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From: Miklos Szeredi <miklos@szeredi.hu>
To: viro@ZenIV.linux.org.uk
Cc: miklos@szeredi.hu, hch@infradead.org, akpm@linux-foundation.org,
	serue@us.ibm.com, linux-fsdevel@vger.kernel.org,
	linux-kernel@vger.kernel.org, haveblue@us.ibm.com
Subject: Re: [patch 00/10] mount ownership and unprivileged mount syscall (v8)
Date: Sat, 23 Feb 2008 20:48:26 +0100	[thread overview]
Message-ID: <E1JT0ME-0003rT-9N@pomaz-ex.szeredi.hu> (raw)
In-Reply-To: <20080223185701.GS27894@ZenIV.linux.org.uk> (message from Al Viro on Sat, 23 Feb 2008 18:57:01 +0000)

> On Sat, Feb 23, 2008 at 06:33:13PM +0100, Miklos Szeredi wrote:
> > > 	c) just what is limited by that sysctl?  AFAICS, rbind is allowed
> > > if mountpoint is on user vfsmount and it seems to create vfsmounts without
> > > eating into that limit just fine...  What's the point of limiting the
> > > amount of vfsmounts marked user when you do not limit the number of vfsmount
> > > one can allocate?
> > 
> > The limit is there, so that unprivileged users cannot create insane
> > number of mounts.  It's just a safety thing, analogous to
> > /proc/sys/fs/file-max.
> 
> Can't they?  Looks like one can create any number of vfsmounts without
> getting more than one marked MNT_USER...

permit_mount() will set MS_SETUSER in flags, and do_loopback() will
set CL_SETUSER based on that flag.

> If you are trying to limit the number of superblocks (i.e. active instances
> of filesystems), then I'd say that vfsmounts make piss-poor proxies for
> those and it would be better to count the objects you really want to count...

I think I really want to limit vfsmounts.  But not because these take
so much memory or anything, just to be safe against a stupid users
playing rbind and propagation, and things like that.

Miklos

      reply	other threads:[~2008-02-23 19:49 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-02-05 21:36 Miklos Szeredi
2008-02-05 21:36 ` [patch 01/10] unprivileged mounts: add user mounts to the kernel Miklos Szeredi
2008-02-05 21:36 ` [patch 02/10] unprivileged mounts: allow unprivileged umount Miklos Szeredi
2008-02-05 21:36 ` [patch 03/10] unprivileged mounts: propagate error values from clone_mnt Miklos Szeredi
2008-02-05 21:36 ` [patch 04/10] unprivileged mounts: account user mounts Miklos Szeredi
2008-02-05 21:36 ` [patch 05/10] unprivileged mounts: allow unprivileged bind mounts Miklos Szeredi
2008-02-05 21:36 ` [patch 06/10] unprivileged mounts: allow unprivileged mounts Miklos Szeredi
2008-02-05 21:36 ` [patch 07/10] unprivileged mounts: add sysctl tunable for "safe" property Miklos Szeredi
2008-02-06 20:21   ` Serge E. Hallyn
2008-02-06 21:11     ` Miklos Szeredi
2008-02-06 22:45       ` Serge E. Hallyn
2008-02-07  8:09         ` Miklos Szeredi
2008-02-07 14:05           ` Serge E. Hallyn
2008-02-07 14:36             ` Miklos Szeredi
2008-02-07 16:57               ` Serge E. Hallyn
2008-02-07 15:33   ` Aneesh Kumar K.V
2008-02-07 16:24     ` Miklos Szeredi
2008-02-05 21:36 ` [patch 08/10] unprivileged mounts: make fuse safe Miklos Szeredi
2008-02-05 21:36 ` [patch 09/10] unprivileged mounts: propagation: inherit owner from parent Miklos Szeredi
2008-02-05 21:36 ` [patch 10/10] unprivileged mounts: add "no submounts" flag Miklos Szeredi
2008-02-15  6:21 ` [patch 00/10] mount ownership and unprivileged mount syscall (v8) Andrew Morton
2008-02-15  9:01   ` Christoph Hellwig
2008-02-15  9:09     ` Andrew Morton
2008-02-15  9:14       ` Christoph Hellwig
2008-02-18 11:47         ` Miklos Szeredi
2008-02-23 16:09           ` Al Viro
2008-02-23 17:33             ` Miklos Szeredi
2008-02-23 18:57               ` Al Viro
2008-02-23 19:48                 ` Miklos Szeredi [this message]

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