Re: [PATCH] cifs: fix loff_t underflow in cifs_remap_file_range() when len == 0

On Sun, Aug 23, 2026 at 6:55 AM Frank Sorenson <[email protected]> wrote:
>
> With len == 0 (clone to EOF), the effective length is computed as:
>
>     len = src_inode->i_size - off;
>
> If off > i_size, this is a negative loff_t, corrupting the ByteCount
> in the FSCTL_DUPLICATE_EXTENTS_TO_FILE request and inverting the range
> in filemap_write_and_wait_range().  The existing off >= i_size check
> fires only after the ioctl has already been sent.
>
> Snapshot i_size_read() once for both the bounds check and the length
> calculation, eliminating the TOCTOU and 32-bit torn-read risk.  Reject
> off > src_size with -EINVAL.  Treat off == src_size as a no-op,
> consistent with __generic_remap_file_range_prep().
>
> Fixes: 04b38d601239 ("vfs: pull btrfs clone API to vfs layer")
> Cc: [email protected]
> Signed-off-by: Frank Sorenson <[email protected]>
Reviewed-by: Namjae Jeon <[email protected]>
Thanks.