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    SubjectRe: [PATCH v8] vfs: fix copy_file_range regression in cross-fs copies
    On Tue, Feb 23, 2021 at 11:03 AM <dai.ngo@oracle.com> wrote:
    >
    >
    > On 2/23/21 7:29 AM, dai.ngo@oracle.com wrote:
    > >
    > > On 2/23/21 2:32 AM, Luis Henriques wrote:
    > >> On Mon, Feb 22, 2021 at 08:25:27AM -0800, dai.ngo@oracle.com wrote:
    > >>> On 2/22/21 2:24 AM, Luis Henriques 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://urldefense.com/v3/__https://lore.kernel.org/linux-fsdevel/20210212044405.4120619-1-drinkcat@chromium.org/__;!!GqivPVa7Brio!P1UWThiSkxbjfjFQWNYJmCxGEkiLFyvHjH6cS-G1ZTt1z-TeqwGQgQmi49dC6w$
    > >>>> Link:
    > >>>> https://urldefense.com/v3/__https://lore.kernel.org/linux-fsdevel/CANMq1KDZuxir2LM5jOTm0xx*BnvW=ZmpsG47CyHFJwnw7zSX6Q@mail.gmail.com/__;Kw!!GqivPVa7Brio!P1UWThiSkxbjfjFQWNYJmCxGEkiLFyvHjH6cS-G1ZTt1z-TeqwGQgQmgCmMHzA$
    > >>>> Link:
    > >>>> https://urldefense.com/v3/__https://lore.kernel.org/linux-fsdevel/20210126135012.1.If45b7cdc3ff707bc1efa17f5366057d60603c45f@changeid/__;!!GqivPVa7Brio!P1UWThiSkxbjfjFQWNYJmCxGEkiLFyvHjH6cS-G1ZTt1z-TeqwGQgQmzqItkrQ$
    > >>>> Reported-by: Nicolas Boichat <drinkcat@chromium.org>
    > >>>> Signed-off-by: Luis Henriques <lhenriques@suse.de>
    > >>>> ---
    > >>>> Changes since v7
    > >>>> - set 'ret' to '-EOPNOTSUPP' before the clone 'if' statement so
    > >>>> that the
    > >>>> error returned is always related to the 'copy' operation
    > >>>> Changes since v6
    > >>>> - restored i_sb checks for the clone operation
    > >>>> Changes since v5
    > >>>> - check if ->copy_file_range is NULL before calling it
    > >>>> Changes since v4
    > >>>> - nfsd falls-back to generic_copy_file_range() only *if* it gets
    > >>>> -EOPNOTSUPP
    > >>>> or -EXDEV.
    > >>>> Changes since v3
    > >>>> - dropped the COPY_FILE_SPLICE flag
    > >>>> - kept the f_op's checks early in generic_copy_file_checks,
    > >>>> implementing
    > >>>> Amir's suggestions
    > >>>> - modified nfsd to use generic_copy_file_range()
    > >>>> Changes since v2
    > >>>> - do all the required checks earlier, in generic_copy_file_checks(),
    > >>>> adding new checks for ->remap_file_range
    > >>>> - new COPY_FILE_SPLICE flag
    > >>>> - don't remove filesystem's fallback to generic_copy_file_range()
    > >>>> - updated commit changelog (and subject)
    > >>>> Changes since v1 (after Amir review)
    > >>>> - restored do_copy_file_range() helper
    > >>>> - return -EOPNOTSUPP if fs doesn't implement CFR
    > >>>> - updated commit description
    > >>>>
    > >>>> fs/nfsd/vfs.c | 8 +++++++-
    > >>>> fs/read_write.c | 49
    > >>>> ++++++++++++++++++++++++-------------------------
    > >>>> 2 files changed, 31 insertions(+), 26 deletions(-)
    > >>>>
    > >>>> diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
    > >>>> index 04937e51de56..23dab0fa9087 100644
    > >>>> --- a/fs/nfsd/vfs.c
    > >>>> +++ b/fs/nfsd/vfs.c
    > >>>> @@ -568,6 +568,7 @@ __be32 nfsd4_clone_file_range(struct nfsd_file
    > >>>> *nf_src, u64 src_pos,
    > >>>> ssize_t nfsd_copy_file_range(struct file *src, u64 src_pos,
    > >>>> struct file *dst,
    > >>>> u64 dst_pos, u64 count)
    > >>>> {
    > >>>> + ssize_t ret;
    > >>>> /*
    > >>>> * Limit copy to 4MB to prevent indefinitely blocking an nfsd
    > >>>> @@ -578,7 +579,12 @@ ssize_t nfsd_copy_file_range(struct file *src,
    > >>>> u64 src_pos, struct file *dst,
    > >>>> * limit like this and pipeline multiple COPY requests.
    > >>>> */
    > >>>> count = min_t(u64, count, 1 << 22);
    > >>>> - return vfs_copy_file_range(src, src_pos, dst, dst_pos, count, 0);
    > >>>> + ret = vfs_copy_file_range(src, src_pos, dst, dst_pos, count, 0);
    > >>>> +
    > >>>> + if (ret == -EOPNOTSUPP || ret == -EXDEV)
    > >>>> + ret = generic_copy_file_range(src, src_pos, dst, dst_pos,
    > >>>> + count, 0);
    > >>>> + return ret;
    > >>>> }
    > >>>> __be32 nfsd4_vfs_fallocate(struct svc_rqst *rqstp, struct svc_fh
    > >>>> *fhp,
    > >>>> diff --git a/fs/read_write.c b/fs/read_write.c
    > >>>> index 75f764b43418..5a26297fd410 100644
    > >>>> --- a/fs/read_write.c
    > >>>> +++ b/fs/read_write.c
    > >>>> @@ -1388,28 +1388,6 @@ ssize_t generic_copy_file_range(struct file
    > >>>> *file_in, loff_t pos_in,
    > >>>> }
    > >>>> EXPORT_SYMBOL(generic_copy_file_range);
    > >>>> -static ssize_t do_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)
    > >>>> -{
    > >>>> - /*
    > >>>> - * Although we now allow filesystems to handle cross sb copy,
    > >>>> passing
    > >>>> - * a file of the wrong filesystem type to filesystem driver
    > >>>> can result
    > >>>> - * in an attempt to dereference the wrong type of
    > >>>> ->private_data, so
    > >>>> - * avoid doing that until we really have a good reason. NFS
    > >>>> defines
    > >>>> - * several different file_system_type structures, but they all
    > >>>> end up
    > >>>> - * using the same ->copy_file_range() function pointer.
    > >>>> - */
    > >>>> - if (file_out->f_op->copy_file_range &&
    > >>>> - file_out->f_op->copy_file_range ==
    > >>>> file_in->f_op->copy_file_range)
    > >>>> - return file_out->f_op->copy_file_range(file_in, pos_in,
    > >>>> - file_out, pos_out,
    > >>>> - len, flags);
    > >>>> -
    > >>>> - return generic_copy_file_range(file_in, pos_in, file_out,
    > >>>> pos_out, len,
    > >>>> - flags);
    > >>>> -}
    > >>>> -
    > >>>> /*
    > >>>> * Performs necessary checks before doing a file copy
    > >>>> *
    > >>>> @@ -1427,6 +1405,25 @@ static int generic_copy_file_checks(struct
    > >>>> file *file_in, loff_t pos_in,
    > >>>> loff_t size_in;
    > >>>> int ret;
    > >>>> + /*
    > >>>> + * Although we now allow filesystems to handle cross sb copy,
    > >>>> passing
    > >>>> + * a file of the wrong filesystem type to filesystem driver
    > >>>> can result
    > >>>> + * in an attempt to dereference the wrong type of
    > >>>> ->private_data, so
    > >>>> + * avoid doing that until we really have a good reason. NFS
    > >>>> defines
    > >>>> + * several different file_system_type structures, but they all
    > >>>> end up
    > >>>> + * using the same ->copy_file_range() function pointer.
    > >>>> + */
    > >>>> + if (file_out->f_op->copy_file_range) {
    > >>>> + if (file_in->f_op->copy_file_range !=
    > >>>> + file_out->f_op->copy_file_range)
    > >>>> + return -EXDEV;
    > >>>> + } else if (file_in->f_op->remap_file_range) {
    > >>>> + if (file_inode(file_in)->i_sb != file_inode(file_out)->i_sb)
    > >>>> + return -EXDEV;
    > >>> I think this check is redundant, it's done in vfs_copy_file_range.
