linux-hardening - Re: [PATCH] Bluetooth: mgmt: Pessimize compile-time bounds-check

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Message-Id: <73F86183-989F-439F-9A92-B186C4E3306E@holtmann.org>
Date:   Thu, 19 Aug 2021 16:52:30 +0200
From:   Marcel Holtmann <marcel@...tmann.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     Johan Hedberg <johan.hedberg@...il.com>,
        Luiz Augusto von Dentz <luiz.dentz@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        "open list:BLUETOOTH SUBSYSTEM" <linux-bluetooth@...r.kernel.org>,
        "open list:NETWORKING [GENERAL]" <netdev@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH] Bluetooth: mgmt: Pessimize compile-time bounds-check

Hi Kees,

> After gaining __alloc_size hints, GCC thinks it can reach a memcpy()
> with eir_len == 0 (since it can't see into the rewrite of status).
> Instead, check eir_len == 0, avoiding this future warning:
> 
> In function 'eir_append_data',
>    inlined from 'read_local_oob_ext_data_complete' at net/bluetooth/mgmt.c:7210:12:
> ./include/linux/fortify-string.h:54:29: warning: '__builtin_memcpy' offset 5 is out of the bounds [0, 3] [-Warray-bounds]
> ...
> net/bluetooth/hci_request.h:133:2: note: in expansion of macro 'memcpy'
>  133 |  memcpy(&eir[eir_len], data, data_len);
>      |  ^~~~~~
> 
> Cc: Marcel Holtmann <marcel@...tmann.org>
> Cc: Johan Hedberg <johan.hedberg@...il.com>
> Cc: Luiz Augusto von Dentz <luiz.dentz@...il.com>
> Cc: "David S. Miller" <davem@...emloft.net>
> Cc: Jakub Kicinski <kuba@...nel.org>
> Cc: linux-bluetooth@...r.kernel.org
> Cc: netdev@...r.kernel.org
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
> net/bluetooth/mgmt.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)

patch has been applied to bluetooth-next tree.

Regards

Marcel