[PATCH] configfs: Fix symlink() to a removing item (4768e9b1) · Commits · 戴 / test

The rule for configfs symlinks is that symlinks always point to valid config_items, and prevent the target from being removed. However, configfs_symlink() only checks that it can grab a reference on the target item, without ensuring that it remains alive until the symlink is correctly attached. This patch makes configfs_symlink() fail whenever the target is being removed, using the CONFIGFS_USET_DROPPING flag set by configfs_detach_prep() and protected by configfs_dirent_lock. This patch introduces a similar (weird?) behavior as with mkdir failures making rmdir fail: if symlink() races with rmdir() of the parent directory (or its youngest user-created ancestor if parent is a default group) or rmdir() of the target directory, and then fails in configfs_create(), this can make the racing rmdir() fail despite the concerned directory having no user-created entry (resp. no symlink pointing to it or one of its default groups) in the end. This behavior is fixed in later patches. 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>

fs/configfs/dir.c

+7 −7

Original line number	Diff line number	Diff line
		@@ -370,6 +370,9 @@ static int configfs_detach_prep(struct dentry dentry, struct mutex *wait_mutex
		struct configfs_dirent *sd;
		int ret;

		/* Mark that we're trying to drop the group */
		parent_sd->s_type \|= CONFIGFS_USET_DROPPING;

		ret = -EBUSY;
		if (!list_empty(&parent_sd->s_links))
		goto out;
		@@ -385,8 +388,6 @@ static int configfs_detach_prep(struct dentry dentry, struct mutex *wait_mutex
		*wait_mutex = &sd->s_dentry->d_inode->i_mutex;
		return -EAGAIN;
		}
		/* Mark that we're trying to drop the group */
		sd->s_type \|= CONFIGFS_USET_DROPPING;

		/*
		* Yup, recursive. If there's a problem, blame
		@@ -414,12 +415,11 @@ static void configfs_detach_rollback(struct dentry *dentry)
		struct configfs_dirent *parent_sd = dentry->d_fsdata;
		struct configfs_dirent *sd;

		list_for_each_entry(sd, &parent_sd->s_children, s_sibling) {
		if (sd->s_type & CONFIGFS_USET_DEFAULT) {
		parent_sd->s_type &= ~CONFIGFS_USET_DROPPING;

		list_for_each_entry(sd, &parent_sd->s_children, s_sibling)
		if (sd->s_type & CONFIGFS_USET_DEFAULT)
		configfs_detach_rollback(sd->s_dentry);
		sd->s_type &= ~CONFIGFS_USET_DROPPING;
		}
		}
		}

		static void detach_attrs(struct config_item * item)

fs/configfs/symlink.c

+6 −0

Original line number	Diff line number	Diff line
		@@ -78,6 +78,12 @@ 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) {
		spin_unlock(&configfs_dirent_lock);
		config_item_put(item);
		kfree(sl);
		return -ENOENT;
		}
		list_add(&sl->sl_list, &target_sd->s_links);
		spin_unlock(&configfs_dirent_lock);
		ret = configfs_create_link(sl, parent_item->ci_dentry,

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