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Subject: Re: Removing Mandatory Locks
From:   Jeff Layton <jlayton@kernel.org>
To:     "H. Peter Anvin" <hpa@zytor.com>,
        Kees Cook <keescook@chromium.org>,
        Linus Torvalds <torvalds@linux-foundation.org>
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Date:   Fri, 20 Aug 2021 17:29:30 -0400
In-Reply-To: <D2325492-F4DD-4E7A-B4F1-0E595FF2469A@zytor.com>
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No, Windows has deny-mode locking at open time, but the kernel's
mandatory locks are enforced during read/write (which is why they are
such a pain). Samba will not miss these at all.

If we want something to provide windows-like semantics, we'd probably
want to start with something like Pavel Shilovsky's O_DENY_* patches.

-- Jeff

On Fri, 2021-08-20 at 12:17 -0700, H. Peter Anvin wrote:
> I thought the main user was Samba and/or otherwise providing file service for M$ systems?
> 
> On August 20, 2021 9:30:31 AM PDT, Kees Cook <keescook@chromium.org> wrote:
> > On Thu, Aug 19, 2021 at 12:15:08PM -0700, Linus Torvalds wrote:
> > > On Thu, Aug 19, 2021 at 11:39 AM Jeff Layton <jlayton@kernel.org> wrote:
> > > > 
> > > > I'm all for ripping it out too. It's an insane interface anyway.
> > > > 
> > > > I've not heard a single complaint about this being turned off in
> > > > fedora/rhel or any other distro that has this disabled.
> > > 
> > > I'd love to remove it, we could absolutely test it. The fact that
> > > several major distros have it disabled makes me think it's fine.
> > 
> > FWIW, it is now disabled in Ubuntu too:
> > 
> > https://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/impish/commit/?h=master-next&id=f3aac5e47789cbeb3177a14d3d2a06575249e14b
> > 
> > > But as always, it would be good to check Android.
> > 
> > It looks like it's enabled (checking the Pixel 4 kernel image), but it's
> > not specifically mentioned in any of the build configs that are used to
> > construct the image, so I think this is just catching the "default y". I
> > expect it'd be fine to turn this off.
> > 
> > I will ask around to see if it's actually used.
> > 
> 

-- 
Jeff Layton <jlayton@kernel.org>