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[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>
master
Louis Rilling 14 years ago
committed by Mark Fasheh
parent
commit
2a109f2a41
  1. 2
      fs/configfs/configfs_internal.h
  2. 91
      fs/configfs/dir.c
  3. 15
      fs/configfs/symlink.c

2
fs/configfs/configfs_internal.h

@ -49,6 +49,7 @@ struct configfs_dirent {
#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;
@ -67,6 +68,7 @@ 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);

91
fs/configfs/dir.c

@ -185,7 +185,7 @@ static int create_dir(struct config_item * k, struct dentry * p,
error = configfs_dirent_exists(p->d_fsdata, d->d_name.name);
if (!error)
error = configfs_make_dirent(p->d_fsdata, d, k, mode,
CONFIGFS_DIR);
CONFIGFS_DIR | CONFIGFS_USET_CREATING);
if (!error) {
error = configfs_create(d, mode, init_dir);
if (!error) {
@ -209,6 +209,9 @@ static int create_dir(struct config_item * k, struct dentry * p,
* configfs_create_dir - create a directory for an config_item.
* @item: config_itemwe're creating directory for.
* @dentry: config_item's dentry.
*
* Note: user-created entries won't be allowed under this new directory
* until it is validated by configfs_dir_set_ready()
*/
static int configfs_create_dir(struct config_item * item, struct dentry *dentry)
@ -231,6 +234,44 @@ static int configfs_create_dir(struct config_item * item, struct dentry *dentry)
return error;
}
/*
* Allow userspace to create new entries under a new directory created with
* configfs_create_dir(), and under all of its chidlren directories recursively.
* @sd configfs_dirent of the new directory to validate
*
* Caller must hold configfs_dirent_lock.
*/
static void configfs_dir_set_ready(struct configfs_dirent *sd)
{
struct configfs_dirent *child_sd;
sd->s_type &= ~CONFIGFS_USET_CREATING;
list_for_each_entry(child_sd, &sd->s_children, s_sibling)
if (child_sd->s_type & CONFIGFS_USET_CREATING)
configfs_dir_set_ready(child_sd);
}
/*
* Check that a directory does not belong to a directory hierarchy being
* attached and not validated yet.
* @sd configfs_dirent of the directory to check
*
* @return non-zero iff the directory was validated
*
* Note: takes configfs_dirent_lock, so the result may change from false to true
* in two consecutive calls, but never from true to false.
*/
int configfs_dirent_is_ready(struct configfs_dirent *sd)
{
int ret;
spin_lock(&configfs_dirent_lock);
ret = !(sd->s_type & CONFIGFS_USET_CREATING);
spin_unlock(&configfs_dirent_lock);
return ret;
}
int configfs_create_link(struct configfs_symlink *sl,
struct dentry *parent,
struct dentry *dentry)
@ -330,7 +371,19 @@ static struct dentry * configfs_lookup(struct inode *dir,
struct configfs_dirent * parent_sd = dentry->d_parent->d_fsdata;
struct configfs_dirent * sd;
int found = 0;
int err = 0;
int err;
/*
* Fake invisibility if dir belongs to a group/default groups hierarchy
* being attached
*
* This forbids userspace to read/write attributes of items which may
* not complete their initialization, since the dentries of the
* attributes won't be instantiated.
*/
err = -ENOENT;
if (!configfs_dirent_is_ready(parent_sd))
goto out;
list_for_each_entry(sd, &parent_sd->s_children, s_sibling) {
if (sd->s_type & CONFIGFS_NOT_PINNED) {
@ -353,6 +406,7 @@ static struct dentry * configfs_lookup(struct inode *dir,
return simple_lookup(dir, dentry, nd);
}
out:
return ERR_PTR(err);
}
@ -1044,6 +1098,16 @@ static int configfs_mkdir(struct inode *dir, struct dentry *dentry, int mode)
}
sd = dentry->d_parent->d_fsdata;
/*
* Fake invisibility if dir belongs to a group/default groups hierarchy
* being attached
*/
if (!configfs_dirent_is_ready(sd)) {
ret = -ENOENT;
goto out;
}
if (!(sd->s_type & CONFIGFS_USET_DIR)) {
ret = -EPERM;
goto out;
@ -1142,6 +1206,8 @@ static int configfs_mkdir(struct inode *dir, struct dentry *dentry, int mode)
spin_lock(&configfs_dirent_lock);
sd->s_type &= ~CONFIGFS_USET_IN_MKDIR;
if (!ret)
configfs_dir_set_ready(dentry->d_fsdata);
spin_unlock(&configfs_dirent_lock);
out_unlink:
@ -1322,13 +1388,24 @@ static int configfs_dir_open(struct inode *inode, struct file *file)
{
struct dentry * dentry = file->f_path.dentry;
struct configfs_dirent * parent_sd = dentry->d_fsdata;
int err;
mutex_lock(&dentry->d_inode->i_mutex);
file->private_data = configfs_new_dirent(parent_sd, NULL);
/*
* Fake invisibility if dir belongs to a group/default groups hierarchy
* being attached
*/
err = -ENOENT;
if (configfs_dirent_is_ready(parent_sd)) {
file->private_data = configfs_new_dirent(parent_sd, NULL);
if (IS_ERR(file->private_data))
err = PTR_ERR(file->private_data);
else
err = 0;
}
mutex_unlock(&dentry->d_inode->i_mutex);
return IS_ERR(file->private_data) ? PTR_ERR(file->private_data) : 0;
return err;
}
static int configfs_dir_close(struct inode *inode, struct file *file)
@ -1499,6 +1576,10 @@ int configfs_register_subsystem(struct configfs_subsystem *subsys)
if (err) {
d_delete(dentry);
dput(dentry);
} else {
spin_lock(&configfs_dirent_lock);
configfs_dir_set_ready(dentry->d_fsdata);
spin_unlock(&configfs_dirent_lock);
}
}

15
fs/configfs/symlink.c

@ -76,6 +76,9 @@ static int create_link(struct config_item *parent_item,
struct configfs_symlink *sl;
int ret;
ret = -ENOENT;
if (!configfs_dirent_is_ready(target_sd))
goto out;
ret = -ENOMEM;
sl = kmalloc(sizeof(struct configfs_symlink), GFP_KERNEL);
if (sl) {
@ -100,6 +103,7 @@ static int create_link(struct config_item *parent_item,
}
}
out:
return ret;
}
@ -129,6 +133,7 @@ int configfs_symlink(struct inode *dir, struct dentry *dentry, const char *symna
{
int ret;
struct nameidata nd;
struct configfs_dirent *sd;
struct config_item *parent_item;
struct config_item *target_item;
struct config_item_type *type;
@ -137,9 +142,19 @@ int configfs_symlink(struct inode *dir, struct dentry *dentry, const char *symna
if (dentry->d_parent == configfs_sb->s_root)
goto out;
sd = dentry->d_parent->d_fsdata;
/*
* Fake invisibility if dir belongs to a group/default groups hierarchy
* being attached
*/
ret = -ENOENT;
if (!configfs_dirent_is_ready(sd))
goto out;
parent_item = configfs_get_config_item(dentry->d_parent);
type = parent_item->ci_type;
ret = -EPERM;
if (!type || !type->ct_item_ops ||
!type->ct_item_ops->allow_link)
goto out_put;

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