linux-hardening - Re: [PATCH 1/2] dmaengine: pxa_dma: Remove an erroneous BUG_ON() in pxad_free

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Date: Sun, 8 Oct 2023 14:03:23 -0700
From: Kees Cook <keescook@...omium.org>
To: Christophe JAILLET <christophe.jaillet@...adoo.fr>
Cc: gustavoars@...nel.org, Daniel Mack <daniel@...que.org>,
	Haojian Zhuang <haojian.zhuang@...il.com>,
	Robert Jarzmik <robert.jarzmik@...e.fr>,
	Vinod Koul <vkoul@...nel.org>, linux-hardening@...r.kernel.org,
	linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, dmaengine@...r.kernel.org
Subject: Re: [PATCH 1/2] dmaengine: pxa_dma: Remove an erroneous BUG_ON() in
 pxad_free_desc()

On Sat, Oct 07, 2023 at 01:13:09PM +0200, Christophe JAILLET wrote:
> If pxad_alloc_desc() fails on the first dma_pool_alloc() call, then
> sw_desc->nb_desc is zero.
> In such a case pxad_free_desc() is called and it will BUG_ON().
> 
> Remove this erroneous BUG_ON().

Perhaps it could be changed to a WARN_ON()?

> It is also useless, because if "sw_desc->nb_desc == 0", then, on the first
> iteration of the for loop, i is -1 and the loop will not be executed.
> (both i and sw_desc->nb_desc are 'int')

Agreed.

> 
> Fixes: a57e16cf0333 ("dmaengine: pxa: add pxa dmaengine driver")
> Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
> ---
>  drivers/dma/pxa_dma.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/drivers/dma/pxa_dma.c b/drivers/dma/pxa_dma.c
> index 3c574dc0613b..94cef2905940 100644
> --- a/drivers/dma/pxa_dma.c
> +++ b/drivers/dma/pxa_dma.c
> @@ -722,7 +722,6 @@ static void pxad_free_desc(struct virt_dma_desc *vd)
>  	dma_addr_t dma;
>  	struct pxad_desc_sw *sw_desc = to_pxad_sw_desc(vd);
>  
> -	BUG_ON(sw_desc->nb_desc == 0);
>  	for (i = sw_desc->nb_desc - 1; i >= 0; i--) {
>  		if (i > 0)
>  			dma = sw_desc->hw_desc[i - 1]->ddadr;
> -- 
> 2.34.1
> 

-- 
Kees Cook