linux-kernel - Re: [PATCH v1 7/8] vfio/type1: Add VFIO_IOMMU_CACHE

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Message-ID: <20200331075603.GB26583@infradead.org>
Date:   Tue, 31 Mar 2020 00:56:03 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     "Liu, Yi L" <yi.l.liu@...el.com>
Cc:     alex.williamson@...hat.com, eric.auger@...hat.com,
        jean-philippe@...aro.org, kevin.tian@...el.com,
        ashok.raj@...el.com, kvm@...r.kernel.org, jun.j.tian@...el.com,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        yi.y.sun@...el.com, hao.wu@...el.com
Subject: Re: [PATCH v1 7/8] vfio/type1: Add VFIO_IOMMU_CACHE_INVALIDATE

> @@ -2629,6 +2638,46 @@ static long vfio_iommu_type1_ioctl(void *iommu_data,
>  		}
>  		kfree(gbind_data);
>  		return ret;
> +	} else if (cmd == VFIO_IOMMU_CACHE_INVALIDATE) {

Please refactor the spaghetti in this ioctl handler to use a switch
statement and a helper function per command before growing it even more.

> +		/* Get the version of struct iommu_cache_invalidate_info */
> +		if (copy_from_user(&version,
> +			(void __user *) (arg + minsz), sizeof(version)))
> +			return -EFAULT;
> +
> +		info_size = iommu_uapi_get_data_size(
> +					IOMMU_UAPI_CACHE_INVAL, version);
> +
> +		cache_info = kzalloc(info_size, GFP_KERNEL);
> +		if (!cache_info)
> +			return -ENOMEM;
> +
> +		if (copy_from_user(cache_info,
> +			(void __user *) (arg + minsz), info_size)) {

The user might have changed the version while you were allocating and
freeing the memory, introducing potentially exploitable racing
conditions.