Re: [PATCH 3/3] ntfs: only alias volume $UpCase to default on exact match

[Hyunchul Lee]

2026년 5월 21일 (목) 오전 2:02, DaeMyung Kang <charsyam@xxxxxxxxx>님이 작성:
>
> load_and_init_upcase() currently aliases vol->upcase to the global
> default upcase whenever the shared prefix matches, and then truncates
> vol->upcase_len to that shorter prefix.  The result is correct only by
> accident: upcase[] accesses in name collation are gated by upcase_len,
> so the prefix-equality alias produces the same fold output as keeping
> the volume's own shorter table.
>
> Still, prefix equality is not equality: the volume table is logically
> distinct from the default and should not be replaced by it unless they
> are byte-for-byte identical.  Use memcmp() to compare the complete table
> in one expression and drop the now-redundant upcase_len rewrite.
>
> No user-visible change is expected for compliant volumes whose $UpCase
> has exactly default_upcase_len entries; shorter volume tables are no
> longer aliased to the default.
>
> Signed-off-by: DaeMyung Kang <charsyam@xxxxxxxxx>

Looks good to me.

Reviewed-by: Hyunchul Lee <hyc.lee@xxxxxxxxx>

> ---
>  super.c | 12 +++---------
>  1 file changed, 3 insertions(+), 9 deletions(-)
>
> diff --git a/super.c b/super.c
> index c90cb5673f98..811640cf5669 100644
> --- a/super.c
> +++ b/super.c
> @@ -1344,7 +1344,6 @@ static bool load_and_init_upcase(struct ntfs_volume *vol)
>  #endif
>         pgoff_t index, max_index;
>         unsigned int size;
> -       int i, max;
>
>         ntfs_debug("Entering.");
>         /* Read upcase table and setup vol->upcase and vol->upcase_len. */
> @@ -1405,16 +1404,11 @@ read_partial_upcase_page:
>                 mutex_unlock(&ntfs_lock);
>                 return true;
>         }
> -       max = default_upcase_len;
> -       if (max > vol->upcase_len)
> -               max = vol->upcase_len;
> -       for (i = 0; i < max; i++)
> -               if (vol->upcase[i] != default_upcase[i])
> -                       break;
> -       if (i == max) {
> +       if (default_upcase_len == vol->upcase_len &&
> +           !memcmp(vol->upcase, default_upcase,
> +                   default_upcase_len * sizeof(*default_upcase))) {
>                 kvfree(vol->upcase);
>                 vol->upcase = default_upcase;
> -               vol->upcase_len = max;
>                 ntfs_nr_upcase_users++;
>                 mutex_unlock(&ntfs_lock);
>                 ntfs_debug("Volume specified $UpCase matches default. Using default.");
> --
> 2.43.0



-- 
Thanks,
Hyunchul