linux-kernel - Re: [PATCH] vfio_iommu_type1: increase the validity check of function parameters

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Date:   Fri, 23 Dec 2022 06:28:32 -0700
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Li kunyu <kunyu@...china.com>
Cc:     cohuck@...hat.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] vfio_iommu_type1: increase the validity check of
 function parameters

On Fri, 23 Dec 2022 15:24:18 +0800
Li kunyu <kunyu@...china.com> wrote:

> Added validity check for count variable, return if count variable does 
> not meet the execution condition (do not execute mutex_lock and 
> mutex_unlock function).
> 
> Signed-off-by: Li kunyu <kunyu@...china.com>
> ---
>  drivers/vfio/vfio_iommu_type1.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index 23c24fe98c00..9bdf96d932e4 100644
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -3137,6 +3137,9 @@ static int vfio_iommu_type1_dma_rw(void *iommu_data, dma_addr_t user_iova,
>  	int ret = 0;
>  	size_t done;
>  
> +	if (count <= 0)
> +		return ret;
> +
>  	mutex_lock(&iommu->lock);
>  	while (count > 0) {
>  		ret = vfio_iommu_type1_dma_rw_chunk(iommu, user_iova, data,

This is only optimizing a case that shouldn't exist, the return value
is the same.  Callers should be smart enough not to call the function
with such values.  As an internal API, we assume reasonable behavior by
the caller.  Thanks,

Alex