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[100.75.92.58]) by tor.source.kernel.org (Postfix) with ESMTP id 4AA426000A; Tue, 13 Jan 2026 11:45:26 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 73A32C116C6; Tue, 13 Jan 2026 11:45:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1768304726; bh=r3fAgtqWrYOpjEcc0WPFdPe/AdLRyr0xvdFog2RxOIc=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=hPYUnVvi9v+0Bh+aUO7p89euuKcL1XxxPaQFiv1yFEfuuQrV9ma8ZqGy9IGWR0Hg2 nGb0xKIRdckHGuAv6pDfw1L6dnPw+sKxpoFEU1i8FIolyU6IeDrULm5dKoLINaYp/f lPrwPJp9HcPXX4GOUuPEu5HtSIzYDfCSS/JXhg1NiKHM+ShGiT3IwwkbUBCVovAIRE xomxTEJ/oYJgVGZYTvc/zcfr/Sqq4CEQ75ONFS/TUXLurVleTTrpavEvncOqd97kb9 M1tQQZ35vEFp6JlLZgDpwcytMAbG40LYkViD6uH7yyE3+w/MdhuXa5ZESoU6U4+6R2 jlclfIVBJ/ubA== Message-ID: <4a38de737a64e9b32092ea1f8a25a61b33705034.camel@kernel.org> Subject: Re: [PATCH 00/24] vfs: require filesystems to explicitly opt-in to lease support From: Jeff Layton To: Christian Brauner , Amir Goldstein Cc: Chuck Lever , Jan Kara , Luis de Bethencourt , Salah Triki , Nicolas Pitre , Christoph Hellwig , Anders Larsen , Alexander Viro , David Sterba , Chris Mason , Gao Xiang , Chao Yu , Yue Hu , Jeffle Xu , Sandeep Dhavale , Hongbo Li , Chunhai Guo , Jan Kara , Theodore Ts'o , Andreas Dilger , Jaegeuk Kim , OGAWA Hirofumi , David Woodhouse , Richard Weinberger , Dave Kleikamp , Ryusuke Konishi , Viacheslav Dubeyko , Konstantin Komarov , Mark Fasheh , Joel Becker , Joseph Qi , Mike Marshall , Martin Brandenburg , Miklos Szeredi , Phillip Lougher , Carlos Maiolino , Hugh Dickins , Baolin Wang , Andrew Morton , Namjae Jeon , Sungjong Seo , Yuezhang Mo , Alexander Aring , Andreas Gruenbacher , Jonathan Corbet , "Matthew Wilcox (Oracle)" , Eric Van Hensbergen , Latchesar Ionkov , Dominique Martinet , Christian Schoenebeck , Xiubo Li , Ilya Dryomov , Trond Myklebust , Anna Schumaker , Steve French , Paulo Alcantara , Ronnie Sahlberg , Shyam Prasad N , Tom Talpey , Bharath SM , Hans de Goede , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-btrfs@vger.kernel.org, linux-erofs@lists.ozlabs.org, linux-ext4@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, linux-mtd@lists.infradead.org, jfs-discussion@lists.sourceforge.net, linux-nilfs@vger.kernel.org, ntfs3@lists.linux.dev, ocfs2-devel@lists.linux.dev, devel@lists.orangefs.org, linux-unionfs@vger.kernel.org, linux-xfs@vger.kernel.org, linux-mm@kvack.org, gfs2@lists.linux.dev, linux-doc@vger.kernel.org, v9fs@lists.linux.dev, ceph-devel@vger.kernel.org, linux-nfs@vger.kernel.org, linux-cifs@vger.kernel.org, samba-technical@lists.samba.org Date: Tue, 13 Jan 2026 06:45:17 -0500 In-Reply-To: <20260113-mondlicht-raven-82fc4eb70e9d@brauner> References: <20260108-setlease-6-20-v1-0-ea4dec9b67fa@kernel.org> <8af369636c32b868f83669c49aea708ca3b894ac.camel@kernel.org> <20260113-mondlicht-raven-82fc4eb70e9d@brauner> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; 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text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.58.2 (3.58.2-1.fc43) MIME-Version: 1.0 X-Rspam-User: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 43B6240003 X-Stat-Signature: obbofbdiaqd1rp1iyt48ojnnujjfsjnz X-HE-Tag: 1768304727-365712 X-HE-Meta: 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DRXlnWMhbrBcBAWtE7EKE3VPSxfiPqcprsSDUGY8QbY3yBSPHl0vjGnWXDKQXy5ZUTCq3XQtOjGR2j5aX6QjpHNCBPXxUkIhUgFpHCR4SfBdtC9sagi/9cxs0Lu9S3YMBt6D4EMUQCp2qydC+iQ6Vh68XM0nnV6d3d4MIbClgQHKcj8SpYx6jaPKXT87USpqO/AX0hCjEhF4VW+kFMbt+kVV67h7mhitE2yIUCvXjZ0rINJzqNQ4wKqGSXK2cFW76F9taduu1/V9L67alETuYRtt5FZDUqglj7ZwAim4O/ZfVF0Ft/b2l8PpWOA== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, 2026-01-13 at 09:54 +0100, Christian Brauner wrote: > On Mon, Jan 12, 2026 at 09:50:20AM -0500, Jeff Layton wrote: > > On Mon, 2026-01-12 at 09:31 -0500, Chuck Lever wrote: > > > On 1/12/26 8:34 AM, Jeff Layton wrote: > > > > On Fri, 2026-01-09 at 19:52 +0100, Amir Goldstein wrote: > > > > > On Thu, Jan 8, 2026 at 7:57=E2=80=AFPM Jeff Layton wrote: > > > > > >=20 > > > > > > On Thu, 2026-01-08 at 18:40 +0100, Jan Kara wrote: > > > > > > > On Thu 08-01-26 12:12:55, Jeff Layton wrote: > > > > > > > > Yesterday, I sent patches to fix how directory delegation s= upport is > > > > > > > > handled on filesystems where the should be disabled [1]. Th= at set is > > > > > > > > appropriate for v6.19. For v7.0, I want to make lease suppo= rt be more > > > > > > > > opt-in, rather than opt-out: > > > > > > > >=20 > > > > > > > > For historical reasons, when ->setlease() file_operation is= set to NULL, > > > > > > > > the default is to use the kernel-internal lease implementat= ion. This > > > > > > > > means that if you want to disable them, you need to explici= tly set the > > > > > > > > ->setlease() file_operation to simple_nosetlease() or the e= quivalent. > > > > > > > >=20 > > > > > > > > This has caused a number of problems over the years as some= filesystems > > > > > > > > have inadvertantly allowed leases to be acquired simply by = having left > > > > > > > > it set to NULL. It would be better if filesystems had to op= t-in to lease > > > > > > > > support, particularly with the advent of directory delegati= ons. > > > > > > > >=20 > > > > > > > > This series has sets the ->setlease() operation in a pile o= f existing > > > > > > > > local filesystems to generic_setlease() and then changes > > > > > > > > kernel_setlease() to return -EINVAL when the setlease() ope= ration is not > > > > > > > > set. > > > > > > > >=20 > > > > > > > > With this change, new filesystems will need to explicitly s= et the > > > > > > > > ->setlease() operations in order to provide lease and deleg= ation > > > > > > > > support. > > > > > > > >=20 > > > > > > > > I mainly focused on filesystems that are NFS exportable, si= nce NFS and > > > > > > > > SMB are the main users of file leases, and they tend to end= up exporting > > > > > > > > the same filesystem types. Let me know if I've missed any. > > > > > > >=20 > > > > > > > So, what about kernfs and fuse? They seem to be exportable an= d don't have > > > > > > > .setlease set... > > > > > > >=20 > > > > > >=20 > > > > > > Yes, FUSE needs this too. I'll add a patch for that. > > > > > >=20 > > > > > > As far as kernfs goes: AIUI, that's basically what sysfs and re= sctrl > > > > > > are built on. Do we really expect people to set leases there? > > > > > >=20 > > > > > > I guess it's technically a regression since you could set them = on those > > > > > > sorts of files earlier, but people don't usually export kernfs = based > > > > > > filesystems via NFS or SMB, and that seems like something that = could be > > > > > > used to make mischief. > > > > > >=20 > > > > > > AFAICT, kernfs_export_ops is mostly to support open_by_handle_a= t(). See > > > > > > commit aa8188253474 ("kernfs: add exportfs operations"). > > > > > >=20 > > > > > > One idea: we could add a wrapper around generic_setlease() for > > > > > > filesystems like this that will do a WARN_ONCE() and then call > > > > > > generic_setlease(). That would keep leases working on them but = we might > > > > > > get some reports that would tell us who's setting leases on the= se files > > > > > > and why. > > > > >=20 > > > > > IMO, you are being too cautious, but whatever. > > > > >=20 > > > > > It is not accurate that kernfs filesystems are NFS exportable in = general. > > > > > Only cgroupfs has