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configfs: fix registered group removal 

This patch fixes a bug where configfs_register_group had added
a group in a tree, and userspace has done a rmdir on a dir somewhere
above that group and we hit a kernel crash. The problem is configfs_rmdir
will detach everything under it and unlink groups on the default_groups
list. It will not unlink groups added with configfs_register_group so when
configfs_unregister_group is called to drop its references to the group/items
we crash when we try to access the freed dentrys.

The patch just adds a check for if a rmdir has been done above
us and if so just does the unlink part of unregistration.

Sorry if you are getting this multiple times. I thouhgt I sent
this to some of you and lkml, but I do not see it.

Signed-off-by: Mike Christie <mchristi@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Joel Becker <jlbec@evilplan.org>
Signed-off-by: Christoph Hellwig <hch@lst.de>
This commit is contained in:
Mike Christie 2018-07-15 18:16:17 -05:00 committed by Christoph Hellwig
parent 1823342a1f
commit cc57c07343
1 changed files with 11 additions and 0 deletions
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11
fs/configfs/dir.c
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@ -1777,6 +1777,16 @@ void configfs_unregister_group(struct config_group *group)
struct dentry *dentry = group->cg_item.ci_dentry;
struct dentry *parent = group->cg_item.ci_parent->ci_dentry;
mutex_lock(&subsys->su_mutex);
if (!group->cg_item.ci_parent->ci_group) {
/*
* The parent has already been unlinked and detached
* due to a rmdir.
*/
goto unlink_group;
}
mutex_unlock(&subsys->su_mutex);
inode_lock_nested(d_inode(parent), I_MUTEX_PARENT);
spin_lock(&configfs_dirent_lock);
configfs_detach_prep(dentry, NULL);
@ -1791,6 +1801,7 @@ void configfs_unregister_group(struct config_group *group)
dput(dentry);
mutex_lock(&subsys->su_mutex);
unlink_group:
unlink_group(group);
mutex_unlock(&subsys->su_mutex);
}