linux-kernel - Re: [PATCH] net/bluetooth: fix erroneous use of bitmap_from

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Date:   Sun, 5 Jun 2022 09:34:37 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Yury Norov <yury.norov@...il.com>
Cc:     Marcel Holtmann <marcel@...tmann.org>,
        Johan Hedberg <johan.hedberg@...il.com>,
        Luiz Augusto von Dentz <luiz.dentz@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, Guo Ren <guoren@...nel.org>,
        linux-bluetooth <linux-bluetooth@...r.kernel.org>,
        Netdev <netdev@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-csky@...r.kernel.org,
        Sudip Mukherjee <sudipm.mukherjee@...il.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        David Hildenbrand <david@...hat.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>
Subject: Re: [PATCH] net/bluetooth: fix erroneous use of bitmap_from_u64()

On Sun, Jun 5, 2022 at 9:25 AM Yury Norov <yury.norov@...il.com> 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