linux-ext4 - Re: e2fsprogs: Richacl support

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Message-ID: <20151016231615.GF15011@thunk.org>
Date:	Fri, 16 Oct 2015 19:16:15 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Andreas Gruenbacher <agruenba@...hat.com>
Cc:	linux-ext4 <linux-ext4@...r.kernel.org>
Subject: Re: e2fsprogs: Richacl support

On Fri, Oct 16, 2015 at 06:03:29PM +0200, Andreas Gruenbacher wrote:
> 
> could the richacl feature flag please be added to e2fsprogs so that we
> won't end up with incompatible file systems?
> 
>   https://github.com/andreas-gruenbacher/e2fsprogs
> 
> Also, should this really be an incompatible feature flag? With a
> read-only compatibility flag, mounting a richacl filesystem on a
> kernel without richacl support would work but it's not safe --- it
> could grant unwanted access to files. (The same applies to the xfs
> support, etc.)

Richacl's are represented using just extended attributes, right?  So
why would this result in incompatible file systems?  For similar
reasons we never had a feature flag for Posix ACL's.

Suppose we mounted a file system with richacl's on a kernel that
didn't understand it, and we write to from that non-richacl kernel.
What's the worse that could happen?

					- Ted
					
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