From: Dave Kleikamp <shaggy@linux.vnet.ibm.com>
Subject: Re: User permissions or UID/GIDs for portable disks?
Date: Thu, 25 Oct 2007 08:56:10 -0500
Message-ID: <1193320570.12664.19.camel@norville.austin.ibm.com>
References: <46c2f4ab0710241110o582dcc27pbd6d2c31474b526b@mail.gmail.com>
	 <1193279915.25351.18.camel@eric-laptop>
Mime-Version: 1.0
Content-Type: text/plain
Content-Transfer-Encoding: 7bit
Cc: Bram Neijt <bneijt@gmail.com>, linux-ext4@vger.kernel.org
To: Eric <erpo41@gmail.com>
In-Reply-To: <1193279915.25351.18.camel@eric-laptop>
Sender: linux-ext4-owner@vger.kernel.org

On Wed, 2007-10-24 at 19:38 -0700, Eric wrote:
> On Wed, 2007-10-24 at 20:10 +0200, Bram Neijt wrote:
> > One of the best solutions I can come up with is if the filesystem
> > would allow for a switch that would help ignore these permissions as
> > part of the filesystem.
> 
> Ignoring file permissions on removable, user-supplied media sounds like
> something that ought to be done above the level of individual
> filesystems, just like how we ignore device files and suid/sgid files in
> certain cases. Maybe this is something that ought to be one level up
> from the ext2/3/4 filesystem driver?

It would be a nice feature to implement at a higher level.  A lot of
file systems do something like this.

> In any case, this raises interesting questions. If we ignore permissions
> on removable media, then anyone logged into your work computer (to which
> you do not have root access) will be able to muck about with your files.
> Is that something you want?

Mount options should override on-media permissions, but those overriding
permissions could still deny access to others:

mount -o uid=1000,gid=1000,fmask=137,dmask=027 /dev/sdb1 /mnt/usbstick

-- 
David Kleikamp
IBM Linux Technology Center