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

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Message-ID: <202310090835.4DEB79C5@keescook>
Date:   Mon, 9 Oct 2023 08:36:08 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Arnd Bergmann <arnd@...nel.org>
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>,
        "Lee, Chun-Yi" <jlee@...e.com>, Arnd Bergmann <arnd@...db.de>,
        Lee@...nel, 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@...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 03:48:19PM +0200, 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.

Yes, good call.

> 
> 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>

Acked-by: Kees Cook <keescook@...omium.org>

-Kees

> ---
>  include/net/bluetooth/bluetooth.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/include/net/bluetooth/bluetooth.h b/include/net/bluetooth/bluetooth.h
> index 7ffa8c192c3f2..27ee1bf51c235 100644
> --- a/include/net/bluetooth/bluetooth.h
> +++ b/include/net/bluetooth/bluetooth.h
> @@ -359,11 +359,11 @@ static inline bool bdaddr_type_is_le(u8 type)
>  #define BDADDR_NONE (&(bdaddr_t) {{0xff, 0xff, 0xff, 0xff, 0xff, 0xff}})
>  
>  /* Copy, swap, convert BD Address */
> -static inline int bacmp(const bdaddr_t *ba1, const bdaddr_t *ba2)
> +static __always_inline int bacmp(const bdaddr_t *ba1, const bdaddr_t *ba2)
>  {
>  	return memcmp(ba1, ba2, sizeof(bdaddr_t));
>  }
> -static inline void bacpy(bdaddr_t *dst, const bdaddr_t *src)
> +static __always_inline void bacpy(bdaddr_t *dst, const bdaddr_t *src)
>  {
>  	memcpy(dst, src, sizeof(bdaddr_t));
>  }
> -- 
> 2.39.2
> 

-- 
Kees Cook