CONFIGFS_NOT_PINNED (CONFIGFS_ITEM_ATTR)
extern struct mutex configfs_symlink_mutex;
extern spinlock_t configfs_dirent_lock;
extern struct vfsmount * configfs_mount;
extern struct kmem_cache *configfs_dir_cachep;
extern int configfs_is_root(struct config_item *item);
extern struct inode * configfs_new_inode(mode_t mode, struct configfs_dirent *);
extern int configfs_create(struct dentry *, int mode, int (*init)(struct inode *));
extern int configfs_inode_init(void);
extern void configfs_inode_exit(void);
extern int configfs_create_file(struct config_item *, const struct configfs_attribute *);
extern int configfs_make_dirent(struct configfs_dirent *,
struct dentry *, void *, umode_t, int);
extern int configfs_dirent_is_ready(struct configfs_dirent *);
extern int configfs_add_file(struct dentry *, const struct configfs_attribute *, int);
extern void configfs_hash_and_remove(struct dentry * dir, const char * name);
extern const unsigned char * configfs_get_name(struct configfs_dirent *sd);
extern void configfs_drop_dentry(struct configfs_dirent *sd, struct dentry *parent);
extern int configfs_setattr(struct dentry *dentry, struct iattr *iattr);
extern int configfs_pin_fs(void);
extern void configfs_release_fs(void);
extern struct rw_semaphore configfs_rename_sem;
extern struct super_block * configfs_sb;
extern const struct file_operations configfs_dir_operations;
extern const struct file_operations configfs_file_operations;
extern const struct file_operations bin_fops;
extern const struct inode_operations configfs_dir_inode_operations;
extern const struct inode_operations configfs_symlink_inode_operations;
extern int configfs_symlink(struct inode *dir, struct dentry *dentry,
const char *symname);
extern int configfs_unlink(struct inode *dir, struct dentry *dentry);
struct configfs_symlink {
struct list_head sl_list;
struct config_item *sl_target;
};
extern int configfs_create_link(struct configfs_symlink *sl,
struct dentry *parent,
struct dentry *dentry);
static inline struct config_item * to_item(struct dentry * dentry)
{
struct configfs_dirent * sd = dentry->d_fsdata;
return ((struct config_item *) sd->s_element);
}
static inline struct configfs_attribute * to_attr(struct dentry * dentry)
{
struct configfs_dirent * sd = dentry->d_fsdata;
return ((struct configfs_attribute *) sd->s_element);
}
static inline struct config_item *configfs_get_config_item(struct dentry *dentry)
{
struct config_item * item = NULL;
spin_lock(&dcache_lock);
if (!d_unhashed(dentry)) {
struct configfs_dirent * sd = dentry->d_fsdata;
if (sd->s_type & CONFIGFS_ITEM_LINK) {
struct configfs_symlink * sl = sd->s_element;
item = config_item_get(sl->sl_target);
} else
item = config_item_get(sd->s_element);
}
spin_unlock(&dcache_lock);
return item;
}
static inline void release_configfs_dirent(struct configfs_dirent * sd)
{
if (!(sd->s_type & CONFIGFS_ROOT)) {
kfree(sd->s_iattr);
kmem_cache_free(configfs_dir_cachep, sd);
}
}
static inline struct configfs_dirent * configfs_get(struct configfs_dirent * sd)
{
if (sd) {
WARN_ON(!atomic_read(&sd->s_count));
atomic_inc(&sd->s_count);
}
return sd;
}
static inline void configfs_put(struct configfs_dirent * sd)
{
WARN_ON(!atomic_read(&sd->s_count));
if (atomic_dec_and_test(&sd->s_count))
release_configfs_dirent(sd);
}