| From | David Howells <> | Subject | [PATCH 36/73] union-mount: Prevent improper union-related remounts [ver #2] | Date | Tue, 21 Feb 2012 18:02:01 +0000 |
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From: Valerie Aurora <vaurora@redhat.com>
A remount request must not (a) convert a union to a non-union (or vice versa), or (b) make the topmost layer of a union read-only.
Note that we only have to worry about attempts to remount the vfsmount of the topmost read-write of the union (the one with MNT_UNION set). The vfsmounts of the read-only layers are hidden in a cloned tree hanging of the superblock of the topmost layer and aren't visible to userspace.
Original-author: Valerie Aurora <vaurora@redhat.com> Signed-off-by: David Howells <dhowells@redhat.com> ---
fs/namespace.c | 12 ++++++++++++ 1 files changed, 12 insertions(+), 0 deletions(-)
diff --git a/fs/namespace.c b/fs/namespace.c index 261944d..aa6b1ef 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -1907,6 +1907,18 @@ static int do_remount(struct path *path, int flags, int mnt_flags, if (!check_mnt(mnt)) return -EINVAL; + if ((path->mnt->mnt_flags & MNT_UNION) && + !(mnt_flags & MNT_UNION)) + return -EINVAL; + + if ((mnt_flags & MNT_UNION) && + !(path->mnt->mnt_flags & MNT_UNION)) + return -EINVAL; + + if ((path->mnt->mnt_flags & MNT_UNION) && + (mnt_flags & MNT_READONLY)) + return -EINVAL; + if (path->dentry != path->mnt->mnt_root) return -EINVAL;
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