KERNFS_ROOT_SUPPORT_EXPORTOP. > > > > >=20 > > > > > If any application is using leases on cgroup files, it must be so= me > > > > > very advanced runtime (i.e. systemd), so we should know about the > > > > > regression sooner rather than later. > > > > >=20 > > > >=20 > > > > I think so too. For now, I think I'll not bother with the WARN_ONCE= (). > > > > Let's just leave kernfs out of the set until someone presents a rea= l > > > > use-case. > > > >=20 > > > > > There are also the recently added nsfs and pidfs export_operation= s. > > > > >=20 > > > > > I have a recollection about wanting to be explicit about not allo= wing > > > > > those to be exportable to NFS (nsfs specifically), but I can't se= e where > > > > > and if that restriction was done. > > > > >=20 > > > > > Christian? Do you remember? > > > > >=20 > > > >=20 > > > > (cc'ing Chuck) > > > >=20 > > > > FWIW, you can currently export and mount /sys/fs/cgroup via NFS. Th= e > > > > directory doesn't show up when you try to get to it via NFSv4, but = you > > > > can mount it using v3 and READDIR works. The files are all empty wh= en > > > > you try to read them. I didn't try to do any writes. > > > >=20 > > > > Should we add a mechanism to prevent exporting these sorts of > > > > filesystems? > > > >=20 > > > > Even better would be to make nfsd exporting explicitly opt-in. What= if > > > > we were to add a EXPORT_OP_NFSD flag that explicitly allows filesys= tems > > > > to opt-in to NFS exporting, and check for that in __fh_verify()? We= 'd > > > > have to add it to a bunch of existing filesystems, but that's fairl= y > > > > simple to do with an LLM. > > >=20 > > > What's the active harm in exporting /sys/fs/cgroup ? It has to be don= e > > > explicitly via /etc/exports, so this is under the NFS server admin's > > > control. Is it an attack surface? > > >=20 > >=20 > > Potentially? > >=20 > > I don't see any active harm with exporting cgroupfs. It doesn't work > > right via nfsd, but it's not crashing the box or anything. > >=20 > > At one time, those were only defined by filesystems that wanted to > > allow NFS export. Now we've grown them on filesystems that just want to > > provide filehandles for open_by_handle_at() and the like. nfsd doesn't > > care though: if the fs has export operations, it'll happily use them. > >=20 > > Having an explicit "I want to allow nfsd" flag see ms like it might > > save us some headaches in the future when other filesystems add export > > ops for this sort of filehandle use. >=20 > So we are re-hashing a discussion we had a few months ago (Amir was > involved at least). >=20 Yep, I was lurking on it, but didn't have a lot of input at the time. > I don't think we want to expose cgroupfs via NFS that's super weird. > It's like remote partial resource management and it would be very > strange if a remote process suddenly would be able to move things around > in the cgroup tree. So I would prefer to not do this. > > So my preference would be to really sever file handles from the export > mechanism so that we can allow stuff like pidfs and nsfs and cgroupfs to > use file handles via name_to_handle_at() and open_by_handle_at() without > making them exportable. Agreed. I think we want to make NFS export be a deliberate opt-in decision that filesystem developers make. How we do that is up for debate, of course. An export ops flag would be fairly simple to implement, but it sounds like you're thinking that we should split some export_operations into struct file_handle_operations and then add a pointer for that to super_block (and maybe to export_operations too)? This would be a good LSF/MM topic, but I'm hoping we can come to a consensus before then. --=20 Jeff Layton