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

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Date:   Fri, 16 Jul 2021 19:20:48 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Len Baker <len.baker@....com>
Cc:     Yan-Hsuan Chuang <tony0620emma@...il.com>,
        Kalle Valo <kvalo@...eaurora.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Stanislaw Gruszka <sgruszka@...hat.com>,
        Brian Norris <briannorris@...omium.org>,
        Pkshih <pkshih@...ltek.com>, linux-wireless@...r.kernel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH v2] rtw88: Fix out-of-bounds write

On Fri, Jul 16, 2021 at 05:53:11PM +0200, Len Baker 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.

If this can never happen, then no, this is not needed.  Why would you
check twice for the same thing?

thanks,

greg k-h