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From: Luis Henriques <lhenriques@suse.de>
To: Amir Goldstein <amir73il@gmail.com>
Cc: Trond Myklebust <trondmy@hammerspace.com>,
	"samba-technical@lists.samba.org"
	<samba-technical@lists.samba.org>,
	"drinkcat@chromium.org" <drinkcat@chromium.org>,
	"iant@google.com" <iant@google.com>,
	"linux-cifs@vger.kernel.org" <linux-cifs@vger.kernel.org>,
	"darrick.wong@oracle.com" <darrick.wong@oracle.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"jlayton@kernel.org" <jlayton@kernel.org>,
	"anna.schumaker@netapp.com" <anna.schumaker@netapp.com>,
	"llozano@chromium.org" <llozano@chromium.org>,
	"linux-nfs@vger.kernel.org" <linux-nfs@vger.kernel.org>,
	"miklos@szeredi.hu" <miklos@szeredi.hu>,
	"viro@zeniv.linux.org.uk" <viro@zeniv.linux.org.uk>,
	"dchinner@redhat.com" <dchinner@redhat.com>,
	"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
	"gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
	"sfrench@samba.org" <sfrench@samba.org>,
	"ceph-devel@vger.kernel.org" <ceph-devel@vger.kernel.org>
Subject: Re: [PATCH v2] vfs: prevent copy_file_range to copy across devices
Date: Tue, 16 Feb 2021 18:55:06 +0000	[thread overview]
Message-ID: <874kibkflh.fsf@suse.de> (raw)
In-Reply-To: <CAOQ4uxiiy_Jdi3V1ait56=zfDQRBu_5gb+UsCo8GjMZ6XRhozw@mail.gmail.com> (Amir Goldstein's message of "Tue, 16 Feb 2021 19:44:48 +0200")

Amir Goldstein <amir73il@gmail.com> writes:

> On Tue, Feb 16, 2021 at 6:41 PM Luis Henriques <lhenriques@suse.de> wrote:
>>
>> Amir Goldstein <amir73il@gmail.com> writes:
>>
>> >> Ugh.  And I guess overlayfs may have a similar problem.
>> >
>> > Not exactly.
>> > Generally speaking, overlayfs should call vfs_copy_file_range()
>> > with the flags it got from layer above, so if called from nfsd it
>> > will allow cross fs copy and when called from syscall it won't.
>> >
>> > There are some corner cases where overlayfs could benefit from
>> > COPY_FILE_SPLICE (e.g. copy from lower file to upper file), but
>> > let's leave those for now. Just leave overlayfs code as is.
>>
>> Got it, thanks for clarifying.
>>
>> >> > This is easy to solve with a flag COPY_FILE_SPLICE (or something) that
>> >> > is internal to kernel users.
>> >> >
>> >> > FWIW, you may want to look at the loop in ovl_copy_up_data()
>> >> > for improvements to nfsd_copy_file_range().
>> >> >
>> >> > We can move the check out to copy_file_range syscall:
>> >> >
>> >> >         if (flags != 0)
>> >> >                 return -EINVAL;
>> >> >
>> >> > Leave the fallback from all filesystems and check for the
>> >> > COPY_FILE_SPLICE flag inside generic_copy_file_range().
>> >>
>> >> Ok, the diff bellow is just to make sure I understood your suggestion.
>> >>
>> >> The patch will also need to:
>> >>
>> >>  - change nfs and overlayfs calls to vfs_copy_file_range() so that they
>> >>    use the new flag.
>> >>
>> >>  - check flags in generic_copy_file_checks() to make sure only valid flags
>> >>    are used (COPY_FILE_SPLICE at the moment).
>> >>
>> >> Also, where should this flag be defined?  include/uapi/linux/fs.h?
>> >
>> > Grep for REMAP_FILE_
>> > Same header file, same Documentation rst file.
>> >
>> >>
>> >> Cheers,
>> >> --
>> >> Luis
>> >>
>> >> diff --git a/fs/read_write.c b/fs/read_write.c
>> >> index 75f764b43418..341d315d2a96 100644
>> >> --- a/fs/read_write.c
>> >> +++ b/fs/read_write.c
>> >> @@ -1383,6 +1383,13 @@ ssize_t generic_copy_file_range(struct file *file_in, loff_t pos_in,
>> >>                                 struct file *file_out, loff_t pos_out,
>> >>                                 size_t len, unsigned int flags)
>> >>  {
>> >> +       if (!(flags & COPY_FILE_SPLICE)) {
>> >> +               if (!file_out->f_op->copy_file_range)
>> >> +                       return -EOPNOTSUPP;
>> >> +               else if (file_out->f_op->copy_file_range !=
>> >> +                        file_in->f_op->copy_file_range)
>> >> +                       return -EXDEV;
>> >> +       }
>> >
>> > That looks strange, because you are duplicating the logic in
>> > do_copy_file_range(). Maybe better:
>> >
>> > if (WARN_ON_ONCE(flags & ~COPY_FILE_SPLICE))
>> >         return -EINVAL;
>> > if (flags & COPY_FILE_SPLICE)
>> >        return do_splice_direct(file_in, &pos_in, file_out, &pos_out,
>> >                                  len > MAX_RW_COUNT ? MAX_RW_COUNT : len, 0);
>>
>> My initial reasoning for duplicating the logic in do_copy_file_range() was
>> to allow the generic_copy_file_range() callers to be left unmodified and
>> allow the filesystems to default to this implementation.
>>
>> With this change, I guess that the calls to generic_copy_file_range() from
>> the different filesystems can be dropped, as in my initial patch, as they
>> will always get -EINVAL.  The other option would be to set the
>> COPY_FILE_SPLICE flag in those calls, but that would get us back to the
>> problem we're trying to solve.
>
> I don't understand the problem.
>
> What exactly is wrong with the code I suggested?
> Why should any filesystem be changed?
>
> Maybe I am missing something.

