linux-kernel - Re: [PATCH] [v3] gpu: ipu-v3: prg: avoid possible array underflow

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Message-ID: <1521132789.4624.4.camel@pengutronix.de>
Date:   Thu, 15 Mar 2018 17:53:09 +0100
From:   Philipp Zabel <p.zabel@...gutronix.de>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Lucas Stach <l.stach@...gutronix.de>,
        Tobias Jordan <Tobias.Jordan@...ktrobit.com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] [v3] gpu: ipu-v3: prg: avoid possible array underflow

Hi Arnd,

On Thu, 2018-03-15 at 17:19 +0100, Arnd Bergmann wrote:
> gcc-8 reports that we access an array with a negative index
> in an error case:
> 
> drivers/gpu/ipu-v3/ipu-prg.c: In function 'ipu_prg_channel_disable':
> drivers/gpu/ipu-v3/ipu-prg.c:252:43: error: array subscript -22 is below array bounds of 'struct ipu_prg_channel[3]' [-Werror=array-bounds]
> 
> This moves the range check in front of the first time that
> variable gets used.
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

thank you, I've replaced v2 with this version in imx-drm/fixes.

regards
Philipp

> ----
> v1: Originally sent on Dec 4, 2017.
> v2: Sent again on Jan 16, after no reply, Phillipp said it was merged
> v3: Ran into a related problem with CONFIG_UBSAN, sent again fixing both
> ---
>  drivers/gpu/ipu-v3/ipu-prg.c | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/ipu-v3/ipu-prg.c b/drivers/gpu/ipu-v3/ipu-prg.c
> index 97b99500153d..83f9dd934a5d 100644
> --- a/drivers/gpu/ipu-v3/ipu-prg.c
> +++ b/drivers/gpu/ipu-v3/ipu-prg.c
> @@ -250,10 +250,14 @@ void ipu_prg_channel_disable(struct ipuv3_channel *ipu_chan)
>  {
>  	int prg_chan = ipu_prg_ipu_to_prg_chan(ipu_chan->num);
>  	struct ipu_prg *prg = ipu_chan->ipu->prg_priv;
> -	struct ipu_prg_channel *chan = &prg->chan[prg_chan];
> +	struct ipu_prg_channel *chan;
>  	u32 val;
>  
> -	if (!chan->enabled || prg_chan < 0)
> +	if (prg_chan < 0)
> +		return;
> +
> +	chan = &prg->chan[prg_chan];
> +	if (!chan->enabled)
>  		return;
>  
>  	pm_runtime_get_sync(prg->dev);
> @@ -280,13 +284,15 @@ int ipu_prg_channel_configure(struct ipuv3_channel *ipu_chan,
>  {
>  	int prg_chan = ipu_prg_ipu_to_prg_chan(ipu_chan->num);
>  	struct ipu_prg *prg = ipu_chan->ipu->prg_priv;
> -	struct ipu_prg_channel *chan = &prg->chan[prg_chan];
> +	struct ipu_prg_channel *chan;
>  	u32 val;
>  	int ret;
>  
>  	if (prg_chan < 0)
>  		return prg_chan;
>  
> +	chan = &prg->chan[prg_chan];
> +
>  	if (chan->enabled) {
>  		ipu_pre_update(prg->pres[chan->used_pre], *eba);
>  		return 0;