linux-ext4 - Re: User permissions or UID/GIDs for portable disks?

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Message-Id: <1193320570.12664.19.camel@norville.austin.ibm.com>
Date:	Thu, 25 Oct 2007 08:56:10 -0500
From:	Dave Kleikamp <shaggy@...ux.vnet.ibm.com>
To:	Eric <erpo41@...il.com>
Cc:	Bram Neijt <bneijt@...il.com>, linux-ext4@...r.kernel.org
Subject: Re: User permissions or UID/GIDs for portable disks?

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

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