linux-kernel - Re: [PATCH] iommu: Don't take group reference in iommu_alloc_default

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Message-ID: <4a9382b1a79ee7ac46abfe8b84601576@codeaurora.org>
Date:   Mon, 25 May 2020 18:54:33 +0530
From:   Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
To:     Joerg Roedel <joro@...tes.org>
Cc:     iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        Joerg Roedel <jroedel@...e.de>,
        saiprakash.ranjan@...eaurora.org
Subject: Re: [PATCH] iommu: Don't take group reference in
 iommu_alloc_default_domain()

Hi Joerg,

On 2020-05-25 18:31, Joerg Roedel wrote:
> From: Joerg Roedel <jroedel@...e.de>
> 
> The iommu_alloc_default_domain() function takes a reference to an IOMMU
> group without releasing it. This causes the group to never be released,
> with undefined side effects.
> 
> The function has only one call-site, which takes a group reference on
> its own, so to fix this leak, do not take another reference in
> iommu_alloc_default_domain() and pass the group as a function parameter
> instead.
> 
> Reference:
> https://lore.kernel.org/lkml/20200522130145.30067-1-saiprakash.ranjan@codeaurora.org/
> Reported-by: Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
> Cc: Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
> Fixes: 6e1aa2049154 ("iommu: Move default domain allocation to
> iommu_probe_device()")
> Signed-off-by: Joerg Roedel <jroedel@...e.de>
> ---
>  drivers/iommu/iommu.c | 21 +++++++++------------
>  1 file changed, 9 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index 374b34fd6fac..bf20674769e0 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -80,7 +80,8 @@ static bool iommu_cmd_line_dma_api(void)
>  	return !!(iommu_cmd_line & IOMMU_CMD_LINE_DMA_API);
>  }
> 
> -static int iommu_alloc_default_domain(struct device *dev);
> +static int iommu_alloc_default_domain(struct iommu_group *group,
> +				      struct device *dev);
>  static struct iommu_domain *__iommu_domain_alloc(struct bus_type *bus,
>  						 unsigned type);
>  static int __iommu_attach_device(struct iommu_domain *domain,
> @@ -251,17 +252,17 @@ int iommu_probe_device(struct device *dev)
>  	if (ret)
>  		goto err_out;
> 
> +	group = iommu_group_get(dev);
> +	if (!group)
> +		goto err_release;
> +
>  	/*
>  	 * Try to allocate a default domain - needs support from the
>  	 * IOMMU driver. There are still some drivers which don't
>  	 * support default domains, so the return value is not yet
>  	 * checked.
>  	 */
> -	iommu_alloc_default_domain(dev);
> -
> -	group = iommu_group_get(dev);
> -	if (!group)
> -		goto err_release;
> +	iommu_alloc_default_domain(group, dev);
> 
>  	if (group->default_domain)
>  		ret = __iommu_attach_device(group->default_domain, dev);
> @@ -1478,15 +1479,11 @@ static int
> iommu_group_alloc_default_domain(struct bus_type *bus,
>  	return 0;
>  }
> 
> -static int iommu_alloc_default_domain(struct device *dev)
> +static int iommu_alloc_default_domain(struct iommu_group *group,
> +				      struct device *dev)
>  {
> -	struct iommu_group *group;
>  	unsigned int type;
> 
> -	group = iommu_group_get(dev);
> -	if (!group)
> -		return -ENODEV;
> -
>  	if (group->default_domain)
>  		return 0;

Tested this out and it works for me.

Tested-by: Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>

Thanks,
Sai
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