[PATCH AUTOSEL 4.18 18/92] configfs: fix registered group removal

From: Sasha Levin
Date: Fri Sep 14 2018 - 21:30:06 EST

From: Mike Christie <mchristi@xxxxxxxxxx>

[ Upstream commit cc57c07343bd071cdf1915a91a24ab7d40c9b590 ]

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@xxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Joel Becker <jlbec@xxxxxxxxxxxx>
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
fs/configfs/dir.c | 11 +++++++++++
1 file changed, 11 insertions(+)

diff --git a/fs/configfs/dir.c b/fs/configfs/dir.c
index 577cff24707b..39843fa7e11b 100644
--- a/fs/configfs/dir.c
+++ b/fs/configfs/dir.c
@@ -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);
configfs_detach_prep(dentry, NULL);
@@ -1791,6 +1801,7 @@ void configfs_unregister_group(struct config_group *group)