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Commit 4768e9b1 authored by Louis Rilling's avatar Louis Rilling Committed by Mark Fasheh
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[PATCH] configfs: Fix symlink() to a removing item 



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: default avatarLouis Rilling <louis.rilling@kerlabs.com>
Signed-off-by: default avatarJoel Becker <joel.becker@oracle.com>
Signed-off-by: default avatarMark Fasheh <mfasheh@suse.com>
parent dacdd0e0

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,