Re: [PATCH v8] vfs: fix copy_file_range regression in cross-fs copies

Olga Kornievskaia
2021-02-24T01:10:41Z

On Mon, Feb 22, 2021 at 5:25 AM Luis Henriques <lhenriques@suse.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@chromium.org>
> Signed-off-by: Luis Henriques <lhenriques@suse.de>

I tested v8 and I believe it works for NFS.

> ---
> 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;
> + } 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);