This is a note to let you know that I've just added the patch titled ovl: fix warning in ovl_create_real() to the 4.19-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: ovl-fix-warning-in-ovl_create_real.patch and it can be found in the queue-4.19 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 1f5573cfe7a7056e80a92c7a037a3e69f3a13d1c Mon Sep 17 00:00:00 2001 From: Miklos Szeredi <mszeredi@xxxxxxxxxx> Date: Thu, 4 Nov 2021 10:55:34 +0100 Subject: ovl: fix warning in ovl_create_real() From: Miklos Szeredi <mszeredi@xxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxxxxxxxxx Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- 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: Patches currently in stable-queue which might be from mszeredi@xxxxxxxxxx are queue-4.19/ovl-fix-warning-in-ovl_create_real.patch queue-4.19/fuse-annotate-lock-in-fuse_reverse_inval_entry.patch