Re: [PATCH V4 2/3] iommu: Take lock before reading iommu group default domain type

[Lu Baolu <baolu.lu@linux.intel.com>]

On 6/5/20 9:32 AM, Sai Praneeth Prakhya wrote:
> "/sys/kernel/iommu_groups/<grp_id>/type" file could be read to find out the
> default domain type of an iommu group. The default domain of an iommu group
> doesn't change after booting and hence could be read directly. But,
> after addding support to dynamically change iommu group default domain, the
> above assumption no longer stays valid.
> 
> iommu group default domain type could be changed at any time by writing to
> "/sys/kernel/iommu_groups/<grp_id>/type". So, take group mutex before
> reading iommu group default domain type so that the user wouldn't see stale
> values or iommu_group_show_type() doesn't try to derefernce stale pointers.
> 
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Joerg Roedel <joro@8bytes.org>
> Cc: Ashok Raj <ashok.raj@intel.com>
> Cc: Will Deacon <will.deacon@arm.com>
> Cc: Lu Baolu <baolu.lu@linux.intel.com>

Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>

Best regards,
baolu

> Cc: Sohil Mehta <sohil.mehta@intel.com>
> Cc: Robin Murphy <robin.murphy@arm.com>
> Cc: Jacob Pan <jacob.jun.pan@linux.intel.com>
> Signed-off-by: Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>
> ---
>   drivers/iommu/iommu.c | 2 ++
>   1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index b023f06f12d6..eb133ee5c13a 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -501,6 +501,7 @@ static ssize_t iommu_group_show_type(struct iommu_group *group,
>   {
>   	char *type = "unknown\n";
>   
> +	mutex_lock(&group->mutex);
>   	if (group->default_domain) {
>   		switch (group->default_domain->type) {
>   		case IOMMU_DOMAIN_BLOCKED:
> @@ -517,6 +518,7 @@ static ssize_t iommu_group_show_type(struct iommu_group *group,
>   			break;
>   		}
>   	}
> +	mutex_unlock(&group->mutex);
>   	strcpy(buf, type);
>   
>   	return strlen(type);
> 
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