Ok, I have to do a full brain reboot and start all over.

Before that, I picked the code you suggested and tested it.  I've mounted
a cephfs filesystem and used xfs_io to execute a 'copy_range' command
using /sys/kernel/debug/sched_features as source.  The result was a
0-sized file in cephfs.  And the reason is thevfs_copy_file_range()
early exit in:

	if (len == 0)
		return 0;

'len' is set in generic_copy_file_checks().

This means that we're not solving the original problem anymore (probably
since v1 of this patch, haven't checked).

Also, re-reading Trond's emails, I read: "... also disallowing the copy
from, say, an XFS formatted partition to an ext4 partition".  Isn't that
*exactly* what we're trying to do here?  I.e. _prevent_ these copies from
happening so that tracefs files can't be CFR'ed?

/me stops now and waits to see if the morning brings some sun :-)

Cheers,
-- 
Luis

  reply	other threads:[~2021-02-16 18:55 UTC|newest]

Thread overview: 136+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-12  4:43 [PATCH 0/6] Add generated flag to filesystem struct to block copy_file_range Nicolas Boichat
2021-02-12  4:44 ` [PATCH 1/6] fs: Add flag to file_system_type to indicate content is generated Nicolas Boichat
2021-02-12  7:46   ` Greg KH
2021-02-12  8:20     ` Nicolas Boichat
2021-02-12  8:37       ` Greg KH
2021-02-12 15:33         ` Ian Lance Taylor
2021-02-12 15:45           ` Greg KH
2021-02-12 15:59             ` Ian Lance Taylor
2021-02-12 16:28               ` Greg KH
2021-02-12 20:22                 ` Ian Lance Taylor
2021-02-12 23:03             ` Dave Chinner
2021-02-12 23:07               ` Ian Lance Taylor
2021-02-12 23:27                 ` Dave Chinner
2021-02-12 23:54                   ` Darrick J. Wong
2021-02-15  0:38                     ` Dave Chinner
2021-02-15  1:12                       ` Ian Lance Taylor
2021-02-15  1:25                         ` Nicolas Boichat
2021-02-15  5:56                           ` Amir Goldstein
2021-02-15  8:30                           ` Greg KH
2021-02-12  8:22     ` Amir Goldstein
2021-02-12  8:39       ` Greg KH
2021-02-12 12:05         ` Luis Henriques
2021-02-12 12:18           ` Greg KH
2021-02-12 12:41             ` Luis Henriques
2021-02-12 14:11               ` Greg KH
2021-02-12 15:01                 ` Luis Henriques
2021-02-15  6:12               ` Amir Goldstein
2021-02-15 10:39                 ` Luis Henriques
2021-02-15 12:22                   ` Luis Henriques
2021-02-15 14:23                     ` Amir Goldstein
2021-02-15 14:51                       ` Luis Henriques
2021-02-15 15:43                       ` [PATCH v2] vfs: prevent copy_file_range to copy across devices Luis Henriques
2021-02-15 16:02                         ` Trond Myklebust
2021-02-16  0:25                           ` Steve French
2021-02-15 16:34                         ` Amir Goldstein
2021-02-15 16:53                           ` Trond Myklebust
2021-02-15 17:24                             ` Amir Goldstein
2021-02-15 18:57                               ` Trond Myklebust
2021-02-15 19:43                                 ` Amir Goldstein
2021-02-16 11:17                                   ` Luis Henriques
2021-02-16 11:28                                     ` gregkh
2021-02-16 12:01                                       ` Luis Henriques
2021-02-16 12:08                                         ` Greg KH
2021-02-16 13:51                                     ` Amir Goldstein
2021-02-16 16:42                                       ` Luis Henriques
2021-02-16 17:44                                         ` Amir Goldstein
2021-02-16 18:55                                           ` Luis Henriques [this message]
2021-02-16 19:20                                             ` Amir Goldstein
2021-02-16 19:27                                               ` Anna Schumaker
2021-02-16 19:31                                                 ` Steve French
2021-02-16 19:40                                                   ` Amir Goldstein
