[PATCH 4.19 50/56] ovl: fix warning in ovl_create_real()

Greg Kroah-Hartman
2021-12-20T14:44:14Z

From: Miklos Szeredi <mszeredi@redhat.com>

commit 1f5573cfe7a7056e80a92c7a037a3e69f3a13d1c upstream.

Syzbot triggered the following warning in ovl_workdir_create() ->
ovl_create_real():

if (!err && WARN_ON(!newdentry->d_inode)) {

The reason is that the cgroup2 filesystem returns from mkdir without
instantiating the new dentry.

Weird filesystems such as this will be rejected by overlayfs at a later
stage during setup, but to prevent such a warning, call ovl_mkdir_real()
directly from ovl_workdir_create() and reject this case early.

Reported-and-tested-by: syzbot+75eab84fd0af9e8bf66b@syzkaller.appspotmail.com
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/overlayfs/dir.c | 3 +--
fs/overlayfs/overlayfs.h | 1 +
fs/overlayfs/super.c | 12 ++++++++----
3 files changed, 10 insertions(+), 6 deletions(-)

--- a/fs/overlayfs/dir.c
+++ b/fs/overlayfs/dir.c
@@ -116,8 +116,7 @@ kill_whiteout:
goto out;
}

-static int ovl_mkdir_real(struct inode *dir, struct dentry **newdentry,
- umode_t mode)
+int ovl_mkdir_real(struct inode *dir, struct dentry **newdentry, umode_t mode)
{
int err;
struct dentry *d, *dentry = *newdentry;
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -402,6 +402,7 @@ struct ovl_cattr {

#define OVL_CATTR(m) (&(struct ovl_cattr) { .mode = (m) })

+int ovl_mkdir_real(struct inode *dir, struct dentry **newdentry, umode_t mode);
struct dentry *ovl_create_real(struct inode *dir, struct dentry *newdentry,
struct ovl_cattr *attr);
int ovl_cleanup(struct inode *dir, struct dentry *dentry);
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -654,10 +654,14 @@ retry:
goto retry;
}

- work = ovl_create_real(dir, work, OVL_CATTR(attr.ia_mode));
- err = PTR_ERR(work);
- if (IS_ERR(work))
- goto out_err;
+ err = ovl_mkdir_real(dir, &work, attr.ia_mode);
+ if (err)
+ goto out_dput;
+
+ /* Weird filesystem returning with hashed negative (kernfs)? */
+ err = -EINVAL;
+ if (d_really_is_negative(work))
+ goto out_dput;

/*
* Try to remove POSIX ACL xattrs from workdir. We are good if: