linux-kernel - Re: [PATCH v5] vfs: fix copy_file_range regression in cross-fs copies

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Message-ID: <87blchibaf.fsf@suse.de>
Date:   Thu, 18 Feb 2021 16:35:36 +0000
From:   Luis Henriques <lhenriques@...e.de>
To:     Amir Goldstein <amir73il@...il.com>
Cc:     Jeff Layton <jlayton@...nel.org>, Steve French <sfrench@...ba.org>,
        Miklos Szeredi <miklos@...redi.hu>,
        Trond Myklebust <trond.myklebust@...merspace.com>,
        Anna Schumaker <anna.schumaker@...app.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        Dave Chinner <dchinner@...hat.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Nicolas Boichat <drinkcat@...omium.org>,
        Ian Lance Taylor <iant@...gle.com>,
        Luis Lozano <llozano@...omium.org>,
        Andreas Dilger <adilger@...ger.ca>,
        Olga Kornievskaia <aglo@...ch.edu>,
        Christoph Hellwig <hch@...radead.org>,
        ceph-devel <ceph-devel@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        CIFS <linux-cifs@...r.kernel.org>,
        samba-technical <samba-technical@...ts.samba.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux NFS Mailing List <linux-nfs@...r.kernel.org>
Subject: Re: [PATCH v5] vfs: fix copy_file_range regression in cross-fs copies

Amir Goldstein <amir73il@...il.com> writes:

> On Thu, Feb 18, 2021 at 5:16 PM Luis Henriques <lhenriques@...e.de> wrote:
>>
>> A regression has been reported by Nicolas Boichat, found while using the
>> copy_file_range syscall to copy a tracefs file.  Before commit
>> 5dae222a5ff0 ("vfs: allow copy_file_range to copy across devices") the
>> kernel would return -EXDEV to userspace when trying to copy a file across
>> different filesystems.  After this commit, the syscall doesn't fail anymore
>> and instead returns zero (zero bytes copied), as this file's content is
>> generated on-the-fly and thus reports a size of zero.
>>
>> This patch restores some cross-filesystem copy restrictions that existed
>> prior to commit 5dae222a5ff0 ("vfs: allow copy_file_range to copy across
>> devices").  Filesystems are still allowed to fall-back to the VFS
>> generic_copy_file_range() implementation, but that has now to be done
>> explicitly.
>>
>> nfsd is also modified to fall-back into generic_copy_file_range() in case
>> vfs_copy_file_range() fails with -EOPNOTSUPP or -EXDEV.
>>
>> Fixes: 5dae222a5ff0 ("vfs: allow copy_file_range to copy across devices")
>> Link: https://lore.kernel.org/linux-fsdevel/20210212044405.4120619-1-drinkcat@chromium.org/
>> Link: https://lore.kernel.org/linux-fsdevel/CANMq1KDZuxir2LM5jOTm0xx+BnvW=ZmpsG47CyHFJwnw7zSX6Q@mail.gmail.com/
>> Link: https://lore.kernel.org/linux-fsdevel/20210126135012.1.If45b7cdc3ff707bc1efa17f5366057d60603c45f@changeid/
>> Reported-by: Nicolas Boichat <drinkcat@...omium.org>
>> Signed-off-by: Luis Henriques <lhenriques@...e.de>
>> ---
>> And v5!  Sorry.  Sure, it makes sense to go through the all the vfs_cfr()
>> checks first.
>
> You missed my other comment on v4...
>
> not checking NULL copy_file_range case.

Ah, yeah I did missed it.  I'll follow up with yet another revision.

Cheers,
-- 
Luis