ovl: fix missing revert_creds() on error path

stable inclusion
from linux-4.19.191
commit a42e385f0a4160709882b9435b874a7cdab24d46

--------------------------------

commit 7b279bbfd2b230c7a210ff8f405799c7e46bbf48 upstream.

Smatch complains about missing that the ovl_override_creds() doesn't
have a matching revert_creds() if the dentry is disconnected.  Fix this
by moving the ovl_override_creds() until after the disconnected check.

Fixes: aa3ff3c1 ("ovl: copy up of disconnected dentries")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>

fs/overlayfs/copy_up.c

@@ -824,7 +824,7 @@ static int ovl_copy_up_one(struct dentry *parent, struct dentry *dentry,
 int ovl_copy_up_flags(struct dentry *dentry, int flags)
 {
 	int err = 0;
-	const struct cred *old_cred = ovl_override_creds(dentry->d_sb);
+	const struct cred *old_cred;
 	bool disconnected = (dentry->d_flags & DCACHE_DISCONNECTED);
 
 	/*
@@ -835,6 +835,7 @@ int ovl_copy_up_flags(struct dentry *dentry, int flags)
 	if (WARN_ON(disconnected && d_is_dir(dentry)))
 		return -EIO;
 
+	old_cred = ovl_override_creds(dentry->d_sb);
 	while (!err) {
 		struct dentry *next;
 		struct dentry *parent = NULL;