linux-kernel - Re: [PATCH] dma: mv_xor: Fix a possible null-pointer dereference in mv_xor_prep_dma

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Date:   Thu, 8 Aug 2019 18:51:40 +0530
From:   Vinod Koul <vkoul@...nel.org>
To:     Jia-Ju Bai <baijiaju1990@...il.com>
Cc:     dan.j.williams@...el.com, dmaengine@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dma: mv_xor: Fix a possible null-pointer dereference in
 mv_xor_prep_dma_xor()

On 27-07-19, 17:30, Jia-Ju Bai wrote:
> In mv_xor_prep_dma_xor(), there is an if statement on line 577 to check
> whether sw_desc is NULL:
>     if (sw_desc)
> 
> When sw_desc is NULL, it is used on line 594:
>     dev_dbg(..., sw_desc, &sw_desc->async_tx);
> 
> Thus, a possible null-pointer dereference may occur.
> 
> To fix this bug, sw_desc is checked before being used.
> 
> This bug is found by a static analysis tool STCheck written by us.
> 
> Signed-off-by: Jia-Ju Bai <baijiaju1990@...il.com>
> ---
>  drivers/dma/mv_xor.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/dma/mv_xor.c b/drivers/dma/mv_xor.c
> index 0ac8e7b34e12..08c0b2a9eb32 100644
> --- a/drivers/dma/mv_xor.c
> +++ b/drivers/dma/mv_xor.c
> @@ -589,9 +589,11 @@ mv_xor_prep_dma_xor(struct dma_chan *chan, dma_addr_t dest, dma_addr_t *src,
>  		}
>  	}
>  
> -	dev_dbg(mv_chan_to_devp(mv_chan),
> -		"%s sw_desc %p async_tx %p \n",
> -		__func__, sw_desc, &sw_desc->async_tx);
> +	if (sw_desc) {
> +		dev_dbg(mv_chan_to_devp(mv_chan),
> +			"%s sw_desc %p async_tx %p \n",
> +			__func__, sw_desc, &sw_desc->async_tx);
> +	}

why not move this into the preceeding if condition?

>  	return sw_desc ? &sw_desc->async_tx : NULL;
>  }
>  
> -- 
> 2.17.0

-- 
~Vinod