Re: [PATCH v2] rtw88: Fix out-of-bounds write

From: Brian Norris <briannorris@chromium.org>
To: Len Baker <len.baker@gmx.com>
Cc: Yan-Hsuan Chuang <tony0620emma@gmail.com>,
	Kalle Valo <kvalo@codeaurora.org>,
	"David S. Miller" <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>,
	Stanislaw Gruszka <sgruszka@redhat.com>,
	Pkshih <pkshih@realtek.com>,
	linux-wireless <linux-wireless@vger.kernel.org>,
	"<netdev@vger.kernel.org>" <netdev@vger.kernel.org>,
	Linux Kernel <linux-kernel@vger.kernel.org>,
	stable <stable@vger.kernel.org>
Subject: Re: [PATCH v2] rtw88: Fix out-of-bounds write
Date: Fri, 16 Jul 2021 09:58:07 -0700	[thread overview]
Message-ID: <CA+ASDXPSL4bFpyjRYGEOG=Df8dOXc19LYBO06wdFN_k8OkiwKQ@mail.gmail.com> (raw)
In-Reply-To: <20210716155311.5570-1-len.baker@gmx.com>

On Fri, Jul 16, 2021 at 8:54 AM Len Baker <len.baker@gmx.com> wrote:
>
> In the rtw_pci_init_rx_ring function the "if (len > TRX_BD_IDX_MASK)"
> statement guarantees that len is less than or equal to GENMASK(11, 0) or
> in other words that len is less than or equal to 4095. However the
> rx_ring->buf has a size of RTK_MAX_RX_DESC_NUM (defined as 512). This
> way it is possible an out-of-bounds write in the for statement due to
> the i variable can exceed the rx_ring->buff size.
>
> However, this overflow never happens due to the rtw_pci_init_rx_ring is
> only ever called with a fixed constant of RTK_MAX_RX_DESC_NUM. But it is
> better to be defensive in this case and add a new check to avoid
> overflows if this function is called in a future with a value greater
> than 512.
>
> Cc: stable@vger.kernel.org

This kinda seems excessive, considering we absolutely know this is not
currently a bug. But then, LWN nicely highlighted this thread, which
reminds me that even without the Cc stable, this is likely to
unnecessarily get picked up:

https://lwn.net/ml/linux-kernel/YO0zXVX9Bx9QZCTs@kroah.com/

And I guess silencing Coverity is a desirable goal in many cases, even
if Coverity is being a bit trigger-happy.

So, *shrug*.

> Addresses-Coverity-ID: 1461515 ("Out-of-bounds write")
> Fixes: e3037485c68ec ("rtw88: new Realtek 802.11ac driver")
> Signed-off-by: Len Baker <len.baker@gmx.com>
> ---
> Changelog v1 -> v2
> - Remove the macro ARRAY_SIZE from the for loop (Pkshih, Brian Norris).
> - Add a new check for the len variable (Pkshih, Brian Norris).

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

Thanks.