linux-kernel - DoS with unprivileged mounts

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Date:	Wed, 14 Aug 2013 19:42:19 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	Al Viro <viro@...iv.linux.org.uk>
Cc:	Linux-Fsdevel <linux-fsdevel@...r.kernel.org>,
	Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: DoS with unprivileged mounts

There's a simple and effective way to prevent unlink(2) and rename(2)
from operating on any file or directory by simply mounting something
on it.  In any mount instance in any namespace.

Was this considered in the unprivileged mount design?

The solution is also theoretically simple: mounts in unpriv namespaces
are marked "volatile" and are dissolved on an unlink type operation.

Such volatile mounts would be useful in general too.

Thanks,
Miklos
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