linux-kernel - [PATCH 4.0 108/220] mnt: Dont propagate umounts in __detach

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Message-Id: <20150502185859.002030647@linuxfoundation.org>
Date:	Sat,  2 May 2015 21:00:23 +0200
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, "Eric W. Biederman" <ebiederm@...ssion.com>
Subject: [PATCH 4.0 108/220] mnt: Dont propagate umounts in __detach_mounts

4.0-stable review patch.  If anyone has any objections, please let me know.

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

From: "Eric W. Biederman" <ebiederm@...ssion.com>

commit 8318e667f176f7ea34451a1a530634e293f216ac upstream.

Invoking mount propagation from __detach_mounts is inefficient and
wrong.

It is inefficient because __detach_mounts already walks the list of
mounts that where something needs to be done, and mount propagation
walks some subset of those mounts again.

It is actively wrong because if the dentry that is passed to
__detach_mounts is not part of the path to a mount that mount should
not be affected.

change_mnt_propagation(p,MS_PRIVATE) modifies the mount propagation
tree of a master mount so it's slaves are connected to another master
if possible.  Which means even removing a mount from the middle of a
mount tree with __detach_mounts will not deprive any mount propagated
mount events.

Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/namespace.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1487,7 +1487,7 @@ void __detach_mounts(struct dentry *dent
 	lock_mount_hash();
 	while (!hlist_empty(&mp->m_list)) {
 		mnt = hlist_entry(mp->m_list.first, struct mount, mnt_mp_list);
-		umount_tree(mnt, UMOUNT_PROPAGATE);
+		umount_tree(mnt, 0);
 	}
 	unlock_mount_hash();
 	put_mountpoint(mp);

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