2021-02-16 21:15                                                     ` Steve French
2021-02-17  8:08                                                       ` Amir Goldstein
2021-02-17 17:26                                                         ` [PATCH v3] vfs: fix copy_file_range regression in cross-fs copies Luis Henriques
2021-02-17 20:47                                                           ` Amir Goldstein
2021-02-18  0:56                                                           ` Nicolas Boichat
2021-02-18  5:32                                                           ` Olga Kornievskaia
2021-02-18  6:47                                                             ` Amir Goldstein
2021-02-18 16:28                                                               ` Olga Kornievskaia
2021-02-18  7:43                                                           ` Christoph Hellwig
2021-02-18  0:50                                                         ` [PATCH v2] vfs: prevent copy_file_range to copy across devices Andreas Dilger
2021-02-18  7:34                                                           ` gregkh
2021-02-16 18:54                                       ` Andreas Dilger
2021-02-17  4:45                         ` Nicolas Boichat
2021-02-18  7:42                         ` Christoph Hellwig
2021-02-18  9:10                           ` Amir Goldstein
2021-02-18 10:29                             ` Luis Henriques
2021-02-18 12:15                               ` Luis Henriques
2021-02-18 12:49                                 ` Amir Goldstein
2021-02-18 14:36                                   ` [PATCH v4] vfs: fix copy_file_range regression in cross-fs copies Luis Henriques
2021-02-18 14:58                                     ` Amir Goldstein
2021-02-18 15:17                                       ` [PATCH v5] " Luis Henriques
2021-02-18 15:53                                         ` Amir Goldstein
2021-02-18 16:35                                           ` Luis Henriques
2021-02-18 17:18                                             ` [PATCH v6] " Luis Henriques
2021-02-19 21:18                                               ` Olga Kornievskaia
2021-02-19 21:52                                                 ` Amir Goldstein
2021-02-21 19:58                                                 ` [PATCH v7] " Luis Henriques
2021-02-22  3:00                                                   ` Nicolas Boichat
2021-02-22 10:24                                                   ` [PATCH v8] " Luis Henriques
2021-02-22 10:46                                                     ` Amir Goldstein
2021-02-22 16:25                                                     ` dai.ngo
2021-02-23 10:32                                                       ` Luis Henriques
2021-02-23 15:28                                                         ` Amir Goldstein
2021-02-23 15:29                                                         ` dai.ngo
2021-02-23 16:02                                                           ` dai.ngo
2021-02-23 16:47                                                             ` Amir Goldstein
2021-02-23 16:57                                                               ` dai.ngo
     [not found]                                                                 ` <e3eed18b-fc7e-e687-608b-7f662017329c@oracle.com>
2021-02-23 17:33                                                                   ` Amir Goldstein
2021-02-24  0:13                                                                     ` dai.ngo
2021-02-23 17:56                                                                 ` Luis Henriques
2021-02-23 17:13                                                             ` Olga Kornievskaia
2021-02-24  1:00                                                     ` Olga Kornievskaia
2021-02-24 10:23                                                       ` Luis Henriques
2021-02-24 10:44                                                         ` Nicolas Boichat
2021-04-09  5:23                                                           ` Nicolas Boichat
