[PATCH 38/73] union-mount: Prevent bind mounts of union mounts [ver#2]

[David Howells]

From: Valerie Aurora <vaurora@xxxxxxxxxx>

Prevent bind mounts of parts of union mounts.

XXX - Bind mounting parts of union mounts is probably easy to
implement, but requires some careful thought about corner cases,
extensive testing, and some refactoring of the code.

Original-author: Valerie Aurora <vaurora@xxxxxxxxxx>
Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
---

 fs/namespace.c |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)

diff --git a/fs/namespace.c b/fs/namespace.c
index 3c950fa..c990f69 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1845,6 +1845,12 @@ static int do_loopback(struct path *path, char *old_name,
 	if (IS_MNT_UNBINDABLE(old))
 		goto out2;
 
+	/* XXX - Mounting a subtree of a union mount elsewhere requires careful
+	 * thought and some refactoring.
+	 */
+	if (IS_MNT_UNION(old_path.mnt))
+		goto out2;
+
 	if (!check_mnt(real_mount(path->mnt)) || !check_mnt(old))
 		goto out2;
 

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