linux-kernel - Re: [PATCH 0/4] exportfs: add flag to allow marking export operations as only supporting file handles

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Message-ID: <2F18FF7D-5AC9-4EE4-A19A-F016CF5B1971@oracle.com>
Date: Sun, 1 Dec 2024 16:22:03 +0000
From: Chuck Lever III <chuck.lever@...cle.com>
To: Jeff Layton <jlayton@...nel.org>, Christian Brauner <brauner@...nel.org>
CC: Amir Goldstein <amir73il@...il.com>, Erin Shepherd <erin.shepherd@....eu>,
        Linux FS Devel <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List
	<linux-kernel@...r.kernel.org>,
        Linux NFS Mailing List
	<linux-nfs@...r.kernel.org>,
        stable <stable@...nel.org>
Subject: Re: [PATCH 0/4] exportfs: add flag to allow marking export operations
 as only supporting file handles



> On Dec 1, 2024, at 8:28 AM, Jeff Layton <jlayton@...nel.org> wrote:
> 
> On Sun, 2024-12-01 at 14:12 +0100, Christian Brauner wrote:
>> Hey,
>> 
>> Some filesystems like kernfs and pidfs support file handles as a
>> convenience to enable the use of name_to_handle_at(2) and
>> open_by_handle_at(2) but don't want to and cannot be reliably exported.
>> Add a flag that allows them to mark their export operations accordingly
>> and make NFS check for its presence.
>> 
>> @Amir, I'll reorder the patches such that this series comes prior to the
>> pidfs file handle series. Doing it that way will mean that there's never
>> a state where pidfs supports file handles while also being exportable.
>> It's probably not a big deal but it's definitely cleaner. It also means
>> the last patch in this series to mark pidfs as non-exportable can be
>> dropped. Instead pidfs export operations will be marked as
>> non-exportable in the patch that they are added in.
>> 
>> Thanks!
>> Christian
>> 
>> ---
>> Christian Brauner (4):
>>      exportfs: add flag to indicate local file handles
>>      kernfs: restrict to local file handles
>>      ovl: restrict to exportable file handles
>>      pidfs: restrict to local file handles
>> 
>> fs/kernfs/mount.c        | 1 +
>> fs/nfsd/export.c         | 8 +++++++-
>> fs/overlayfs/util.c      | 7 ++++++-
>> fs/pidfs.c               | 1 +
>> include/linux/exportfs.h | 1 +
>> 5 files changed, 16 insertions(+), 2 deletions(-)
>> ---
>> base-commit: 74e20c5946ab3f8ad959ea34f63f21e157d3ebae
>> change-id: 20241201-work-exportfs-cd49bee773c5
>> 
> 
> I've been following the pidfs filehandle discussion and this is exactly
> what I was thinking we needed: a way to explicitly label certain
> fstypes as unexportable via nfsd.
> 
> Reviewed-by: Jeff Layton <jlayton@...nel.org>
> 

Acked-by: Chuck Lever <chuck.lever@...cle.com <mailto:chuck.lever@...cle.com>>

Though, I wonder if a similar but separate prohibition
mechanism might be necessary for other in-kernel network
file system server implementations (eg, ksmbd).


--
Chuck Lever