linux-kernel - Re: [PATCH] iommu/amd: Check if domain is NULL before dereference it

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Date:   Thu, 24 Aug 2017 20:47:33 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        joro@...tes.org
Subject: Re: [PATCH] iommu/amd: Check if domain is NULL before dereference it

On 08/24/17 at 03:32pm, Dan Carpenter wrote:
> Take a look at this code for example.  But all the places which call
> get_domain() are the same:
> 
> drivers/iommu/amd_iommu.c
>   2648          page = virt_to_page(virt_addr);
>   2649          size = PAGE_ALIGN(size);
>   2650  
>   2651          domain = get_domain(dev);
>                          ^^^^^^^^^^^^^^
> imagined get_domain() returns NULL.
> 
>   2652          if (IS_ERR(domain))
>   2653                  goto free_mem;
>   2654  
>   2655          dma_dom = to_dma_ops_domain(domain);
>                           ^^^^^^^^^^^^^^^^^^^^^^^^^
> This will Oops.

I see, it's a problem. Thanks for telling!

How about below change? But I am not very sure which errno should be
picked, seems the latter one, EBUSY is better since it has passed the
check_device() checking.

diff --git a/drivers/iommu/amd_iommu.c b/drivers/iommu/amd_iommu.c
index 16f1e6af00b0..2d7d04472555 100644
--- a/drivers/iommu/amd_iommu.c
+++ b/drivers/iommu/amd_iommu.c
@@ -2262,6 +2262,9 @@ static struct protection_domain *get_domain(struct device *dev)
 		domain = to_pdomain(io_domain);
 		attach_device(dev, domain);
 	}
+	if (domain == NULL)
+		return ERR_PTR(-EBUSY);
+
 	if (!dma_ops_domain(domain))
 		return ERR_PTR(-EBUSY);
 
-- 
2.5.5