Re: [PATCH v14 05/17] overlayfs: Implement splice-read

[Miklos Szeredi]

On Tue, 14 Feb 2023 at 18:14, David Howells <dhowells@xxxxxxxxxx> wrote:
>
> Implement splice-read for overlayfs by passing the request down a layer
> rather than going through generic_file_splice_read() which is going to be
> changed to assume that ->read_folio() is present on buffered files.
>
> Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
> cc: Christoph Hellwig <hch@xxxxxx>
> cc: Jens Axboe <axboe@xxxxxxxxx>
> cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
> cc: John Hubbard <jhubbard@xxxxxxxxxx>
> cc: David Hildenbrand <david@xxxxxxxxxx>
> cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> cc: Miklos Szeredi <miklos@xxxxxxxxxx>
> cc: linux-unionfs@xxxxxxxxxxxxxxx
> cc: linux-block@xxxxxxxxxxxxxxx
> cc: linux-fsdevel@xxxxxxxxxxxxxxx
> cc: linux-mm@xxxxxxxxx
> ---
>  fs/overlayfs/file.c | 36 +++++++++++++++++++++++++++++++++++-
>  1 file changed, 35 insertions(+), 1 deletion(-)
>
> diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
> index c9d0c362c7ef..267b61df6fcd 100644
> --- a/fs/overlayfs/file.c
> +++ b/fs/overlayfs/file.c
> @@ -419,6 +419,40 @@ static ssize_t ovl_write_iter(struct kiocb *iocb, struct iov_iter *iter)
>         return ret;
>  }
>
> +static ssize_t ovl_splice_read(struct file *in, loff_t *ppos,
> +                              struct pipe_inode_info *pipe, size_t len,
> +                              unsigned int flags)
> +{
> +       const struct cred *old_cred;
> +       struct fd real;
> +       ssize_t ret;
> +
> +       ret = ovl_real_fdget(in, &real);
> +       if (ret)
> +               return ret;
> +
> +       ret = -EINVAL;
> +       if (in->f_flags & O_DIRECT &&
> +           !(real.file->f_mode & FMODE_CAN_ODIRECT))
> +               goto out_fdput;

This is unnecessary, as it was already done in ovl_real_fdget() ->
ovl_real_fdget_meta() -> ovl_change_flags().

> +       if (!real.file->f_op->splice_read)
> +               goto out_fdput;
> +
> +       ret = rw_verify_area(READ, in, ppos, len);

Should be on real.file.

> +       if (unlikely(ret < 0))
> +               return ret;

Leaks fd.

> +
> +       old_cred = ovl_override_creds(file_inode(in)->i_sb);
> +       ret = real.file->f_op->splice_read(real.file, ppos, pipe, len, flags);
> +
> +       revert_creds(old_cred);
> +       ovl_file_accessed(in);
> +out_fdput:
> +       fdput(real);
> +
> +       return ret;
> +}
> +
>  /*
>   * Calling iter_file_splice_write() directly from overlay's f_op may deadlock
>   * due to lock order inversion between pipe->mutex in iter_file_splice_write()
> @@ -695,7 +729,7 @@ const struct file_operations ovl_file_operations = {
>         .fallocate      = ovl_fallocate,
>         .fadvise        = ovl_fadvise,
>         .flush          = ovl_flush,
> -       .splice_read    = generic_file_splice_read,
> +       .splice_read    = ovl_splice_read,
>         .splice_write   = ovl_splice_write,
>
>         .copy_file_range        = ovl_copy_file_range,
>