[PATCH 3/7] namespace: move unbindable check out of clone_private_mount()

[Christian Brauner <brauner@kernel.org>]

From: Christian Brauner <christian.brauner@ubuntu.com>

We're about to switch all filesystems that stack on top or otherwise use
a struct path of another filesystem to use clone_private_mount() in the
following commits. Most of these filesystems like ecryptfs and
cachefiles don't need the MS_UNBDINDABLE check that overlayfs currently
wants. So move the check out of clone_private_mount() and into overlayfs
itself.

Note that overlayfs can probably be switched to not rely on the
MS_UNBDINDABLE check too but for now keep it.

[1]: df820f8de4e4 ("ovl: make private mounts longterm")
Cc: Amir Goldstein <amir73il@gmail.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Miklos Szeredi <mszeredi@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
---
 fs/namespace.c       |  3 ---
 fs/overlayfs/super.c | 13 +++++++++++--
 2 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/fs/namespace.c b/fs/namespace.c
index 7ffefa8b3980..f6efe1272b9d 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1976,9 +1976,6 @@ struct vfsmount *clone_private_mount(const struct path *path)
 	struct mount *old_mnt = real_mount(path->mnt);
 	struct mount *new_mnt;
 
-	if (IS_MNT_UNBINDABLE(old_mnt))
-		return ERR_PTR(-EINVAL);
-
 	new_mnt = clone_mnt(old_mnt, path->dentry, CL_PRIVATE);
 	if (IS_ERR(new_mnt))
 		return ERR_CAST(new_mnt);
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index fdd72f1a9c5e..c942bb1073f6 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -15,6 +15,7 @@
 #include <linux/seq_file.h>
 #include <linux/posix_acl_xattr.h>
 #include <linux/exportfs.h>
+#include "../pnode.h"
 #include "overlayfs.h"
 
 MODULE_AUTHOR("Miklos Szeredi <miklos@szeredi.hu>");
@@ -1175,6 +1176,14 @@ static int ovl_report_in_use(struct ovl_fs *ofs, const char *name)
 	}
 }
 
+static inline struct vfsmount *ovl_clone_private_mount(const struct path *path)
+{
+	if (IS_MNT_UNBINDABLE(real_mount(path->mnt)))
+		return ERR_PTR(-EINVAL);
+
+	return clone_private_mount(path);
+}
+
 static int ovl_get_upper(struct super_block *sb, struct ovl_fs *ofs,
 			 struct ovl_layer *upper_layer, struct path *upperpath)
 {
@@ -1201,7 +1210,7 @@ static int ovl_get_upper(struct super_block *sb, struct ovl_fs *ofs,
 	if (err)
 		goto out;
 
-	upper_mnt = clone_private_mount(upperpath);
+	upper_mnt = ovl_clone_private_mount(upperpath);
 	err = PTR_ERR(upper_mnt);
 	if (IS_ERR(upper_mnt)) {
 		pr_err("failed to clone upperpath\n");
@@ -1700,7 +1709,7 @@ static int ovl_get_layers(struct super_block *sb, struct ovl_fs *ofs,
 			}
 		}
 
-		mnt = clone_private_mount(&stack[i]);
+		mnt = ovl_clone_private_mount(&stack[i]);
 		err = PTR_ERR(mnt);
 		if (IS_ERR(mnt)) {
 			pr_err("failed to clone lowerpath\n");
-- 
2.27.0