From 9d6c5babc04522ff85b550f14563970279ab8f90 Mon Sep 17 00:00:00 2001
From: Miklos Szeredi <mszeredi@suse.cz>
Date: Fri, 24 Oct 2014 00:14:39 +0200
Subject: [PATCH] fs: limit filesystem stacking depth

commit 69c433ed2ecd2d3264efd7afec4439524b319121 upstream.

Add a simple read-only counter to super_block that indicates how deep this
is in the stack of filesystems.  Previously ecryptfs was the only stackable
filesystem and it explicitly disallowed multiple layers of itself.

Overlayfs, however, can be stacked recursively and also may be stacked
on top of ecryptfs or vice versa.

To limit the kernel stack usage we must limit the depth of the
filesystem stack.  Initially the limit is set to 2.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
[bwh: Backported to 3.2:
 - Drop changes to overlayfs
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
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