linux-kernel - Re: UDF filesystem image with Write-Once UDF Access Type

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Message-ID: <20190801074404.GB25064@quack2.suse.cz>
Date:   Thu, 1 Aug 2019 09:44:04 +0200
From:   Jan Kara <jack@...e.cz>
To:     Steve Magnani <steve.magnani@...idescorp.com>
Cc:     Roald Strauss <mr_lou@...fall.dk>,
        Pali Rohár <pali.rohar@...il.com>,
        Jan Kara <jack@...e.com>, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: UDF filesystem image with Write-Once UDF Access Type

On Fri 26-07-19 12:44:34, Steve Magnani wrote:
> Hi,
> 
> On 7/12/19 5:02 AM, Pali Rohár wrote:
> > In my opinion without support for additional layer, kernel should treat
> > UDF Write-Once Access Type as read-only mount for userspace. And not
> > classic read/write mount.
> > 
> > ...
> > 
> > It seems that udf.ko does not support updating VAT table, so probably it
> > should treat also filesystem with VAT as read-only too.
> > 
> 
> I thinkb085fbe2ef7fa7489903c45271ae7b7a52b0f9ab  <https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/fs/udf?h=v5.1&id=b085fbe2ef7fa7489903c45271ae7b7a52b0f9ab>, deployed in 4.20,
> does both of the things you want.
> 
> One case I ran across today that Windows handles, but Linux doesn't,
> is write-protection via flags in the DomainIdentifier fields of the
> Logical Volume Descriptor and File Set Descriptor. Linux allows
> RW mount when those are marked protected, but Windows forces RO mount.

Yeah, you're right. We are currently completely ignoring the
DomainIdentifier field and at least for read-write mounts we should make
sure it is valid. So that's something that needs fixing.

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR