Re: [PATCH] net/bluetooth: fix erroneous use of bitmap_from_u64()

[Linus Torvalds]

On Sun, Jun 5, 2022 at 9:25 AM Yury Norov <yury.norov@xxxxxxxxx> wrote:
>
> The commit 0a97953fd221 ("lib: add bitmap_{from,to}_arr64") changed
> implementation of bitmap_from_u64(), so that it doesn't typecast
> argument to u64, and actually dereferences memory.

Gaah.

That code shouldn't use DECLARE_BITMAP() at all, it should just use

    struct bdaddr_list_with_flags {
            ..
            unsigned long flags;
    };

and then use '&br_params->flags' when it nneds the actual atomic
'set_bit()' things and friends, and then when it copies the flags
around it should just use 'flags' as an integer value.

The bitmap functions are literally defined to work as "bit N in a set
of 'unsigned long'" exactly so that you can do that mixing of values
and bit operations, and not have to worry about insane architectures
that do big-endian bit ordering or things like that.

Using a 'bitmap' as if it's some bigger or potentially variable-sized
thing for this kind of flags usage is crazy, when the code already
does

  /* Make sure number of flags doesn't exceed sizeof(current_flags) */
  static_assert(__HCI_CONN_NUM_FLAGS < 32);

because other parts are limited to 32 bits.

I wonder how painful it would be to just fix that odd type mistake.

                  Linus