    > >>> If this check is removed then the else clause below should be removed
    > >>> also. Once this check and the else clause are removed then might as
    > >>> well move the the check of copy_file_range from here to
    > >>> vfs_copy_file_range.
    > >>>
    > >> I don't think it's really redundant, although I agree is messy due to
    > >> the
    > >> fact we try to clone first instead of copying them.
    > >>
    > >> So, in the clone path, this is the only place where we return -EXDEV if:
    > >>
    > >> 1) we don't have ->copy_file_range *and*
    > >> 2) we have ->remap_file_range but the i_sb are different.
    > >>
    > >> The check in vfs_copy_file_range() is only executed if:
    > >>
    > >> 1) we have *valid* ->copy_file_range ops and/or
    > >> 2) we have *valid* ->remap_file_range
    > >>
    > >> So... if we remove the check in generic_copy_file_checks() as you
    > >> suggest
    > >> and:
    > >> - we don't have ->copy_file_range,
    > >> - we have ->remap_file_range but
    > >> - the i_sb are different
    > >>
    > >> we'll return the -EOPNOTSUPP (the one set in line "ret =
    > >> -EOPNOTSUPP;" in
    > >> function vfs_copy_file_range() ) instead of -EXDEV.
    > >
    > > Yes, this is the different.The NFS code handles both -EOPNOTSUPP and
    > > -EXDEVV by doing generic_copy_file_range. Do any other consumers of
    > > vfs_copy_file_range rely on -EXDEV and not -EOPNOTSUPP and which is
    > > the correct error code for this case? It seems to me that -EOPNOTSUPP
    > > is more appropriate than EXDEV when (sb1 != sb2).
    >
    > So with the current patch, for a clone operation across 2 filesystems:

    Wait, I can't get passed "a clone operation across 2 filesystems", I
    thought there are not any options. It's not allowed? Then we go do try
    the copy. Those are two different steps so errors code might be
    different.

    > . if src and dst filesystem support both copy_file_range and
    > map_file_range then the code returns -ENOTSUPPORT.
    >
    > . if the filesystems only support map_file_range then the
    > code returns -EXDEV
    >
    > This seems confusing, shouldn't only 1 error code returned for this case?
    >
    > -Dai
    >
    > >
    > >>
    > >> But I may have got it all wrong. I've looked so many times at this code
    > >> that I'm probably useless at finding problems in it :-)
    > >
    > > You're not alone, we all try to do the right thing :-)
    > >
    > > -Dai
    > >
    > >>
    > >> Cheers,
    > >> --
    > >> Luís
    > >>
    > >>> -Dai
    > >>>
    > >>>> + } else {
    > >>>> + return -EOPNOTSUPP;
    > >>>> + }
    > >>>> +
    > >>>> ret = generic_file_rw_checks(file_in, file_out);
    > >>>> if (ret)
    > >>>> return ret;
    > >>>> @@ -1495,6 +1492,7 @@ ssize_t vfs_copy_file_range(struct file
    > >>>> *file_in, loff_t pos_in,
    > >>>> file_start_write(file_out);
    > >>>> + ret = -EOPNOTSUPP;
    > >>>> /*
    > >>>> * Try cloning first, this is supported by more file
    > >>>> systems, and
    > >>>> * more efficient if both clone and copy are supported (e.g.
    > >>>> NFS).
    > >>>> @@ -1513,9 +1511,10 @@ ssize_t vfs_copy_file_range(struct file
    > >>>> *file_in, loff_t pos_in,
    > >>>> }
    > >>>> }
    > >>>> - ret = do_copy_file_range(file_in, pos_in, file_out, pos_out, len,
    > >>>> - flags);
    > >>>> - WARN_ON_ONCE(ret == -EOPNOTSUPP);
    > >>>> + if (file_out->f_op->copy_file_range)
    > >>>> + ret = file_out->f_op->copy_file_range(file_in, pos_in,
    > >>>> + file_out, pos_out,
    > >>>> + len, flags);
    > >>>> done:
    > >>>> if (ret > 0) {
    > >>>> fsnotify_access(file_in);

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