2021-04-09 13:39                                                             ` Luis Henriques
2021-04-09 13:50                                                               ` Amir Goldstein
2021-04-23  4:40                                                                 ` Nicolas Boichat
2021-05-03  8:54                                                                   ` Luis Henriques
2021-05-10  4:59                                                                     ` Amir Goldstein
2021-05-10  9:10                                                                       ` Luis Henriques
2021-02-24 14:23                                                     ` [PATCH] copy_file_range.2: Kernel v5.12 updates Luis Henriques
2021-02-24 16:10                                                       ` Amir Goldstein
2021-02-25 10:21                                                         ` Luis Henriques
2021-02-26 10:13                                                           ` Alejandro Colomar (man-pages)
2021-02-26 10:34                                                             ` Amir Goldstein
2021-02-26 11:15                                                               ` Alejandro Colomar (man-pages)
2021-02-26 13:59                                                                 ` Jeff Layton
2021-02-26 21:26                                                                   ` Alejandro Colomar (man-pages)
2021-02-26 22:18                                                         ` Alejandro Colomar (man-pages)
2021-02-27  5:41                                                           ` Amir Goldstein
2021-02-27 12:20                                                             ` Alejandro Colomar (man-pages)
2021-02-27 13:49                                                               ` [RFC v2] copy_file_range.2: Update cross-filesystem support for 5.12 Alejandro Colomar
2021-02-27 16:00                                                                 ` Amir Goldstein
2021-02-27 23:08                                                             ` [PATCH] copy_file_range.2: Kernel v5.12 updates Steve French
2021-02-28  7:35                                                               ` Amir Goldstein
2021-02-28 22:25                                                                 ` Steve French
2021-03-01  6:18                                                                   ` Amir Goldstein
2021-03-01 14:41                                                       ` [RFC v3] copy_file_range.2: Update cross-filesystem support for 5.12 Alejandro Colomar
2021-03-01 14:58                                                         ` Amir Goldstein
2021-03-04  9:38                                                       ` [RFC v4] " Alejandro Colomar
2021-03-04 17:13                                                         ` Darrick J. Wong
2021-03-04 18:24                                                           ` Alejandro Colomar (man-pages)
2021-03-04 23:50                                                             ` Darrick J. Wong
2021-02-24  7:15                                     ` [PATCH v4] vfs: fix copy_file_range regression in cross-fs copies Amir Goldstein
2021-02-24  8:30                                       ` Petr Vorel
2021-02-18 20:41                             ` [PATCH v2] vfs: prevent copy_file_range to copy across devices Steve French
2021-02-12 23:15       ` [PATCH 1/6] fs: Add flag to file_system_type to indicate content is generated Dave Chinner
2021-02-12  7:54   ` Amir Goldstein
2021-02-12  4:44 ` [PATCH 2/6] proc: Add FS_GENERATED_CONTENT to filesystem flags Nicolas Boichat
2021-02-12  4:44 ` [PATCH 6/6] vfs: Disallow copy_file_range on generated file systems Nicolas Boichat
2021-02-12  4:53   ` Darrick J. Wong
2021-02-12  4:59     ` Darrick J. Wong
2021-02-12  5:24       ` Nicolas Boichat
2021-02-14 23:09 ` [PATCH 0/6] Add generated flag to filesystem struct to block copy_file_range Al Viro

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