Re: DoS with unprivileged mounts

From: Miklos Szeredi
Date: Thu Aug 15 2013 - 01:00:22 EST

On Wed, Aug 14, 2013 at 9:32 PM, Eric W. Biederman
<ebiederm@xxxxxxxxxxxx> wrote:

>> 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.
> Agreed.
> This is a problem that is a general pain with mount namespaces in
> general.
> I think the real technical hurdle is finding the mounts t in some random
> mount namespace. Once we can do that relatively efficiently the rest
> becomes simple.

We already have a "struct mountpoint" hashed on the dentry. Chaining
mounts on that mountpoint would be trivial. And we need a
MNT_VOLATILE flag and that's it. If we fear that traversing the list
of mounts on the dentry to check for non-volatile ones then we could
also add a separate volatile counter to struct mountpoint and a
matching flag to the dentry. But I don't think that's really

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