[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>

1 files changed, 86 insertions, 5 deletions

diff --git a/fs/configfs/dir.c b/fs/configfs/dir.c
index 4e228c80fe9f..647499a3479b 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_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);
                 }
         }