linux-kernel - Re: [PATCH v11 21/48] ext4: Add richacl feature flag

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Message-ID: <5624ED40.7040206@gmail.com>
Date:	Mon, 19 Oct 2015 09:16:48 -0400
From:	Austin S Hemmelgarn <ahferroin7@...il.com>
To:	Andreas Gruenbacher <agruenba@...hat.com>
Cc:	Alexander Viro <viro@...iv.linux.org.uk>,
	Theodore Ts'o <tytso@....edu>,
	Andreas Dilger <adilger.kernel@...ger.ca>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	Jeff Layton <jlayton@...chiereds.net>,
	Trond Myklebust <trond.myklebust@...marydata.com>,
	Anna Schumaker <anna.schumaker@...app.com>,
	Dave Chinner <david@...morbit.com>,
	linux-ext4 <linux-ext4@...r.kernel.org>, xfs@....sgi.com,
	LKML <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Linux NFS Mailing List <linux-nfs@...r.kernel.org>,
	linux-cifs@...r.kernel.org, Linux API <linux-api@...r.kernel.org>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Subject: Re: [PATCH v11 21/48] ext4: Add richacl feature flag

On 2015-10-16 13:41, Andreas Gruenbacher wrote:
> On Fri, Oct 16, 2015 at 7:31 PM, Austin S Hemmelgarn
> <ahferroin7@...il.com> wrote:
>> I would like to re-iterate, on both XFS and ext4, I _really_ think this
>> should be a ro_compat flag, and not an incompat one.  If a person has the
>> ability to mount the FS (even if it's a read-only mount), then they by
>> definition have read access to the file or partition that the filesystem is
>> contained in, which means that any ACL's stored on the filesystem are
>> functionally irrelevant,
>
> It is unfortunately not safe to make such a file system accessible to
> other users, so the feature is not strictly read-only compatible.
>
OK, seeing as I wasn't particularly clear as to why I object to this in 
my other e-mail, let's try this again.

Can you please explain exactly why it isn't safe to make such a 
filesystem accessible to other users?  Because that _really_ sounds to 
me like you are trying to rely on this being un-mountable on a kernel 
that doesn't support richacls to try and provide the illusion of better 
security.



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