From: "Darrick J. Wong" <djwong@kernel.org>
To: Gregory Price <gourry@gourry.net>
Cc: John Groves <john@jagalactic.com>, John Groves <John@groves.net>,
Miklos Szeredi <miklos@szeredi.hu>,
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Subject: Re: [PATCH v13 10/12] famfs: Add runtime operation-permission (opts) framework
Date: Sat, 22 Aug 2026 10:40:29 -0700 [thread overview]
Message-ID: <20260822174029.GC6110@frogsfrogsfrogs> (raw)
In-Reply-To: <aokdSo9li0RtEt35@gourry-fedora-PF4VCD3F>
On Sat, Aug 22, 2026 at 12:18:58AM -0400, Gregory Price wrote:
> On Fri, Aug 21, 2026 at 05:07:28PM -0700, Darrick J. Wong wrote:
> >
> > But what prevents a malicious program that is /not/ the famfs client
> > software but has CAP_SYS_ADMIN from doing that?
> >
>
> Such a program can already unmount famfs, rebind the device to
> device_dax, and mmap the whole range directly. MAP_CREATE isn't
> handing it reach it didn't have.
Thinking about this a little more -- some random root process that
accidentally tries to create/modify a directory tree on a famfs mount
will just end up with fmap-less files that won't work for IO or
mmapping. That's dorky, but I think you're right that it's no big deal.
A bigger question I just thought of is sharing cxlmem between files (aka
reflink). Is that allowed? I could see a theoretical usecase for
programs A and B wanting to share some cxlmem for communication or
heartbeats whilst having their own /a and /b files for their private
memory. Probably you'd just create a /common file to do that and not
map the same cxlmem page into /a and /b, right?
But having said that, the fsdax code /can/ support sharing between
files, so I wonder if famfs is prepared either (a) to enable that
sharing or (b) reject a mapping that would overlap with an existing
mapping? Things will go very badly in the kernel if famfs doesn't set
up the dax_folio state correctly.
--D
next prev parent reply other threads:[~2026-08-22 17:40 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20260810202325.96202-1-john@jagalactic.com>
2026-08-10 20:23 ` [PATCH v13 00/12] famfs: the Fabric-Attached Memory File System (standalone) John Groves
2026-08-10 20:24 ` [PATCH v13 01/12] dax: replace exported dax_dev_get() with non-allocating dax_dev_find() John Groves
2026-08-10 20:24 ` [PATCH v13 02/12] famfs: Module operations, fs_context, and mount John Groves
2026-08-10 20:24 ` [PATCH v13 03/12] famfs: Add daxdev table and dax notify_failure support John Groves
2026-08-10 20:24 ` [PATCH v13 04/12] famfs: Introduce inode_operations and super_operations John Groves
2026-08-10 20:24 ` [PATCH v13 05/12] famfs: Introduce file_operations read/write John Groves
2026-08-10 20:25 ` [PATCH v13 06/12] famfs: Introduce mmap and VM fault handling John Groves
2026-08-10 20:25 ` [PATCH v13 07/12] famfs: MAP_CREATE ioctl and fmap ingest (ABI 44) John Groves
2026-08-11 8:03 ` Richard Cheng
2026-08-11 22:17 ` John Groves
2026-08-22 0:17 ` Darrick J. Wong
2026-08-22 19:23 ` John Groves
2026-08-10 20:25 ` [PATCH v13 08/12] famfs: iomap_begin and file-to-dax offset resolution John Groves
2026-08-10 20:25 ` [PATCH v13 09/12] famfs: Register secondary daxdevs by path (FAMFSIOC_DAXDEV_OPEN) John Groves
2026-08-10 20:25 ` [PATCH v13 10/12] famfs: Add runtime operation-permission (opts) framework John Groves
2026-08-22 0:07 ` Darrick J. Wong
2026-08-22 4:18 ` Gregory Price
2026-08-22 17:40 ` Darrick J. Wong [this message]
2026-08-22 21:57 ` John Groves
2026-08-23 16:43 ` Gregory Price
2026-08-23 16:57 ` Gregory Price
2026-08-10 20:25 ` [PATCH v13 11/12] famfs: Report device capacity via statfs so df works John Groves
2026-08-10 20:26 ` [PATCH v13 12/12] famfs: Add documentation John Groves
2026-08-20 12:37 ` [PATCH v13 00/12] famfs: the Fabric-Attached Memory File System (standalone) Jeff Layton
2026-08-22 0:19 ` Darrick J. Wong
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