linux-kernel - Re: [PATCH] mwifiex: Avoid memset() over-write of WEP key

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Message-ID: <CA+ASDXOE2EgkiqyqkiXrUCMas+aVU1hJy4uDwafhWv6REjsefg@mail.gmail.com>
Date:   Thu, 17 Jun 2021 12:29:47 -0700
From:   Brian Norris <briannorris@...omium.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     Kalle Valo <kvalo@...eaurora.org>,
        Amitkumar Karwar <amitkarwar@...il.com>,
        Ganapathi Bhat <ganapathi017@...il.com>,
        Sharvari Harisangam <sharvari.harisangam@....com>,
        Xinming Hu <huxinming820@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Linux Kernel <linux-kernel@...r.kernel.org>,
        linux-wireless <linux-wireless@...r.kernel.org>,
        "<netdev@...r.kernel.org>" <netdev@...r.kernel.org>,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH] mwifiex: Avoid memset() over-write of WEP key_material

On Thu, Jun 17, 2021 at 10:15 AM Kees Cook <keescook@...omium.org> wrote:
>
> In preparation for FORTIFY_SOURCE performing compile-time and run-time
> field bounds checking for memset(), avoid intentionally writing across
> neighboring array fields.
>
> When preparing to call mwifiex_set_keyparamset_wep(), key_material is
> treated very differently from its structure layout (which has only a
> single struct mwifiex_ie_type_key_param_set). Instead, add a new type to
> the union so memset() can correctly reason about the size of the
> structure.
>
> Note that the union ("params", 196 bytes) containing key_material was
> not large enough to hold the target of this memset(): sizeof(struct
> mwifiex_ie_type_key_param_set) == 60, NUM_WEP_KEYS = 4, so 240
> bytes, or 44 bytes past the end of "params". The good news is that
> it appears that the command buffer, as allocated, is 2048 bytes
> (MWIFIEX_SIZE_OF_CMD_BUFFER), so no neighboring memory appears to be
> getting clobbered.

Yeah, this union vs. the underlying buffer size always throws me for a
loop on figuring out whether there's truly a buffer overflow on some
of this stuff...

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

Looks like a valid refactor to me:

Reviewed-by: Brian Norris <briannorris@...omium.org>