linux-kernel - Re: [PATCH 4.19 016/125] media: pci: ttpci: av7110: fix possible buffer overflow caused by bad DMA value in debiirq()

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Date:   Tue, 1 Sep 2020 17:25:12 +0100
From:   Sean Young <sean@...s.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Jia-Ju Bai <baijiaju@...nghua.edu.cn>,
        Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
        Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 4.19 016/125] media: pci: ttpci: av7110: fix possible
 buffer overflow caused by bad DMA value in debiirq()

Greg,

On Tue, Sep 01, 2020 at 05:09:31PM +0200, Greg Kroah-Hartman wrote:
> From: Jia-Ju Bai <baijiaju@...nghua.edu.cn>
> 
> [ Upstream commit 6499a0db9b0f1e903d52f8244eacc1d4be00eea2 ]
> 
> The value av7110->debi_virt is stored in DMA memory, and it is assigned
> to data, and thus data[0] can be modified at any time by malicious
> hardware. In this case, "if (data[0] < 2)" can be passed, but then
> data[0] can be changed into a large number, which may cause buffer
> overflow when the code "av7110->ci_slot[data[0]]" is used.
> 
> To fix this possible bug, data[0] is assigned to a local variable, which
> replaces the use of data[0].

See the discussion here:

https://lkml.org/lkml/2020/8/31/479

It does not seem worthwhile merging to the stable trees.

Thanks

Sean

> 
> Signed-off-by: Jia-Ju Bai <baijiaju@...nghua.edu.cn>
> Signed-off-by: Sean Young <sean@...s.org>
> Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
> Signed-off-by: Sasha Levin <sashal@...nel.org>
> ---
>  drivers/media/pci/ttpci/av7110.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/media/pci/ttpci/av7110.c b/drivers/media/pci/ttpci/av7110.c
> index d6816effb8786..d02b5fd940c12 100644
> --- a/drivers/media/pci/ttpci/av7110.c
> +++ b/drivers/media/pci/ttpci/av7110.c
> @@ -424,14 +424,15 @@ static void debiirq(unsigned long cookie)
>  	case DATA_CI_GET:
>  	{
>  		u8 *data = av7110->debi_virt;
> +		u8 data_0 = data[0];
>  
> -		if ((data[0] < 2) && data[2] == 0xff) {
> +		if (data_0 < 2 && data[2] == 0xff) {
>  			int flags = 0;
>  			if (data[5] > 0)
>  				flags |= CA_CI_MODULE_PRESENT;
>  			if (data[5] > 5)
>  				flags |= CA_CI_MODULE_READY;
> -			av7110->ci_slot[data[0]].flags = flags;
> +			av7110->ci_slot[data_0].flags = flags;
>  		} else
>  			ci_get_data(&av7110->ci_rbuffer,
>  				    av7110->debi_virt,
> -- 
> 2.25.1
> 
>