[BUGFIX][PATCH 1/2] configfs: Prevent userspace from creating new entries under attaching directories
From: Louis Rilling
Date: Thu Jun 26 2008 - 14:06:48 EST
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@xxxxxxxxxxx>
---
fs/configfs/configfs_internal.h | 1 +
fs/configfs/dir.c | 77 ++++++++++++++++++++++++++++++++++++---
fs/configfs/symlink.c | 17 ++++++++-
3 files changed, 89 insertions(+), 6 deletions(-)
diff --git a/fs/configfs/configfs_internal.h b/fs/configfs/configfs_internal.h
index 5f61b26..51d76bf 100644
--- a/fs/configfs/configfs_internal.h
+++ b/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;
diff --git a/fs/configfs/dir.c b/fs/configfs/dir.c
index 2c873fd..bfd2620 100644
--- a/fs/configfs/dir.c
+++ b/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_validate_dir()
*/
static int configfs_create_dir(struct config_item * item, struct dentry *dentry)
@@ -231,6 +234,23 @@ 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_validate_dir(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_validate_dir(child_sd);
+}
+
int configfs_create_link(struct configfs_symlink *sl,
struct dentry *parent,
struct dentry *dentry)
@@ -332,6 +352,21 @@ static struct dentry * configfs_lookup(struct inode *dir,
int found = 0;
int err = 0;
+ /*
+ * 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.
+ */
+ spin_lock(&configfs_dirent_lock);
+ if (parent_sd->s_type & CONFIGFS_USET_CREATING)
+ err = -ENOENT;
+ spin_unlock(&configfs_dirent_lock);
+ if (err)
+ goto out;
+
list_for_each_entry(sd, &parent_sd->s_children, s_sibling) {
if (sd->s_type & CONFIGFS_NOT_PINNED) {
const unsigned char * name = configfs_get_name(sd);
@@ -353,6 +388,7 @@ static struct dentry * configfs_lookup(struct inode *dir,
return simple_lookup(dir, dentry, nd);
}
+out:
return ERR_PTR(err);
}
@@ -1027,7 +1063,7 @@ EXPORT_SYMBOL(configfs_undepend_item);
static int configfs_mkdir(struct inode *dir, struct dentry *dentry, int mode)
{
- int ret, module_got = 0;
+ int ret = 0, module_got = 0;
struct config_group *group;
struct config_item *item;
struct config_item *parent_item;
@@ -1043,6 +1079,18 @@ 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
+ */
+ spin_lock(&configfs_dirent_lock);
+ if (sd->s_type & CONFIGFS_USET_CREATING)
+ ret = -ENOENT;
+ spin_unlock(&configfs_dirent_lock);
+ if (ret)
+ goto out;
+
if (!(sd->s_type & CONFIGFS_USET_DIR)) {
ret = -EPERM;
goto out;
@@ -1137,6 +1185,8 @@ 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_validate_dir(dentry->d_fsdata);
spin_unlock(&configfs_dirent_lock);
out_unlink:
@@ -1317,13 +1367,26 @@ 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 = 0;
mutex_lock(&dentry->d_inode->i_mutex);
- file->private_data = configfs_new_dirent(parent_sd, NULL);
- mutex_unlock(&dentry->d_inode->i_mutex);
+ /*
+ * Fake invisibility if dir belongs to a group/default groups hierarchy
+ * being attached
+ */
+ spin_lock(&configfs_dirent_lock);
+ if (parent_sd->s_type & CONFIGFS_USET_CREATING)
+ err = -ENOENT;
+ spin_unlock(&configfs_dirent_lock);
- return IS_ERR(file->private_data) ? PTR_ERR(file->private_data) : 0;
+ if (!err) {
+ file->private_data = configfs_new_dirent(parent_sd, NULL);
+ if (IS_ERR(file->private_data))
+ err = PTR_ERR(file->private_data);
+ }
+ mutex_unlock(&dentry->d_inode->i_mutex);
+ return err;
}
static int configfs_dir_close(struct inode *inode, struct file *file)
@@ -1494,6 +1557,10 @@ int configfs_register_subsystem(struct configfs_subsystem *subsys)
if (err) {
d_delete(dentry);
dput(dentry);
+ } else {
+ spin_lock(&configfs_dirent_lock);
+ configfs_validate_dir(dentry->d_fsdata);
+ spin_unlock(&configfs_dirent_lock);
}
}
diff --git a/fs/configfs/symlink.c b/fs/configfs/symlink.c
index 21bd751..65623fb 100644
--- a/fs/configfs/symlink.c
+++ b/fs/configfs/symlink.c
@@ -81,7 +81,7 @@ static int create_link(struct config_item *parent_item,
if (sl) {
sl->sl_target = config_item_get(item);
spin_lock(&configfs_dirent_lock);
- if (target_sd->s_type & CONFIGFS_USET_DROPPING) {
+ if (target_sd->s_type & (CONFIGFS_USET_CREATING | CONFIGFS_USET_DROPPING)) {
spin_unlock(&configfs_dirent_lock);
config_item_put(item);
kfree(sl);
@@ -129,6 +129,7 @@ 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 +138,23 @@ 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 = 0;
+ spin_lock(&configfs_dirent_lock);
+ if (sd->s_type & CONFIGFS_USET_CREATING)
+ ret = -ENOENT;
+ spin_unlock(&configfs_dirent_lock);
+ if (ret)
+ 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;
--
1.5.5.3
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