linux-kernel - Re: [PATCH] Bluetooth: mark bacmp() and bacpy() as __always

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Date:   Mon, 9 Oct 2023 09:02:27 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Arnd Bergmann <arnd@...nel.org>,
        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>,
        "Lee, Chun-Yi" <jlee@...e.com>,
        Luiz Augusto von Dentz <luiz.von.dentz@...el.com>,
        stable@...r.kernel.org, Iulia Tanasescu <iulia.tanasescu@....com>,
        Wenjia Zhang <wenjia@...ux.ibm.com>,
        linux-bluetooth@...r.kernel.org, Netdev <netdev@...r.kernel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Bluetooth: mark bacmp() and bacpy() as __always_inline

On Mon, Oct 09, 2023 at 05:36:55PM +0200, Arnd Bergmann wrote:
> On Mon, Oct 9, 2023, at 15:48, Arnd Bergmann wrote:
> > From: Arnd Bergmann <arnd@...db.de>
> >
> > These functions are simple wrappers around memcmp() and memcpy(), which
> > contain compile-time checks for buffer overflow. Something in gcc-13 and
> > likely other versions makes this trigger a warning when the functions
> > are not inlined and the compiler misunderstands the buffer length:
> >
> > In file included from net/bluetooth/hci_event.c:32:
> > In function 'bacmp',
> >     inlined from 'hci_conn_request_evt' at 
> > net/bluetooth/hci_event.c:3276:7:
> > include/net/bluetooth/bluetooth.h:364:16: error: 'memcmp' specified 
> > bound 6 exceeds source size 0 [-Werror=stringop-overread]
> >   364 |         return memcmp(ba1, ba2, sizeof(bdaddr_t));
> >       |                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >
> > Use the __always_inline annotation to ensure that the helpers are
> > correctly checked. This has no effect on the actual correctness
> > of the code, but avoids the warning. Since the patch that introduced
> > the warning is marked for stable backports, this one should also
> > go that way to avoid introducing build regressions.
> >
> > Fixes: d70e44fef8621 ("Bluetooth: Reject connection with the device 
> > which has same BD_ADDR")
> > Cc: Kees Cook <keescook@...omium.org>
> > Cc: Lee, Chun-Yi <jlee@...e.com>
> > Cc: Luiz Augusto von Dentz <luiz.von.dentz@...el.com>
> > Cc: Marcel Holtmann <marcel@...tmann.org>
> > Cc: stable@...r.kernel.org
> > Signed-off-by: Arnd Bergmann <arnd@...db.de>
> 
> Sorry, I have to retract this, something went wrong on my
> testing and I now see the same problem in some configs regardless
> of whether the patch is applied or not.

Perhaps turn them into macros instead?

-- 
Kees Cook