[3.13.y-ckt stable] Patch "umount: Disallow unprivileged mount force" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    umount: Disallow unprivileged mount force

to the linux-3.13.y-queue branch of the 3.13.y-ckt extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.13.y-queue

This patch is scheduled to be released in version 3.13.11-ckt15.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.13.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 45bc149eea4bb5a839a072278d90015bf67fff3f Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <ebiederm at xmission.com>
Date: Sat, 4 Oct 2014 14:44:03 -0700
Subject: umount: Disallow unprivileged mount force

commit b2f5d4dc38e034eecb7987e513255265ff9aa1cf upstream.

Forced unmount affects not just the mount namespace but the underlying
superblock as well.  Restrict forced unmount to the global root user
for now.  Otherwise it becomes possible a user in a less privileged
mount namespace to force the shutdown of a superblock of a filesystem
in a more privileged mount namespace, allowing a DOS attack on root.

Signed-off-by: "Eric W. Biederman" <ebiederm at xmission.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 fs/namespace.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/namespace.c b/fs/namespace.c
index 32f2b2d..a67e3c0 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1428,6 +1428,9 @@ SYSCALL_DEFINE2(umount, char __user *, name, int, flags)
 		goto dput_and_out;
 	if (mnt->mnt.mnt_flags & MNT_LOCKED)
 		goto dput_and_out;
+	retval = -EPERM;
+	if (flags & MNT_FORCE && !capable(CAP_SYS_ADMIN))
+		goto dput_and_out;

 	retval = do_umount(mnt, flags);
 dput_and_out:
--
1.9.1