Re: [PATCH 06/15] vfs: strengthen checking of file range inputs to clone/dedupe range

[Amir Goldstein <amir73il@gmail.com>]

On Fri, Oct 5, 2018 at 3:46 AM Darrick J. Wong <darrick.wong@oracle.com> wrote:
>
> From: Darrick J. Wong <darrick.wong@oracle.com>
>
> Clone range is an optimization on a regular file write.  File writes
> that extend the file length are subject to various constraints which are
> not checked by clonerange.  This is a correctness problem, because we're
> never allowed to touch ranges that the page cache can't support
> (s_maxbytes); we're not supposed to deal with large offsets
> (MAX_NON_LFS) if O_LARGEFILE isn't set; and we must obey resource limits
> (RLIMIT_FSIZE).
>
> Therefore, add these checks to the new generic_clone_checks function so
> that we curtail unexpected behavior.
>
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> ---
>  mm/filemap.c |   31 +++++++++++++++++++++++++++++++
>  1 file changed, 31 insertions(+)
>
>
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 68ec91d05c7b..f74391721234 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -3015,6 +3015,37 @@ int generic_clone_checks(struct file *file_in, loff_t pos_in,
>                 return -EINVAL;
>         count = min(count, size_in - (uint64_t)pos_in);
>
> +       /* Don't exceed RLMIT_FSIZE in the file we're writing into. */
> +       if (limit != RLIM_INFINITY) {
> +               if (pos_out >= limit) {
> +                       send_sig(SIGXFSZ, current, 0);
> +                       return -EFBIG;
> +               }
> +               count = min(count, limit - (uint64_t)pos_out);
> +       }
> +
> +       /* Don't exceed the LFS limits. */
> +       if (unlikely(pos_out + count > MAX_NON_LFS &&
> +                               !(file_out->f_flags & O_LARGEFILE))) {
> +               if (pos_out >= MAX_NON_LFS)
> +                       return -EFBIG;
> +               count = min(count, MAX_NON_LFS - (uint64_t)pos_out);
> +       }
> +       if (unlikely(pos_in + count > MAX_NON_LFS &&
> +                               !(file_in->f_flags & O_LARGEFILE))) {
> +               if (pos_in >= MAX_NON_LFS)
> +                       return -EFBIG;
> +               count = min(count, MAX_NON_LFS - (uint64_t)pos_in);
> +       }
> +
> +       /* Don't operate on ranges the page cache doesn't support. */
> +       if (unlikely(pos_out >= inode_out->i_sb->s_maxbytes ||
> +                    pos_in >= inode_in->i_sb->s_maxbytes))
> +               return -EFBIG;
> +

Forget my standards, this doesn't abide by your own standards ;-)
Please factor out generic_write_checks() and use it instead of
duplicating the code. The in/out variant doesn't justify not calling
the helper twice IMO.

Thanks,
Amir.