linux-kernel - Re: Re: [PATCH] dma: Fix a double free in dma_async_device

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Date:   Wed, 31 Mar 2021 09:46:32 +0800 (GMT+08:00)
From:   lyl2019@...l.ustc.edu.cn
To:     "Dave Jiang" <dave.jiang@...el.com>
Cc:     vkoul@...nel.org, dmaengine@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: Re: [PATCH] dma: Fix a double free in dma_async_device_register




> -----原始邮件-----
> 发件人: "Dave Jiang" <dave.jiang@...el.com>
> 发送时间: 2021-03-31 00:05:15 (星期三)
> 收件人: "Lv Yunlong" <lyl2019@...l.ustc.edu.cn>, vkoul@...nel.org
> 抄送: dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org
> 主题: Re: [PATCH] dma: Fix a double free in dma_async_device_register
> 
> 
> On 3/30/2021 2:01 AM, Lv Yunlong wrote:
> > In the first list_for_each_entry() macro of dma_async_device_register,
> > it gets the chan from list and calls __dma_async_device_channel_register
> > (..,chan). We can see that chan->local is allocated by alloc_percpu() and
> > it is freed chan->local by free_percpu(chan->local) when
> > __dma_async_device_channel_register() failed.
> >
> > But after __dma_async_device_channel_register() failed, the caller will
> > goto err_out and freed the chan->local in the second time by free_percpu().
> >
> > The cause of this problem is forget to set chan->local to NULL when
> > chan->local was freed in __dma_async_device_channel_register(). My
> > patch sets chan->local to NULL when the callee failed to avoid double free.
> 
> Thanks for the fix. I think it would make sense to set it to NULL in 
> __dma_async_device_channel_register() cleanup path after it calls 
> free_percpu(chan->local) right? That would address any other instances 
> of this issue happening else where.
> 
> 
> >
> > Fixes: d2fb0a0438384 ("dmaengine: break out channel registration")
> > Signed-off-by: Lv Yunlong <lyl2019@...l.ustc.edu.cn>
> > ---
> >   drivers/dma/dmaengine.c | 4 +++-
> >   1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
> > index fe6a460c4373..fef64b198c95 100644
> > --- a/drivers/dma/dmaengine.c
> > +++ b/drivers/dma/dmaengine.c
> > @@ -1249,8 +1249,10 @@ int dma_async_device_register(struct dma_device *device)
> >   	/* represent channels in sysfs. Probably want devs too */
> >   	list_for_each_entry(chan, &device->channels, device_node) {
> >   		rc = __dma_async_device_channel_register(device, chan);
> > -		if (rc < 0)
> > +		if (rc < 0) {
> > +			chan->local = NULL;
> >   			goto err_out;
> > +		}
> >   	}
> >   
> >   	mutex_lock(&dma_list_mutex);

Ok, that is a good idea. I have submitted the PATCH v2.

Thanks.